Combined Science GCSE

Combined Science GCSE glossary

2937 key terms for Combined Science GCSE, A to Z, each linked to the topic pages that use it.

Find a term in Combined Science GCSE

2937 terms found. Open a term to try a short memory check.

A

a = F ÷ m: The relationship combining the two proportionalities, where F is the resultant force in newtons, m is mass in kilograms and a is acceleration in metres per…AQA
a = Δv / Δt: An equation used to find acceleration from velocity changes.AQA
Abiotic: The non-living conditions, including light intensity, temperature, moisture, soil pH, mineral content, wind and oxygen availability.AQA
abiotic components: The non-living parts of an ecosystem, such as air, water, soil and sunlight.AQA
Abiotic factor: A non-living factor, such as wind, studied alongside temperature, light, moisture and soil pH when investigating an ecosystem.AQA
Abiotic factors: Non-living physical or chemical conditions of a habitat which can affect a community.AQA
Abiotic factors and species distribution: Recording a factor such as light intensity at each sampling point to show whether the species becomes more or less abundant as the factor changes.AQA
Absorber: The thing that receives the energy, such as a surface that heats up, a radio receiver or a photographic film.AQA
Absorption: Tested by measuring the heating of cold water using an external infrared source, with black matt surfaces being the best absorbers and shiny silver surfaces…AQA
Absorption and transport of digestion products: The products of digestion are absorbed into the blood and transported to cells.AQA
Absorption by water molecules: Microwaves penetrate the outer layers of food and are absorbed by water molecules, causing them to vibrate and gain kinetic energy.AQA
Absorption of electromagnetic radiation: The electron arrangements may change by taking in electromagnetic radiation, which moves an electron further from the nucleus to a higher energy level.AQA
Abstaining: Not having sexual intercourse during the fertile period, when a mature egg may be in the oviduct.AQA
Abundance estimate: Sampling gives an estimate rather than a complete count, and a mean count per quadrat can be scaled to a value per m².AQA
Accelerated motion and curved graphs: When an object accelerates, its distance–time graph is curved, so the gradient changes continuously and no single straight-line gradient gives the speed…AQA
Acceleration: A quantity proportional to the resultant force acting on an object and inversely proportional to the mass of the object.AQA
Acceleration and change of direction: Changing direction at constant speed is still a change in velocity and requires a resultant force.AQA
Acceleration and deceleration: Acceleration is calculated from a speed change and time using a = Δv ÷ t, and deceleration is included as a negative acceleration.AQA
Acceleration of free fall: Near the Earth's surface, about 9.8 m/s², the same for all objects regardless of mass, shape or size when drag is absent.AQA
Accuracy and control of variables: Keep the compass away from other magnets or magnetic materials to avoid a distorted pattern.AQA
Accuracy of plotting: Plot each point with a small cross, reading the scale carefully so points sit within half a small square of the true value.AQA
Acetylsalicylic acid: The active ingredient in aspirin, made by chemists modifying salicin and more effective and gentler on the stomach than raw willow preparations.AQA
Acid anions: The acid used determines the anion in the salt: hydrochloric acid gives chloride, nitric acid gives nitrate, and sulfuric acid gives sulfate.AQA
Acid deposition and environmental damage: The gases dissolve in atmospheric water and are oxidised, producing acidic solutions that fall as acid rain, lowering the pH of lakes and soils and damaging…AQA
Acid rain: Formed when acidic gases dissolve in rainwater, and can damage trees, acidify lakes and corrode limestone buildings.AQA
Acid rain and environmental damage: Sulfur dioxide and nitrogen oxides dissolve in rainwater to form acid rain, which acidifies soils and lakes and corrodes limestone buildings.AQA
Acid rain and pollutant gases: Burning coal, oil and gas releases sulfur dioxide, which contributes to acid rain.AQA
Acid strength and extent of ionisation: A strong acid is completely ionised, whereas a weak acid is only partially ionised.AQA
Acid–base neutralisation: An acid reacts with an alkali or base to form a salt and water.AQA
Acid–metal reactions as displacement reactions: When an acid reacts with a metal, the metal displaces hydrogen from the acid, producing a salt and hydrogen gas.AQA
Acidic: Describes a solution with a pH below 7, for example a solution with pH 2.AQA
Acidic behaviour of chlorine in water: Chlorine reacts with water on the damp paper to form acidic species that first turn the litmus red.AQA
Acidic solution: Has a pH below 7, and the lower the pH, the more acidic the solution.AQA
Acidic solutions: Solutions that have a pH below 7 and a higher hydrogen ion concentration than neutral solutions.AQA
Acids: Substances that produce hydrogen ions, H⁺, when dissolved in water, and only show acidic behaviour when water is present.AQA
Acids and alkalis: Aqueous solutions of acids have pH values below 7, while aqueous solutions of alkalis have pH values above 7.AQA
Acids as proton donors: An acid acts as a proton donor, releasing H⁺ ions in aqueous solution.AQA
Acids, bases and alkalis: Alkalis are soluble metal hydroxides, while bases include insoluble metal hydroxides and metal oxides, and both react with acids to form a salt and water only.AQA
Action at a distance: A non-contact force acts between objects that are not touching, because it acts at a distance through a field.AQA
Activation energy: The vertical distance from the reactant energy level to the highest point of the curve, representing the minimum energy particles need to react.AQA
Active compound: The chemical produced by the plant that is responsible for the medical effect, rather than the whole plant being the drug.AQA
Active site: Part of the enzyme molecule that is complementary in shape to its substrate, so the substrate binds and the reaction is catalysed.AQA
Active substance: A compound from a natural source that can be extracted, purified and later modified to make medicines.AQA
Active transport: The process by which root hair cells absorb nitrate ions from soil water, used because the concentration of nitrate ions in soil water is usually lower than…AQA
Active transport against a concentration gradient: Ions are moved from the more dilute soil solution into the more concentrated cell contents, against the concentration gradient, using energy from respiration…AQA
Activity: The rate at which a source of unstable nuclei decays, measured in decays per unit time.AQA
Actual size: Estimated by dividing the measured image size by the magnification, or by using a scale bar.AQA
Adaptation: An inherited feature that increases an organism's chance of survival and reproduction in its normal habitat.AQA
Adaptations of exchange surfaces: Folded, flattened or branched shapes that increase the area without greatly increasing volume, as in alveoli, villi and root hair cells.AQA
Addition reaction: The reaction in which the C=C double bond reacts with bromine, so the orange colour is decolourised and the mixture turns colourless.AQA
adrenal gland: An endocrine gland located above the kidneys, which students must identify on a diagram of the human body.AQA
Adrenal glands: Endocrine glands located above the kidneys that produce adrenaline in times of fear or stress.AQA
Adrenaline: A hormone produced by the adrenal glands in times of fear or stress, which increases the heart rate and boosts the delivery of oxygen and glucose to the brain…AQA
Adult cell cloning: Involves removing the nucleus from a body cell of the rare species and inserting it into an egg cell whose nucleus has been removed.AQA
Adult stem cells: Unspecialised cells found in body tissues such as bone marrow that can divide to replace worn-out or damaged cells.AQA
Adult stem cells and potency: They can form many cell types, including blood cells, but their potency is more limited than that of embryonic stem cells.AQA
Adverse road and weather conditions: Conditions such as a wet or icy surface that reduce friction, so the tyres grip less and the vehicle takes longer to stop.AQA
Adverse road conditions: Conditions that include wet or icy conditions, and can also include snow or mud, which reduce the friction between the tyres and the road.AQA
Advertising and green claims: Presenting a technically correct but misleading figure as proof that a product is 'green'.AQA
Aerobic biological treatment: Treatment of the liquid effluent in which aerobic bacteria break down organic matter and microbes.AQA
Aerobic respiration: Requires oxygen and produces carbon dioxide and water from glucose and oxygen, transferring a relatively larger amount of energy per glucose molecule.AQA
Age: Can reduce maximum walking, running or cycling speed because of lower muscle strength, stamina or reaction time.AQA
Agricultural applications of genetic engineering: Genetic engineering has been applied to crop plants to give characteristics useful to farmers and consumers, such as disease resistance or improved fruit.AQA
Agricultural emissions and waste decomposition: Agriculture increases methane through livestock digestion and rice paddy fields, and can release nitrous oxide from fertilisers, while organic waste decaying…AQA
Agricultural products: Products such as crops, manure and compost that come from farming and can supplement natural products.AQA
Agriculture: Farming crops and livestock, which supplements natural supply for food, fibres and biofuel crops.AQA
Agriculture and waste as methane sources: Human activities including farming cattle and other livestock, growing rice in flooded paddy fields, and decomposing organic waste in landfill sites.AQA
AIDS: Late stage HIV infection, occurring when the body's immune system becomes so badly damaged it can no longer deal with other infections or cancers.AQA
Air pollution: Pollution can occur in air, from smoke and acidic gases, and each route harms organisms in a different way.AQA
Air pollution from fuels: Sulfur dioxide from sulfur-containing fuel contributes to acid rain, and nitrogen oxides form when nitrogen and oxygen from the air react at the high…AQA
Air resistance: A form of friction acting on an object moving through air, opposing its motion.AQA
Air spaces: Gaps between spongy mesophyll cells that connect to the stomata on the lower surface, so carbon dioxide can diffuse through the leaf to reach the…AQA
Algae: Organisms that first produced oxygen about 2.7 billion years ago, with oxygen appearing in the atmosphere soon after.AQA
Alignment of a freely suspended magnet: A freely suspended magnet aligns with the local magnetic field, so the compass needle rotates until it lies along the Earth's magnetic field at that place.AQA
Alkaline solution: Has a pH above 7, and the higher the pH, the more alkaline the solution.AQA
Alkalis: Soluble bases that produce hydroxide ions, OH⁻, when dissolved in water.AQA
Alkane: A hydrocarbon with only single C–C bonds that does not react this way under the same conditions, so the orange colour persists.AQA
Alkanes: Saturated hydrocarbons with only single carbon–carbon bonds, with the general formula CₙH₂ₙ₊₂.AQA
Alkenes: Unsaturated hydrocarbons with a C=C double bond that are more reactive than alkanes, so they are useful for making polymers.AQA
Alkenes as chemical feedstocks: Alkenes are used as starting materials for the production of many other chemicals, such as ethanol.AQA
Alkenes as polymer feedstocks: Reactive starting materials for polymers such as poly(ethene) and for other chemicals.AQA
allele: One of the different versions of a gene that can occupy the same locus on a chromosome.AQA
Allele frequency change: Over generations, the frequency of advantageous alleles in the population increases.AQA
Allele frequency over time: The frequency of alleles responsible for advantageous characteristics increases in the population over generations.AQA
Alleles: Alternative versions of a gene, of which a diploid organism inherits one from each parent.AQA
Allergies: Conditions such as skin rashes and asthma that can be triggered by an immune reaction initially caused by a pathogen.AQA
Alloys: Made by mixing pure metals with other metals, these are harder than the pure metals.AQA
Alpha decay: A decay in which the nucleus loses an alpha particle, so the mass number decreases by 4 and the atomic number decreases by 2.AQA
Alpha emission: Removes two protons and two neutrons, so the mass number decreases by 4 and the atomic number decreases by 2.AQA
Alpha particle emission: The parent loses 4 from its mass number and 2 from its atomic number, with the alpha particle represented as ⁴₂α.AQA
alpha particle scattering experiment: An experiment whose results led to the conclusion that the mass of an atom was concentrated at the centre and that the nucleus was charged.AQA
Alpha radiation: A helium nucleus, 2 protons and 2 neutrons, with charge 2⁺; it is highly ionising but stopped by a few centimetres of air or a sheet of paper.AQA
alpha-scattering experiment: Showed most alpha particles passed straight through gold foil, but a few were deflected strongly.AQA
alternating current: A supply in which the potential difference repeatedly reverses direction, so the current changes direction many times each second.AQA
Alternating potential difference: A potential difference whose polarity swaps repeatedly, so current reverses direction, as in the UK mains supply.AQA
alveoli: Structures in the lungs whose walls are damaged by emphysema, reducing the surface area for gas exchange so less oxygen diffuses into the blood.AQA
Amino acid sequence: The particular order of amino acids coded for by a gene, which determines the specific protein that is made.AQA
Amino acids: The monomers of proteins, which join by condensation in a sequence determined by DNA, forming polypeptides that fold into functional proteins.AQA
Ammeter: A meter that measures current and is connected in series with the component, because the same current must pass through both.AQA
Amount in moles: Calculated as mass in g divided by relative formula mass.AQA
Amount of substance and the mole: A mole is an amount of substance containing a fixed number of stated particles, not a fixed mass.AQA
Amount of substance in moles: The quantity of reactant used or product formed, calculated from mass and molar mass using moles = mass ÷ molar mass.AQA
Ampere: The unit of current, where 'amp' is an acceptable written and spoken form of ampere.AQA
Amperes (A): The unit in which current is measured, alongside coulombs (C) for charge flow and seconds (s) for time.AQA
Amplitude: The maximum displacement of a point on a wave away from its undisturbed position, measured from the centre line to a crest or to a trough.AQA
Amylase: Produced in the salivary glands and the pancreas, it catalyses the breakdown of starch to maltose.AQA
Anabolic reactions: Reactions that build larger molecules from smaller ones, for example joining glucose molecules to form glycogen or amino acids to form proteins.AQA
Anaerobic digestion: Breakdown of the sludge by microorganisms, which reduces its volume and can produce biogas.AQA
Anaerobic respiration: Respiration that releases less energy per glucose molecule and produces lactic acid in animal cells or ethanol and carbon dioxide in plant and yeast cells.AQA
Ancient biomass: Crude oil is the remains of an ancient biomass consisting mainly of plankton that was buried in mud.AQA
Anemometer: An instrument used to measure wind speed.AQA
Animal and plant differences: Most animal cells differentiate early and usually lose the ability to divide, whereas many plant cells keep the ability to differentiate throughout the…AQA
Animals: Organisms that evolved once the percentage of oxygen gradually increased to a level that enabled them to evolve.AQA
Anode: The positive electrode, made positive by a direct current from a power supply, towards which negatively charged ions move.AQA
Anode oxidation and discharge of negative ions: Negative ions such as oxide ions are attracted to the positive electrode and lose electrons there.AQA
Anode process: The reaction at the anode in aqueous electrolysis, where hydroxide ions may be discharged instead of other anions.AQA
Anomalous results: Points that do not follow the overall pattern, which should be rechecked or excluded from the line of best fit.AQA
Antagonistic effectors and set points: Each controlled factor has a normal set point, and control is automatic and antagonistic, for example insulin and glucagon or sweating and shivering.AQA
Antibiotic development: Discovering and testing a new antibiotic takes many years and large amounts of money, requiring laboratory research, safety testing and clinical trials.AQA
Antibiotic resistance: Mutations of bacterial pathogens produce new strains, and some strains might be resistant to antibiotics, so they are not killed.AQA
Antibiotic stewardship and patient adherence: Patients should follow the prescribed dose, interval and duration rather than stopping when symptoms improve, so all bacteria are killed and none survive to…AQA
Antibiotics: Substances that work by interfering with structures or processes found in bacteria, such as bacterial cell walls or bacterial protein synthesis.AQA
Antibody production: A defence mechanism in which white blood cells release antibodies that bind to antigens on pathogens.AQA
Antibody specificity: Antibodies produced are specific to the pathogen's antigens, so they bind and prevent infection.AQA
Antigen-antibody binding: Binding sites on an antibody have a shape complementary to a specific antigen on a pathogen, and binding clumps pathogens and marks them for destruction.AQA
Antigen–antibody binding: Antibodies produced by lymphocytes bind to antigens on a pathogen's surface, causing pathogens to clump so phagocytes can destroy them more easily.AQA
antiretroviral drugs: Drugs that successfully control HIV but do not cure it, reducing the risk of progression to AIDS.AQA
Antitoxin: A protein produced by lymphocytes that binds to toxins released by pathogens and neutralises them.AQA
Antitoxins: Substances produced by some white blood cells that neutralise toxins released by bacteria.AQA
Antivirals: Medicines that may be used to treat viral infections.AQA
aorta: The vessel through which blood is pumped out of the left ventricle to the body.AQA
Application of average bond energies: These calculations use average bond energies, meaning the results are approximations.AQA
Application of genetic engineering: The vector inserts the gene into the required cells, where it can function, and the host cells are often cultured or cloned so many cells carry the gene.AQA
Application to all wave types: The equation applies to all waves, including sound, water and electromagnetic waves.AQA
Applying the equation to everyday devices: A heater transferring 36 000 J in 60 s has power 36 000 J ÷ 60 s = 600 W, and the answer's unit is stated as W.AQA
Approximate typical speeds: Guides rather than exact constants, such as walking about 1.5 m/s, running about 3 m/s and cycling about 6 m/s.AQA
Approximately: Shown by the symbol ̴, meaning the value is an estimate rather than exact.AQA
Approximation: A value or answer that is not exact, shown using the symbol ̴ placed between two quantities that are close in value or as a prefix before a number.AQA
Approximation and estimation in physics: The symbol ̴ means approximately, so 3 m/s is an estimate for an average person jogging, and individual values vary.AQA
Aqueous: Describes a solution in which a substance is dissolved in water, so that ions are free in solution.AQA
Aqueous electrolytes and water ionisation: Water adds H⁺ and OH⁻ to the list of ions present in the aqueous solution before discharge is compared.AQA
Aquifers: Groundwater sources that are often cleaner because soil and rock filter the water, but which can still contain dissolved minerals and microbes.AQA
Archaea: Single-celled prokaryotes placed in their own domain, separate from true bacteria, usually living in extreme environments.AQA
Area under a curve: The enclosed area on a velocity–time graph with a curved line or irregular shape, representing the distance travelled.AQA
Area under a velocity–time graph: The area between the line and the time axis represents the distance travelled, or displacement when direction is included.AQA
arithmetic mean: Add every value in the data set and divide the total by the number of values.AQA
Arrow: Means 'is converted into' and points from the large substrate to the small products.AQA
Arrow length and arrowhead: The length represents the magnitude of a force and the arrowhead gives its direction.AQA
Arteries: Blood vessels that carry blood away from the heart at high pressure, with walls containing thick elastic and muscular tissue and a narrow lumen that maintains…AQA
Artificial heart: A mechanical pump that takes over the pumping action to keep a patient alive whilst waiting for a heart transplant, or to allow the heart to rest as an aid to…AQA
artificial pacemaker: An electrical device used to correct irregularities in the heart rate.AQA
artificial selection: Humans decide which variants become parents of the next generation, choosing a characteristic for usefulness or appearance.AQA
Artificial selection by humans: Humans choose which organisms reproduce, rather than leaving reproduction to natural selection.AQA
Asexual reproduction: Involves only one parent and no fusion of gametes, with no mixing of genetic information.AQA
Asexual reproduction by binary fission: A single parent cell divides into two genetically identical daughter cells, and under favourable conditions this can happen every 20 minutes or so.AQA
Aspirin: A painkiller and anti-inflammatory medicine whose active ingredient is acetylsalicylic acid, developed from a compound found in willow.AQA
Asthma: An allergic reaction affecting the airways that can be triggered by an overactive immune response following an infection.AQA
Atmospheric composition: The proportions of different gases in the atmosphere, with nitrogen about 78% and oxygen about 21%.AQA
Atmospheric evolution: Over geological time, repeated photosynthesis by vast numbers of algae and plants reduced the percentage of carbon dioxide in the atmosphere.AQA
Atmospheric pollutants from fuels: Gases released into the atmosphere when a fuel is burned may include carbon dioxide, water vapour, carbon monoxide, sulfur dioxide and oxides of nitrogen.AQA
Atmospheric pollution: Sulfur dioxide and oxides of nitrogen are atmospheric pollutants released mainly by burning fossil fuels.AQA
Atmospheric pollution from combustion: Increased levels of carbon monoxide, sulfur dioxide, nitrogen oxides and particulates in the air arise mainly from burning fossil fuels in power stations,…AQA
Atom: The smallest part of an element that can exist.AQA
Atomic models: The plum pudding model pictures a sphere of positive charge with electrons embedded in it, while the nuclear model has a small, dense, positive nucleus with…AQA
Atomic number: Gives the number of protons and hence the number of electrons, so it determines the electron arrangement and the reactivity pattern.AQA
Atomic radius: A typical atom has a radius of about 1 × 10⁻¹⁰ m.AQA
Atomic structure: The atom is mostly empty space with a tiny, dense, positively charged centre called the nucleus, which repels positive alpha particles.AQA
atomic weight: The quantity by which early periodic tables arranged elements, though following its strict order could place elements in inappropriate groups.AQA
Atoms, molecules and ions: The particles in a mole may be atoms, molecules or ions, and the particle type must be stated.AQA
ATP: The cell's immediate energy currency, to which energy is transferred from the bonds of glucose.AQA
Attraction and repulsion: A magnet and a magnetic material always attract, while two permanent magnets repel when like poles face each other and attract when unlike poles do.AQA
Automatic control systems: The control of body temperature is an automatic control system involving nervous and chemical responses, not a conscious action.AQA
Autosomes: The 22 pairs of chromosomes that carry genes controlling characteristics other than sex.AQA
Average acceleration: A measure of how quickly velocity changes over a time interval, calculated by finding the change in velocity and dividing by the time taken.AQA
Average and instantaneous speed from graphs: For a curved line, find average speed using total distance and total time, or estimate instantaneous speed by drawing a tangent and finding its gradient.AQA
Average global temperature: A long-term mean calculated from worldwide measurements, not the temperature of one place or one day.AQA
Average kinetic energy and molecular speed: Increasing temperature increases the average kinetic energy and average speed of the molecules.AQA
Average rate: The total change in amount divided by the total time over a period.AQA
Average speed: A single value that describes the whole journey, calculated using total distance divided by total time, which smooths out the changes.AQA
Average speed for changing motion: The total distance travelled divided by the total time taken, used when speed changes during a journey.AQA
Average speed in context: If speed changes, the equation gives an average speed, and the result can be interpreted as the distance covered or the average speed over a journey.AQA
Avogadro constant: The number of atoms, molecules or ions in a mole of a given substance, with a value of 6.02 x 10²³ per mole.AQA
Avogadro constant 6.02 × 10²³: One mole contains the Avogadro constant of particles, 6.02 × 10²³, just as a dozen contains 12.AQA
Avogadro constant and particle number: The number of particles in one mole is the Avogadro constant, 6.02 × 10²³ per mole.AQA

B

Bacterial infections and antibiotic action: Penicillin kills bacteria without directly damaging human cells and is effective only against bacteria, not viruses.AQA
Bacterial reproduction by binary fission: Surviving bacteria reproduce quickly by this method, so a resistant mutation can increase in frequency in the population.AQA
Balanced and unbalanced forces: At uniform velocity the forward and resistive forces balance, so the resultant force is zero.AQA
Balanced chemical equation: Uses formulae to show reactants and products with the same number of each type of atom on both sides.AQA
Balanced equations and state symbols: Writing the products as a word equation and, where asked, as a balanced symbol equation with correct formulae and state symbols.AQA
Balanced equations as mole ratios: The coefficients tell you the number of moles of each substance that react or form.AQA
Balanced forces: When the forward and backward arrows are equal, the resultant force is zero and the object stays at rest or moves at constant velocity.AQA
Balanced ionic equations for monoprotic and diprotic acids: Hydrochloric acid ionises completely as HCl(aq) → H⁺(aq) + Cl⁻(aq), and sulfuric acid, being diprotic, as H₂SO₄(aq) → 2H⁺(aq) + SO₄²⁻(aq).AQA
balanced nuclear equation: One in which the sum of the mass numbers on the left equals the sum on the right, and the same for the atomic numbers.AQA
Balanced symbol equation: Equation written with the correct state symbols if they are given or can be deduced, with the same number of atoms of each element on both sides.AQA
Balanced symbol equations: Symbol equations which are balanced in terms of the numbers of atoms of each element involved on both sides of the equation.AQA
Balancing: Achieved by placing or adjusting normal-script multipliers in front of formulae until the number of each type of atom is equal on both sides.AQA
Balancing a half equation: Atoms and charge must both balance, with the number of electrons added matching the charge change.AQA
Balancing benefits against drawbacks: Weighing benefits, such as less ore extracted and less energy used, against drawbacks, such as sorting, transport and loss of properties.AQA
Balancing chemical equations: Adjusting whole-number coefficients so that every element has the same number of atoms on both sides.AQA
Balancing half equations: Ensuring the number of atoms and total electrical charge are equal on both sides of a half equation.AQA
Balancing numbers: The values in a symbol equation that can be calculated from the masses of reactants and products using moles and a simple whole number ratio.AQA
Balancing symbol equations using coefficients: Writing correct formulae and then adjusting coefficients so every element has the same number of atoms on each side.AQA
Ball and stick models: Show the shape and the angles between bonds clearly, but the balls are not the real size of the atoms and the sticks suggest a solid connection where there is…AQA
Barrier method: A method such as a condom or diaphragm that spermicides are often used with to increase effectiveness.AQA
Basal metabolic rate: The rate at which the resting body releases energy from its stored fuels.AQA
Becquerel: The unit of activity, where one becquerel equals one decay per second.AQA
Behaviour recorded by traces: Trace fossils reveal behaviour and movement, which body fossils often cannot, adding evidence about how organisms lived.AQA
Behavioural adaptation: An inherited action, such as migrating, hibernating or basking in the sun, that is typical of the species and helps it survive.AQA
Bending: Forces act at different points, for example a downward push on the middle of a ruler with upward forces at the supports.AQA
Benedict's solution: Reagent added to the food sample and heated in a water bath, where a blue to green, yellow, orange or brick-red colour indicates a reducing sugar.AQA
Benign: Describes tumours that grow in one place and do not invade or spread.AQA
Beta decay: A decay in which a neutron changes into a proton and an electron, so the mass number stays the same while the atomic number increases by 1.AQA
Beta emission: Converts a neutron into a proton and emits an electron, so the mass number stays the same but the atomic number increases by 1.AQA
beta particle: A fast-moving electron emitted from a nucleus during beta decay, written with the symbol β or e.AQA
Beta particle emission: The mass number is unchanged and the atomic number increases by 1, with the beta particle represented as ⁰₋₁β.AQA
Beta radiation: A fast-moving electron emitted when a neutron changes into a proton, with charge 1⁻; it is moderately ionising and stopped by a few millimetres of aluminium.AQA
Bias and pre-determined conclusions: Choosing boundaries that flatter a product so the study reaches a conclusion decided in advance.AQA
Bias and source credibility: Looking for bias, selective use of data, missing uncertainties and conflicts of interest, and checking whether sources are peer-reviewed.AQA
Bias in data collection: Selection without bias, for example choosing every tenth name from a list rather than only asking people in a gym, is needed or the estimate of risk may be…AQA
Bile: Made in the liver and stored in the gall bladder, it is alkaline to neutralise hydrochloric acid from the stomach and emulsifies fat to form small droplets.AQA
Binary fission: A process in which one parent cell divides into two genetically identical daughter cells.AQA
binary ionic compound: A compound that contains a metal cation and a non-metal anion.AQA
Binomial nomenclature: A naming system in which the genus is the first, capitalised word and the species is the second, lower-case word.AQA
Biodiversity: The variety of different species and the range of genetic variation within them, which matters because stable ecosystems depend on many interlinked organisms.AQA
Biodiversity and habitat protection: Recycling helps maintain biodiversity by reducing habitat destruction, pollution and resource extraction.AQA
Biodiversity decline: Each activity lowers the area and quality of habitat, so populations shrink and biodiversity falls.AQA
Biodiversity loss: A reduction in the variety of different plant, animal and microorganism species that live in a habitat.AQA
Biofuels: An alternative energy source produced from crops such as palm oil or sugar cane.AQA
Bioleaching: Using bacteria to convert insoluble copper compounds into soluble ones, producing a leachate from which copper is obtained.AQA
Biological catalysts: Enzymes are catalysts in biological systems and speed up reactions such as digestion.AQA
Biological drawings: Produced with sharp pencil lines, no shading, and labels with straight lines that touch the structure.AQA
Biological valve: A replacement valve taken from an animal or a human donor, which may wear out sooner.AQA
Biomass: Biological material formed from the biological molecules built using glucose, including carbohydrates, lipids, proteins and nucleic acids.AQA
Biomass and carbon storage: The carbon from carbon dioxide becomes part of glucose and then biomass, stored in living tissue and able to be buried later.AQA
Biosynthesis of new biological molecules: The products of digestion are used by cells to build new carbohydrates, lipids and proteins.AQA
Biotic: The living organisms, including plants, animals, fungi and microorganisms, and their interactions such as feeding, competition and disease.AQA
biotic components: The living parts of an ecosystem, such as plants, animals and bacteria.AQA
Biotic factor: A living (or virus) influence from another organism, such as a new pathogen arriving in a population.AQA
Biotic factors: Living factors which can affect a community.AQA
Biuret reagent: Reagent added to the sample, where a purple or violet colour indicates protein.AQA
Bleaching action of chlorine: The litmus dye is chemically destroyed by chlorine, so the paper loses its colour and turns white.AQA
Blood: Transports the absorbed products to body cells, where they are used for processes such as respiration, growth and repair.AQA
Blood cell function: Red blood cells carry oxygen and white blood cells defend against pathogens.AQA
Blood flow rate: Volume of blood passing a point each second, calculated as volume divided by time.AQA
Blood flow speed: Speed of blood flow calculated as distance divided by time.AQA
Blood glucose homeostasis: Keeping glucose steady between meals, with the pancreas detecting a fall and secreting glucagon so blood glucose concentration rises back towards normal.AQA
Blood glucose regulation: Blood glucose concentration is monitored and controlled by the pancreas, which detects changes and releases hormones.AQA
Blood pressure and clotting: Smoking damages artery lining, raises blood pressure and makes platelets stickier, increasing clot risk.AQA
Blood supply: A rich network of capillaries close to the exchange surface, which removes the substance that has diffused in and brings a fresh supply of blood.AQA
Bohr's model: Electrons in shells or energy levels at set distances from the nucleus.AQA
Boiling: A change of state in which energy is transferred to the particles to overcome the forces holding them together in the liquid, so the particles separate into a…AQA
Boiling point: As hydrocarbon molecules get larger, this increases because larger molecules have stronger intermolecular forces, so more energy is needed to overcome them.AQA
Bond breaking: Energy must be supplied to break bonds in the reactants, and this step is endothermic because energy is taken in from the surroundings.AQA
Bond breaking and bond formation: Every reaction involves breaking bonds in the reactants and forming bonds in the products; breaking a bond requires an input of energy, while forming a bond…AQA
Bond breaking and bond making: Bond breaking takes in energy, while bond making releases it.AQA
bond energy: The average energy required to break one mole of a specific covalent bond in the gaseous state.AQA
Bond forming: Releases energy to the surroundings, so it is exothermic.AQA
Bonding and structure: The type present, such as simple molecular, giant ionic, giant covalent or metallic, which determines the energy needed to overcome the forces.AQA
Brackets: These are treated in the same way as subscripts, with the subscript after the bracket multiplying every atom inside.AQA
Brain: A coordination centre that processes information from many receptors and coordinates responses such as movement.AQA
Braking distance: The distance travelled between the driver applying the brakes and the vehicle coming to rest.AQA
Braking force: A larger braking force produces a larger deceleration in the direction opposing motion.AQA
Braking force, braking distance and temperature rise: A larger braking force does more work over the same distance, removing kinetic energy faster and increasing brake temperature more.AQA
Bread and alcoholic drinks: Products of manufacture in which fermentation has economic importance.AQA
Breakdown reactions: Reactions that split larger molecules into smaller ones, such as hydrolysis of starch to glucose.AQA
Breaking the chain of infection: Interrupting any link in the process of a pathogen leaving one host, travelling, and entering a new host, which reduces transmission.AQA
Breath volume: Increases so that each breath moves a larger volume of air and gas exchange in the alveoli is greater.AQA
Breathing rate: Increases so that oxygen enters the blood and carbon dioxide leaves it more rapidly.AQA
Breeding programme: A managed attempt to increase the numbers of an endangered species by controlling reproduction, usually in zoos, wildlife parks or specialist centres.AQA
Bromine water: An orange solution used as a test for unsaturation, which is decolourised when shaken with an alkene.AQA
Buckminsterfullerene: A hollow sphere of carbon that can trap atoms or small molecules inside its cage, so it is investigated for drug delivery, as a lubricant and as a catalyst.AQA
Build-up of nitrogen: Volcanoes produced nitrogen which gradually built up in the atmosphere.AQA
Burning splint: A splint that is lit and held at the open end of a test tube of the gas, not inserted into the tube.AQA
but-: Prefix used in the names of alkanes to indicate four carbon atoms.AQA

C

c = E ÷ (m × ∆θ): The rearranged equation used to find specific heat capacity from energy, mass and temperature rise.AQA
C₆H₁₂O₆: Glucose, one molecule of which contains six carbon, twelve hydrogen and six oxygen atoms.AQA
Calcium carbonate: The insoluble solid formed when carbon dioxide reacts with calcium hydroxide, appearing as a fine white precipitate.AQA
Calculating a mean rate: Dividing the measured change by the time taken and attaching the correct unit, which must match the quantity measured.AQA
Calculating change in distance and time: Pick two points, read the change in distance (Δd) and time (Δt), then divide: speed = Δd ÷ Δt.AQA
Calculating rates from measurements: Working out a rate from numerical data using rate = change in mass ÷ time, or reading a rate directly from a graph and quoting its unit.AQA
Calibration: The scale of a spring-balance is calibrated in newtons, often using known weights or a known gravitational field strength.AQA
Capillaries: Vessels that exchange substances, with walls one cell thick and a narrow lumen, giving a large surface area and short diffusion distance.AQA
Carbohydrases: Enzymes that catalyse the breakdown of carbohydrates into simple sugars.AQA
Carbohydrate controlled diet: Reduces the amount of glucose entering the blood from digestion, helping to lower blood glucose concentration.AQA
Carbon and nitrogen cycles: Carbon moves between the atmosphere, producers, consumers, decomposers and fossil fuels, while microorganisms in the soil convert nitrogen compounds into…AQA
Carbon as the basis of biological molecules: Carbon forms the backbone of carbohydrates, proteins, lipids and DNA, so it is needed to build living cells.AQA
Carbon cycle: Returns carbon from organisms to the atmosphere as carbon dioxide to be used by plants in photosynthesis, so carbon is continuously recycled between organisms…AQA
Carbon dioxide: A product of anaerobic respiration in plant and yeast cells that makes bread rise.AQA
Carbon dioxide absorption: Trees absorb carbon dioxide during photosynthesis, so removing them reduces this absorption and increases carbon dioxide in the atmosphere.AQA
Carbon dioxide equivalent: A way of expressing emissions so that greenhouse gases with different warming effects can be added together, written kg CO₂e or t CO₂e.AQA
Carbon footprint: The total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event.AQA
Carbon nanotubes: Cylinders of hexagonal carbon rings, often just nanometres wide, that are very strong with a low mass and conduct electricity and heat well.AQA
Carbon store: Peat is a long-term store of carbon because carbon taken from the atmosphere by living plants becomes locked in it.AQA
Carbon stores: Sedimentary rocks and fossil fuels, which lock carbon away for millions of years.AQA
Carcinogen: Any agent that increases the chance of cancer developing by damaging DNA, so cells may divide in an uncontrolled way and form a tumour.AQA
Cardiac glycosides: Active compounds, such as digoxin, isolated from foxglove tissue.AQA
Carl Linnaeus: The scientist who developed the traditional system for classifying living things into groups.AQA
Carl Woese and scientific models: He used evidence from chemical analysis to propose the three-domain system, a classification model reflecting biochemical evidence rather than only visible…AQA
Carrier proteins: Proteins in the cell membrane of gut lining cells that bind the sugar and use energy from ATP to change shape and transfer it into the blood.AQA
carriers: People who have one recessive disorder allele but do not show the condition and can pass the allele to offspring.AQA
Cartilage rings: C-shaped rings in the walls of the trachea and bronchi that hold the airway open, preventing collapse when pressure changes during breathing.AQA
Catabolic reactions: Reactions that break larger molecules into smaller ones, for example respiration breaking down glucose or digestion hydrolysing starch to maltose.AQA
Catalysis and alternative reaction pathways: A catalyst provides an alternative pathway with a lower activation energy, so the peak is lower while the overall energy change stays the same.AQA
Catalyst: A substance that increases the rate of a reaction without being used up or chemically changed at the end.AQA
Catalyst specificity: Catalysts are specific, so different reactions need different catalysts.AQA
Catalysts: A catalyst provides an alternative pathway with a lower activation energy, increasing the rate without being used up.AQA
Catalytic cracking: Passes vaporised long-chain hydrocarbons over a hot catalyst, commonly a zeolite, at a high temperature, and the catalyst speeds up the breakdown.AQA
Cathode: The negative electrode, made negative by a direct current from a power supply, towards which positively charged ions move.AQA
Cathode reactions in electrolysis: At the negative electrode, positively charged ions are attracted and gain electrons, so the reactions are reductions.AQA
Causal mechanism: A biological explanation of how the factor produces the disease.AQA
Causal reasoning in chemistry: Explaining an effect requires a causal chain linking the pollutant's property to the harm caused, for example sulfur dioxide dissolving in rain to form acid…AQA
Causation: A proven cause-and-effect relationship, which should not be assumed from data showing correlation without further evidence.AQA
Cause: A reason linked to each change, such as cost, availability, government policy, technology, environmental concern or demand.AQA
Cause and effect: Identifying what produces a change and describing the resulting change, then testing whether the link is genuine.AQA
Causes of carbon dioxide decrease: Carbon dioxide decreased because it dissolved in oceans to form sedimentary rocks, and photosynthesis by algae and plants removed more carbon dioxide.AQA
Causes of global climate change: Driven mainly by increased greenhouse gases such as carbon dioxide and methane.AQA
Causes of oxygen and nitrogen increase: Oxygen increased because photosynthesis by algae and plants released it, while nitrogen increased because it was released by volcanoes and being unreactive it…AQA
Cell: The basic building block of all living organisms, and the smallest unit that can be called living.AQA
Cell cycle and copying: Copying happens before division begins, and the number of chromosomes is unchanged by copying.AQA
Cell cycle stages: The three overall stages are cell growth and replication of DNA, nuclear division, then division of the cytoplasm and cell membranes.AQA
Cell damage: Replication inside the cell disrupts normal cell activity and damages or destroys the cell, and the cell may burst.AQA
Cell differentiation: As the embryo develops, cells become specialised for particular jobs, allowing a multicellular organism to carry out many different functions.AQA
Cell division and the cell cycle: Mitosis is a type of cell division that produces two genetically identical diploid cells from one parent cell.AQA
Cell division by mitosis: The process by which the fertilised egg divides to produce genetically identical cells.AQA
Cell growth and DNA replication: The first stage, in which the cell grows, increases its mass, replicates its DNA to form two copies of each chromosome, and increases sub-cellular structures.AQA
Cell membrane: The thin partially permeable barrier that surrounds every cell and controls which substances enter and leave.AQA
Cell membrane and transport: A partially permeable barrier that controls what enters and leaves the cell.AQA
Cell respiration: The process in which sugar molecules are broken down to release energy for processes such as muscle contraction and active transport itself.AQA
cell sap: A solution of sugars and salts that fills the permanent vacuole.AQA
Cell size and organism size: As a cell gets bigger, volume grows faster than surface area, so the ratio falls and diffusion alone becomes too slow to meet demand.AQA
Cell specialisation: Specialised plant cells have shapes and features matched to their jobs, and comparing the three cell types shows how structure links to function.AQA
Cell specialisation and adaptation: The sperm has a tail to swim and many mitochondria to release energy, while the egg is larger and non-motile with food reserves in the cytoplasm.AQA
Cell structure and adaptation: Phloem is composed of tubes of elongated cells joined end to end, with pores in the end walls between adjacent cells.AQA
Cell structure and function: Plant and algal cells have a cell wall outside the cell-surface membrane, and this wall strengthens the cell and helps maintain its shape.AQA
Cell turgor and plasmolysis: In plant cells, water entering the vacuole increases turgor pressure, making the cell firm; water leaving causes plasmolysis.AQA
Cell wall: The structure strengthened by cellulose, which supports the cell, resists osmotic pressure and helps the plant remain upright.AQA
Cells: Individual units grown in culture, used first to see whether a new drug harms them or changes how they grow.AQA
Cellular control of pore size: Guard cells surround each stoma and change shape by gaining or losing water; turgid guard cells open the pore and flaccid guard cells close it.AQA
Cellular respiration: The controlled release of energy from organic compounds such as glucose, broken down in enzyme-controlled reactions.AQA
Cellulose: A structural polysaccharide that forms plant cell walls and gives strength, with straight chains held by hydrogen bonds, and is not used as an energy store in…AQA
Cellulose as a biological polymer: A carbohydrate polymer that forms strong fibres, giving the wall its strength.AQA
Central nervous system: The brain and spinal cord, which sensory neurones run to and relay neurones connect within.AQA
change in allele frequency over generations: Repeating the process over many generations increases the proportion of alleles for large or unusual flowers in the population.AQA
Change in height: Found by identifying the start and end heights and subtracting the lower height from the higher height.AQA
Change in mass: Found by subtracting the original mass from the final mass, where a positive change is a gain and a negative change is a loss.AQA
Change in thermal energy: The mass of the substance multiplied by its specific heat capacity and by the temperature change.AQA
Change in velocity: The difference between the final velocity and the initial velocity, found by subtracting the initial velocity from the final velocity.AQA
Change in velocity Δv = v − u: Found by subtracting the initial velocity from the final velocity.AQA
Change of state: Occurs when energy instead breaks or loosens bonds between particles, so the arrangement changes while the temperature stays constant.AQA
Change of state and latent heat: At boiling point, further energy transfer causes a change of state from liquid to gas without a change in temperature; this energy is the latent heat of…AQA
Change over geological time: Whether a body plan stayed stable or was modified, seen by arranging fossils by rock age as life developed on Earth.AQA
Changes in a system: There are changes in the way energy is stored when a system changes.AQA
Changes in atmospheric composition over geological time: Earth's atmosphere changed from an early mixture of carbon dioxide, water vapour, methane and ammonia to today's atmosphere of 78% nitrogen and 21% oxygen.AQA
Changes in atomic nuclei and radioactive emissions: An unstable atomic nucleus changes its composition and this causes emission of alpha, beta or gamma radiation, the nuclear change being the cause.AQA
Changes in motion: A non-zero resultant force is needed to start, stop, speed up, slow down or change direction.AQA
Changes of state: Water is continuously evaporated and precipitated, and water vapour condenses into clouds as moist air rises and cools.AQA
Changes of state and energy transfer: Heating transfers energy to the particles so they vibrate or move faster, and freezing and condensing are the reverse changes as energy is transferred away.AQA
Changing scientific models: Classification systems are provisional models that are revised when new evidence emerges, such as molecular data leading to reclassification.AQA
Changing speed: Shown on a distance–time graph by a curve, including acceleration when the curve gets steeper and deceleration when it gets shallower.AQA
Charge: Determined by the difference between the number of protons and the number of electrons, not by the number of neutrons.AQA
Charge and mass distribution: How charge and mass are arranged in the atom: spread throughout in the plum pudding model, concentrated in the nucleus in the nuclear model.AQA
Charge and neutrality: In a neutral atom the number of electrons equals the number of protons, so the positive and negative charges balance and there is no overall charge.AQA
Charge and notation: The size of the charge equals the number of electrons transferred, and the sign shows whether electrons were lost or gained, written as a superscript on the…AQA
Charge and potential difference: Work done can be calculated using E = Q × V, where Q is charge flow and V is potential difference.AQA
Charge and repulsion: A tiny, dense, positively charged nucleus repels the positive alpha particles strongly at close range, which explains the deflections.AQA
Charge balance: Atoms are balanced first, then charge is balanced by adding electrons to the more positive side.AQA
Charge balance in ionic compounds: The total positive charge equals the total negative charge overall.AQA
Charge carriers and electrons: Charge is carried by electrons in metal wires, and each electron carries 1.6 × 10⁻¹⁹ C.AQA
Charge carriers in semiconductors: At low temperatures few charge carriers are available, so resistance is high; at higher temperatures more charge carriers are released, so resistance falls.AQA
Charge distribution: In the plum pudding model positive charge is spread throughout, whereas in the nuclear model it is concentrated in a very small central nucleus.AQA
Charge flow: Measured in coulombs (C), it is the charge passing through a component and equals energy transferred divided by potential difference.AQA
Charge flow and current: Current is the rate of flow of electrical charge, measured in amperes with an ammeter connected in series.AQA
Charge, current and time relationships: Charge is current multiplied by time, Q = It, so the energy equation can also be written as E = VIt.AQA
Charges: Shown outside the square brackets for each ion, such as a 1⁺ charge on the sodium ion and a 1⁻ charge on the chloride ion.AQA
Chemical change: A change in which new substances with different properties form and simple reversal does not recover the original material.AQA
Chemical formula: Shows the elements in a substance and the number of atoms of each, using symbols and subscript numbers.AQA
Chemical formulae and relative atomic masses: The relative atomic masses of all atoms in the formula are added to find the relative formula mass.AQA
Chemical modification: The process by which chemists change a natural lead compound to develop a related medicine, which can make it more effective or reduce side effects.AQA
Chemical properties as a basis for classification: His approach showed that chemical properties, not mass alone, were the better basis for arranging elements.AQA
Chemical reactions: Processes that always involve the formation of one or more new substances and often involve a detectable energy change.AQA
Chemical reactions in cells: Many of the cell's chemical reactions take place in the cytoplasm, which is mainly water with dissolved substances.AQA
Chemical reactivity and ion formation: Metals form positive ions by losing electrons, whereas non-metals gain or share electrons, forming negative ions or covalent bonds.AQA
Chemical symbol: A representation of an atom of each element, such as O for an atom of oxygen or Na for an atom of sodium.AQA
Chemical symbols: A shorthand way of representing substances, such as C₆H₁₂O₆ for glucose, O₂ for oxygen, CO₂ for carbon dioxide and H₂O for water.AQA
Chemical symbols and names: Use the periodic table to find element names and symbols, particularly for the first 20 elements, Groups 1 and 7, and others in the specification.AQA
Chemosynthesis: An energy pathway without sunlight, using dissolved chemicals such as hydrogen sulfide instead of light.AQA
Chlorination: Adding chlorine to water to kill microorganisms such as bacteria that could cause disease.AQA
Chlorine: Added as a gas or compound, it kills bacteria by disrupting their cell processes and leaves a residual that protects water in pipes.AQA
Chlorophyll: The green pigment inside chloroplasts, which absorbs light energy so that the plant can make glucose.AQA
Chloroplasts: Green structures containing chlorophyll that absorb light energy for photosynthesis and are found mainly in leaf cells.AQA
Cholesterol and plaque formation: A diet high in saturated fat raises LDL cholesterol, which forms fatty plaques in coronary arteries.AQA
Choosing apparatus and units: A balance is used for mass in g and a gas syringe for volume in cm³, and the method must match the reaction.AQA
Choosing scales: Selecting a scale where each major square represents a simple value such as 1, 2, 5 or 10 units, so the data fill most of the grid.AQA
Chromatogram: Shows spots produced by substances carried different distances by a solvent, and is interpreted by identifying the solvent front, the start line and each spot.AQA
Chromatography: Separating dissolved substances using a stationary phase and a moving solvent, relying on different solubilities and therefore different distances travelled.AQA
Chromosome: A thread-like structure of DNA found in the nucleus of eukaryotic cells, carrying genes in a fixed linear order.AQA
Chromosome number: Each gamete has half the normal chromosome number, so when they join the zygote has the full, normal number again.AQA
Chromosome number and meiosis: Both gametes are produced by meiosis, so each nucleus contains half the normal chromosome number, 23 in humans.AQA
Chromosomes: Structures in the nucleus that contain the DNA, each being a coiled molecule of DNA.AQA
Chromosomes and DNA: Genetic information is carried as DNA in chromosomes in the nucleus.AQA
Cilia action: Tiny hair-like structures on epithelial cells beat rhythmically to sweep mucus containing trapped microbes towards the throat.AQA
Circuit applications: The application of LDRs in circuits, for example switching lights on when it gets dark, is required.AQA
Circuit construction and diagrams: Using circuit diagrams to construct appropriate circuits, with a cell, ammeter in series, voltmeter in parallel with the test component, and a variable…AQA
Circuit construction from diagrams: Building circuits from circuit diagrams, with an ammeter in series and a voltmeter in parallel with the component under test.AQA
Circuit design for valid measurement: Connecting the component in series with the cell, switch and ammeter, and the voltmeter in parallel across the component only, so the meters do not alter the…AQA
Circuit representation: Drawing circuits with standard symbols, straight lines with right-angled corners, and no gaps at component symbols.AQA
Circuit rules: In parallel the potential difference across each component is the same, whereas in series the supply potential difference is shared between components.AQA
Circular motion: Motion in a circle in which the direction of travel changes continuously, so the velocity is constantly changing even if the speed remains constant.AQA
Circulatory system: Delivers glucose and oxygen and removes carbon dioxide by the blood, on which movement depends.AQA
Classification: Sorting living things into groups depending on their structure and characteristics.AQA
Classification of waves with examples: Sorting waves as transverse, such as light, water surface ripples and waves on a rope, or longitudinal, such as sound in air.AQA
Climate: The long-term pattern over decades, rather than short-term and local conditions.AQA
Climate change: A consequence of increased carbon dioxide concentration, including rising sea levels and changing weather patterns.AQA
Clinical testing: Testing that follows promising preclinical results, starting with small groups of healthy volunteers to check safety and dose, then patients to check…AQA
Clinical trials: Compare groups receiving the drug with controls, using placebos where appropriate, to measure efficacy and refine dose.AQA
Clones: Genetically identical offspring, produced because only mitosis is involved.AQA
Cloning: Allowing the embryo to divide in the laboratory to produce many genetically identical stem cells, giving a large supply for research or treatment.AQA
Closed circuits: A complete closed conducting path is needed so charge can complete a continuous path.AQA
Closed system: A system in which no energy enters or leaves, so the total energy stored inside stays constant.AQA
Closed systems: No energy transfers in or out, so the total energy remains exactly the same, though the way it is stored changes.AQA
Cloudiness: The milky appearance of limewater caused by suspended calcium carbonate, which is the positive result of the test.AQA
Coal: Formed from plant material buried in swampy conditions where there was little oxygen, so decay was incomplete, with heat and pressure over geological time…AQA
Coarse and fine adjustment knobs: Used to focus the slide, starting on the lowest power objective.AQA
Coefficient: The value A in standard form, which must be at least 1 and less than 10 and adjusted with the index if it is not.AQA
Coefficients: The large numbers in front of formulae, adjusted to balance an equation, never changing the subscripts inside a formula.AQA
Collision frequency and force: Faster particles hit the walls more often and each impact is harder, so the pressure rises.AQA
Collision frequency and force on container walls: Faster molecules collide with the container walls more frequently, and each collision produces a greater change of momentum, so the average force on the walls…AQA
Collision theory: A hypothesis is justified by referring to the frequency or energy of collisions between reacting particles, including the proportion of particles with energy…AQA
Collisions and explosions: Interactions to which the principle that total momentum before an event equals total momentum after it applies.AQA
colour code: A safety code that lets anyone wiring a plug or inspecting a cable connect the correct conductor to the correct terminal.AQA
combination of genes and the environment: The way many features, such as height, mass and skin tone, are affected by both, so the observed value is not fixed by genes alone.AQA
Combustion: A return process in which fossil fuels and other organic material are burned, releasing carbon dioxide into the atmosphere.AQA
Combustion of fossil fuels: Sulfur dioxide forms when sulfur impurities in coal or oil burn, and oxides of nitrogen form when nitrogen and oxygen from the air react at the high…AQA
Combustion products: Carbon atoms can form carbon dioxide or carbon monoxide, hydrogen atoms form water vapour, and any sulfur forms sulfur dioxide.AQA
Common ancestry: All species share ancestors with simple early life, including humans, as indicated by fossils and shared biochemistry.AQA
Common ancestry and biodiversity: All organisms share a common ancestry, so they are related to varying degrees, and different environments select for different features, explaining the…AQA
Communicable disease: A disease spread between organisms by pathogens such as bacteria and viruses, for example influenza or malaria.AQA
Communicating results: Sharing results with audiences such as other scientists, policymakers, industry and the public, each needing different depth and language.AQA
Communication technologies: Radio waves are used for television and radio, microwaves for satellite communications and visible light for fibre optic communications.AQA
Community: All the populations of different species living and interacting in a habitat.AQA
Commutator action: The split-ring commutator reverses the current in the coil every half rotation so the coil continues turning in the same direction.AQA
Compare: Read values across rows or columns and state which resource is larger or changing faster, quoting figures with units.AQA
Comparing cell types: Contrasting a bacterial cell with a plant cell, where both may have a cell wall but only the plant cell has a true nucleus, chloroplasts and mitochondria.AQA
Comparing fossil and living structures: Showing whether the body plan has changed a lot or only a little over time by comparing the structure of a fossil with a living organism.AQA
Comparing measured and known values: To distinguish pure from impure, compare the measured melting point or boiling point with the known value for that substance.AQA
Comparing modes of transport: Setting typical speeds against each other, such as cycling being roughly twice running speed.AQA
Comparing products over their lifetimes: Asking which product uses more energy or resources while operating, and weighing the use stage against manufacture and disposal.AQA
Comparing strong and weak acids at equal concentration: At the same total acid concentration, a greater degree of ionisation results in a higher concentration of H⁺ ions, so the stronger acid has the lower pH.AQA
Comparing temperature with fixed points: Checking a given temperature against the melting point and boiling point to decide whether a substance is solid, liquid or gas.AQA
Comparison of diabetes types: The two types can be compared by stating the cause, the insulin status and the main treatment for each.AQA
Comparison of graphite and metals: Both conduct because charged particles can move, but graphite has a layered covalent lattice rather than a lattice of positive ions.AQA
Comparison of stem cell sources: Embryonic stem cells build the body once, adult stem cells maintain and repair it, and meristem cells keep a plant growing for its whole life.AQA
Comparison with Mars and Venus: The early atmosphere may have been like the atmospheres of Mars and Venus today, consisting of mainly carbon dioxide with little or no oxygen gas.AQA
Compass use: Move the compass so its centre is at the last mark and mark the new direction, repeating this to form a line.AQA
Competing ions in aqueous electrolysis: In aqueous solution, water molecules dissociate slightly to give hydrogen ions, H⁺, and hydroxide ions, OH⁻, as well as the ions from the dissolved compound,…AQA
Competing ions in aqueous solutions: In an aqueous solution, water molecules break down producing hydrogen ions and hydroxide ions that are discharged, and these ions compete with those from the…AQA
Competition: Occurs when organisms require the same resource that is in limited supply, and may be between individuals of the same species or between different species.AQA
Competition and survival: Organisms compete for limited resources such as food, mates and space, and those with variations better suited to the environment are more likely to survive…AQA
Competition for finite land: Land is a finite resource shared by humans and wildlife, so human activities reduce the amount of land available for other animals and plants.AQA
Competition for limited resources: Organisms in a community share a habitat, so when a resource is in short supply they compete for it.AQA
Competition for resources between species: Competition between species is a biotic factor, and if a competitor is removed the remaining species may gain resources and increase.AQA
Competition in plants and animals: Plants compete for light, space, water and mineral ions, while animals compete for food, mates and territory.AQA
Complete combustion: Burning a hydrocarbon in a plentiful supply of oxygen, producing carbon dioxide and water only.AQA
Complete ionisation in aqueous solution: A strong acid is completely ionised in aqueous solution, leaving no undissociated acid molecules.AQA
Complexity and uncertainty in environmental systems: Many interacting components mean a single simple cause-and-effect chain is inadequate, and simplification creates uncertainty in predictions.AQA
Composite materials: Materials in which carbon nanotubes are useful because they are strong and light.AQA
Composition of fuels: Most fuels, including coal, contain carbon and/or hydrogen, and may also contain some sulfur.AQA
Composition of the atmosphere: The modern atmosphere is a mixture of gases, with nitrogen by far the most abundant.AQA
Composition of the atmosphere as a mixture: The atmosphere is a mixture of gases, so the proportions can be described as percentages by volume.AQA
Compound measure: A quantity made from two other measurements, used here to express how quickly water enters plant tissue by osmosis.AQA
Compound measures and units: A measure that combines two different quantities, so its unit is a combination of two units.AQA
Compounds: Substances containing two or more elements chemically combined in fixed proportions, which can be represented by formulae using the symbols of the atoms from…AQA
Compression: Two pushing forces act along the object towards each other, for example squeezing a spring between two hands.AQA
Compressions and rarefactions: The regions of high and low pressure or density produced in a longitudinal wave.AQA
concentrated: Describes an acid that contains a large amount of acid per unit volume.AQA
Concentration: The mass of solute dissolved in a given volume of solution, measured for example in grams per dm³.AQA
Concentration and pressure: Higher concentration means more reactant particles per unit volume in solution, and higher gas pressure means the same particles occupy a smaller volume, so…AQA
Concentration changes and equilibrium position: Increasing a reactant concentration shifts equilibrium to the right, increasing product yield, while increasing a product concentration shifts equilibrium to…AQA
Concentration gradient: The difference in concentration between two regions, which blood flow keeps steep by removing the diffused substance and bringing blood with a lower…AQA
Concentration gradients: A rich blood supply and a counter-current flow of water and blood maintain a steep one so that diffusion continues.AQA
Concentration of mass and charge in the nucleus: The mass of an atom was concentrated at the centre and the nucleus was charged, so the positive charge and most of the mass must be concentrated in a tiny…AQA
Concentration of solutions: Measures how much solute is dissolved in a given volume of solution, linking mass and volume through concentration = mass ÷ volume.AQA
Condensation: A reaction in which glucose units are joined together, with the loss of a water molecule each time a unit is added.AQA
Condensation and formation of oceans: As the planet cooled, water vapour condensed into liquid water, forming the oceans.AQA
Conditions needed by microorganisms: Warmth, moisture and oxygen are needed to break down dead material.AQA
Conduction: The way heat is transferred from the water to the rest of the food after the temperature of the water is raised.AQA
Consequence: The harm itself, such as cell death, tissue damage, radiation sickness at high doses and long-term health effects.AQA
Conservation and sustainability: Measures have only recently been taken to try to stop the reduction in biodiversity caused by many human activities.AQA
Conservation of atoms in equations: A balanced symbol equation for a reversible reaction must have the same number of each type of atom on both sides.AQA
Conservation of charge: Charge is conserved, so the rate of flow of charge (current) cannot change unless charge accumulates, which it does not in a simple series loop.AQA
Conservation of charge and mass: Ensuring that both atoms and electrical charges are fully balanced across the equation, with the number of atoms of each element and the total electrical…AQA
Conservation of charge in a single loop: Because there is a single loop, the current is the same at every point, so the same current passes through each component.AQA
Conservation of chemical properties in physical mixtures: The chemical properties of each substance in the mixture are unchanged.AQA
Conservation of energy: The principle that the total energy is conserved, so the decrease in kinetic energy equals the increase in thermal energy stores, assuming no change in…AQA
Conservation of energy during braking: Energy is conserved, so the energy removed from the vehicle does not disappear but is transferred to the brakes and surroundings.AQA
Conservation of energy in chemical reactions: Energy is not lost when bonds break; it is stored in the separated atoms, and overall change is found by comparing energy in with energy out.AQA
Conservation of limited metal ores: Recycling means metal is used again instead of being discarded, which conserves limited metal ores.AQA
Conservation of mass: Law meaning the number of atoms of each element is the same before and after reaction, so the mole ratio must be a simple whole-number ratio.AQA
Conservation of mass in equations: The equation shows the reaction quantitatively, so the number of each type of atom is the same on both sides.AQA
Conservation of mass number and proton number: In a nuclear equation, the total mass number and total proton number must balance on both sides.AQA
Conservation of momentum: In a closed system, the total momentum before an event equals the total momentum after it, provided no external resultant force acts.AQA
Conservation of natural resources: Recycling reduces the need to extract and process raw materials such as metal ores, crude oil and timber.AQA
Conservation of nucleon number: In every balanced equation, the total mass number (top number) must be the same on both sides.AQA
Conservation of proton number: In every balanced equation, the total atomic number (bottom number) must be the same on both sides.AQA
Conservation of raw materials: Both approaches reduce demand for raw materials, which saves materials such as sand compared with starting from scratch.AQA
Conservation programmes: Programmes put in place by scientists and concerned citizens to reduce the negative effects of humans on ecosystems and biodiversity.AQA
Conservation strategies: Named methods such as breeding programmes for endangered species, protection of rare habitats, reintroduction of hedgerows and field margins, reduction of…AQA
Consistent units: Ensuring units are consistent, for example converting minutes to seconds before multiplying by 1.5 m/s.AQA
Constant speed: The value does not change during the motion, so the same speed can be used throughout the calculation.AQA
Constant speed of electromagnetic waves in a vacuum: All types of electromagnetic wave travel at the same velocity through a vacuum or air.AQA
Constant velocity: A moving object with zero resultant force continues at the same speed in the same straight line.AQA
Consumers: The homes, schools, hospitals and factories that electrical power is transferred to from power stations.AQA
Contact and non-contact forces: Forces between objects are either contact forces, which require the objects to be touching, or non-contact forces, which act at a distance without touching.AQA
Contact force: A force that acts only where two objects or surfaces touch, so removing the contact removes the force.AQA
Contact interaction: An interaction in which the objects touch, and each object in the pair experiences a force.AQA
Containment by a membrane: The growth remains in one area and is usually enclosed within a membrane, which helps keep it contained.AQA
Contamination: Where radioactive atoms are left on or in the object, so the radioactive material remains while it stays there.AQA
Continuous energy supply: The constant provision of energy that cells need to carry out living processes; without it the organism dies.AQA
Continuous respiration: In plants, respiration occurs continuously in all living cells, including at night when photosynthesis cannot occur.AQA
Continuous sampling: Small samples are removed from the reaction mixture at regular intervals and tested, rather than testing the whole mixture once at the end.AQA
Continuous variation: The range of phenotype features produced when several genes plus environmental factors contribute, rather than two clear categories.AQA
Contrast with malignant tumours: Benign tumours are contained and non-invasive, whereas malignant tumours do invade and spread.AQA
Contrast with the early atmosphere: The early atmosphere was very different, formed mainly by volcanic activity and containing little or no oxygen.AQA
Control of variables in practical work: Changing only the independent variable and keeping all others constant, such as temperature and wire material.AQA
Control variables: Key variables such as temperature, carbon dioxide concentration and the distance of the light source, kept constant to make the test valid.AQA
Control variables and reliability: Keeping temperature, volume and other conditions constant, and repeating to improve reliability.AQA
Control variables and valid conclusions: Temperature, volumes and concentrations of starch and amylase are controlled variables because they also affect enzyme activity.AQA
Controlling variables: Comparing materials fairly requires keeping thickness, area and temperature difference fixed.AQA
Controls and reliability: A negative result is the reagent’s original colour, so a water control can confirm that the reagent has not changed colour.AQA
Convenience, cost and emissions in heating: Heating buildings and water can use natural gas boilers, electricity, solar thermal panels, geothermal heat or biomass, where storage and convenience matter.AQA
Conventional current: The direction the second finger points, from positive to negative.AQA
Conventional current direction: Shown by the long line of a cell symbol as the positive terminal, so the direction is clear.AQA
Conventional representation: Shows the identity as the element symbol, the charge as a superscript, and the mass as a superscript mass number.AQA
Conversion table: A standard table used to convert the distance the ruler falls into a reaction time.AQA
Converting units: Centimetres or kilometres must be converted to metres before substituting into an equation, for example 250 cm becomes 2.5 m.AQA
Cooperation of organs: Several organs working together as an integrated whole rather than as isolated organs to perform a shared function.AQA
Coordination and control: The CNS coordinates the response of effectors which may be muscles contracting or glands secreting hormones.AQA
Coordination by the central nervous system: Electrical impulses travel along neurones to the central nervous system, which processes the information and coordinates the response.AQA
Coordination centre: Receives and processes information from receptors, such as the brain, spinal cord or pancreas.AQA
Coordination centres: Structures such as the brain, spinal cord and pancreas that receive and process information from receptors.AQA
Coordinator: The brain or spinal cord; it receives impulses, processes information and determines the appropriate response.AQA
coronary arteries: The vessels that branch from the aorta and supply blood to the heart muscle itself.AQA
Coronary heart disease: A non-communicable disease in which layers of fatty material build up inside the coronary arteries, narrowing them.AQA
Corpus luteum: The structure that releases progesterone, which rises after ovulation to maintain the uterus lining.AQA
Correlation: A statistical link that is not proof of cause, and may exist because a third variable influences both the factor and the disease.AQA
Correlation and causation: A statistical link does not prove that the variant causes the disease, because other factors such as diet or environment may also differ.AQA
Correlation and cause: Scientists study large groups to link habits with disease rates, since individual cases cannot prove cause.AQA
Correlation versus causation: A correlation between a risk factor and a disease does not prove causation, because other factors may differ between groups.AQA
Correlation versus causation in epidemiological data: A correlation does not prove causation, because other variables such as age, diet or occupation may confound results.AQA
Coulomb: The charge transferred when a current of one ampere flows for one second.AQA
Count rate: The reading from a detector, which is usually lower than activity because not every emitted particle or wave reaches the detector.AQA
Counting atoms in models: Identify each distinct element present, then count how many atoms of each element appear in one molecule, checking every atom is counted exactly once.AQA
Counting gas molecules from a symbol equation: Count the gas molecules on each side of the symbol equation using the balancing numbers, ignoring solids and liquids.AQA
Counting gas moles in equilibrium equations: Counting the number of gas molecules on each side of the given equation, treating only gaseous species as relevant to pressure.AQA
Covalent bond: A bond formed when atoms share pairs of electrons, and these bonds between atoms are strong.AQA
Covalent bonding: A bond that forms when a pair of electrons is shared between two non-metal atoms, with the shared pair attracted to the nuclei of both atoms.AQA
Covalent bonding and delocalised electrons: Each carbon atom forms three covalent bonds with three other carbon atoms, leaving one outer electron delocalised.AQA
Covalent bonding as shared pairs of electrons: A shared pair of electrons between two non-metal atoms, which chemists often draw as a single straight line between the atom symbols.AQA
Covalent bonding in diatomic molecules: Two halogen atoms can share a pair of electrons in a single covalent bond, forming diatomic molecules.AQA
Covalent bonds: Strong bonds within a molecule that hold atoms together and remain intact when a molecular substance melts or boils.AQA
Cracking: Converts large hydrocarbon molecules into smaller molecules that are more useful as fuels or chemical feedstocks, producing a mixture.AQA
Cracking and alkenes: A chemical reaction that converts larger hydrocarbon molecules into smaller, more useful molecules, including alkenes such as ethene.AQA
Cracking as a chemical process: Turns long-chain hydrocarbons from crude oil into shorter, more useful molecules, including alkenes.AQA
Cracking of hydrocarbons: Breaks large hydrocarbon molecules into smaller, more useful ones, supplying fuels such as petrol and diesel components as well as alkenes for making polymers.AQA
Cracking of long-chain alkanes: Breaking a long-chain alkane into a shorter, more useful alkane and an alkene.AQA
Crests and troughs: The high and low points of a transverse water wave.AQA
Critical evaluation of evidence: Asking what was included, what was left out and who paid for the study.AQA
Critical evaluation of media and secondary sources: Checking the evidence base, the source and its interests, whether other scientists agree, and whether the language matches the strength of the data.AQA
Crude oil: A finite mixture of hydrocarbons that must be separated into fractions with different boiling point ranges.AQA
Crude oil and natural gas: Formed mainly from marine plankton buried in mud on the seabed, where absence of oxygen prevented full decay and heat and pressure converted the organic…AQA
Crystallisation: Recovers a dissolved salt from its solution by removing the solvent, causing the dissolved salt to exceed its solubility and precipitate out as solid crystals.AQA
Current: The rate of flow of electric charge, measured in amperes, A, where one ampere is one coulomb of charge passing a point each second.AQA
Current as rate of flow of charge: The rate of flow of charge cannot change around a series loop because charge is conserved.AQA
Current conservation at junctions: The total current from the supply is the sum of the currents in the separate branches.AQA
Current conservation in loops: In a series circuit the components form one loop, so the same current passes through each component in turn.AQA
Current–potential difference characteristics: Graphs for ohmic and non-ohmic components, where the shape shows what happens to resistance rather than only reading coordinates.AQA
Curve of best fit: A single smooth curve drawn through plotted points when the relationship is not clearly a straight line.AQA
curved line: A curved line shows changing speed, meaning the object is accelerating or decelerating.AQA
Cuttings: A section of stem or leaf is taken from a parent plant and grown into a new plant.AQA
cycles: Closed loops formed by the continual transfer of materials between the abiotic and biotic components of an ecosystem.AQA
Cycles maintaining supplies for life: Both cycles keep supplies available to organisms, so disruption such as deforestation or drought can limit growth and survival.AQA
Cycling of matter: Water is continuously evaporated and precipitated, so the cycle repeats as water moves between the oceans, atmosphere and land.AQA
Cytokinesis: The process that divides the cytoplasm, forming two separate daughter cells.AQA
Cytoplasm: Jelly-like substance that fills the cell and surrounds the organelles, mainly water with dissolved substances where many chemical reactions take place.AQA

D

Dalton's atomic theory: Pictured atoms as solid, indivisible spheres, like tiny billiard balls, and explained why elements react in definite proportions.AQA
Data handling and graph interpretation: Reading values accurately from the axes of a graph or from cells in a table, including correct units, and describing patterns or trends in the data.AQA
Data handling from charts, graphs and tables: Reading the axes, units, labels and key carefully, then quoting specific values and describing the trend shown.AQA
Data interpretation: Reading values from graphs, charts and tables and explaining what they show about a biological process.AQA
Data interpretation from charts and tables: Reading values accurately from charts and tables of fossil ages or species numbers and describing the trend shown.AQA
Data presentation: Plotting points accurately with small crosses or dots at the correct coordinates, then drawing a line or curve of best fit to show the trend.AQA
deamination: The liver removes the amino group from excess amino acids, and the nitrogen from the removed amino group is converted into urea.AQA
Decay: Microorganisms decompose the exposed peat aerobically, respiring and releasing carbon dioxide.AQA
Decay and preservation: Soft-bodied organisms decay quickly and lack hard parts, so they fossilise far less often than organisms with shells or skeletons.AQA
Deceleration: A larger braking force produces a larger deceleration, and deceleration can be treated as negative acceleration.AQA
Deceleration as negative acceleration: A negative value shows deceleration, meaning the object slows down.AQA
Decolourisation: The loss of the orange colour when an alkene is shaken with bromine water, leaving the solution colourless.AQA
Decolourised: Describes the loss of the orange colour of bromine water when it reacts with an alkene, leaving a colourless mixture.AQA
decomposers: Microorganisms that break down dead material and waste, releasing simple compounds that plants can absorb and reuse.AQA
Decomposition: A return process in which microorganisms break down dead organisms and waste, releasing carbon dioxide into the atmosphere.AQA
Decomposition and decay: Carried out by microorganisms, which break down dead material.AQA
Decomposition of complex shapes: The area is split into simple shapes: rectangles for constant velocity, triangles for uniform acceleration, and trapezia for combined changes.AQA
Deep sea vent bacteria: Extremophiles that experience high temperature and high pressure where superheated water rich in dissolved minerals escapes from the ocean floor.AQA
Deforestation: The large-scale removal of trees from an area, often to make land available for other uses including agriculture.AQA
Deforestation and carbon sinks: Clearing forest removes trees that would otherwise remove carbon dioxide by photosynthesis, so carbon dioxide rises further.AQA
Deformation of stationary objects: Stretching, bending or compressing needs more than one force so that the resultant force is zero and the object stays stationary while deforming.AQA
Degrees Celsius: The unit for temperature change in energy calculations, the same size as the kelvin.AQA
Delocalised electrons: Outer-shell electrons of metal atoms that are not associated with any particular atom and are free to move through the entire metallic structure.AQA
Delocalised electrons and conductivity: The fourth outer electron of each carbon atom is delocalised, so it is free to move within a layer and allows graphite to conduct electricity along the layers.AQA
Delocalised electrons and metallic bonding: Metals contain a lattice of positive ions surrounded by delocalised electrons, which are free to move throughout the metal structure.AQA
Denaturation: Caused by high temperature or extreme pH, altering the active site shape so the substrate no longer fits.AQA
Denaturation and active site shape: Above the optimum temperature, enzymes denature because the active site changes shape and substrate molecules no longer fit.AQA
Denaturation and reaction conditions: High temperature or extreme pH changes the shape of the active site, so the substrate can no longer bind and the rate of reaction falls.AQA
Denatured: When bonds holding the tertiary structure break, the active site changes shape and substrate can no longer bind, so activity falls sharply.AQA
Density: The mass per unit volume of a material, calculated as density = mass ÷ volume, with units such as kg/m³ or g/cm³.AQA
Density and particle spacing: Diagrams can be used to explain differences in density: closer particles mean more mass in the same volume, and gases are much less dense than solids and…AQA
Density as mass per unit volume: Density = mass ÷ volume, so a gas has the same mass spread through a much larger volume and its density is far lower.AQA
Density differences between states: Density changes between states because the same mass occupies a different volume, as density = mass ÷ volume.AQA
Desalination: Treatment needed when the only supply is seawater, which contains a high concentration of dissolved salts, for example by distillation or by processes using…AQA
Describing relationships between variables: Stating patterns shown by data, for example as light intensity rises, transpiration rate rises until stomata are fully open, then levels off.AQA
Design features that control reactions: A seal, a compartment or a permeable wrapper controls when the reaction starts and how much heat is released.AQA
Desired characteristic: A particular genetic characteristic that humans choose parents to show, so that it becomes more common in later generations.AQA
Detergents: Substances that help water remove grease and dirt, for example in washing-up liquid.AQA
Determine phenotype: The mutation alone decides the characteristic, as in a genetic disorder or a decisive change such as antibiotic resistance.AQA
Development of scientific ideas: The change from the plum pudding model to the nuclear model followed the scattering experiment evidence.AQA
Development of scientific models over time: Bohr adapted the existing nuclear model rather than replacing the nucleus, which stays at the centre with electrons occupying the space around it.AQA
Development of the atomic model: The model of the atom changed as new evidence emerged, with the neutron added about 20 years after the nucleus became an accepted idea.AQA
Development of the periodic table: Mendeleev improved on earlier periodic tables by prioritising chemical and physical properties over strict atomic weight order.AQA
Diabetes: A condition in which the insulin-secreting pancreatic cells are damaged or destroyed, so a patient cannot control blood glucose normally.AQA
Diagram identification: Recognising and locating the gland on a diagram by using anatomical position rather than size or colour.AQA
Diamond, graphite and silicon dioxide: Forms of carbon and silica given as examples of giant covalent structures.AQA
Diet and health: A poor diet lacking vitamins can cause deficiency disease, while excess energy intake contributes to obesity and type 2 diabetes.AQA
Difference between antibiotics and antivirals: Antibiotics do not kill viruses, which is why viral infections are not treated with antibiotics, whereas antiviral drugs target virus-specific enzymes or…AQA
Differential survival and reproduction: Individuals with advantageous phenotypes are more likely to survive and pass on their alleles to offspring.AQA
Differentiation: The process by which a cell becomes specialised, which scientists can direct by controlling the conditions and chemical signals the cells receive.AQA
Diffract: Bend around obstacles such as hills, which longer radio wavelengths can do, allowing reception without direct line of sight.AQA
Diffusion: The spreading out of the particles of any substance in solution, or particles of a gas, resulting in a net movement from an area of higher concentration to an…AQA
Diffusion and exchange surfaces: Diffusion across the membrane is fast enough to supply oxygen and nutrients to the whole cell and to remove carbon dioxide and other wastes.AQA
Diffusion distance: A shorter distance increases the rate of diffusion because particles travel less far to cross the exchange surface.AQA
Digestion: The process that converts large insoluble molecules into small soluble ones that can cross the gut lining.AQA
Digestion and defence in the stomach: The low pH provides optimum conditions for protease enzymes that digest proteins, while the acid also kills many pathogens.AQA
Digestive enzymes: Biological catalysts that break large insoluble food molecules into smaller soluble molecules.AQA
Digitalis: A medicine used to strengthen the force of heart contractions, originally obtained from the foxglove plant.AQA
dilute: Describes an acid that contains a small amount of acid per unit volume.AQA
Diminishing returns: Adding more of a factor gives little or no effect once another factor becomes limiting, so further enhancement is no longer cost-effective.AQA
Diode: A component with very high resistance in reverse bias and a much lower resistance in forward bias once the threshold potential difference is exceeded.AQA
diploid: Describes a cell containing 23 pairs of chromosomes, so 46 in total, as in most human body cells.AQA
Direct and inverse proportionality: Acceleration is directly proportional to the resultant force when mass is constant, and inversely proportional to mass when force is constant.AQA
Direct potential difference: A potential difference whose polarity stays fixed, so current flows one way around the circuit, as from a cell or battery.AQA
Direct proportion: A method that converts a ratio into a fraction or percentage of the total by adding the parts to find the total and dividing each part by that total.AQA
Direct proportionality: A relationship in which weight and mass are directly proportional, so their ratio is constant for a given gravitational field.AQA
Direct proportionality at constant mass: For a fixed mass, doubling the resultant force doubles the acceleration, so acceleration is directly proportional to resultant force.AQA
direct supply: A supply such as a battery that keeps potential difference and current in one direction.AQA
Direct timing method: A method that measures the time for sound to travel a measured distance through air, so the calculated value is the speed of sound in air.AQA
Direction: Which way a quantity acts or moves, which may be given as left, right, up, down, north, or as an angle from a stated line.AQA
Direction of a magnetic field: Shown by arrowheads on field lines, pointing away from the north pole and towards the south pole.AQA
Direction of bending relative to the normal: If the wave slows down, it bends towards the normal; if it speeds up, it bends away from the normal.AQA
Direction of magnetic field: A plotting compass near the wire aligns with the field, and reversing the battery reverses the current and reverses the field direction.AQA
Direction of magnetic fields: The direction of the magnetic field reverses if the direction of the current reverses.AQA
Direction of movement relative to concentration gradients: Diffusion moves any particles down a concentration gradient and osmosis moves water down a water potential gradient, whereas active transport moves substances…AQA
Directly proportional: Describes how resistance relates to length for a metallic wire kept at constant temperature, so that doubling the length doubles the resistance.AQA
Discovery of antibiotics: Penicillin was the first antibiotic discovered, found by Alexander Fleming from the Penicillium mould.AQA
Discrete molecules with a fixed number of atoms: A small molecule is a discrete group of a limited number of atoms joined by covalent bonds.AQA
Disease incidence: The number of new cases of a disease in a population over a stated time.AQA
Disease prevention and control: Control measures target the mosquito vector, for example using mosquito nets and insecticides, rather than relying on antibacterial drugs.AQA
Disease resistance: A special feature that crop plants can carry, which cloning passes on unchanged to genetically identical offspring.AQA
Disease resistance in crops: Crop plants can be genetically engineered so they are resistant to diseases, which reduces losses caused by pathogens and can improve crop yield.AQA
Disease-associated gene variants: Gene variants that are more common in people with a particular disease than in people without it.AQA
Displacement: The distance an object moves, measured in a straight line from the start point to the finish point, together with the direction of that straight line.AQA
Displacement in the direction of the force: Used when a force changes direction or the object moves back and forth, rather than the total path length.AQA
Displacement of hydrogen from dilute acids: Metals above hydrogen displace it from dilute acids, while metals below hydrogen generally do not.AQA
Displacement reactions: Reactions in which a more reactive metal displaces a less reactive metal from a solution of its salt.AQA
Displacement technique: A way of finding the volume of an irregularly shaped object by recording the starting volume of water in a measuring cylinder, lowering the object in fully,…AQA
displacement–distance graph: A graph on which amplitude is read from the vertical axis as the height of a crest or the depth of a trough above or below the centre line.AQA
Displacement–time graph: A graph on which the period is the horizontal distance between two identical points on consecutive cycles, such as crest to crest.AQA
Displayed formulae: A representation that uses lines to represent shared pairs, for example H—H.AQA
Disposal: Deciding what happens when a product no longer works or is no longer wanted, such as recycling, landfill, incineration or reuse.AQA
Disposal and transport: Disposal at the end of a product's useful life, with transport and distribution considered at each stage.AQA
Dissipated: Wasted energy is not destroyed but transferred to less useful stores, commonly thermal energy in the surroundings.AQA
Dissipation and air resistance: Work done against air resistance dissipates some energy to the thermal store of the surroundings, so less energy is returned as kinetic.AQA
Dissipation of energy: In all system changes, energy is transferred to the surroundings, often as thermal energy, so that it is stored in less useful ways.AQA
Dissipation to the surroundings: Energy transferred to the thermal store of the surroundings by heating, rather than being 'lost' or 'used up'.AQA
Dissipation to thermal stores: Friction and deformation transfer energy to thermal energy stores of the object, obstacle and surroundings.AQA
Dissolved oxygen: Oxygen gas dissolved in the water, entering by diffusion from the air and produced by photosynthesis of aquatic plants and algae.AQA
Dissolved oxygen and decomposition: Bacteria decomposing organic matter use dissolved oxygen, so fish may suffocate.AQA
dissolved solids: Substances tested for by evaporating a measured volume of each sample to dryness and comparing the mass of residue left.AQA
Distance: The total length of the path travelled by an object, measured in metres (m), and a scalar quantity so no direction is required.AQA
Distance and displacement: Distance travelled can be calculated from the area under a velocity–time graph, and displacement is found when direction is included.AQA
Distance moved along the direction of the force: The displacement in metres (m) along the force's direction, which is multiplied by the force to give work done.AQA
Distance moved by solvent: The length from the same origin line to the solvent front.AQA
Distance moved by substance: The length from the pencil origin line to the centre of the spot.AQA
Distance s: Measured in metres (m), it must be the distance moved along the direction of the force.AQA
Distance-time graph: A graph from which distance is read from the vertical axis, with the distance travelled being the change in distance between two times.AQA
distance–time graph: A graph showing changes in motion, where a steeper line means higher speed, a horizontal line means stationary, and a curve means changing speed.AQA
Distance, speed and time relationship: Distance travelled = speed × time, linking the distance covered to the speed and the time taken.AQA
distillate: The collected product that should have a pH closer to 7 and leave little or no residue on evaporation.AQA
Distillation: Heating the salty water so that pure water evaporates and is then condensed, leaving dissolved salts behind.AQA
Distinguishing data from models: Checking whether the report distinguishes measured data from computer-model projections and commenting on the assumptions involved.AQA
Distinguishing metals from non-metals in a comparative list: Hydrogen and carbon are non-metals placed within the series as reference points, not as metals.AQA
Distractions: Things such as a ringing phone, loud passengers or looking at a satnav compete for attention, so a hazard may be detected later or the response delayed.AQA
Distribution: The spread of results, represented by tabulating every reading and plotting a suitable graph such as a dot plot, tally chart or histogram.AQA
Distribution between phases: Each component distributes differently between the stationary phase, which is the chromatography paper, and the mobile phase, which is the solvent that moves…AQA
Distribution of mass within the atom: Most of the mass of an atom is concentrated in the nucleus, because protons and neutrons each have a relative mass of 1 while electrons have a relative mass…AQA
Division of labour: Different cells carrying out different jobs, so that tissues and organs work efficiently in multicellular organisms.AQA
DNA: A polymer of nucleotides whose base sequence stores genetic information, with two strands pairing by complementary bases.AQA
DNA and mutation: Random changes in the base sequence of DNA that occur continuously, for example when DNA is copied before cell division or when radiation or chemicals damage…AQA
DNA replication: Produces two identical copies of each chromosome, so each chromosome consists of two sister chromatids.AQA
DNA structure: A polymer made up of two strands that coil around each other to form a structure known as a double helix.AQA
Dominant allele: An allele that is always expressed, even if only one copy is present.AQA
Dominant alleles: Alleles that are expressed in the phenotype even when only one copy is present.AQA
Dominant disorder: A disorder that appears if at least one dominant allele is present, for example polydactyly.AQA
Dominant disorder alleles: Versions of a gene that cause the condition when at least one copy is inherited.AQA
Donor heart and heart-lung transplantation: A treatment in which a donor heart, or heart and lungs, is transplanted to replace the failing organs.AQA
Dose: Asks what amount gives the desired effect with acceptable side effects, because too little may not work and too much may be toxic.AQA
Dose and exposure: The level and duration of exposure to a factor, which affect the size of the risk.AQA
Dose and risk of harm: Radiation dose, in sieverts, is a measure of the risk of harm resulting from an exposure of the body to the radiation, and a larger dose means a greater risk…AQA
Dose control: Reducing the dose received by people or objects being irradiated by controlling time, distance and shielding.AQA
Dot and cross diagram: A diagram that represents the electron transfer during the formation of an ionic compound, for example sodium chloride.AQA
Dot-and-cross diagrams: Show which electrons are shared and can show lone pairs, but do not show the shape of the molecule, the relative sizes of atoms or the three-dimensional…AQA
Double blind trial: A way of testing a new medicine fairly in which neither the patients nor the doctors or researchers assessing them know which treatment each patient received.AQA
Double circulatory system: A system in which blood passes through the heart twice per complete circuit of the body.AQA
Double helix: The shape formed by two strands winding around each other, like a twisted ladder.AQA
Double helix model: The structure formed when two strands coil around each other.AQA
Double insulated: Appliances with plastic cases may be this and need no earth wire.AQA
double insulation: A measure that avoids the need for an earth connection and can reduce the risk by preventing a person from becoming the path to earth.AQA
Drag: A force from the fluid that increases with speed and acts upwards opposing motion through the fluid.AQA
Drug synthesis in the pharmaceutical industry: Most new drugs are synthesised by chemists in the pharmaceutical industry, meaning they are made by chemical reactions.AQA
Drug-development pathway: A natural source provides a starting compound, which is then purified, tested for efficacy and toxicity, and formulated into a medicine.AQA
Drugs and alcohol: Can slow brain activity, impair judgement and reduce coordination, again lengthening reaction time.AQA
Dynamic equilibrium: A reversible reaction in a closed system where forward and reverse reactions continue at equal rates, so concentrations stay constant.AQA
Dynamic equilibrium in closed systems: In a closed system, reversible reactions can reach dynamic equilibrium, where the rates of the forward and reverse reactions are equal and the concentrations…AQA

E

E = m × L: The equation used to calculate the energy required for a given mass, where E is energy in joules, m is mass in kilograms and L is specific latent heat in J/kg.AQA
E = m × Lv: The equation used to calculate specific latent heat of vaporisation, where E is energy in joules, m is mass in kilograms and Lv is in J/kg.AQA
E = mc∆θ: The equation showing that energy transferred depends on mass, temperature change and the material.AQA
E = mL: The equation used in specific latent heat calculations, with E in joules, m in kilograms and L in J/kg.AQA
E = P × t: Equation used to calculate the total energy transferred, where E is energy in joules, P is power in watts and t is time in seconds.AQA
E = Q × V: The equation showing that the energy transferred by an appliance depends on the charge flow and the potential difference across it.AQA
E = QV: The equation linking energy transferred in joules, charge in coulombs and potential difference in volts.AQA
Early stage development: Genes are transferred at an early stage of development so the organism develops with the desired characteristics.AQA
Early stage of development: When the organism is an embryo or a single cell, so that every cell produced by subsequent division contains the new gene.AQA
Earth reference: Earth is taken as 0 V, and the potential difference between the live wire and earth is about 230 V.AQA
Earth wire: Provides a low-resistance path so a fault current is large enough to melt the fuse, carrying current only when a fault occurs.AQA
Earth's magnetic field: Produced as though a giant bar magnet is inside the Earth, exerting a turning force on a compass needle so it aligns with the local field line.AQA
Economic barriers: Limits that include the upfront cost of solar panels or an electric car, which many people cannot afford.AQA
Economic importance: The use of fermentation on a commercial scale in baking and brewing.AQA
Economic issues: These include the cost of embryo screening and IVF, the cost of lifelong care for a child with a disorder, and who pays, such as the NHS or families.AQA
Ecosystem: The community of organisms plus the non-living conditions of their environment, such as light, temperature, water and soil.AQA
Ecosystem services and physical environment: Physical environmental processes such as nutrient cycling, decomposition and soil stability, maintained through the activities of many species.AQA
Ecosystem stability: Ensured by high biodiversity, which reduces the dependence of one species on another for food, shelter and the maintenance of the physical environment.AQA
Ecosystems and species distribution: Changes as organisms migrate or decline when their habitats become unsuitable, including reduced biodiversity and possible extinction where organisms cannot…AQA
Ectothermic animals: Animals such as reptiles that rely on external heat sources and may behaviourally regulate their temperature, for example by basking or seeking shade.AQA
Effect of changing conditions on reaction direction: Changing a condition such as temperature, pressure or concentration alters the relative rates of the forward and reverse reactions, so the direction of the…AQA
Effect of impurities on boiling point: Impurities raise the boiling point, so an impure sample boils above the known value.AQA
Effect of impurities on melting and boiling points: Impurities generally lower the melting point and raise the boiling point of a substance.AQA
Effect of impurities on melting point: Impurities lower the melting point, so an impure sample melts over a range starting below the known value.AQA
Effect of pH on enzyme activity: A pH close to the enzyme's optimum gives the shortest time and fastest rate, while extremes of pH slow the reaction because the enzyme is denatured.AQA
Effect of pressure and concentration on equilibrium: If pressure increases, the side with fewer gas molecules is favoured; increasing a reactant favours the forward reaction and increasing a product favours the…AQA
Effect of pressure on change of state: Melting and boiling points are stated at a pressure, so the data must apply to the pressure in the question before predicting.AQA
Effect of pressure on equilibrium position: A decrease in pressure causes the equilibrium position to shift towards the side with the larger number of molecules as shown by the symbol equation for that…AQA
Effect of squaring a variable: Speed is squared in the equation, so doubling the speed has a much bigger effect than doubling the mass.AQA
Effect of temperature on density: Heating usually decreases density because the particles move further apart while the mass stays the same.AQA
Effect of temperature on equilibrium: If the forward direction is exothermic, an increase in temperature shifts the equilibrium to favour the endothermic reverse reaction, decreasing the relative…AQA
Effect of wall thickness on energy transfer: Increasing the thickness of a wall reduces the rate of energy transfer and therefore slows cooling, because energy must conduct through more material.AQA
Effectiveness: The drug produces the intended therapeutic benefit at a suitable dose, which trials establish.AQA
Effector: A muscle or gland that responds to the impulse, either by contracting or by secreting a substance.AQA
Effector responses: The CNS coordinates the response of effectors, which may be muscles contracting or glands secreting hormones.AQA
Effectors: Muscles or glands that produce the response, either by contracting or by secreting a substance.AQA
Effects of introduced species: A new predator entering an ecosystem where prey have not evolved defences against it can quickly reduce prey numbers, and its impact depends on how many…AQA
Effects on sea level and ice: Rising global temperatures melt ice sheets and glaciers, adding water to oceans, while warmer water expands, so sea levels rise and low-lying coasts flood.AQA
Effects on weather and ecosystems: Weather may become more extreme, with heatwaves, droughts, storms and heavy rainfall occurring more often, and habitats shift so some species move towards the…AQA
Efficacy: Asks whether the drug produces the intended therapeutic effect, such as lowering blood pressure or killing a pathogen.AQA
Efficiency: Measures how much of the energy supplied to a device is transferred usefully rather than wasted, calculated as useful output energy transfer divided by total…AQA
Efficiency and energy dissipation: Some energy is dissipated by heating to the surroundings, reducing efficiency, so the kettle is not 100% efficient.AQA
Effluent: The clearer liquid remaining above the sludge, drawn off from the top so the two streams can be treated separately.AQA
Egg cells (ova): The female gametes, found inside the ovule within the ovary.AQA
Elastic deformation: The object returns to its original length and shape when the stretching force is removed, because the particles spring back to their original arrangement.AQA
Elastic potential energy: The energy associated with a stretched spring, calculated as E_e = ½ke², where k is the spring constant in newtons per metre and e is the extension in metres.AQA
Elastic potential energy equation: Ee = ½ke², in which e is squared, so the unit must be metres before substitution.AQA
Elastic potential energy store: The store that energy is transferred to when work is done against a spring's stiffness as the spring is stretched.AQA
Elastic tissue: Tissue in artery walls that stretches and recoils as the heart pumps, helping to maintain blood pressure and giving a pulse.AQA
Electric charge and current: Current is the rate of flow of electric charge, measured in amperes, and one ampere means one coulomb of charge passing a point each second.AQA
Electric current: A flow of electrical charge, commonly electrons in a metal conductor.AQA
Electric current as a rate of flow: The rate of flow of charge, measured in amperes (A).AQA
Electrical charge: A proton carries a 1⁺ charge and an electron carries a 1⁻ charge, so equal numbers cancel exactly.AQA
Electrical conduction by mobile charged particles: Charge can flow when charged particles are free to move, as the ions are when an ionic compound is melted or dissolved in water.AQA
Electrical conductivity: Poor in simple molecular substances because they have no overall electric charge and lack mobile charged particles, not because of weak forces.AQA
Electrical conductivity and free electrons: Diamond does not conduct electricity because there are no free electrons or ions to carry charge.AQA
Electrical conductivity in materials: The delocalised electrons can move along the layers, so graphite conducts electricity.AQA
Electrical energy transfer: Work is done when charge flows through a circuit component, transferring energy from the power supply.AQA
electrical impulses: Signals produced by the pacemaker cells that spread through the heart muscle and make it contract rhythmically.AQA
Electrical neutrality: Atoms have no overall electrical charge because equal numbers of protons and electrons produce equal but opposite total charges that cancel completely.AQA
Electrical power: In electrical circuits, power can be calculated using P = V I, where V is potential difference in volts and I is current in amperes, or P = I² R.AQA
Electrical safety: The earth wire is a safety conductor, not part of the normal current path, connecting the metal case of an appliance to earth.AQA
Electrical safety in the home: Touching the live wire can drive a current through the person to earth, which is the danger.AQA
Electrical work and heating: Electrical work is done on the kettle's heating element by the current, and energy is then transferred by heating to the thermal store of the water.AQA
Electricity generation: A use of energy resources such as coal, natural gas, nuclear fuel, wind, solar and hydroelectricity to produce electricity.AQA
Electrolysis: A method where a solution of a metal compound is electrolysed so that metal ions gain electrons at the cathode to form metal atoms.AQA
Electrolysis and ionic conduction: The mixture must still contain mobile ions so that it conducts electricity and electrolysis can occur.AQA
Electrolysis of molten compounds: A direct electrical current is passed through a molten compound, causing positive metal ions to move to the cathode and negative non-metal ions to the anode.AQA
Electrolysis of molten mixtures: The molten mixture of aluminium oxide and cryolite is electrolysed, with aluminium metal forming at the cathode and oxygen gas forming at the carbon anode.AQA
electrolyte: An ionic compound that is molten or dissolved in water so that its ions are free to move and carry charge.AQA
Electromagnet: A solenoid with an iron core, giving a magnetic field that can be switched on and off.AQA
electromagnetic spectrum: A continuous family of transverse waves that all travel at the same speed in a vacuum, yet differ in wavelength and frequency.AQA
electron: A smaller, negatively charged particle contained within atoms, whose discovery showed that the solid-sphere model had to be replaced.AQA
Electron arrangement: The arrangement of electrons in the shells of an atom, which can be used to deduce the position of an element in the periodic table.AQA
Electron arrangement and outer electrons: The outer electrons are the ones most easily removed because they are furthest from the nucleus and least strongly attracted.AQA
Electron configuration: The arrangement of electrons written as numbers such as 2,8,1, which makes the outer-electron count visible.AQA
Electron configuration and the outer shell: Each Group 1 atom has one electron in its outer shell, and this single outer electron controls its properties.AQA
Electron configuration notation: A way of representing electronic structure as numbers, such as 2,8,1 for sodium.AQA
Electron loss: Process in which a metal atom loses electrons from its outer shell when it reacts, producing a positively charged ion.AQA
Electron loss and gain to achieve full outer shells: Atoms gain or lose electrons to reach a full outer shell, and the charge follows from the number of electrons transferred.AQA
Electron microscopy and resolution: Uses a beam of electrons instead of light, giving much higher magnification and resolution than light microscopes.AQA
Electron sharing: The mechanism that happens when non-metal atoms bond covalently, such as two hydrogen atoms sharing a pair of electrons.AQA
Electron transfer: In ionic bonding, a metal atom transfers one or more electrons to a non-metal atom, forming positive and negative ions held in a giant lattice.AQA
Electron transfer and ion formation: Atoms in Groups 1 and 2 lose their outer-shell electrons to form positive ions, while atoms in Groups 6 and 7 gain electrons to complete their outer shell and…AQA
Electron transfer and sharing: The metal loses electrons and becomes a positive ion, while the halogen becomes a negative ion; with non-metals the atoms share electrons instead.AQA
Electron transfer between atoms: Metal atoms lose electrons to form positive ions, while non-metal atoms gain those electrons to form negative ions.AQA
Electron transfer between metal and non-metal atoms: An arrow or equivalent shows electron transfer from metal to non-metal, with dots for one atom's electrons and crosses for the other's.AQA
Electron transfer in equations: Tracking the loss or gain of electrons, where a species that has lost electrons is oxidised and one that has gained electrons is reduced.AQA
Electronic structure: The arrangement of electrons in energy levels around the nucleus, with the lowest energy level filled first.AQA
Electronics: An application area where carbon nanotubes are useful, for example in tiny circuits or conductive components.AQA
Electrostatic attraction: The force between positive metal ions and delocalised electrons, which is the metallic bond.AQA
Electrostatic forces: Chemical bonds arise from the attraction between oppositely charged particles, and in every case the bond is this attraction between opposite charges.AQA
Electrostatic forces of attraction: Strong forces acting in all directions between oppositely charged ions, holding them together and needing a large amount of energy to overcome.AQA
Element: A substance made of only one type of atom, of which about 100 occur naturally.AQA
Elements and identity: All atoms of a particular element have the same number of protons, and changing the proton number changes the element.AQA
Embryo: Formed when the zygote divides, it is kept in controlled conditions for a few days before transfer to the mother's uterus.AQA
Embryo development: Repeated division produces a small ball of cells, and the word 'develop' covers this cell division and the gradual formation of a ball of cells.AQA
Embryo transfer in IVF: One or two embryos are inserted into the mother's uterus (womb) when they are tiny balls of cells.AQA
Embryonic development and pluripotency: Embryonic stem cells are pluripotent, meaning they can differentiate into almost any cell type, so they build all the tissues and organs of the developing…AQA
Embryos: Tiny balls of cells that the fertilised eggs develop into, and one or two are inserted into the mother's uterus.AQA
Emission: Tested by measuring the cooling of hot water or using a Leslie cube, with black matt surfaces being the best emitters and shiny silver surfaces the poorest.AQA
Emission of electromagnetic radiation: The electron arrangements may change by giving out electromagnetic radiation, which moves an electron closer to the nucleus to a lower energy level.AQA
Emotional impact of uncertain medical outcomes: The process is highly stressful due to the uncertainty of success, the disappointment of failed cycles, and disruption to daily life and relationships.AQA
Empirical formula: Gives the simplest whole-number ratio of ions in a compound.AQA
Empty space: The nuclear model implies the atom is mostly empty space, unlike the plum pudding model.AQA
Empty space within atoms: Most of an atom is empty space because the nucleus is so small, with electrons occupying the outer regions.AQA
Empty space within the atom: Most alpha particles passed straight through, showing that atoms are mostly empty space, leaving most of the atom as empty space.AQA
Emulsification: Breaks fat into small droplets, which increases the surface area for lipase to act on.AQA
Emulsifies: Breaks lipids into small droplets, increasing surface area for lipase action.AQA
End point: The time at which no blue-black colour remains, which is the time taken for starch to be completely digested.AQA
Endangered: The population is so small or declining so fast that extinction is likely without help.AQA
Endangerment: A situation where some individuals of the species remain alive, unlike extinction.AQA
Endocrine gland: Secretes hormones directly into the bloodstream, acting on distant target tissues rather than through ducts.AQA
Endocrine glands: These are effectors that secrete hormones directly into the bloodstream.AQA
endocrine system: A system composed of various glands that secrete chemicals called hormones directly into the bloodstream.AQA
Endothermic: A reaction in which the product level is higher than the reactant level, so energy has been taken in from the surroundings and the overall energy change is…AQA
Endothermic and exothermic processes: Photosynthesis is endothermic overall because energy is transferred from light to chemical stores in glucose.AQA
Endothermic animals: Animals that maintain a constant internal temperature using energy released by respiration, so they can remain active in a range of environmental temperatures.AQA
Endothermic direction: The direction that takes in energy, and is favoured when the temperature of a system at equilibrium is increased.AQA
Endothermic forward reaction: A forward reaction that takes in the added thermal energy, so heating the equilibrium mixture favours that forward direction.AQA
endothermic process: A process in which energy must be supplied, such as breaking existing bonds in the reactants.AQA
Endothermic reaction: A reaction in which energy is transferred from the surroundings to the system, so the surroundings cool down and the thermometer reading falls.AQA
Endothermic reactions: Reactions that absorb energy, lowering temperature.AQA
Energy: A measure of the capacity to do work or transfer heat, with symbol E and the unit joule, J.AQA
Energy absorption: The reaction takes in energy from the surroundings, which is why the surroundings cool.AQA
Energy accounting in systems: The total energy before and after a change is the same, so energy input equals useful output plus dissipated energy.AQA
Energy and changes of state: The amount of energy needed to change state from solid to liquid and from liquid to gas depends on the strength of the forces between the particles of the…AQA
Energy and resource consumption in use: The inputs consumed during use, such as electricity, fuel, water or replacement parts.AQA
Energy and resource use in extraction versus recycling: Recycling can use less energy than extracting metal from its ore, though transport and processing still use resources.AQA
Energy changes in exothermic and endothermic reactions: For an exothermic reaction the product level is below the reactant level; for an endothermic reaction it is above.AQA
Energy conservation and dissipation: In a resistor, energy transferred by electrical work increases the thermal store, which may be dissipated as wasted energy.AQA
Energy costs in industrial processes: Large amounts of energy are used to melt the compounds and to produce the electrical current, making electrolysis an expensive extraction method.AQA
Energy demand: Both methods require large amounts of energy, making desalination expensive and potentially environmentally demanding.AQA
Energy dissipated: Energy lost to the surroundings, often by heating, which together with the useful energy equals the energy transferred to a device.AQA
Energy efficiency in industry: A lower melting point means less energy is needed to keep the electrolyte molten, which reduces costs.AQA
Energy efficiency in the National Grid: A smaller current is needed to transfer the same power, significantly reducing energy wasted as heating in the cables and increasing efficiency.AQA
Energy input: The energy transferred to the system, where doubling it roughly doubles the temperature change provided no change of state occurs.AQA
Energy level changes in atoms and nuclei: Changes in atoms and the nuclei of atoms can result in electromagnetic waves being generated or absorbed over a wide frequency range.AQA
Energy level diagrams and bond energy: Energy diagrams show reactant and product energy levels, with the vertical difference representing the energy transferred.AQA
Energy level diagrams and enthalpy changes: The magnitude is the same, but an exothermic change has a negative sign and an endothermic change has a positive sign when expressed as enthalpy change.AQA
Energy levels: Electrons are arranged at different distances from the nucleus, and these different distances are called energy levels.AQA
Energy levels and shells: Levels around the nucleus that hold up to 2 electrons in the first, 8 in the second, 8 in the third and up to 2 in the fourth for the first 20 elements.AQA
Energy pathways vs stores: Electrical work transfers energy to a component's thermal store, whereas heating transfers energy to the surroundings.AQA
Energy release: What aerobic respiration does with glucose and oxygen, providing energy the cell needs for processes such as growth, movement and active transport.AQA
Energy release without oxygen: Glucose is partially broken down, releasing some energy for muscle contraction but less than aerobic respiration.AQA
Energy requirements and carrier proteins: Active transport requires energy from respiration and uses carrier proteins in a membrane, whereas diffusion and osmosis are passive and do not require energy…AQA
Energy resource decision making: Acting on scientific knowledge about energy resources involves political, social, ethical and economic factors that science cannot decide alone.AQA
Energy saving: Recycling glass by crushing and melting it saves energy compared with starting from scratch.AQA
Energy stores and pathways: Energy can be stored in stores such as kinetic, gravitational potential, elastic potential, thermal, chemical and nuclear stores, and transferred by pathways…AQA
Energy stores and transfer pathways: Kinetic, thermal and chemical are stores, while work, heating and radiation are transfer pathways.AQA
Energy stores and transfers: The kinetic energy store of the vehicle decreases because its speed falls, and the energy is transferred to the thermal energy store of the brakes and…AQA
Energy transfer: The way each resource supplies energy, such as burning fossil fuels or bio-fuel releasing chemical energy, or wind and water waves driving turbines.AQA
Energy transfer and absorption: The suitability of a wave depends on its properties, such as whether it is reflected, absorbed, transmitted or ionising.AQA
Energy transfer and amplitude: A wave with a larger amplitude transfers more energy than one with a smaller amplitude.AQA
Energy transfer and conservation: Energy transferred is given by E in the equation E = P t, measured in joules (J).AQA
Energy transfer between surroundings and reacting particles: Energy is taken in from the surroundings to break bonds, and this energy is not lost but stored in the separated atoms.AQA
Energy transfer by conduction: Energy is transferred from the warmer inside of the building to the cooler outside through the walls, driven by the temperature difference.AQA
Energy transfer by electromagnetic radiation: Oscillating electric and magnetic fields transfer energy from a source to an absorber without needing a medium.AQA
Energy transfer by electromagnetic waves: Electromagnetic waves carry energy from a source to an absorber without needing a medium.AQA
Energy transfer by heating: As the current increases, more energy is transferred to the filament each second, so its temperature rises.AQA
Energy transfer by waves: The wave, meaning the disturbance and its energy, moves from source to detector while the medium stays in place.AQA
Energy transfer calculations: Combining P = VI with E = Pt allows calculation of the energy transferred by a device over a given time.AQA
Energy transfer chains: A continuous account of how energy moves, for example chemical to thermal to kinetic to electrical in a gas-fired power station.AQA
energy transfer direction: Whether energy is transferred to the surroundings or taken in from the surroundings, which explains a classification rather than the temperature value alone.AQA
Energy transfer from light to chemical stores: Light energy is absorbed by chlorophyll and transferred to chemical stores in glucose.AQA
Energy transfer from respiration: Respiration supplies the energy needed for reactions that build larger molecules from smaller ones.AQA
Energy transfer from the Sun: Energy from the Sun drives evaporation, while gravity drives precipitation and drainage.AQA
Energy transfer in circuits: The source does work on the charge, giving energy to the charges so they move around the circuit.AQA
Energy transfer to and from the surroundings: Breaking bonds in reactants requires an input of energy from the surroundings, and forming bonds in products releases energy to the surroundings.AQA
Energy transfer to the surroundings: Energy is transferred from chemical stores to the surroundings, causing a temperature rise, rather than being created.AQA
Energy transferred: Over a period of time, the power multiplied by the time, linking the two quantities to total energy in joules or kilowatt-hours.AQA
Energy transfers during heating: Heating transfers energy to particles, increasing their kinetic energy until the forces can no longer hold them in place.AQA
Energy use and carbon dioxide emissions: Recycling saves energy and lowers carbon dioxide emissions compared with extracting and processing raw materials.AQA
Energy use and environmental impact: Extraction and manufacture use energy and water and may release pollutants, and extraction can damage habitats.AQA
Energy use in cells: Some metabolic reactions use energy transferred by respiration, while others release energy.AQA
Energy use in manufacturing: Manufacturing usually needs energy for heating, machinery and transport between factories.AQA
Enhanced greenhouse effect: Occurs when extra gases strengthen the natural effect, which is essential, and tends to raise the mean global temperature.AQA
entity: The specified particle being counted, such as atoms, molecules, ions, electrons or formula units.AQA
environment: Everything an organism encounters after fertilisation, including diet, exercise, sunlight, accidents and upbringing.AQA
Environmental and economic evaluation: Weighs benefits against drawbacks, considering energy demand, cost, ore grade, land use, timescale and environmental impact, and is justified by the data given.AQA
Environmental change: A change such as climate change that can make conditions unsuitable for a species.AQA
Environmental change and allele frequency: If the new phenotype is suited to an environmental change, the allele becomes more common in the population, and this can change the species relatively rapidly.AQA
Environmental costs: The different impacts each disposal route has, and the fuel burned and emissions released when materials and products are moved.AQA
Environmental impact: Assessed at every stage through energy use, resource depletion, waste and pollution.AQA
Environmental implications: Loss of biodiversity, altered habitats, ocean acidification, disrupted food chains and changes to water and nutrient cycles.AQA
Environmental influence on characteristics: Environmental factors such as diet or sunlight can affect phenotype, so identical genotypes need not always look identical.AQA
Environmental influence on phenotype: The environment includes diet, temperature, light, water, and disease, which influence an organism's characteristics.AQA
Environmental risk factors: Factors present in the environment that affect disease risk, including air pollutants, carcinogens and ionising radiation.AQA
Environmental substances: Substances in the person's environment, such as air pollution or secondhand smoke, that act as risk factors for non-communicable diseases.AQA
Environmental variation: Caused by the conditions in which an organism develops, including diet, temperature, light, water, minerals, exercise and accidents.AQA
Enzyme action and denaturation: Temperature affects enzyme-controlled reactions, with the rate increasing up to an optimum and then falling sharply as enzymes denature above it.AQA
Enzyme action and optimum conditions: Enzymes have an optimum temperature and pH at which their rate of action is highest.AQA
Enzyme action and specificity: Amylase catalyses the breakdown of starch to maltose, so starch concentration falls as the reaction proceeds.AQA
Enzyme activity: Affected by temperature, peaking at an optimum before denaturation reduces the rate.AQA
Enzyme activity and metabolism: Enzyme-controlled reactions increase as temperature rises towards an optimum, then decrease if temperature becomes too high because enzymes denature.AQA
Enzyme control: All metabolic reactions are controlled by enzymes, so temperature and pH affect their rate.AQA
Enzyme optimum temperature: Maintaining an optimum temperature is essential because high temperatures denature enzymes and low temperatures slow down reaction rates.AQA
Enzyme specificity: Each enzyme catalyses only one reaction or a small group of similar reactions because the active site shape is specific.AQA
Enzyme-controlled reactions: These synthesis reactions are controlled by enzymes and require energy transferred by respiration.AQA
Enzyme–substrate complex: Formed when the substrate binds to the active site.AQA
Enzymes: Biological catalysts: globular proteins that lower the activation energy of a reaction and speed it up without being used up.AQA
Enzymes in genetics: Used to 'cut out' the required gene from the chromosome of the donor organism.AQA
Epidermal tissue: The thin outer layer of cells covering leaves, stems and roots, usually one cell thick in leaves and transparent so light passes through.AQA
Equal and opposite force pairs: The two forces are equal in magnitude and opposite in direction, and are always the same type of force.AQA
Equals sign: Used only when two sides are exactly equal, such as exact arithmetic like 1.0 N ÷ 0.50 kg = 2.0 m/s², and not for a rounded answer.AQA
Equation manipulation: Rearranging gives force equals work done divided by distance, or distance equals work done divided by force, useful when energy transferred is known.AQA
Equation manipulation and substitution: Rearranged forms are I = V ÷ R and R = V ÷ I, allowing any one quantity to be found when the other two are known.AQA
Equation rearrangement: The relationship can be rearranged to give speed = distance ÷ time and time = distance ÷ speed.AQA
Equation use: The work done by a force on an object can be calculated using the equation work done = force × distance.AQA
Equilibrium: A state in which the forward and reverse reaction rates are equal, so the amounts of reactants and products remain constant.AQA
Equilibrium between intact acid molecules and ions: Many intact acid molecules remain alongside a relatively low concentration of H⁺(aq) ions, shown using the equilibrium arrow (⇌).AQA
Equivalence of force systems: The two component forces together have the same effect as the single force, so the components are a mathematical replacement simplifying analysis.AQA
Equivalence of work and energy: Work done and energy transferred are equivalent quantities, which is why the joule is the same unit used for all forms of energy.AQA
Equivalent resistance: The single resistance that would replace a group of resistors without changing the current drawn from the supply.AQA
Estimating physical quantities: Sensible approximate values for speed, time and mass are chosen and the assumptions made are stated.AQA
Estimation: Making a sensible approximate judgement of size or area without measuring every detail, using known reference sizes and simple calculations.AQA
Estimation and approximation: Using typical values, which are not exact constants, to estimate a distance or time, keeping the unit m/s.AQA
Estimation and reasonableness: Using typical values to estimate times or distances and to judge whether a calculated answer is reasonable.AQA
Estimation in physics: Choosing a typical value, such as 6 m/s for a bicycle, to work out an approximate answer when no measured value is given.AQA
eth-: Prefix used in the names of alkanes to indicate two carbon atoms.AQA
Ethanol: One of the products of anaerobic respiration in plant and yeast cells, and the alcohol in drinks.AQA
Ethanol and carbon dioxide: The products of anaerobic respiration in plants and yeast, made from glucose.AQA
Ethical concerns: Concerns about privacy, insurance and editing genes that limit the use of human genome information.AQA
Ethical issues: These include the moral status of the embryo, the right to life, disability rights, parental choice and concerns about designer babies.AQA
Ethical issues in genetics: Concerns about genetic changes made to sex cells or embryos, as these modifications would be passed on to future generations.AQA
Ethical responsibility and future generations: A consideration about responsibility to future generations or to wildlife that shapes which actions are judged acceptable.AQA
Ethics in science: Some people believe an embryo should not be used or destroyed for research because they regard it as a potential human life.AQA
Ethics of embryo research: Ethical questions raised because the technique creates and destroys embryos.AQA
Ethics of genetic information: Studying the genome raises ethical questions about privacy and insurance.AQA
Ethics of research involving humans: Ethical and safety aspects of studies involving humans can be scrutinised when findings are shared.AQA
Eukaryota: One of the major taxonomic groups used in classification, whose members share cells containing a nucleus and other membrane-bound organelles.AQA
Eukaryotic and prokaryotic cell organisation: In prokaryotic cells such as bacteria, the cytoplasm also holds the genetic material because there is no nucleus.AQA
Eukaryotic cell structure: Plant and animal cells share a cell membrane, cytoplasm and genetic material enclosed in a nucleus.AQA
eukaryotic cells: Cells that possess a true nucleus enclosing the genetic material and also contain membrane-bound organelles such as mitochondria.AQA
Eutrophication: Fertiliser run-off supplies nitrate and phosphate ions, causing algae to bloom, block light, die, and decomposition removes oxygen.AQA
evaluate: Compare effectiveness, side effects, convenience, reversibility and STI protection, then reach a justified judgement for a given situation.AQA
Evaluating: Using supplied information to judge how well a method reduces use of a limited resource, then reaching a supported conclusion.AQA
Evaluating experimental data: A large range warns that the mean is less trustworthy, so technique or apparatus may need checking.AQA
Evaluating fertility treatments: Weighing the ultimate benefit of having a baby against the low probability of success in a single cycle and the significant physical and emotional burdens.AQA
Evaluating significance: Judging whether a difference of one order of magnitude or more matters when considering resource use or sustainability, whereas a small difference may not.AQA
Evaluating theories: Comparing how well each theory fits the evidence, considering strengths and limitations, and stating which fits better and why.AQA
Evaluation: Judging how well a reaction fits the job by weighing the useful energy change against practical factors such as safety, cost and control.AQA
Evaporation and condensation: Crude oil is heated until most of it evaporates, and a hydrocarbon condenses when the temperature falls below its boiling point.AQA
Everyday appliance energy use: Applying the relationship between energy transferred, power and time to any appliance, from a phone charger to an electric shower.AQA
Everyday appliance power ratings: The power rating of an everyday appliance is linked to the rate at which it transfers energy from the mains supply.AQA
Everyday appliances: Devices in which electrical energy from the mains is transferred into useful stores or pathways, such as thermal energy in a heater or kinetic energy in a…AQA
Everyday applications: Some sports injury packs are based on endothermic reactions, absorbing energy from the injured area to provide a cold compress.AQA
Everyday applications of exothermic reactions: Self-heating cans and hand warmers are everyday uses that release energy to the surroundings.AQA
Everyday dependence on petrochemicals: Hydrocarbon feedstocks provide plastics, medicines, detergents, lubricants, solvents and synthetic fibres.AQA
Everyday examples of exothermic reactions: The combustion of fuels such as methane, where the surroundings become hot, and the reaction of an acid with an alkali, which warms the mixture.AQA
Everyday versus chemical meaning of pure: In everyday language a pure substance has had nothing added to it, while chemists use pure to mean only one element or compound with no other substances mixed…AQA
Evidence and explanation: Linking each observation from the scattering experiment to a conclusion about atomic structure, for example most alpha particles passed through because the…AQA
Evidence and model revision: New evidence that conflicts with predictions can overturn an accepted idea, so a model survives only while evidence fits and is revised when new data…AQA
Evidence for classification: Current classification data for living organisms and fossil data for extinct organisms are used to build evolutionary trees.AQA
Evidence for evolution and the fossil record: Fossils formed this way are rare and give an incomplete record of past life.AQA
Evidence for relationships between organisms: Evidence from a chart, graph or table can support a conclusion about relationships or change, quoting specific values or labels.AQA
Evidence from alpha-particle scattering: Alpha particles mostly pass straight through gold foil but a few bounce back, because the atom is empty but its dense nucleus repels them.AQA
Evidence from population studies: Studies used by scientists to estimate how strongly each factor raises risk, because individuals vary in exposure and susceptibility.AQA
Evidence quality and reliability: Judging how trustworthy a climate report is by considering sample size, timescale, geographical spread and whether measurements are reliable and repeatable.AQA
Evidence supporting a theoretical model: Bohr's theoretical calculations agreed with experimental observations, so his adapted model was accepted and replaced earlier ideas.AQA
Evidence-based classification: Systems are updated as new evidence is discovered, so they are not fixed and are revised when new molecular or fossil evidence emerges.AQA
Evidence-based conclusions: Evaluating whether the data support a stated conclusion, stating that the data show a relationship and only claiming causation if the evidence and…AQA
Evidence-driven model replacement: The nuclear model replaced the plum pudding model because it explained the scattering pattern, including the small number of large deflections.AQA
Evidence-informed decisions: Decisions about emissions informed by a claim that survives review and is clearly communicated, making it more trustworthy.AQA
Evolution: A change in the inherited characteristics of a population over generations, not a change in an individual during its lifetime.AQA
Evolutionary relationships: Classification now aims to reflect these rather than just appearance, using biochemical data including DNA and RNA analysis as evidence.AQA
Evolutionary trees: A method used by scientists to show how they believe organisms are related.AQA
excess: Added a little at a time until no more dissolves, so all the acid is neutralised.AQA
excess solid: Added deliberately so that all the acid reacts and the solution is neutral, with a little solid remaining.AQA
exchange of body fluids: A route by which HIV is spread, such as blood when drug users share needles.AQA
Exchange surface: A surface where substances cross a thin membrane, which is one adaptation of an efficient exchange surface alongside a large surface area and a steep…AQA
Exchange surfaces: In organisms these are adapted by having a large surface area, a thin membrane and a good blood supply to maintain steep concentration gradients.AQA
Excretion: The removal of waste products, such as urea being removed from the blood plasma by the kidney and excreted in urine.AQA
Exercise and health: Regular exercise lowers blood pressure, improves cholesterol balance and helps maintain a healthy weight, reducing CVD risk.AQA
Exercise physiology: Lactic acid accumulates in the muscles and blood, contributing to fatigue, and extra oxygen is taken in afterwards to break it down.AQA
Exercise regime: Regular exercise increases glucose uptake by muscles and can improve the body's response to insulin.AQA
Exothermic: A reaction in which the product level is lower than the reactant level, so energy has been transferred to the surroundings and the overall energy change is…AQA
Exothermic and endothermic energy transfers: If the forward reaction releases energy to the surroundings it is exothermic, and the reverse reaction must then absorb the same quantity of energy, so it is…AQA
Exothermic and endothermic processes: A negative result means more energy is released than absorbed, so the reaction is exothermic; a positive value indicates an endothermic reaction.AQA
Exothermic and endothermic reactions: In an exothermic reaction energy is transferred to the surroundings, causing them to warm up, while in an endothermic reaction energy is transferred from the…AQA
Exothermic direction: The direction favoured when temperature is decreased, doing the opposite of the endothermic direction.AQA
exothermic process: A process in which energy is released, such as when new bonds form to create products.AQA
Exothermic reaction: A reaction in which energy is transferred from the reacting system to the surroundings, so the surroundings warm up and the thermometer reading rises.AQA
Exothermic reactions: A reaction that transfers energy to the surroundings so the temperature of the surroundings increases.AQA
Expected ratios: Ratios that describe large numbers of offspring, while actual small samples may differ because fertilisation is random.AQA
Experimental comparison: Comparing how vigorously different metals react with water or dilute acid, or comparing displacement reactions, to deduce reactivity.AQA
Experimental design and control variables: A valid investigation tests one factor at a time, such as pondweed and bubble counting, keeping other variables constant.AQA
Experimental design and variables: Identifying the independent variable and dependent variable in a data set about nervous function, and recognising limitations such as small sample size or…AQA
Experimental evidence and observation: A floating marker on water moves up and down but does not travel along with the ripple, and a smoke trail or suspended light object shows air vibrating…AQA
Experimental evidence and scientific method: Changes in the model are justified using evidence from experiments rather than accepting ideas without evidence.AQA
Experimental evidence from water and dilute acid reactions: Metals can be put in order of their reactivity from their reactions with water and dilute acids.AQA
Experimental measurement and error: Recording paired ammeter and voltmeter readings, including negative values where the circuit allows, and repeating readings and checking connections to reduce…AQA
Experimental observation of metal reactions: Bubbles, heat or a metal salt solution seen when a metal reacts with water or dilute acid, supporting the link between the reaction and ion formation.AQA
Experimental variation and reliability of measurements: A single count-rate reading is unreliable because the count over the next minute might be higher or lower than the last.AQA
Extension: The increase in length of an elastic object when a stretching force acts on it, measured in metres, symbol m, and represented by the symbol e.AQA
Extension or compression: The change in length of a spring in metres (m), represented by e in the equation Eₑ = ½ke².AQA
External forces: The forces acting upon an isolated object or system, which can be balanced or unbalanced.AQA
Extinction: When species no longer exist, shown by fossils appearing in older rocks but no living examples existing.AQA
Extract: Read the axes, units and key first, then locate the value or trend asked for in a chart, graph or table.AQA
Extract data: Reading values directly off the axes, such as the exact day of the LH peak.AQA
Extraction: Obtaining raw materials from the Earth, such as quarrying limestone, mining metal ores, drilling crude oil or harvesting timber.AQA
Extraction of metals: Metals can be extracted from molten compounds using electrolysis, which is used if the metal is too reactive for reduction with carbon or reacts with carbon.AQA
Extraction of reactive metals: In aluminium extraction, aluminium oxide is dissolved in molten cryolite to lower the working temperature.AQA
Extreme weather: More frequent and severe events including heatwaves, droughts, storms and heavy rainfall, affecting people and infrastructure.AQA
Extreme-environment adaptations: Features such as membrane lipids and cell-wall material that are distinct, and enzymes that stay active at high temperature.AQA
Extremophiles: Organisms adapted to survive in extreme environments such as high temperature, high pressure or high salt concentration.AQA

F

Factors affecting health: Communicable diseases, non-communicable diseases, diet, stress, life situations and access to healthcare all interact to affect health.AQA
Factors affecting rates: Concentration, pressure, surface area, temperature and catalysts change the rate by altering the frequency of collisions or the proportion of particles with…AQA
Factors affecting success: The patient's age and the cause of infertility, on which success depends heavily and which influence the outcome.AQA
Family tree: A diagram showing inheritance over generations, with squares for males, circles for females and shaded symbols showing the trait.AQA
Fatty acids and glycerol: The components of lipids, where one glycerol molecule combines with fatty acid molecules by condensation to synthesise a lipid.AQA
Fault current: Flows to earth when a fault occurs, and the large current melts the fuse or trips the circuit breaker.AQA
Faulty heart valve: A valve that may become faulty by preventing the valve from opening fully, or by developing a leak.AQA
Feedstock and the petrochemical industry: Starting materials for the petrochemical industry, which can be processed from fractions of crude oil.AQA
Fermentation: Anaerobic respiration in yeast cells, in which glucose is converted into ethanol and carbon dioxide.AQA
Fertilisation: The fusion of two gametes to form a diploid zygote, restoring the full chromosome number and creating new allele combinations.AQA
Fertilisation and zygote formation: The sperm nucleus fuses with the egg nucleus, forming a zygote with the full 46 chromosomes.AQA
Fertility awareness: Predicting ovulation using calendar calculations, body temperature changes or cervical mucus observations, though predictions are not exact.AQA
Fertility drug: A treatment containing FSH and LH that can be given to a woman whose own FSH level is too low to stimulate eggs to mature.AQA
Fertility treatment: Gives a woman the chance to have a baby of her own by mimicking the hormonal control of the menstrual cycle.AQA
Fetal alcohol syndrome: A condition caused by alcohol crossing the placenta and damaging the developing brain and other organs, which may cause learning difficulties, distinctive…AQA
Field: A region in which a mass, a charge or a magnetic pole experiences a force.AQA
Field line direction: Join the marks with smooth lines and add arrows showing the direction from the north to the south pole.AQA
Field lines: Lines that show the direction of the force on a small positive test charge or a small compass needle, with closer lines indicating a stronger field.AQA
Field margin: An uncropped strip around a field, often sown with wildflowers or left as rough grass, providing food, shelter and nesting sites.AQA
Field shape and polarity: Inside the field is strong and approximately uniform along the axis; outside it resembles the field around a bar magnet, with field lines emerging from the…AQA
Field strength: Shown by line spacing, with closely spaced lines at the poles showing a strong field and wider spacing away showing a weaker field.AQA
Field strength and distance: The strength of the magnetic field depends on the current through the wire and the distance from the wire.AQA
Filament lamp: A non-ohmic component in which increasing current raises the filament temperature, increasing lattice ion vibration and so increasing resistance.AQA
filter beds: Layers of sand and gravel, sometimes with other materials, through which water is passed to trap solid particles suspended in the water.AQA
filtrate: The salt solution kept after the mixture is filtered to remove the excess unreacted solid.AQA
filtration: Separating an insoluble solid from a liquid using filter paper and a funnel, naming the solid as the residue and the liquid as the filtrate.AQA
Final mass: The mass recorded after the tissue has been removed and any surface water has been blotted.AQA
Final velocity: The velocity of an object at the end of the time interval being considered, measured in metres per second (m/s).AQA
Financial cost: Money spent or income lost, such as paying for medicines, transport to hospital or adapting a home, plus lost wages.AQA
finite: The supply of elements such as carbon, oxygen, hydrogen, nitrogen and phosphorus on Earth is limited, so the same atoms are reused repeatedly.AQA
Finite and renewable resources: Plastic bags use crude oil, a finite resource, while paper bags use wood, which can be renewable if forests are managed sustainably.AQA
Finite resource: Crude oil is being used up much faster than it is formed, so once used it cannot be replaced within a human timescale.AQA
Finite resources: Resources such as metal ores, fossil fuels and fresh water are finite, and demand for them multiplies as population and living standards rise.AQA
Finite stores: Stores that exist in limited amounts, formed over millions of years, and are used faster than they form.AQA
First 20 elements: The elements from hydrogen (H) to calcium (Ca) whose names and symbols must be recalled.AQA
Fitness: Allows a person to sustain a higher speed for longer, especially over greater distances.AQA
Fixed melting and boiling points of pure substances: Pure elements and compounds melt and boil at specific temperatures, giving a sharp, fixed melting point and boiling point at a given pressure.AQA
Flame colours: Atoms can be excited by heating in a flame, and as the electrons drop back to lower levels they emit visible light of characteristic colours.AQA
Flammability: How easily a substance catches fire, which decreases with increasing molecular size because larger molecules need more energy and oxygen to vaporise and burn.AQA
Fleming's left-hand rule: A rule relating the mutually perpendicular directions of current, field and force, using the first finger for field, second finger for current and thumb for…AQA
Floating and sinking: Less dense objects float on denser fluids, so comparing the density of an object with the density of the fluid predicts whether it floats or sinks.AQA
Follicle: The structure inside the ovary in which an egg matures.AQA
Food availability: Affects how many organisms can survive and reproduce.AQA
Food chain: A representation of feeding relationships within a community, in which arrows show the direction of energy transfer from one organism to the next.AQA
Force: A vector quantity, measured in newtons, N, whose direction as well as size matters and which acts on the current-carrying conductor.AQA
Force and displacement: Work is done when a force causes displacement along the force's line of action.AQA
Force and energy: The equation links the mechanics of forces to energy transfer, so it is used whenever a force moves an object and energy changes store.AQA
Force and mass in road transport: The resultant force during acceleration or braking is estimated using F = m × a with an estimated vehicle mass.AQA
Force at right angles to motion: Does no work because there is no movement along the force.AQA
Force on a current-carrying conductor: F in the equation, measured in newtons (N), greatest when perpendicular to the field and zero when parallel.AQA
force-extension graph: A plot of force against extension whose gradient in the straight-line region equals k.AQA
Force–extension graphs: A graph with force on the vertical axis and extension on the horizontal axis, showing a linear or non-linear relationship.AQA
Force, current and length relationships: For a conductor at right angles to the field, these combine as F = B I l, with F in newtons, I in amperes and l in metres.AQA
Force, mass and acceleration calculations: The equation F = m × a can be used to calculate any one of the three quantities when the other two are known.AQA
Forces and motion: If the force and motion are at right angles, no work is done by that force, so only the component of motion in the force direction counts.AQA
Forces as interactions: A push or pull that acts on an object due to the interaction with another object.AQA
Forces between particles: The stronger these are, the higher the melting point and boiling point of the substance.AQA
Formation of 1⁺ ions: Reactivity is judged by how readily the metal loses its outer electron to form a 1⁺ ion.AQA
Formation of new species: Complete when two populations can no longer interbreed to produce fertile offspring, so they are recognised as separate species.AQA
Formation of oxides of nitrogen: The high temperature of combustion makes nitrogen and oxygen from the air react to form oxides of nitrogen.AQA
Formation of positive and negative ions: Metal atoms lose electrons to form positive ions, while non-metal atoms gain those electrons to form negative ions.AQA
Formation of the early atmosphere: One theory suggests intense volcanic activity released gases that formed the early atmosphere during the first billion years of the Earth's existence.AQA
Formation of the oceans by condensation: As the early Earth cooled, water vapour in the atmosphere condensed to form liquid oceans.AQA
Formation of useful by-products: In aqueous sodium chloride, hydrogen ions and chloride ions are discharged, leaving sodium ions and hydroxide ions in solution to form sodium hydroxide.AQA
Formation over millions of years: Plankton and other tiny marine organisms died, sank into mud and were buried, and without oxygen decay was incomplete, so heat and pressure slowly converted…AQA
Formula: Shows how many atoms of each element are present, for example H₂O contains two hydrogen atoms and one oxygen atom.AQA
Formulae: Representations of compounds using the symbols of the atoms from which they were formed, showing the fixed proportions of the elements.AQA
Forward and reverse reactions: The forward reaction is A + B → C + D, and the reverse reaction is C + D → A + B.AQA
Forward bias: The connection in which conventional current flows easily from the anode to the cathode, so the diode conducts and its resistance is low.AQA
Forward reaction: The change that converts reactants into products.AQA
Fossil formation and preservation: Parts of organisms that have not decayed because one or more of the conditions needed for decay are absent.AQA
Fossil fuel combustion: Burning coal, oil and natural gas, a major human source of carbon dioxide.AQA
Fossil fuels: Coal, crude oil and natural gas, formed from buried remains of plants and marine organisms, that contain carbon.AQA
Fossil fuels and nuclear fuel: Energy sources including coal, oil and gas, which are non-renewable, and nuclear fuel, which releases thermal energy without combustion.AQA
Fossil record: Shows changes in organisms over time and links between ancestral and modern forms, though it is incomplete.AQA
Fossils: Remains or traces of organisms preserved in rocks, ice or amber, whose age can be estimated from the rock layer in which they are found.AQA
Fraction: A mixture of hydrocarbons with a similar number of carbon atoms, collected separately and used as a fuel or as feedstock.AQA
Fractional distillation: A separation process using a fractionating column with a temperature gradient, hot at the bottom and cooler at the top, where each fraction condenses at a…AQA
Fragments of giant covalent structures: A representative part drawn so that every atom shown has its full bonding, such as four single lines around each carbon in diamond.AQA
Free body diagram: A diagram showing one chosen object as a dot or box with arrows for every force acting on it from its surroundings.AQA
Free fall: A situation where the only force acting on an object is gravity, so air resistance is negligible.AQA
Free-body diagrams: Used to model the forces acting on the isolated object when describing them.AQA
Freezing: The change from liquid back to solid, in which the same amount of energy is released.AQA
Frequency: The number of waves passing a point each second, or the number of complete cycles each second on a displacement–time graph.AQA
Frequency table: Records categories or intervals with their counts.AQA
fresh water: Water with low levels of dissolved salts, obtained from sources such as rivers, lakes, reservoirs and groundwater held in aquifers.AQA
Fresh water supply for living organisms: The water cycle provides fresh water for plants and animals on land before draining into the seas.AQA
Friction: A force that opposes relative sliding between surfaces, for example a book dragged across a desk.AQA
FSH: Given to stimulate eggs to mature as part of fertility treatment that mimics the natural control of the menstrual cycle.AQA
FSH and LH: Hormones given to the mother during IVF that stimulate the maturation of several eggs.AQA
Fuels and energy resources: Small-molecule fuels are in high demand because they release energy readily when burned, making them valuable for cooking, heating and transport.AQA
Fuels from crude oil: Fractions from crude oil can be used directly as fuels, for example petrol, diesel and kerosene.AQA
Fuels from hydrocarbons: Shorter alkanes make fuels such as petrol, which burn more cleanly and are in high demand.AQA
Full life cycle: Every stage from raw material extraction, processing, manufacture, transport, use and disposal or recycling.AQA
Full outer shell: A stable electron arrangement, with 2 electrons for helium and 8 for the other Group 0 elements, so atoms do not need to gain, lose or share electrons.AQA
Full outer shells: The arrangement each atom reaches by pairing electrons, with two outer-shell electrons for hydrogen and eight for carbon, nitrogen, oxygen and chlorine.AQA
Full outer shells and noble gas electron configurations: Each ion is drawn with a complete outer shell, and electrons are counted before and after transfer to check each ion has a full outer shell.AQA
Fullerenes: Molecules of carbon atoms with hollow shapes, based on hexagonal rings but possibly containing rings with five or seven carbon atoms.AQA
Function: The specific job an organ carries out, emerging from its different tissues working together rather than independently.AQA
Function and impact of packaging: Packaging protects the product, keeps it clean, provides information and helps it sell, but it also uses materials such as paper, glass, plastic, steel and…AQA
Function and placement of switches: Switches and fuses are placed in the live wire so that opening the switch or melting the fuse isolates the appliance from the high potential.AQA
Functional adaptation: An internal process, such as reduced sweating or concentrated urine, that helps an organism survive in its habitat.AQA
Functional unit: A basis such as one kilogram of material, used so that comparisons between products are fair.AQA
Further treatment: Sludge may be digested anaerobically to produce biogas and a residue used as fertiliser, while effluent undergoes aerobic biological treatment and…AQA
fuse: Melts when the current exceeds its rating because the heating effect of the current raises the temperature of the fuse wire, breaking the live connection.AQA
Fuses and circuit breakers: The surge from a fault melts the fuse or trips the circuit breaker, disconnecting the live supply before anyone can receive a shock.AQA

G

g/cm³: A smaller unit often used in laboratory work, where 1 g/cm³ equals 1000 kg/m³.AQA
Gamete: A sex cell produced by meiosis, such as sperm and egg cells in humans or pollen and egg cells in flowering plants.AQA
Gamete formation: The process in which a cell in a reproductive organ divides twice to form four gametes, such as sperm and egg cells.AQA
Gametes: Sex cells such as sperm and eggs in animals, or pollen and eggs in flowering plants, each receiving a single set of chromosomes.AQA
Gametes in animals: The male gamete is the sperm cell and the female gamete is the egg cell, also called the ovum.AQA
Gamma emission: Releases energy without changing either the mass number or the atomic number, because it is electromagnetic radiation carrying energy only.AQA
Gamma radiation: A high-energy electromagnetic wave with no charge and no mass; it is weakly ionising and absorbed by thick lead or concrete.AQA
Gamma ray: A high-energy electromagnetic wave that carries energy away but has no mass and no charge.AQA
Gas exchange: A process in which oxygen diffuses into cells and carbon dioxide diffuses out of cells because each gas moves down its own concentration gradient.AQA
Gas exchange and diffusion: The movement of carbon dioxide and oxygen through the leaf, made efficient by the loose packing and air spaces of the spongy mesophyll.AQA
Gas exchange and transport in plants: Carbon dioxide enters the leaf by diffusion through stomata, while water is drawn up the xylem from the roots.AQA
Gas tests and observations: Carbon dioxide produced when a metal carbonate neutralises an acid is observed as effervescence and turns limewater milky.AQA
Gas volume collection: Volume in cm³ suits reactions that produce a gas you can collect, for example in a gas syringe or over water.AQA
Geiger-Muller tube: A detector that produces a pulse each time ionising radiation enters it.AQA
Gene: A small section of DNA on a chromosome that codes for a particular sequence of amino acids to make a specific protein.AQA
Gene delivery by vectors: The vector is used to insert the gene into the required cells, acting as a delivery vehicle rather than the final destination.AQA
Gene expression: The switching on of genes for particular proteins, which changes a cell's shape and organelles and controls specialisation.AQA
Gene expression producing new traits: The improvement arises because the introduced gene is expressed and produces a protein giving the new characteristic.AQA
Gene function and proteins: Genes code for proteins that build and control the body.AQA
Gene isolation using enzymes: Enzymes are used to cut the DNA, isolating the required gene from the donor genome.AQA
Gene therapy: An experimental approach that aims to replace or repair faulty alleles.AQA
Gene transfer between species: The human insulin gene is cut out and inserted into a bacterial cell so the bacterium makes a human protein.AQA
Gene–environment interaction: Phenotype depends on genetic information interacting with environmental factors, with genes setting a potential range and the environment determining where…AQA
General equation for reversible reactions: A + B ⇌ C + D is a general model of a reversible reaction, and the letters are placeholders that can be replaced with real substances.AQA
General formula CnH2n+2: The formula applied to a given molecular formula, checking that the hydrogen count equals twice the carbon count plus two.AQA
genes: Lengths of DNA passed from parents in gametes, so offspring inherit alleles that set features.AQA
Genetic cause: The inherited alleles are the genetic cause of a characteristic.AQA
Genetic continuity: The DNA is copied before division and each new cell receives a full set of chromosomes, so daughter cells can carry out the same functions as the parent cell.AQA
Genetic counselling: Support that uses understanding of inheritance so families can make informed decisions.AQA
Genetic diagram: A diagram using letters such as P for the dominant polydactyly allele and p for the recessive allele to show possible outcomes and predict genotypes and…AQA
Genetic engineering: A process which involves modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic.AQA
Genetic engineering steps: Enzymes are used to isolate and cut out the required gene from the donor organism, and the gene is inserted into a vector.AQA
genetic material: Material held in the nucleus, mainly DNA arranged into chromosomes, which is passed to daughter cells during cell division.AQA
Genetic modification in medicine: Research exploring the insertion of a normal, working copy of the allele into the cells of a person with a disorder.AQA
Genetic risk factors: Inherited alleles that raise susceptibility to particular cancers, for example BRCA variants linked to breast and ovarian cancer.AQA
Genetic testing: Identifies alleles, for example testing for the allele that causes cystic fibrosis, and is not the same as gene therapy.AQA
Genetic uniformity: All the plants are identical, so a new disease or pest could affect all of them because they share the same resistance alleles.AQA
Genetic variation: Differences caused by differences in the alleles inherited, new alleles formed by mutation, and the random combination of parental alleles during sexual…AQA
Genetically identical diploid daughter cells: The outcome of mitosis, where a parent cell divides into two cells that are genetically identical and diploid.AQA
Genome: The full set of genetic material an organism inherits, with genes coding for proteins that help build and control the cell.AQA
Genotype: The allele combination, such as PP or Pp, with an uppercase letter for the dominant allele and the matching lowercase letter for the recessive allele.AQA
gentle evaporation: Slow evaporation of the filtrate using a water bath or electric heater, not a direct Bunsen flame, to avoid spitting and decomposition.AQA
Genus and species: The genus name is written first and begins with a capital letter; the species name follows and begins with a lower-case letter.AQA
Geological change over time: Geological activity such as heat, pressure, melting and plate movement destroys many fossils over long periods.AQA
Giant covalent structure: A three-dimensional network of atoms joined by covalent bonds, with no separate molecules and no overall charge.AQA
Giant covalent structures: Structures in which every atom is joined to its neighbours by strong covalent bonds throughout the whole solid, such as diamond and silicon dioxide.AQA
Giant ionic lattice: The structure the ions formed by electron transfer pack into, held together by strong electrostatic attraction.AQA
Giant ionic lattice structure: A regular repeating pattern in which Na⁺ and Cl⁻ ions are arranged, with each ion surrounded by six ions of opposite charge.AQA
Giant ionic lattices: A regular, repeating grid of ions held in fixed positions, repeating in three dimensions with each ion surrounded by oppositely charged neighbours.AQA
Giant lattice structure: A regular arrangement of positive ions surrounded by a sea of delocalised electrons.AQA
Giant metallic lattices: Layers of positive ions can slide over each other, explaining why metals are malleable and ductile.AQA
Giant structures: Metals consist of giant structures containing very large numbers of atoms packed together.AQA
Glands as chemical effectors secreting hormones: They respond by secreting a chemical, such as a hormone or enzyme.AQA
Glandular sources and target organs: FSH and LH are released by the pituitary gland, while oestrogen and progesterone are released by the ovaries, each acting on its target.AQA
Glandular tissue: Animal tissue that secretes substances such as enzymes or hormones.AQA
Global climate change: The long-term shift in average weather patterns, driven mainly by increased greenhouse gases such as carbon dioxide and methane.AQA
Global dimming: A phenomenon where the amount of sunlight reaching Earth's surface is reduced, as particulates reflect sunlight back into space and increase cloud formation.AQA
Global warming: Warming of the Earth's surface caused by methane absorbing and re-emitting infrared radiation, with rising global temperatures linked to increased methane…AQA
Glowing splint: A splint that has been lit and blown out so that it is still glowing, then inserted into a test tube containing the gas.AQA
Glucagon: Secreted by the pancreas when blood glucose concentration is too low, it stimulates the liver to convert stored glycogen back into glucose, which is released…AQA
Glucose: A product of photosynthesis that stores energy and is used in respiration, stored as starch, or used to build cellulose, amino acids and lipids.AQA
Glycogen: The storage polysaccharide in animals and fungi, stored in the liver and muscles, which is compact, insoluble and readily hydrolysed to glucose for respiration.AQA
Glycogen as a glucose store: A storage polysaccharide made of many glucose units, which is converted into glucose and released into the blood.AQA
Glycogen storage and release: Insulin promotes uptake of glucose into cells and storage as glycogen in the liver and muscles, while at Higher Tier only, glucagon stimulates the liver to…AQA
Gradient: A measure of rate found from a straight-line section by dividing the change in the y-axis quantity by the change in the x-axis quantity, including units.AQA
Gradient as acceleration: The slope of a velocity–time graph, found as change in velocity divided by change in time, in m/s².AQA
Gradient as speed: Speed is found from a distance–time graph by calculating the gradient.AQA
Gradient of a tangent: The rate at any point on a graph of amount against time, found by drawing a tangent at that point.AQA
Gradual increase: The slow rise in the percentage of oxygen over billions of years, not a sudden change.AQA
Graph interpretation: Comparing curves of rate against a factor to identify which changed factor gives the greatest increase in rate and is therefore limiting.AQA
Graph interpretation and proportionality: A larger calculated rate means water is being lost more quickly, and the gradient of a volume against time graph can be used to find the rate and compare rates.AQA
Graph skills: Axes are labelled with quantity and time in s with units, a sensible scale is chosen, points are plotted accurately and joined with a smooth curve of best fit.AQA
Graphene: A giant covalent form of carbon in which each carbon atom bonds covalently to three others, forming a single sheet one atom thick of interlocking hexagons.AQA
Graphical analysis: Deducing limiting factors from graphs, where a rising curve indicates the x-axis factor is limiting and a plateau indicates another factor is limiting.AQA
Graphical analysis of rate: Plotting quantity on the y-axis and time on the x-axis, where the gradient of a tangent gives the rate at a specific moment.AQA
Graphical estimation: Counting squares on the grid to estimate the area under a velocity–time graph, giving an approximate value.AQA
Graphs of linear relationships: A graph of weight against mass is a straight line through the origin, and its gradient equals g.AQA
Gravitational field: The region around the Earth where a mass experiences a force.AQA
Gravitational field strength: A quantity measured in newtons per kilogram that varies from place to place, so the same object can have different weights in different locations.AQA
Gravitational potential energy: Energy transferred to the gravitational store when an object is raised; a horizontal movement at constant height transfers none.AQA
Gravitational potential store: A store of the object–Earth system that increases as the object rises and is maximum at the highest point.AQA
Gravity and weight: Gravitational field strength, g, is the force in newtons acting on each kilogram of mass.AQA
Gravity, electrostatics and magnetism: Gravitational force attracts any two masses, electrostatic force acts between electric charges, and magnetic force acts between magnetic poles or between a…AQA
Greenhouse effect: A natural process that keeps Earth warm, strengthened when greenhouse gases absorb outgoing infrared radiation and re-emit it so less heat escapes to space.AQA
Greenhouse gas: Carbon dioxide and methane are examples, and their atmospheric concentrations are rising because human activities add them faster than natural processes…AQA
Greenhouse gases: Gases such as methane that absorb outgoing infrared radiation and re-emit it, contributing to the greenhouse effect and global warming.AQA
Greenhouse gases and climate change: Burning coal, oil and gas releases carbon dioxide, a greenhouse gas linked to climate change.AQA
Greenhouse gases and their sources: Carbon dioxide and methane trap infrared radiation, and human activity raises their atmospheric amounts.AQA
Grit removal: Lets dense particles settle or be spun out in a grit channel or vortex tank, because grit would otherwise erode machinery and accumulate in tanks.AQA
Ground water: Water from aquifers, often filtered naturally through rock, so treatment may only need screening, aeration and chlorination.AQA
Group: Elements in the same group have the same number of outer-shell electrons, which is why they show similar chemical properties.AQA
Group 0: Noble gases that are unreactive due to full outer shells.AQA
Group 0 noble gases: Elements whose boiling points increase with increasing relative atomic mass going down the group.AQA
Group 1: Metals that become more reactive down the group because the outer electron is lost more easily as atomic radius increases and shielding increases.AQA
Group 1 alkali metals: Metals in Group 1 that each have one electron in their outer shell.AQA
Group 7: Non-metals that become less reactive down the group because it becomes harder to gain an electron.AQA
Group chemistry: Elements in the same group have the same number of outer electrons, which gives them similar chemical properties.AQA
Group number and ion charge: Group 1 and Group 2 metals lose one or two electrons respectively, forming 1⁺ and 2⁺ ions, while Group 6 and Group 7 non-metals gain two or one electrons…AQA
Group trends and reactivity: Group 1 reactivity increases down the group while Group 7 reactivity decreases down the group, and Group 0 noble gases are unreactive because they have full…AQA
Groups: Vertical columns in the periodic table containing elements with similar properties.AQA
Groups 1 and 7: Groups whose elements' names and symbols must be recalled, such as sodium (Na), potassium (K), chlorine (Cl) and bromine (Br).AQA
Growth and development of multicellular organisms: An increase in cell number, not just cell enlargement, allows an organism to become larger, and cells become organised into tissues and organs with…AQA
Growth and repair: Situations involving growth, repair or replacement of body cells are contexts where mitosis is occurring.AQA
Growth, repair and storage: The products of these synthesis reactions are used for growth, repair, storage, and the building of new cells and tissues.AQA
Guard cells: Two cells surrounding each stomatal pore that change shape to open or close the pore, controlling gas exchange and water loss.AQA

H

Habitat and land use: Renewables release little carbon dioxide while running but can affect habitats, landscapes or wildlife, for example dams and flooded valleys.AQA
Habitat destruction and fragmentation: Building, quarrying, farming and dumping waste remove or damage habitat, and surrounding habitats are also fragmented and polluted.AQA
Habitat loss: Loss or destruction of habitat, such as deforestation, which removes food, shelter or breeding sites.AQA
Habitat loss and restoration: Removal of habitats, food or breeding sites, or gaining them again through replanting woodland, restoring wetlands or creating hedgerows and wildlife corridors.AQA
Haemoglobin: A protein that binds oxygen in the lungs and releases it in respiring tissues.AQA
Half equation: A representation of electron loss and gain in which electrons on the right mean oxidation and electrons on the left mean reduction.AQA
Half equations: A representation of the reaction at one electrode only, including the reactant ion or molecule, the product, and the electrons gained or lost.AQA
Half equations and balancing: These represent the changes at electrodes, balancing both atoms and charges, adding electrons to the left side for reduction.AQA
Half-equations and ionic equations: Each product can be supported by a half-equation such as Cu²⁺ + 2e⁻ → Cu or 2Cl⁻ → Cl₂ + 2e⁻.AQA
half-life: The time it takes for the number of nuclei of the isotope in a sample to halve, or for the count rate from a sample to fall to half its initial level.AQA
Half-life and activity: The activity falls by half in each half-life, giving a smooth decay curve.AQA
Half-life as a measurable constant: The time for half the nuclei, or half the count rate, to remain.AQA
Halide ions: Negative ions such as Cl⁻, Br⁻ or I⁻; when present, the halogen is produced instead of oxygen.AQA
Halogen reactivity: The halogen achieves a full outer shell of eight electrons, which is why it reacts.AQA
Halving of nuclei number and count rate: After each half-life the number of nuclei of the isotope halves, and the count rate or activity falls to half its initial level.AQA
Haploid: Gametes are haploid and contain one chromosome from each pair, so that fertilisation restores the diploid number.AQA
Hard part preservation: Bones, shells, teeth or wood resist decay better than soft tissue and may be preserved.AQA
Hazard and risk: Ultraviolet waves, X-rays and gamma rays can have hazardous effects on human body tissue, and the risk of harm depends on the type of radiation and the size…AQA
Hazard from contamination: Due to the decay of the contaminating atoms, and the type of radiation emitted affects the level of hazard.AQA
Health: The state of physical and mental well-being, not merely the absence of disease.AQA
Health and disease risk: A defect in the immune system reduces the body's ability to recognise or destroy pathogens, so infectious diseases are more likely.AQA
Health as physical and mental wellbeing: A state of physical and mental wellbeing, not only the absence of disease.AQA
Heart failure: A condition in which the heart cannot pump blood effectively around the body.AQA
Heart rate: Increases during exercise so that oxygenated blood is pumped to the muscles more quickly.AQA
Heating: A use of energy resources that includes warming buildings and providing hot water, often using natural gas, biomass or solar thermal panels.AQA
Heating curve: A curve whose flat sections show changes of state, where energy supplied changes internal energy but not temperature.AQA
Heating effect of current: Power dissipated by a resistor is transferred as thermal energy to the surroundings, and doubling the current increases the power dissipated by a factor of…AQA
Hedgerow: A line of shrubs and trees along a boundary that gives cover, berries and corridors for wildlife moving between habitats.AQA
Height: The vertical distance an object is raised or lowered, measured in metres (m), not the distance along a slope.AQA
Hertz: The unit of frequency, Hz, where 1 Hz means one wave per second.AQA
Heterozygous: Describes a genotype in which the two alleles of a gene carried by an organism are different.AQA
Hierarchical classification: Linnaeus arranged living things into a hierarchy of seven groups: kingdom, phylum, class, order, family, genus and species, where each level contains fewer…AQA
Hierarchical grouping: A system in which larger groups contain smaller, more closely related groups.AQA
Hierarchy: The order that runs cells → tissues → organs, with each tissue itself a group of similar cells with a shared role.AQA
High and low thermal conductivity: Metals have high thermal conductivity, while gases and foams have low thermal conductivity.AQA
High melting points: The very high melting points of these solids arise because many strong covalent bonds must be overcome to melt or boil them.AQA
Histogram: Shows continuous numerical data grouped into intervals, so bars touch and the area of each bar represents frequency.AQA
Historical development of drugs: Early drug discovery often guided by traditional knowledge and observation of natural effects.AQA
Homeostasis: The regulation of internal conditions, such as water levels, to maintain optimum conditions for enzyme action and all cell functions.AQA
Homeostasis and internal conditions: Body temperature is an internal condition controlled by homeostasis and kept close to 37 °C in humans.AQA
Homeostatic control of temperature, pH and glucose: Homeostasis maintains conditions such as blood glucose concentration and water content so that cells can function.AQA
Homologous series: A family of compounds with the same general formula and similar chemical properties, in which each member differs from the next by a CH₂ unit.AQA
Homozygous: If the two alleles present are the same, the organism is homozygous for that trait, for example AA or aa.AQA
Homozygous dominant: An individual with two dominant alleles, such as BB, that shows the dominant phenotype.AQA
Homozygous recessive: An individual with two recessive alleles, such as bb, that shows the recessive phenotype.AQA
Hooke's law: The condition under which the equation is valid, so the force–extension graph is a straight line through the origin and the spring has not passed its limit of…AQA
Hooke's law and the elastic limit: For a spring obeying Hooke's law the force grows steadily from zero to F, so the average force is F/2; beyond the elastic limit the spring is inelastically…AQA
Hormonal control by the pancreas: The pancreas produces and secretes the hormone glucagon into the blood when blood glucose is too low.AQA
Hormonal coordination of the menstrual cycle: Four interacting hormones control the cycle in a sequence, from FSH maturing a follicle to progesterone maintaining the uterus lining.AQA
Hormonal methods: Methods that use hormones, including oral contraceptives, the injection, implant, skin patch, and hormone-releasing intrauterine devices.AQA
Hormonal responses: Usually slower to begin than nervous responses but often last longer and affect more widespread areas.AQA
Hormonal signalling and control: TSH is the key intermediate signal, making the thyroid gland release more thyroxine, while high thyroxine inhibits the hypothalamus and pituitary.AQA
Hormones: Chemicals secreted by glands directly into the bloodstream, which the blood carries to a target organ where they produce an effect.AQA
Hormones in the bloodstream: Hormones secreted into the blood in response to body conditions, travelling in the blood to target organs such as the thyroid gland or the ovaries.AQA
Host cell: A virus particle attaches to a host cell and uses its ribosomes and enzymes to make new virus particles.AQA
Host cell gene expression: Once inside the host cell, the inserted gene is expressed so the cell manufactures the desired protein.AQA
Human and economic consequences: Crop yields may fall where drought and heat stress plants, threatening food security, and human health is affected by heat stress and changing ranges of…AQA
Human cost: Suffering such as pain, reduced mobility, anxiety, stigma, lost independence and premature death.AQA
Human dependence on biodiversity: The future of the human species on Earth relies on us maintaining a good level of biodiversity.AQA
Human endocrine system: The system that includes glands such as the thyroid, pituitary, pancreas, adrenal glands, ovaries and testes.AQA
Human genome: The whole human genome has now been studied and sequenced, base by base, and stored as a reference sequence.AQA
Human health effects: Both gases irritate the airways, triggering coughing, wheezing and worsening asthma or other respiratory problems.AQA
Human health effects of air pollutants: Carbon monoxide binds to haemoglobin and reduces oxygen transport, nitrogen oxides cause respiratory problems, and particulates can be inhaled deep into the…AQA
Human impact: Human activities such as hunting, overfishing or pollution that reduce population numbers.AQA
Human impact on biodiversity: Human activities such as deforestation and pollution can reduce biodiversity.AQA
Human impact on ecosystems: Positive and negative human interactions with an ecosystem, such as deforestation or replanting woodland, and their effect on biodiversity.AQA
Human impact on the atmosphere: Human activities increase the amounts of the greenhouse gases carbon dioxide and methane in the atmosphere.AQA
Human impact on the carbon and water cycles: Disruption of either cycle, such as drought or burning fossil fuels, has effects on living organisms.AQA
Human impact on the environment: Activity such as deforestation, pollution and overfishing that reduces the variety of species and genetic variation, so conservation methods aim to keep…AQA
Human impacts on ecosystems: Many human activities are reducing biodiversity, and only recently have measures been taken to try to stop this reduction.AQA
Human influence on Earth systems: Human activities such as burning fossil fuels and farming increase greenhouse gas concentrations, which many scientists believe will raise surface temperatures.AQA
Human population growth: Rapid growth in the human population means that increasingly more resources are used and more waste is produced.AQA
Hydrocarbon: A molecule made up of hydrogen and carbon atoms only, with no other element in the molecule itself.AQA
Hydrocarbons: Liquid and gaseous substances into which heat and pressure converted buried organic material, migrating through porous rock and trapped beneath impermeable…AQA
Hydrogen: A non-metal that forms H⁺ in acids, so it is a recognised exception to the simple rule.AQA
Hydrogen ion concentration and acidity: As the pH decreases by one unit, the hydrogen ion concentration of the solution increases by a factor of 10.AQA
Hydrogen ion concentration and pH: As the concentration of H⁺ ions increases, the pH decreases.AQA
Hydrolysis: The breakdown process in which carbohydrates are broken down to sugars, proteins to amino acids, and lipids to fatty acids and glycerol.AQA
Hydroxide ions: Ions with the formula OH⁻ that lose one electron each and rearrange to form oxygen and water.AQA
Hygiene and sanitation: Measures such as hand-washing, disinfecting surfaces, clean water supplies, sewage treatment and hygienic food handling that remove or contain pathogens.AQA
Hypothalamus, pituitary and thyroid axis: The hypothalamus detects a change and releases a releasing hormone, the pituitary secretes TSH, and the thyroid gland releases more thyroxine.AQA
Hypothesis: A testable prediction linking the ions present in the aqueous solution to the products expected at each inert electrode.AQA
Hypothesis development: An investigation begins with a testable hypothesis that names the independent variable, the dependent variable and the direction of change, and links to…AQA

I

Ideal transformer power balance: For a 100% efficient transformer, the electrical power entering the primary coil equals the electrical power leaving the secondary coil.AQA
Identification by comparison: Identification requires running a known pure sample under the same conditions and comparing R_f values or spot positions.AQA
Identification of chlorine gas: Damp litmus paper is put into the gas and the paper is bleached and turns white.AQA
Identification of compounds: A compound's R_f under fixed conditions is characteristic, so this measurement underpins identification.AQA
Identification of substances: Comparing spots from a mixture with spots from known dyes can identify the components, using the different distances moved.AQA
Identification using reference values: A known reference substance must be run on the same chromatogram under the same conditions to identify a compound by matching R_f values.AQA
Identifying oxidised and reduced species: Working out which species are oxidised and which are reduced in given chemical equations by tracking electron transfer and looking at the charges on the atoms…AQA
Identifying substances: Comparing R_f values of unknown spots with those of known substances, where matching values suggest the same substance.AQA
image size: The measured length of the image, found by multiplying magnification by real size, and measured carefully with a ruler.AQA
Immune reaction: A reaction initially caused by a pathogen that can trigger allergies such as skin rashes and asthma.AQA
Immune system: Defends the body against pathogens using white blood cells such as lymphocytes and phagocytes that recognise and destroy pathogens.AQA
Immunity: Inherited or acquired protection that, when absent, allows a pathogen to spread rapidly and cause illness.AQA
Immunity and memory cells: Memory lymphocytes remain after an infection, so a later exposure to the same antigen triggers faster, larger antibody production.AQA
Immunological memory: Memory cells remain after an infection, so a later infection by the same pathogen triggers a faster, larger antibody response.AQA
Improved fruit characteristics: Crop plants can be genetically engineered to produce bigger or better fruits, where better can include improved size, flavour, texture or shelf life.AQA
Improving evidence through further data: Scientists reduce uncertainty with more measurements, better instruments and multiple independent lines of evidence, but some uncertainty always remains.AQA
Impure substance: A substance that contains two or more substances, so it produces two or more spots, or a smeared streak, under the same conditions.AQA
In vitro fertilisation: Eggs are collected from the mother and fertilised by sperm from the father in the laboratory.AQA
In Vitro Fertilisation (IVF): A treatment in which FSH and LH are given to the mother, eggs are collected and fertilised by sperm in a laboratory, and embryos are inserted into the uterus.AQA
Inappropriate groups: Groups in which some elements were placed if the strict order of atomic weights was followed, where their properties did not match.AQA
Inbreeding: Breeding between closely related individuals, which happens when a small number of chosen organisms are repeatedly bred together.AQA
Incidence: The number of new cases in a population over a period, so explanations concern changing numbers of cases rather than individual symptoms.AQA
incident ray: The ray drawn meeting the point where the boundary is crossed, before the wave passes into the second medium.AQA
Incomplete: Describes early periodic tables that could only include known elements, leaving no gaps for undiscovered ones.AQA
Incomplete combustion: Burning a fuel in a limited supply of oxygen, producing carbon monoxide and soot instead of just carbon dioxide and water.AQA
Incomplete fossil record: The fossil record is incomplete because early soft-bodied life left few traces and geological activity destroyed most of them.AQA
incomplete oxidation: In anaerobic respiration glucose is only partially broken down, so carbon–oxygen bonds remain in the products and oxidation is incomplete.AQA
Incomplete oxidation of glucose: Causes a build up of lactic acid and releases less energy because glucose is not fully oxidised.AQA
Increase in frequency of desired alleles: Because the chosen parents carry alleles for the desired feature, those alleles become more common in the population.AQA
Increasing egg numbers: Raising the number of mature eggs available, which improves the chance that some will be fertilised successfully in the laboratory.AQA
Independent and dependent variables: The independent variable, such as salt or sugar concentration, goes on the x-axis, and the dependent variable, such as change in mass, goes on the y-axis.AQA
Independent scrutiny: Other specialists checking the method, data and interpretation of a study they did not carry out before the claim is accepted.AQA
Independent variable: The variable that is changed in an investigation, such as the carbon dioxide level.AQA
Index laws: Applied when multiplying or dividing numbers in standard form, for example adding indices when multiplying powers of ten.AQA
Indicator species: Organisms used in monitoring against a reference site to show whether protection and regeneration are working.AQA
Indirect evidence: Because the evidence is indirect and spans such an enormous time scale, theories have changed as new data emerged, showing that scientific explanations are…AQA
indivisible: Describes atoms that could not be divided into smaller parts, as they were thought to be before the electron was discovered.AQA
Induced magnet: A material that becomes a magnet when it is placed in a magnetic field.AQA
Induced magnetism: When a magnetic material is brought near a magnet, the magnet induces magnetism in it so the near face becomes an opposite pole.AQA
Industrial extraction of aluminium: Aluminium is manufactured by the electrolysis of a molten mixture of aluminium oxide and cryolite using carbon as the positive electrode.AQA
Industrial uses of alkenes: Cracking produces alkenes, which are useful for making polymers.AQA
Industrial uses of crude oil fractions: Each collected group is a fraction, not a pure substance, and the fractions have different uses such as petrol, diesel and bitumen.AQA
Inelastic deformation: The object does not return to its original length and shape when the force is removed, so it remains permanently stretched.AQA
Inert electrodes: Electrodes such as graphite or platinum that must be used so they do not react and affect the products.AQA
Inert electrodes and electrode products: When an aqueous solution is electrolysed using inert electrodes, the ions discharged depend on the relative reactivity of the elements involved.AQA
Inertial mass: A measure of how difficult it is to change the velocity of an object, or its resistance to acceleration.AQA
Infection prevention: Preventing infection through hygiene and vaccination helps slow resistance, so existing antibiotics remain useful for longer.AQA
Infectious disease: A disease caused by a microorganism, which may infect plants or animals.AQA
Infertility treatment: A treatment in which eggs are collected from the mother and fertilised outside the body, and several fertilised eggs may develop.AQA
Influence phenotype: The mutation contributes to the phenotype by altering the protein produced, and the effect may be slight or depend on the environment.AQA
Informed judgement: Weighing benefits against drawbacks, using the given information and reaching a clear, justified conclusion rather than listing points.AQA
Infrared: Electromagnetic radiation with a wavelength slightly longer than red visible light, emitted by all objects, with intensity rising as temperature rises.AQA
Infrared absorption and re-emission: Methane absorbs infrared radiation emitted by the Earth's surface and re-emits it, so more energy is retained and average global temperature rises.AQA
Infrared radiation: A region of the electromagnetic spectrum beyond red visible light, which all objects emit, and the amount radiated or absorbed depends on surface colour and…AQA
Inheritance: Characteristics are passed on to offspring in genes, which Darwin lacked a mechanism for.AQA
Inheritance of alleles: Offspring receive the alleles linked to high yield from the parents chosen for breeding.AQA
Inheritance of desired characteristics: Selected alleles are passed on in gametes, so the change is genetic rather than an environmental effect.AQA
Inheritance of harmful recessive alleles: Inbred offspring are more likely to inherit two copies of the same harmful recessive allele, so inherited defects become more common.AQA
Inherited and internal factors: Factors inside the body that affect disease risk, including inherited faulty genes, hormones and chemicals produced by the body.AQA
Inherited disorders: Conditions caused by the inheritance of certain alleles, passed from parents to offspring in gametes.AQA
inherited variation: Differences within a species that are controlled by genes, so they can be passed on to offspring.AQA
Initial rate: The rate at the start of the reaction, found by drawing a tangent at t=0.AQA
Initial velocity, u: The velocity of an object at the moment timing starts, measured in metres per second (m/s).AQA
Instantaneous speed: The speed at one particular moment, such as a car speedometer reading.AQA
Instantaneous speed as a tangent gradient: The speed at one instant equals the gradient of the tangent at that point, found by dividing the change in distance by the change in time between two…AQA
Instrument resolution and precision: Every instrument has a smallest scale division, so a reading is only known to lie within a range around the recorded value.AQA
Insulation: The coloured plastic sleeve around each metal conductor, so the colour identifies the wire without touching exposed copper.AQA
Insulin: Secreted by the pancreas when blood glucose concentration is too high, it increases the uptake of glucose by cells and stimulates the conversion of glucose to…AQA
Insulin injections: The normal treatment for type 1 diabetes, replacing the missing hormone so that cells take up glucose and store it as glycogen.AQA
Insulin production and response: In Type 1 diabetes the pancreas produces little or no insulin, whereas in Type 2 diabetes the pancreas produces insulin but body cells no longer respond well…AQA
Interaction between body and mind: A two-way link in which severe physical ill health can lead to mental illness and mental illness can worsen physical health.AQA
Interaction of body and mind: The two aspects influence each other, so a physical illness can worsen mental health and poor mental health can affect physical health.AQA
Interaction of factors: The way these factors interact so that any one of them may be the factor that limits photosynthesis.AQA
Interaction of genes and environment: Some characteristics, such as height or body mass, are affected by both genes and the environment.AQA
Interaction of genetic, lifestyle and environmental factors: Genetic inheritance, lifestyle choices and environmental influences can combine, and their effects may be additive or multiplicative.AQA
Interactions between different types of disease: An example is an immune reaction to a pathogen leading to non-communicable health issues, showing how communicable and non-communicable diseases can interact.AQA
Interactions between diseases: Different types of disease can interact, for example a communicable disease can make a non-communicable disease worse.AQA
Interdependence: Each species in a community depends on other species for food, shelter, pollination, seed dispersal etc, so removing one species can affect the whole community.AQA
Interdependence and food webs: The way species affect each other, so that a change such as reduced prey numbers can affect other species, for example plants that the prey used to eat may…AQA
Interdependence of living organisms and the environment: Chemicals such as carbon, water and nitrogen are recycled between the living and non-living parts of ecosystems, with plants taking up minerals through their…AQA
Interdependence of organisms in a community: A community is all the interacting populations in a habitat, so a change to one population can be traced through feeding relationships and numbers to other…AQA
Interdependence shown by population changes: A fall in one species can lead to a fall in a species that depends on it for food or pollination.AQA
Intermolecular bonds: The bonds that hold the particles in a particular arrangement, broken or formed during a change of state.AQA
Intermolecular forces: Forces that, when weak, let short-chain hydrocarbons vaporise easily and mix rapidly with oxygen, and when stronger make longer-chain hydrocarbons harder to…AQA
Intermolecular forces and boiling point: The atoms become larger with more electron shells, increasing the strength of intermolecular forces, so more energy is required to overcome them and the…AQA
Internal energy: The total energy stored in a system, made up of the kinetic energy of its particles and the potential energy linked to their positions and bonds.AQA
Interphase: The stage before mitosis in which the cell grows and carries out DNA replication.AQA
Interpret: Describe the pattern and explain what it means for sustainability, such as a falling line of reserves suggesting a finite resource being used up.AQA
Interpret data: Linking each peak to its specific reproductive role, such as identifying imminent ovulation from an LH surge.AQA
Interpreting: Extracting meaning, for example reading a table of energy costs to decide which method is most viable.AQA
Interpreting data to draw conclusions: Using data from graphs or tables, quoting figures, and connecting the evidence to the reason.AQA
Interpreting distance–time graphs: Using the overall change in distance divided by the overall time to find average speed for non-uniform motion.AQA
Interpreting equilibrium data: Using data, such as tables of equilibrium yields or graphs of concentration against time, to work out how a change in concentration affects a reversible…AQA
Interpreting evidence: Explaining what data suggests about past conditions, such as what a rock sample indicates about the early atmosphere.AQA
Interpreting evolutionary trees: Tracing lines from a species back to a node, then following the other branch, shows its closest relative.AQA
Interpreting fossil evidence: Trace fossils show behaviour such as walking, burrowing or anchoring, which body fossils may not show.AQA
Interpreting rate graphs: The limiting factor is identified from the shape of the graph as the factor whose increase raises the rate before the plateau.AQA
Interpreting tabulated and graphical data: Using supplied data, such as equilibrium yields or concentrations at different temperatures, to decide how heating or cooling shifts a reversible reaction at…AQA
Interpreting trends and intercepts: Describing the trend, such as mass change falling from positive to negative as concentration increases, and reading values including the intercept.AQA
Interpreting visual models and diagrams: Counting the ions of each type shown, or using the ratio in which they appear, to work out the formula.AQA
Interpreting yield and concentration data: Reading the trend in given yield, percentage or concentration data and linking it to the mole count to state the direction of shift and the resulting change.AQA
Intraspecific competition: Competition between members of the same species.AQA
Intrauterine devices: Devices that can either prevent implantation of an embryo or release a hormone.AQA
Invasion of neighbouring tissues: Malignant cells break into the tissues around them and damage their normal function.AQA
Inverse proportionality at constant resultant force: For a fixed resultant force, doubling the mass halves the acceleration, so acceleration is inversely proportional to mass.AQA
inverse relationship: Because all EM waves travel at the same speed in a vacuum, long wavelength means low frequency and short wavelength means high frequency.AQA
Inverse square law: Light intensity is inversely proportional to the square of the distance from the light source.AQA
Iodine reagent: Added to each sample and the colour observed; blue-black indicates starch is still present, while a yellow-brown colour indicates starch has been completely…AQA
Iodine solution: Reagent added as a few drops to the sample, where a blue-black colour is a positive result for starch.AQA
Ion: A particle that becomes charged when electrons are gained or lost, so the numbers of protons and electrons become unequal.AQA
Ion formation: Atoms turn into positive ions if they lose one or more outer electron(s), so the number of protons exceeds the number of electrons and the overall charge…AQA
Ion formation and charge: Group 1 atoms lose their single outer electron to form a 1⁺ ion with a stable noble-gas configuration.AQA
Ion formation and full outer shells: A halogen atom gains one electron to form a 1⁻ ion with a full outer shell.AQA
Ionic bonding: A metal atom transfers one or more electrons to a non-metal atom, forming positive and negative ions that attract electrostatically.AQA
Ionic bonding and electron transfer: Sodium atoms lose one electron to form Na⁺ ions and chlorine atoms gain one electron to form Cl⁻ ions, giving full outer electron shells.AQA
Ionic composition of acids: Hydrochloric acid supplies chloride ions, nitric acid supplies nitrate ions and sulfuric acid supplies sulfate ions.AQA
Ionic compound: A giant structure of ions held together by strong electrostatic forces of attraction between oppositely charged ions.AQA
Ionic equation: An equation showing only the reacting ions and atoms, with correct state symbols and charges, after spectator ions are cancelled.AQA
Ionic formulae and charge balance: Formulae must have balanced charges, using the lowest whole-number ratio, such as Mg²⁺ with Cl⁻ giving MgCl₂.AQA
Ionic half-equations: Equations that clearly show the electron transfer, such as the loss of electrons by metal atoms and the gain by hydrogen ions.AQA
Ionic reactions in solution: The H⁺ ions from the acid combine with the OH⁻ ions from the alkali to form water, and the remaining ions form the dissolved salt.AQA
Ionic, covalent and metallic bonding: The type of bonding present depends on whether electrons are transferred or shared, with positive ions attracted to a sea of delocalised electrons in the…AQA
Ionising power and penetration: Alpha is the most ionising and least penetrating; gamma is the least ionising and most penetrating.AQA
Ionising radiation: A physical carcinogen whose high-energy waves or particles can break chemical bonds in DNA, producing mutations.AQA
Ionising radiation safety: Reducing exposure by using shielding, distance and short exposure time, with safety advice linked to the specific source.AQA
Irradiated object: An object that absorbs or scatters some of the radiation but does not become radioactive, so it can be handled safely once the external source is removed or…AQA
Irradiation: Exposure to radiation from a source outside the body, where the person does not become radioactive and exposure stops when they move away or the source is…AQA
Isolated object or system: One considered on its own, allowing you to describe the external forces acting upon it.AQA
Isolation from the supply: A safe isolation check is to confirm that the wire is no longer connected to the supply, not merely that the appliance has stopped working.AQA
Isotonic point: The concentration giving no change in mass, which is approximately isotonic with the tissue.AQA
Isotopes: Atoms of the same element with the same number of protons but different numbers of neutrons, so they have the same atomic number but different mass numbers.AQA
Isotopes and nuclear composition: Isotopes have the same proton number but different mass numbers, and neutrons account for the extra mass of the nucleus and for isotopes.AQA
IVF: A technique in which FSH and LH stimulate several eggs to mature, eggs are collected before release and mixed with sperm in a laboratory, and embryos are…AQA

J

J/kg: The energy in joules needed to change the state of each kilogram of a substance.AQA
J/kg °C: Joules per kilogram per degree Celsius, showing energy divided by mass and temperature change.AQA
J/kg°C: The unit that combines joules of energy with kilograms and degrees Celsius.AQA
Joule: The energy transferred when a force of one newton moves an object one metre, and also the energy needed to raise about 0.24 g of water by 1 °C.AQA
joule (J): The unit of energy, equal to the energy transferred when a force of one newton moves an object one metre.AQA
Junction: Any point where three or more wires meet.AQA
Justified conclusions: Weighing strengths against weaknesses to reach a justified overall judgement about how much confidence the evidence deserves.AQA
Justifying practical choices from data: Referring to the property given, such as insoluble, dissolved, different boiling points or different solubilities, to justify the choice.AQA

K

kBq: A larger multiple of the becquerel, where 1 kBq = 1000 Bq.AQA
kg/m³: The SI unit of density, meaning the mass in kilograms contained in one cubic metre of material.AQA
kidneys: Urea travels in the blood plasma to these organs, where it is filtered out of the blood.AQA
kilogram: The SI base unit of mass, and in calculations grams are converted to it by dividing by 1000.AQA
Kilogram metre per second: The unit of momentum, kg m/s, which comes from multiplying kilograms by metres per second.AQA
Kilojoule: A larger unit for work done and energy transfer, where 1 kJ = 1000 J.AQA
Kinetic and potential energy of particles: Particles have kinetic energy because they move or vibrate, and potential energy because of their positions and the forces between them.AQA
Kinetic energy: The energy associated with a moving object, calculated as E_k = ½mv², where m is mass in kilograms and v is speed in metres per second.AQA
Kinetic energy and temperature: Heating a gas transfers energy to the particles, so their mean kinetic energy and average speed increase.AQA
kinetic energy equation: E_k = ½mv², in which the speed is squared, so doubling speed quadruples kinetic energy.AQA
Kinetic particle model of gases: Gas molecules move randomly and rapidly, colliding with each other and with the walls of the container.AQA
Kinetic store: A store the object has because it is moving, which decreases as it rises and is momentarily zero at the highest point.AQA
Kinetic theory and pressure: Collisions between gas molecules and with the container walls are elastic and exert a pressure on the walls.AQA

L

Lactic acid: Carried by blood flowing through the muscles to the liver, where it is converted back into glucose.AQA
Land pollution: Pollution can occur on land, from landfill and toxic chemicals, and each route harms organisms in a different way.AQA
Land use and habitat disruption: Wind turbines and solar farms alter landscapes and habitats, hydroelectric schemes flood valleys, and tidal barrages disturb estuaries.AQA
Land use change and agriculture: Deforestation removes trees that absorb carbon dioxide and burning cleared vegetation adds more, while rearing livestock produces methane from digestion.AQA
Land use change and deforestation: Removing trees reduces carbon dioxide absorption by photosynthesis and can release stored carbon when trees are burned or decompose.AQA
Landfill: The burial of waste on land, where decomposition produces methane and can produce leachate.AQA
Large molecules: Very large molecules found in some covalently bonded substances, such as polymers, which can be recognised by a repeating unit and the subscript n.AQA
Large-scale production using microorganisms: The genetically engineered bacteria are grown on a large scale in a fermenter under controlled conditions, multiplying by binary fission.AQA
Latent heat: The energy needed for a substance to change state, transferred at constant temperature.AQA
Lattice ions: Particles in the wire that charge carriers collide with more often as the wire gets longer, increasing opposition to current.AQA
law of octaves: Newlands arranged elements in order of atomic weight and proposed a repeating pattern, but his ideas were not widely accepted because the pattern did not hold…AQA
Layered structures and lubrication: Only weak forces exist between the layers, so layers can slide over one another, making graphite soft and slippery and useful as a lubricant.AQA
Le Chatelier's principle: A principle that predicts how a system at equilibrium responds to a change: the equilibrium shifts in the direction that opposes the change.AQA
Leachate: The solution containing soluble copper compounds produced by bacteria from insoluble copper compounds in low-grade ore.AQA
Lead compounds and drug development: The process involves identifying a lead compound, testing it, and then developing a safe, effective medicine through trials.AQA
Leaf adaptations: Leaves are thin and flat to give a large surface area for diffusion, but that same surface lets water evaporate.AQA
Leaky valve: A valve that does not close tightly, so blood flows backwards instead of moving on.AQA
Left ventricle: The chamber with a thicker muscular wall that pumps oxygenated blood at higher pressure around the rest of the body.AQA
Length of conductor: l in the equation, the length of conductor inside the field in metres (m).AQA
Levels of ecological organisation: The sequence of increasing inclusiveness from individual organism to population to community to ecosystem.AQA
Levels of organisation from cell to organism: A cell contributes to a tissue, an organ, an organ system or the whole organism carrying out its function.AQA
Life cycle assessment: Carried out to assess the environmental impact of products in each of the stages, from raw materials to end of life.AQA
Life cycles of pathogens: The protist life cycle includes both the mosquito and a human host, and control measures interrupt the life cycle.AQA
Lifestyle and cardiovascular disease: Diet, smoking and exercise affect the risk of cardiovascular disease, which affects the heart and blood vessels.AQA
Lifestyle and risk: Diet, alcohol and smoking increase the risk or incidence of disease in a population, not certainty for an individual.AQA
Lifestyle choices: The choices and habits a person repeats over years, which can raise or lower the risk of non-communicable diseases.AQA
Lifestyle risk factors: Factors such as smoking tobacco, drinking alcohol, obesity, poor diet, lack of exercise, and overexposure to ultraviolet radiation that increase the chance of…AQA
Light: Shown above the arrow in the word equation, it is required but not a reactant and is absorbed by chlorophyll in chloroplasts.AQA
Light intensity: Varies by changing the distance between the lamp and the pondweed, and is inversely proportional to the square of the distance.AQA
Light intensity and distance: Light intensity decreases with distance from a lamp, and doubling the distance reduces light intensity to one quarter of its original value.AQA
Light-dependent resistance: The resistance of an LDR decreases as light intensity increases, because more charge carriers are released in the semiconductor material.AQA
Lignin: A rigid material that strengthens xylem walls, preventing the tubes collapsing under tension and helping support the plant.AQA
Limestone: Mostly calcium carbonate, CaCO₃, precipitated or compacted from the shells and skeletons of marine organisms such as corals and molluscs, so it forms in warm…AQA
Limewater: An aqueous solution of calcium hydroxide, Ca(OH)₂(aq), used as the reagent to test for carbon dioxide.AQA
Limit of proportionality: The point on a force-extension graph where the straight line through the origin starts to curve, after which the relationship is no longer directly…AQA
Limitations of indirect evidence: Evidence supports a theory but may not prove it conclusively, including because of incomplete or indirect evidence and the vast time scale.AQA
Limitations of scientific models: The spheres are a simple representation, and the model does not show the true nature of the particles.AQA
Limited resources: Resources such as metal ores and crude oil, for which these actions lower demand.AQA
Limiting factor: The factor in shortest supply that restricts the rate of photosynthesis.AQA
Limiting factor of photosynthesis: A factor such as light intensity, carbon dioxide concentration or temperature that, when in short supply, limits the rate of photosynthesis.AQA
Limiting factors: Light intensity, carbon dioxide concentration, temperature, or the amount of chlorophyll, which interact so that any one of them may limit photosynthesis.AQA
Limiting reactant: The reactant that is used up first and therefore determines the maximum amount of product it is possible to obtain.AQA
Limiting reactants: A reactant that has been used up, so the quantity no longer changes and the curve shows a plateau.AQA
Limits of required knowledge: Detailed structures of other ionic compounds such as magnesium oxide or calcium chloride need not be recalled; only the general ideas of ionic bonding are…AQA
Line of best fit: A line drawn through plotted points that shows the trend, used when a straight line is justified.AQA
Line or curve of best fit: A single smooth line or curve showing the overall trend, drawn rather than joining points dot-to-dot.AQA
Linear element: A component whose graph shows a straight line through the origin, obeying V = IR with constant resistance.AQA
linear region: The part of a force–extension graph that is a straight line through the origin, where force and extension are directly proportional and k is constant.AQA
Lines and curves of best fit: A smooth line or curve drawn through or near the plotted points to show the overall trend, rather than joining every point dot-to-dot.AQA
Lines of best fit: A smooth line drawn through the trend of plotted points, or straight lines joining points only if instructed.AQA
Link between particle counts and overall charge: Knowing these relative charges lets you work out the overall charge of any atom or ion from its particle counts.AQA
Links between moles and mass: Equations can be used to calculate masses of reactants and products once amounts in moles are known.AQA
Links to group and ion formation: The outer-shell electron explains an element's position in a group and its tendency to form an ion.AQA
Lipase: The alkaline conditions and large surface area increase the rate of fat breakdown by this enzyme.AQA
Lipases: Produced in the pancreas and the small intestine, they catalyse the breakdown of lipids (fats) to fatty acids and glycerol.AQA
Live animals: Whole living bodies, for example mice or rats, used because they show how the drug moves around, how it is broken down and whether it harms organs.AQA
Live wire: Carries the alternating potential difference from the supply, so its potential difference changes direction and magnitude with time.AQA
Live wire potential relative to earth: The live wire remains at the alternating mains potential relative to earth even when the switch is open, because it is still connected to the supply.AQA
Liver: The organ where lactic acid is converted back into glucose, which requires oxygen.AQA
local conditions: Factors such as energy costs, distance from the sea, rainfall and the scale of demand that influence the choice of method.AQA
Local disappearance: A situation where individuals survive elsewhere, differing from extinction.AQA
Location of endocrine glands: The thyroid lies at the front of the neck, below the larynx and around the upper trachea, while the pituitary is in the brain and the adrenal glands are above…AQA
locus: The fixed position on a chromosome at which a gene is found.AQA
Lone pairs: Outer-shell electrons not used in bonding, such as the three lone pairs on each chlorine atom or the two lone pairs on oxygen.AQA
Long wavelength infrared radiation: Radiation emitted by the warmed Earth's surface, some of which is absorbed by greenhouse gases in the atmosphere.AQA
Long-term stability: For 200 million years the proportions of different gases have been much the same as they are today.AQA
Longitudinal wave: A wave in which the vibrations are along the same line as the direction of energy transfer.AQA
Longitudinal wave examples: Sound and ultrasound, in which the oscillations are parallel to the direction of energy transfer.AQA
Loss of control: Large decelerations can cause loss of control, for example through skidding or wheel lock-up.AQA
Loss of induced magnetism: When removed from the magnetic field, an induced magnet loses most or all of its magnetism quickly.AQA
Low birth mass: A measure of size that can result when smoking reduces the oxygen supply to the fetus, so it may grow more slowly.AQA
Low-grade ores: Ores too low in concentration for traditional extraction, which bioleaching can work on.AQA
Lower H⁺(aq) concentration and less acidic behaviour: The H⁺(aq) concentration is lower than in a strong acid of the same concentration, so the pH is higher and reactions are slower and less vigorous.AQA
Lubricants: Substances that reduce friction between moving parts, such as engine oil.AQA
Lumen: The central channel of a blood vessel, with a narrow one maintaining pressure and a wide one found in veins.AQA
Luteinising hormone (LH): Produced and secreted by the pituitary gland and transported in the blood plasma to the ovaries.AQA

M

m = E ÷ L: The rearrangement used to calculate mass from energy and specific latent heat.AQA
Macromolecular structure: Understanding n helps explain why polymers are macromolecules rather than simple molecules.AQA
magnetic compass: Contains a small magnet that is free to rotate and always settles with its north-seeking pole pointing roughly towards the Earth's geographic north.AQA
magnetic core: The only plausible source of the Earth's magnetic field, because the field is present everywhere on the surface.AQA
Magnetic declination: The compass indicates magnetic north, which differs slightly from geographic north because of this.AQA
Magnetic effect of a current: When a current flows through a conductor, a magnetic field forms around it, and the effect is temporary and disappears when the current stops.AQA
Magnetic field: The region around a magnet where a force acts on another magnet or on a magnetic material.AQA
Magnetic field direction: The direction the first finger points, along the external magnetic field, from north to south.AQA
Magnetic field pattern: A two-dimensional pattern of field lines used in exam answers to show the three-dimensional magnetic field produced by a bar magnet.AQA
Magnetic field patterns: Iron filings sprinkled on a card around a straight wire form concentric circles centred on the wire, while a solenoid produces a field pattern similar to that…AQA
Magnetic flux density: Increasing this property of the external field increases the force on a current-carrying conductor within it.AQA
Magnetic materials: Materials such as iron, steel, cobalt or nickel that are attracted towards a magnet.AQA
Magnification: A ratio comparing image size to real size, so it has no units and is given as a plain number, often with a multiplication sign.AQA
Magnification scale: A line labelled with its actual length and the calculated magnification, so the size of the specimen is communicated.AQA
Magnitude: A length, such as 5 m, giving how far the finish point is from the start point in a straight line.AQA
Mains supply: A supply with a potential difference of about 230 V in the UK, determining how much energy each coulomb carries.AQA
Malignant: Describes tumours that invade neighbouring tissues and spread to other parts of the body through the blood or lymph.AQA
Malignant tumour cells: Cells that are cancers, which invade neighbouring tissues and spread to different parts of the body in the blood.AQA
Mass: The amount of matter in the object, measured in kilograms, kg, which does not change with temperature, unlike volume.AQA
Mass and volume distribution in atoms: Almost all the mass of an atom is in the nucleus, but the nucleus occupies only a tiny fraction of the atom's volume, while electrons occupy most of the volume.AQA
Mass and volume measurements: The quantity may be a mass in grams or a volume in cm³, so the rate carries units such as g/s or cm³/s.AQA
Mass calculations: The law allows you to calculate an unknown mass in a reaction by subtraction or addition.AQA
Mass distribution in atoms: Although it is tiny, the nucleus contains nearly all the mass of the atom.AQA
Mass distribution in the atom: Most of the atom's mass is in the nucleus, while most of its volume is the space occupied by electrons.AQA
Mass in g: Calculated by rearranging the equation to amount in moles multiplied by relative formula mass.AQA
Mass in grams: A quantity found by converting moles using mass = moles × relative formula mass when the question asks for masses in grams.AQA
Mass loss and gas escape: Mass in grams suits reactions that release a gas into the air, because the total mass falls as the gas escapes.AQA
Mass number: The number written as a superscript before the element symbol, counting protons plus neutrons in the nucleus.AQA
Mass–mole conversion: Amount in moles equals mass in grams divided by molar mass, which lets you convert between mass and moles.AQA
Mass, volume and concentration relationships: Expressed as concentration = mass of solute ÷ volume of solution, and used to justify the proportionalities and predict how concentration changes when…AQA
Master gland: A name for the pituitary because its hormones act on other endocrine glands, stimulating them to release different hormones that bring about specific effects.AQA
Matching resource properties to the demands of each use: Comparing uses means matching each resource to the demands of the application and weighing advantages against drawbacks.AQA
Matching technique to physical property: Choosing a technique that matches the physical properties given when a question supplies information about a mixture.AQA
Material identification: A common task of comparing a calculated density with a table of known values to identify an unknown material.AQA
maternal risks: Risks to the mother associated with multiple pregnancies, including high blood pressure and severe bleeding.AQA
Maturation of an egg: The process caused by FSH in the ovary, preparing the egg for potential release and fertilisation.AQA
Maturation of several eggs: The process stimulated by FSH and LH in the ovaries, raising the number of mature eggs available.AQA
Maximum product: The smaller of the product amounts that each reactant could form, chosen as the maximum possible amount.AQA
MBq: A larger multiple of the becquerel, where 1 MBq = 1 000 000 Bq.AQA
Mean: A value calculated after repeating the test several times, ignoring anomalies, to improve reliability.AQA
Mean rate of reaction: Calculated as quantity of reactant used divided by time taken, or quantity of product formed divided by time taken.AQA
Measurement and uncertainty: Whenever a measurement is made there is always some uncertainty about the result obtained, an unavoidable doubt about the true value rather than a mistake.AQA
Measurement and units: Extension must be expressed in metres before substitution into an equation, and a length given in centimetres or millimetres is converted to metres first.AQA
Measurement from a baseline: Both the distance moved by the solvent front and the distance moved by the solute are measured from the pencil baseline.AQA
Measurement from a common origin: Both distances are measured from the pencil origin line, not from the bottom edge of the paper or plate.AQA
Measurement of chemical amount: Chemical amounts are measured in moles, and the symbol for the unit mole is mol.AQA
Measurement of current and potential difference: An ammeter in series measures the current through a component, while a voltmeter in parallel measures the potential difference across it.AQA
Measurement of current using ammeters: An ammeter placed anywhere in a series circuit will read the same value.AQA
Measurement of current with an ammeter: An ammeter is connected in series with the component being investigated, because the same current must pass through the meter and the component.AQA
Measurement uncertainty: Arises from instrument accuracy and calibration, for example a thermometer reading of 15.0 °C carries an uncertainty of about ±0.5 °C.AQA
Measurement with ammeters: Ammeters placed anywhere in the loop give the same reading, and ammeters at different positions in the same series loop give identical readings.AQA
Measurement with ammeters and voltmeters: Ammeters go in series with the component being measured, and voltmeters go in parallel across it.AQA
Measuring change over time: Recording the quantity of a reactant used or product formed at regular time intervals so that a rate can be calculated.AQA
Measuring product formation: The quantity of product formed is the change in mass in g or volume in cm³ between two chosen times.AQA
Measuring rate of reaction: A suitable method measures rate, such as volume of gas collected at timed intervals or loss in mass over time, and results are used to judge whether the…AQA
Measuring reaction progress: A measurable quantity that changes as reactants are used up or products form is needed to follow a reaction.AQA
Mechanical valve: A replacement valve made from materials such as metal or polymer, which is durable but usually requires long-term medication to reduce clotting.AQA
Mechanical work and contact forces: The contact force between object and obstacle does mechanical work, transferring energy.AQA
Mechanical work and friction: Energy is transferred by mechanical work done against resistive forces, mainly friction from the brakes and air resistance.AQA
Mechanism: How a named method prevents pregnancy, such as inhibiting FSH, blocking sperm or preventing implantation.AQA
Median: The middle value once the data are arranged in order; with an even number of values, it is the mean of the two middle values.AQA
Medical application of biotechnology: The human insulin produced is extracted and purified before being used to treat people with diabetes.AQA
Medical applications of genetics: Understanding the genome will have great importance for medicine in the future, such as identifying genes linked to inherited disorders and matching medicines…AQA
Medical imaging and treatment: X-rays and gamma rays are used for medical imaging and treatments.AQA
Medical uses of stem cells: Bone marrow transplants can restore blood cell production in patients whose marrow is damaged or diseased.AQA
Medium: Sound is a wave that travels through a medium by making particles vibrate, and it cannot travel through a vacuum.AQA
Medium-dependent wave speed: The medium determines the speed, for example sound travels faster in solids than gases.AQA
Meiosis: The process during which the X and Y chromosomes separate, so a male produces roughly equal numbers of X-bearing and Y-bearing sperm.AQA
Meiosis and gamete formation: The formation of gametes involves meiosis, in which copies of the genetic information are made and then the cell divides twice to form four gametes.AQA
Melting and boiling points: Relatively low for small-molecule substances because melting and boiling involve overcoming weak intermolecular forces rather than breaking strong covalent…AQA
Melting and boiling ranges of mixtures: A mixture usually melts and boils over a range of temperatures rather than at one exact value, because its components have different melting and boiling points.AQA
Melting point: The fixed point at which a substance changes between solid and liquid, with solid and liquid coexisting at exactly that temperature.AQA
Melting point depression by mixing: Mixing the compound with another substance lowers the melting point of the electrolyte.AQA
Melting point trends: A property that decreases down the group, so rubidium has a lower melting point than potassium.AQA
Melting points: Very high for giant covalent substances because melting requires breaking many strong covalent bonds.AQA
Membrane-bound organelles: Structures within the cell, such as mitochondria, that are enclosed by a membrane and are found in eukaryotic cells.AQA
Memory cells: Cells that remain after the primary response and respond quickly if the same live pathogen later re-enters the body.AQA
Mendeleev's periodic table: A table arranging elements mainly by atomic weight but leaving gaps for undiscovered elements and placing some elements out of strict weight order to keep…AQA
Mendeleev's table: Elements were arranged mainly by atomic weight, with gaps left for undiscovered elements and properties predicted for those gaps.AQA
Menstruation: The shedding of the uterus lining as a period, caused by a fall in progesterone when the corpus luteum breaks down.AQA
Mental well-being: Covers emotional and social aspects, such as feeling able to cope, having supportive relationships and functioning without persistent distress.AQA
Meristem tissue: Tissue containing unspecialised cells, found in regions such as root tips, shoot tips and cambium, that can divide and then differentiate throughout the…AQA
Meristems: Regions at root tips and shoot tips where mitosis occurs in a plant, adding new cells for growth.AQA
Meristems and specialised tissues: A root tip or shoot tip in a plant contains meristem cells that divide by mitosis, adding new cells behind the tip so the plant grows taller or longer.AQA
Metabolic reactions: The other chemical reactions necessary for life, such as protein synthesis and active transport, which are powered by the energy transferred in respiration.AQA
Metabolic reactions in cells: Homeostasis keeps internal conditions close to the optima so metabolic reactions continue.AQA
Metabolism: The sum of all the chemical reactions in the body, including both building and breaking-down reactions.AQA
Metabolism and biosynthesis: Energy is needed for chemical reactions that build larger molecules from smaller ones, such as joining amino acids to form proteins or glucose molecules to…AQA
Metabolism and cellular use of nutrients: Building new molecules from digestion products is part of metabolism, linking digestion to growth and repair.AQA
Metal and ammonium ions: The base or alkali used determines the metal or ammonium ion in the salt, such as sodium hydroxide giving sodium salts and ammonia giving ammonium salts.AQA
Metal extraction: Metal oxides are reduced to extract the pure metal, using carbon to remove the oxygen.AQA
Metal oxides: Compounds of a metal and oxygen, produced when metals react with oxygen, and many are basic and can neutralise acids to form a salt and water.AQA
metallic bonding: Bonding in which the particles are atoms which share delocalised electrons.AQA
Metallic bonding and melting point: Melting points decrease down the group because atomic radius increases and the metallic bond weakens as the outer electron is further from the positive nucleus.AQA
Metallic bonding model: The bonding in metals may be represented by the sharing of delocalised electrons, which gives rise to strong metallic bonds.AQA
Metalloids: Elements touching the stepped dividing line, such as silicon, with intermediate properties.AQA
Metals: Elements on the left and centre of the periodic table that lose outer-shell electrons to form positive ions.AQA
meth-: Prefix used in the names of alkanes to indicate one carbon atom.AQA
Metres: The unit of extension, symbol m, with centimetre measurements converted by dividing by 100.AQA
Metres per second squared: The unit of acceleration, written as m/s², arising from dividing a velocity change in m/s by a time in seconds.AQA
Microorganism-derived drugs: Drugs traditionally obtained from microorganisms, for example penicillin from the mould Penicillium.AQA
Microorganisms as decomposers: Bacteria and fungi that break down dead material and waste, respiring carbon dioxide to the atmosphere and releasing mineral ions into the soil.AQA
Microwaves: Electromagnetic waves with shorter wavelengths and higher frequencies than radio waves, used for satellite communications and cooking food.AQA
Mineral content: The dissolved ions in soil, such as nitrate, phosphate, potassium and magnesium, each with specific roles in plants.AQA
Mineral ion cycling: The release of mineral ions such as nitrate ions into the soil when microorganisms break down nitrogen-containing compounds, where plants absorb them through…AQA
Mineral ion uptake in plants: Active transport allows mineral ions to be absorbed into plant root hairs from very dilute solutions in the soil.AQA
Mineral ions and healthy plant growth: Plants require ions for healthy growth, and the absorbed ions are used to make compounds needed for healthy growth, including proteins, DNA and chlorophyll.AQA
Mitochondria: Organelles found in the cytoplasm of eukaryotic cells, including animal, plant, algal and fungal cells.AQA
Mitosis: One parent cell divides once to give two daughter cells that are genetically identical to each other and to the parent, so chromosome number is unchanged.AQA
Mitosis and growth: A type of cell division that produces genetically identical cells, so the number of cells increases rapidly as the embryo grows.AQA
Mixture: Two or more different elements or compounds present but not chemically bonded together, even if it looks uniform.AQA
Mixtures and purity: A mixture contains two or more substances not chemically joined, so each keeps its own properties and can be separated by physical processes.AQA
Mixtures versus single substances: A pure substance contains only one element or compound, with no other substances mixed in, whereas pure milk is a mixture of water, fats, proteins, sugars and…AQA
Mobile phase: The phase that moves, for example a solvent rising up paper or a gas carrying vapour through a column.AQA
Mode: The value that appears most often; a data set can have one mode, several modes, or no mode if every value is different.AQA
Model: A simplified representation of a real system, such as treating a moving car as a point object with constant speed.AQA
Model limitations: Computer models carry uncertainty because future emissions, feedbacks and cloud behaviour are not fully known.AQA
Model replacement in science: The plum pudding model could not account for large deflections because its positive charge was spread out, so the evidence led to the nuclear model.AQA
Modelling motion: Momentum is a model that predicts motion during interactions, such as a collision.AQA
modern periodic table: Orders elements by atomic (proton) number, which removes the anomalies and explains the repeating pattern.AQA
Moisture level: The amount of water held in soil or air in a habitat, and an abiotic factor because it is non-living.AQA
Molar mass: The value used with mass to calculate the amount in moles, since moles = mass ÷ molar mass.AQA
Molar mass and mass–mole calculations: Mass is converted to moles using molar mass, since equal numbers of moles of different substances generally have different masses.AQA
Molar mass and the mole: The mass of one mole of a substance in grams is numerically equal to its relative formula mass.AQA
mole: An amount obtained by converting a mass in grams, used with relative formula mass to find the balancing numbers in a symbol equation.AQA
Mole calculations: The method involves converting a known mass to moles using moles = mass ÷ relative formula mass, then converting back to mass.AQA
Mole ratio: The ratio of amounts in moles, read from the coefficients of a balanced equation and applied to the substance whose mass is required.AQA
mole ratios: The ratios given by coefficients in a balanced equation between reactants and products.AQA
Mole ratios from balanced equations: This concept lets you compare reacting quantities directly using balanced equations, for example 2 mol of hydrogen molecules reacts with 1 mol of oxygen…AQA
Molecular evidence in classification: Evidence from chemical analysis of molecules such as ribosomal RNA showing that some prokaryotes differ as much from each other as they do from eukaryotes.AQA
Molecular formulae: Written using element symbols with counts as subscripts, in the conventional order and omitting the subscript 1, to describe one molecule.AQA
Moles: An amount found by dividing the given mass by the relative formula mass.AQA
Momentum: A vector property of a moving object, defined by the equation p = mv, where p is momentum in kilogram metres per second (kg m/s).AQA
Momentum as a vector: Momentum has direction, so one direction is assigned as positive and velocities in the opposite direction are given a negative sign.AQA
Monatomic: Existing as single, unbonded atoms rather than molecules, because noble gases do not need to bond to become stable.AQA
Monatomic structure: Existing as single atoms, so there are no covalent bonds between atoms to break during boiling.AQA
Monitoring biodiversity: Judging the success of a programme by comparing species counts, water quality or habitat area before and after the programme.AQA
Monoculture: Growing one crop over a large area, which reduces plant variety and removes food and shelter for many animals.AQA
Monomer units: Many identical small units that are joined by strong covalent bonds into a very large molecule.AQA
Mosaic pattern of discolouration: A distinctive pattern on the leaves with patchy light and dark areas rather than uniform green.AQA
Motor effect: When a conductor carrying a current is placed in a magnetic field, the magnet producing the field and the conductor exert a force on each other.AQA
Motor neurone: Carries impulses from the central nervous system to an effector, such as a muscle or gland.AQA
Moulds, casts and impressions: A dissolved organism leaves a cavity or shape that may later be filled by minerals.AQA
Movement and temperature regulation: Energy is needed for muscle contraction, so animals can move, and for maintaining a constant internal body temperature in mammals and birds.AQA
Movement of dissolved substances: Cell sap, a fluid containing dissolved sugars and other solutes, moves from one phloem cell to the next through the pores.AQA
Mucus: A sticky substance that traps particles such as dust, pollen and microorganisms in the airways.AQA
Multi-step problem solving in dc circuits: Solving multi-step problems by finding R_eq first, then the current, then any required potential difference or resistance.AQA
Multicellular: Describes an organism made of many cells, such as a human or oak tree.AQA
Multicellular organisms: Organisms in which differentiated cells work together as tissues, organs and organ systems, allowing the organism to carry out life processes efficiently.AQA
Multifactorial causation of disease: Many diseases are caused by the interaction of a number of factors rather than a single cause.AQA
multiple births: Twins or triplets, which carry a higher risk of premature birth and low birth mass for the babies.AQA
Multiple pregnancy risk: Transferring two embryos increases the chance of pregnancy but also the chance of multiple births.AQA
Multiplicative change across pH units: A two-unit drop in pH means a 10² = 100-fold increase in H⁺ concentration.AQA
Muscle cell: Contains protein filaments that shorten the cell during contraction and many mitochondria to release energy.AQA
Muscle fatigue: Occurs during long periods of vigorous activity, when muscles stop contracting efficiently.AQA
Muscles as mechanical effectors: They respond by contracting or relaxing, changing movement or the diameter of passages.AQA
Muscular tissue: Tissue in artery walls that adjusts the lumen, controlling its diameter and hence flow.AQA
Mutation: Random mutations produce new alleles, providing the genetic variation on which natural selection acts.AQA
Mutation and genetic variation: Mutation introduces new alleles, and natural selection acting on these variants increases the differences between the populations.AQA
Mutation and new strains: Mutations of bacterial pathogens produce new strains with different inherited characteristics.AQA
Mutation and variation: Mutation produces variation, which is the raw material on which natural selection acts, and mutations occur randomly during DNA replication.AQA
Mutualism: An interaction between organisms in which both species benefit.AQA
Myelin sheath: Insulation around the axon that speeds up impulse transmission.AQA

N

N/kg: The unit of gravitational field strength, following from weight = mass × gravitational field strength.AQA
Named biological molecules: Metabolism includes forming proteins from amino acids and lipids from fatty acids and glycerol, and breaking down excess protein to urea in the liver.AQA
Naming compounds: Name compounds correctly when given their chemical formulae or symbol equations, such as naming NaCl as sodium chloride.AQA
Nanotechnology: A field in which the nanoscale dimensions and large surface area of carbon nanotubes make them suitable for use.AQA
Narrow lumen: Roughly the width of a red blood cell, so blood flows slowly and cells pass close to the wall.AQA
National Grid: A nationwide network of cables and transformers that links power stations to homes, schools, hospitals and factories.AQA
National Grid efficiency: A step-up transformer raises potential difference and lowers current for the same power, and this lower current reduces thermal energy dissipation in National…AQA
Native metals: Unreactive metals such as gold are found in the Earth as the metal itself, as the uncombined metal, because they do not readily react to form compounds.AQA
Natural carbon compounds: Compounds obtained from living organisms or geological sources, for example hydrocarbons in crude oil and carbohydrates in plants.AQA
natural pacemaker: A group of cells located in the right atrium that controls the natural resting heart rate.AQA
Natural products: Products that humans use, such as rubber, cotton, wool, silk, timber and natural fertilisers.AQA
Natural resources: Materials obtained directly from the environment, such as wild plants, animals, timber, coal and crude oil.AQA
Natural selection: Individuals with a phenotype that gives an advantage are more likely to survive and reproduce, so the allele becomes more common in the population over many…AQA
Natural selection and evolution of resistance: Surviving bacteria are more likely to include individuals with random mutations that make them less affected by the antibiotic, and these reproduce so the…AQA
Natural selection and selective advantage: Resistant bacteria survive and reproduce, so the population of the resistant strain rises, and this is natural selection.AQA
Natural selection of resistant bacteria: When an antibiotic is used, susceptible bacteria die while resistant bacteria survive and reproduce, so the resistant strain spreads.AQA
Natural selection over generations: Over time, the useful alleles become more common in the population, and the population changes.AQA
Natural variability: Such as El Niño years, makes short records hard to interpret.AQA
Nature of scientific models: A representation or explanation of observations that can be used to make predictions.AQA
Nature versus nurture in characteristic development: Many characteristics, including body mass and height, are influenced by both the genome and the environment.AQA
Negative correlation: A relationship where y decreases as x increases, shown by points trending downwards on a scatter diagram.AQA
Negative feedback: A system in which progesterone inhibits the release of FSH and LH, and when progesterone falls the inhibition is removed so FSH rises to begin a new cycle.AQA
Negative feedback and antagonistic hormones: At Higher Tier only, insulin and glucagon are antagonistic hormones that act in a negative feedback loop to keep the concentration stable.AQA
Negative feedback and restoration of optimum levels: The response is corrective, opposing the original stimulus, which is why it is called negative feedback.AQA
Negative ion: A non-metal atom gains electrons to become a negatively charged ion.AQA
Negative temperature change: A fall in temperature, meaning energy is transferred away from the system.AQA
Negative velocity value: A value that indicates motion in the opposite direction to the chosen positive axis.AQA
Nerve cell: Has a long axon to carry electrical impulses over distance and branched dendrites to connect with other cells.AQA
Nervous system: A system where electrical impulses travel along neurones and produce rapid, short-lived, precisely targeted responses.AQA
net decline: The fall in a radioactive emission after a given number of half-lives, expressed as a ratio of the final emission to the original emission.AQA
Net movement: The overall movement from an area of higher concentration to an area of lower concentration, produced by random particle motion even though individual…AQA
Neurone transmission: Information from receptors passes along cells (neurones) as electrical impulses.AQA
neutral atom: An atom in which the positive charge balances the total negative charge, so it is neutral overall.AQA
Neutral atom electron count: In a neutral atom, the number of electrons equals the number of protons, so the atomic number also tells you the electron count.AQA
Neutral atoms and ions: Atoms have no overall electrical charge, but if the numbers differ the particle is an ion, not an atom.AQA
Neutral solution: Has a pH of exactly 7, as in pure water.AQA
Neutral solutions: A solution with pH 7 is neutral, for example pure water at room temperature.AQA
Neutral wire: It is at, or close to, earth potential, about 0 V, because it is connected to earth at the supply substation, and it still completes the circuit and carries…AQA
Neutralisation: When an acid reacts with a base, a proton is transferred, and the H⁺ ion from the acid transfers to the OH⁻ ion from the alkali to form water.AQA
Neutralisation reactions: Reactions in which acids are neutralised by alkalis and bases to produce salts and water, or by metal carbonates to produce salts, water and carbon dioxide.AQA
Neutrality of atoms: In a neutral atom, the number of electrons equals the number of protons, so the total negative charge balances the total positive charge.AQA
neutron: An uncharged particle in the nucleus, discovered by Chadwick.AQA
New evidence: Findings such as the discovery of the electron that caused the solid-sphere model of the atom to be replaced.AQA
New pathogen: Can spread through a population, reducing the population size of susceptible species.AQA
New predator: Reduces prey numbers and may also affect plants or animals the prey fed on.AQA
Newlands' law of octaves: An early attempt that forced elements into groups of eight and left no gaps, so it failed when new elements were found.AQA
Newton: The unit of force, equal to 1 kg m/s², written after the number.AQA
Newton meter: A device, along with a force sensor, used to measure weight by giving a reading in newtons.AQA
Newton's First Law: Without a resultant force, velocity cannot change, so the object continues at constant velocity in a straight line.AQA
Newton's second law: F = m × a, where acceleration is directly proportional to the resultant force when mass is constant and inversely proportional to mass when force is constant.AQA
Newton’s Third Law: When two objects interact, they exert equal and opposite forces on each other, and these two forces act on different objects, so they do not cancel.AQA
Nitrate: A mineral ion needed for amino acids and proteins.AQA
Nitrate ions: Mineral ions absorbed from the soil that supply the nitrogen needed to make amino acids, which are joined to form proteins.AQA
Nitrogen as the most abundant atmospheric gas: About four-fifths, or approximately 80%, of dry air, and it is unreactive under normal conditions.AQA
Nitrogen oxides: Acidic gases formed when nitrogen and oxygen react at high temperatures in engines, which dissolve in rainwater to form acid rain.AQA
No net change: The sum of all energy stores before and after any transfer is equal.AQA
Noble gas electronic structure: The ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 have the electronic structure of a noble gas (Group 0).AQA
Noble gases: Group 0 elements whose atoms have full outer electron shells, giving them very low chemical reactivity.AQA
Non-communicable: Describes diseases such as lung cancer and chronic lung diseases that cannot be passed from person to person but are linked to lifestyle risk factors.AQA
Non-communicable disease: A disease that is not passed between people, so risk factors are usually lifestyle, environmental or genetic.AQA
Non-communicable diseases: Diseases that cannot be passed between people, yet still impose heavy costs.AQA
Non-contact forces: Forces that act at a distance rather than by physical touching, in contrast to contact forces.AQA
Non-contact interaction: An interaction in which the objects still exert equal and opposite forces on each other without touching.AQA
Non-hormonal methods: Methods such as condoms, diaphragms, copper IUDs and sterilisation, with condoms also reducing STI risk and sterilisation intended to be permanent.AQA
Non-invasive growth: The growth does not invade neighbouring tissues, so it cannot travel in the blood to start new growths elsewhere.AQA
Non-ionising carcinogen: A carcinogen such as ultraviolet light, which is distinguished from ionising sources like X-rays, gamma rays and radon gas.AQA
Non-linear: Describes a circuit element whose curve is not a straight line, such as a filament lamp or a diode.AQA
Non-metals: Elements found towards the upper right of the periodic table that gain or share electrons and typically form negative ions.AQA
Non-ohmic: Describes a component whose resistance changes as current changes because physical conditions such as temperature or current direction alter.AQA
Non-ohmic behaviour: A component shows this when its resistance alters as current changes, so it does not keep the ratio of potential difference to current constant.AQA
Non-ohmic components: Components such as filament lamps and LDRs whose resistance changes with temperature or light intensity, so R = V ÷ I gives the resistance at that particular…AQA
Non-ohmic conductors: A lamp is non-ohmic because its resistance changes, so it does not obey Ohm's law.AQA
Non-renewable: Exists in finite stores formed over millions of years and is used faster than it forms, so it will eventually run out.AQA
Non-renewable resource: Because formation takes millions of years and oil is burned far faster than it forms, the resource is described as non-renewable.AQA
Non-renewable resources: Resources such as coal, oil and natural gas that are used far faster than they form, so their stores will eventually run out.AQA
Non-specific defence: A defence that acts against a wide range of potential pathogens before they reach the alveoli, without distinguishing between different types of pathogen.AQA
Non-specific human defence systems: A defence that destroys a wide range of pathogens, not just one type, such as the acid in the stomach.AQA
normal: A dashed construction line at 90° to the boundary at the point of incidence, from which angles are measured.AQA
Normal-script multiplier: A number in normal script before a formula that multiplies every atom in that formula.AQA
nuclear charge: The positive charge of a nucleus, which can be subdivided into a whole number of smaller particles each having the same amount of positive charge.AQA
Nuclear division: The second stage, in which the nucleus divides, distributing one complete set of chromosomes to each end of the cell.AQA
Nuclear division by mitosis: The second stage, in which one set of chromosomes is pulled to each end of the cell and the nucleus divides.AQA
Nuclear equation: A symbolic summary of a radioactive decay process, showing the starting nucleus on the left and the products on the right.AQA
Nuclear equations: Must balance in both mass number and atomic number, so the emitted particle's symbol explains exactly how the nucleus changes.AQA
nuclear model: A model in which positive charge and most mass are concentrated in a tiny central nucleus, with electrons outside it.AQA
Nuclear model of the atom: Describes an atom as a small, dense, positively charged nucleus surrounded by electrons in shells or energy levels.AQA
Nucleus: A membrane-bound organelle found in eukaryotic cells such as animal and plant cells that contains the cell's genetic material and controls the cell's…AQA
Nucleus and genetic material: Encloses the genetic material, DNA arranged in chromosomes, and controls the activities of the cell.AQA
Nuclide notation: A standard symbolic representation of an atom in which the mass number is written as a superscript and the atomic number as a subscript before the element…AQA

O

Obesity: A risk factor for Type 2 diabetes because excess body fat is associated with reduced insulin sensitivity.AQA
Obligate parasites: Viruses are obligate parasites because they cannot carry out life processes independently and reproduce only inside living host cells.AQA
Observation as evidence: Recording fizzing, movement, temperature change and any flame when a small cleaned sample is added to water or acid, then comparing results to build the order.AQA
Oestrogen: The main female reproductive hormone produced by the ovaries, causing secondary sex characteristics such as breast development and hip widening.AQA
Ohm: The unit of resistance, symbol Ω, where one ohm means one volt is needed to drive one ampere through the component.AQA
Ohm's law relationship: The equation V = I R describes ohmic behaviour at constant temperature, where V is potential difference, I is current and R is resistance.AQA
Ohmic conductor: A component at constant temperature whose resistance stays constant as current changes, giving a straight line through the origin on its current–potential…AQA
Ohmic conductors: Components that obey the equation at constant temperature, unlike filament lamps and diodes, which behave non-linearly.AQA
Ohmic versus non-ohmic behaviour: The equation describes ohmic behaviour at constant temperature, but for a filament lamp the resistance rises as the current increases, so V and I are not…AQA
One cell thick: Describes capillary walls, giving a short diffusion distance between blood and body cells.AQA
Open end: The position at the top of the test tube where the burning splint is held rather than inserted deep into the tube.AQA
Optical fibres: Thin strands of glass or plastic used to transmit pulses of light over long distances.AQA
Optimum: The point where the rate of photosynthesis is maximised for the lowest additional cost, rather than simply maximised at any cost.AQA
Optimum conditions: The conditions maintained by homeostasis that are needed for enzyme action and all cell functions.AQA
Optimum dose: The amount that gives the best balance between treating the condition and causing acceptable side effects.AQA
Optimum pH: The pH at which each enzyme works best, with deviation altering bonds in the enzyme and reducing activity.AQA
Optimum temperature: The temperature up to which the rate of reaction increases as molecules and substrates gain kinetic energy and collide more frequently.AQA
Oral contraceptives: Medicines taken by mouth that contain hormones, commonly a mixture of oestrogen and a progestogen.AQA
Order of magnitude calculations: An order of magnitude is a factor of ten, found by comparing how many powers of ten apart two values are.AQA
Orders of magnitude: A way of comparing quantities by powers of ten, so a value ten times another differs by one order of magnitude.AQA
Ores and compounds: Most metals are found as compounds in ores and need chemical reactions to release the metal.AQA
Organ: An aggregation of tissues performing specific functions, built from several different tissues that cooperate so it can carry out one or more specific jobs in…AQA
Organ shortage: Donor organs are scarce, so patients may wait a long time and must be matched to reduce rejection.AQA
Organ system: A group of organs working together to carry out a major life process, such as the digestive system.AQA
Organ systems: A group of organs that cooperate to carry out a major function, such as the digestive system.AQA
Organelle positioning and support: The cytoplasm contains the nucleus, mitochondria, ribosomes and other structures, holding them in position and separating the cell's structures.AQA
Organism: The whole living thing formed when organ systems work together.AQA
Origin of gamma rays from nuclear changes: Gamma rays originate from changes in the nucleus of an atom.AQA
Original mass: The mass of the plant tissue recorded before placing it in the solution, used as the denominator when finding the proportional change.AQA
Original value: The whole or starting amount, identified before calculating any percentage, and used as the denominator.AQA
Osmosis: Water moves down a water potential gradient across a partially permeable membrane from the more dilute soil solution into the cell contents.AQA
Osmotic pressure: Pressure that a strong cellulose cell wall resists when water enters the cell, preventing bursting.AQA
Outer-shell electrons: For Groups 1 to 7, the group number equals the number of these, and reactions are determined especially by them.AQA
outlier: An extreme value that can pull the mean away from the typical value.AQA
Ovary: The target organ for LH, where the release of a mature egg is stimulated.AQA
Overall energy change: The vertical difference between the reactant level and the product level, negative for an exothermic reaction and positive for an endothermic reaction.AQA
Overall energy change of a reaction: The difference between energy released and energy absorbed; in an exothermic reaction it is negative because more energy is released than absorbed.AQA
Overall energy change of reactions: The difference between the sum of the energy needed to break bonds in the reactants and the sum of the energy released when bonds in the products are formed.AQA
Overheating: Rapid energy transfer during large deceleration can cause brakes to overheat and become less effective.AQA
Overuse: Using antibiotics too much, which increases the selection pressure so resistant strains spread.AQA
Ovulation: The release of a mature egg, which does not occur when the pituitary gland secretes less FSH.AQA
Oxidation: A reaction in which a substance gains oxygen, and at this level the definition is the gain of oxygen by a substance.AQA
Oxidation and electron loss: When a metal reacts it is oxidised, written as M → Mⁿ⁺ + n e⁻, so the metal atom loses electrons as it forms its positive ion.AQA
Oxidation and reduction: Oxidation is the loss of electrons and occurs at the anode, while reduction is the gain of electrons and occurs at the cathode.AQA
Oxidation of fuel elements: Each element in the fuel is combined with oxygen: carbon to carbon dioxide or carbon monoxide, hydrogen to water, sulfur to sulfur dioxide.AQA
Oxidation of iron in hand warmers: Air reaching the iron in an opened packet causes exothermic oxidation that releases heat for a period.AQA
Oxides of nitrogen: Formed when nitrogen and oxygen from the air react at the high temperatures found in car engines and furnaces, giving NOₓ.AQA
Oxidising agent: The species that gains electrons and is itself reduced.AQA
Oxygen: A product of photosynthesis released as a by-product into the environment.AQA
Oxygen as the second most abundant atmospheric gas: Oxygen is the second most abundant gas in the modern atmosphere, making up about one-fifth of dry air, while nitrogen is the most abundant at about four-fifths.AQA
Oxygen debt: The amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells.AQA
Oxygen requirement: Aerobic respiration requires oxygen, whereas anaerobic respiration does not require oxygen.AQA
Oxygen transfer: The movement of oxygen atoms from reactants to products, essential for explaining how metals are extracted from their ores using carbon.AQA
Ozone: A strong oxidising agent that destroys microorganisms and leaves no chemical residual, but must be generated on site and does not protect the water afterwards.AQA

P

P = E ÷ t: The equation used to calculate power, where E is energy transferred in joules and t is time in seconds.AQA
P = I² R: For a resistor, this follows from P = V I and V = I R, showing that power depends on the square of the current.AQA
P = V I: For any circuit device, power transfer is given by this, where V is the potential difference across the device and I is the current through it.AQA
Painkillers: Medicines that relieve symptoms such as pain and fever but do not kill pathogens, so the immune system still has to clear the infection.AQA
Paired forces: Forces that are equal in size and opposite in direction, acting on different objects, so they do not cancel when either object is considered alone.AQA
Palisade cell: A cell that contains many chloroplasts near the top of the leaf, which increases the amount of light absorbed for photosynthesis.AQA
Palisade mesophyll: The main photosynthetic tissue of a leaf, sitting just below the upper epidermis and packed with chloroplasts so it absorbs most of the light that reaches the…AQA
Palisade mesophyll tissue: Plant tissue whose cells are packed with chloroplasts for photosynthesis.AQA
Pancreas: A coordination centre for blood glucose that receives information about glucose concentration and releases hormones such as insulin.AQA
Pancreatic hormones: Insulin is secreted when blood glucose is too high, and at Higher Tier only, glucagon is secreted when it is too low.AQA
Parallel: The potential difference across each branch is the same and the currents in the branches add to give the total current.AQA
Parallel circuits: Circuits in which each branch is connected directly across the same two points of the supply, so every branch receives the full supply potential difference.AQA
Parallel circuits and current pathways: Adding a second resistor in parallel provides an additional pathway for the current to flow.AQA
Parallel connection: Components sit on separate branches between the same two points, so the current splits between the branches.AQA
Paralysis: A condition in which nerve cells of the spinal cord are damaged and cannot carry impulses to muscles.AQA
Partial and reversible ionisation: Only some molecules donate a hydrogen ion, and both forward ionisation and reverse recombination occur simultaneously.AQA
Partially permeable: Allowing only some substances to pass through, so gases, water and dissolved substances can cross.AQA
Partially permeable membranes: The membrane allows small water molecules through but restricts larger solute molecules.AQA
Particle arrangement and motion in solids, liquids and gases: Solids have particles packed in fixed positions, liquids have particles close but able to slide, and gases have large spaces and fast random motion.AQA
Particle explanation of deformation: In elastic deformation the particles are displaced only slightly and return to their original positions; in inelastic deformation they are displaced enough…AQA
Particle identity: atoms, molecules and ions: The particle must be stated because the same substance can be described using atoms, molecules or ions.AQA
Particle model and conservation of particles: During a change of state the particle arrangement and energy change, but the particles themselves are unchanged.AQA
Particle model of matter: A model that represents matter as tiny particles in constant motion, with spacing and energy explaining density, changes of state and gas pressure.AQA
Particle number and amount of substance: The number of particles is the number of moles multiplied by 6.02 × 10²³, and the number of moles is the number of particles divided by 6.02 × 10²³.AQA
Particle oscillation about equilibrium positions: The particles of water or air only vibrate about equilibrium positions rather than being carried along with the wave.AQA
Particle oscillation versus wave motion: Particles oscillate about fixed positions while the disturbance passes, so energy, not matter, is transferred.AQA
Particle oscillations and energy transfer: The pattern of compressions and rarefactions moves forward while air particles oscillate about fixed positions and do not travel with the sound.AQA
Particle spacing and arrangement: How far apart particles are and how they are arranged, which explains why solids are usually densest, liquids slightly less dense, and gases much less dense.AQA
Particulates: Tiny solid particles or droplets released into the air, largely from the incomplete combustion of fossil fuels and from industrial processes.AQA
Particulates in the atmosphere: Solid particles and unburned hydrocarbons may be released and together form tiny solid or liquid particles suspended in the air.AQA
Passive: Describes a process that does not require energy from respiration, such as diffusion, distinguishing it from active transport.AQA
Passive process: A process that does not require energy from respiration.AQA
Passive versus active transport: Diffusion and osmosis are passive and do not require energy from respiration, whereas active transport requires energy from respiration.AQA
Pathogen: A microorganism that causes disease, such as a bacterium, virus, fungus or protist.AQA
Pathogen entry: The immune system tries to destroy a pathogen once it has entered the body.AQA
Pathogen groups: Viruses, bacteria, protists and fungi are the groups that may cause infectious disease.AQA
Pathogen groups and disease: Viruses, bacteria, protists and fungi are the four groups named, and each group has characteristic routes by which it spreads.AQA
Pathogen removal: Swallowed mucus carries pathogens to the stomach, where acid destroys them, reducing the number reaching the lungs.AQA
Pathogens and disease: Rose black spot is a fungal disease, so the pathogen is a fungus rather than a bacterium or virus.AQA
Pathogens and disease in populations: A new pathogen is a biotic factor, and if a pathogen spreads, susceptible species decline while resistant ones may increase.AQA
Pathogens and infectious disease: Infectious diseases are caused by pathogens, and a weakened immune system increases the likelihood that pathogens will cause disease.AQA
Paths for charge: Adding a parallel branch gives more paths for charge, so total resistance falls.AQA
Pattern: A repeated relationship seen when comparing fuels, countries or decades, such as wealthier countries using more energy per person.AQA
Patterns and trends in the periodic table: Clear trends in physical and chemical properties shown down Group 7, such as melting and boiling points increasing and colour deepening.AQA
Patterns in chemical reactions: The salt formed depends on which acid is used, while the metal or ammonium part comes from the base, alkali or carbonate.AQA
Patterns in the periodic table: The charge on the ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 relates to the group number of the element.AQA
Patterns of national and global energy use: The global reliance on fossil fuels and the growing contribution of renewables, described using comparative language such as more reliable than or less…AQA
peak value: The higher value of the alternating waveform, which is above the stated value of about 230 V.AQA
Peat as a slow-forming, carbon-rich resource: Peat accumulates very slowly over thousands of years from partly decayed plant material in waterlogged, oxygen-poor conditions and stores carbon.AQA
Peer review: Independent experts examine the report before or after publication, checking whether the evidence supports the claims and whether calculations and conclusions…AQA
Peer-reviewed evidence: Research checked by independent experts before publication, giving it greater reliability than unverified claims.AQA
Penicillium mould: The mould that produced a substance killing bacteria growing on a culture plate, named penicillin by Fleming.AQA
Peptide bonds: The bonds that join amino acids together in proteins, which are polymers of amino acids.AQA
Percentage: A way of expressing a quantity as a fraction of 100, allowing fair comparison between samples of different starting sizes.AQA
Percentage abundance: How common each isotope is, given as a percentage; these must total 100%, and the data should be checked before calculating if they do not.AQA
Percentage composition: The fraction of a compound's mass contributed by a particular element, found by dividing the element's total mass by the compound's relative formula mass and…AQA
Percentage gain: A result stated clearly as a gain, found by dividing the change by the original value and multiplying by 100.AQA
Percentage gain or loss of mass: Found by dividing the change in mass by the original mass and multiplying by 100, stating whether it is a gain or a loss.AQA
Percentage loss: A result stated clearly as a loss, found by dividing the change by the original value and multiplying by 100.AQA
percolates: Describes how water moves through the filter beds, leaving behind insoluble grit, soil, plant fragments and some microorganisms.AQA
Period: The time taken for one complete wave cycle to pass a fixed point, or for one point on the wave to complete one full oscillation, measured in seconds, s.AQA
Periodic: Describes how similar properties occur at regular intervals in the table.AQA
Periodic arrangement by atomic number: Elements are arranged in order of increasing atomic number, so that elements with similar properties recur at regular intervals.AQA
Periodic table: Arranges elements by increasing atomic number, so elements in the same group have the same number of outer-shell electrons and therefore similar chemical…AQA
Periodic table groups: An element's position is linked to its number of outer-shell electrons, so sodium with one outer electron is in Group 1.AQA
Periodic table patterns: The group number tells you how many outer electrons a metal loses, whereas for non-metals, 8 minus the group number gives the number of electrons gained.AQA
Periodic table trends: Group 0 noble gases are unreactive non-metals with full outer shells, while Group 1 metals are highly reactive because they lose one electron easily.AQA
Permanent magnet: A magnet that produces its own magnetic field continuously, without needing another magnet nearby.AQA
permanent vacuole: A large organelle found in plant cells that is filled with cell sap and is absent in animal cells.AQA
Perpendicular components of a force: Two component forces acting at right angles to each other that together have the same effect as the single force.AQA
pH probe: Gives a numerical reading and is more precise, so it is better when you need an exact value.AQA
pH scale: Runs from 0 to 14 and is a measure of the acidity or alkalinity of a solution.AQA
Phagocytosis: A defence mechanism in which a white blood cell engulfs a pathogen and digests it.AQA
Phenotype: The observable characteristics that actually appear, often resulting from both genes giving a range and the environment deciding where within that range the…AQA
Phenotype and variation: Most mutations have no effect on the phenotype, some affect it, and very rarely a mutation produces a new phenotype.AQA
Phloem: Carries dissolved sugars, mainly sucrose, from the leaves to other parts of the plant for use or storage, and is made of living cells, including sieve tubes…AQA
Photosynthesis: The process that occurs in chloroplasts, in which light energy is absorbed so that the plant can make glucose from carbon dioxide and water.AQA
Photosynthesis and growth: Leaves make glucose by photosynthesis, and this coordination allows the whole plant to survive, grow and reproduce.AQA
Photosynthesis and plant growth: Losing leaf area reduces photosynthesis, so growth is reduced because less glucose is made.AQA
Physical change: A change in which no new substance forms and the particles keep their identity.AQA
Physical changes: Processes that do not involve chemical reactions and make no new substances, so substances are only separated physically.AQA
Physical demands of IVF and hormone treatment: Treatment involves repeated hormone injections, frequent blood tests, ultrasound scans and invasive egg collection procedures, often causing side effects.AQA
Physical law: A relationship between measurable quantities that can be written as an equation.AQA
Physical properties of the halogens: Fluorine and chlorine are gases, bromine is a liquid and iodine is a solid, with melting and boiling points increasing down the group.AQA
Physical separation techniques: Purely physical steps in which no chemicals are added and no dissolved substances are removed, preparing the water for sedimentation and biological treatment…AQA
Physical well-being: Covers the body working properly, with no infections, injuries or long-term conditions, and enough fitness and energy for daily life.AQA
Physiological adaptation: A feature of the body's processes such as water retention or antifreeze proteins.AQA
Phytomining: Grows plants that absorb metal ions from soil; the plants are harvested and burned, and the ash is processed to recover the metal.AQA
Pituitary gland: A gland in the brain which secretes several hormones into the blood in response to body conditions, and whose hormones act on other glands.AQA
Placebo: A dummy treatment with no active drug, made to look, taste and be given in the same way as the real medicine.AQA
Placenta: The organ through which substances in tobacco smoke and alcohol can cross from the mother's blood into the fetus.AQA
Planetary comparisons: g differs between planets and moons, so weight changes while mass stays constant.AQA
Plant and algal cells as eukaryotic cells: These cells possess a cell wall, which helps distinguish them from animal cells in microscopy and in cell models.AQA
Plant and animal hosts: Organisms that pathogens may infect, including plants and animals.AQA
Plant disease symptoms: Purple or black spots develop on leaves, which often turn yellow and drop early.AQA
Plant growth and meristems: Stem cells sit in meristems at growing tips of shoots and roots and in cambium, dividing throughout life to produce new plant tissues so roots and shoots grow…AQA
Plant organ system: The roots, stem and leaves form a plant organ system for transport of substances around the plant.AQA
Plant stem cells: Unspecialised cells found in meristems, such as the tips of roots and shoots, that can divide and differentiate into any plant cell type.AQA
Plant transport tissues: Tissues such as phloem that carry substances around the plant, with phloem arranged as tubes running through the plant.AQA
Plant-derived drugs: Drugs traditionally extracted from plants, such as digitalis from foxglove and aspirin from willow.AQA
Plant-derived starting chemicals: A starting point for a new drug may still be a chemical extracted from a plant.AQA
Plants: Organisms that evolved over the next billion years and continued to produce oxygen, gradually increasing its percentage.AQA
Plasma: The liquid part of blood that acts as the transport medium for dissolved glucose, amino acids, mineral ions, carbon dioxide, urea and hormones.AQA
Plasmids: Small circular DNA molecules that a bacterial cell may also carry in addition to its single circular DNA molecule.AQA
Plateau: The part of a rate graph where the line levels off, showing the maximum rate under those conditions.AQA
Platelets: Fragments that release chemicals to start clotting, forming a scab that reduces blood loss and prevents pathogens entering.AQA
Plotting compass: Placed at a point, it aligns with the local field line so its north-seeking pole points along the arrow.AQA
Plotting data accurately: Translating numerical to graphical form by choosing a sensible scale, plotting each pair of values accurately, and drawing a line or curve of best fit.AQA
Plotting from measurements: Recording velocity at regular time intervals, choosing scales that use most of the grid, and plotting each point accurately.AQA
plum pudding model: A model picturing the atom as a ball of positive charge with negative electrons embedded in it, like fruit in a pudding.AQA
Pluripotent: Able to differentiate into almost any cell type, because the genes that make a cell specialised have not yet been switched on.AQA
point of crystallisation: The stage of evaporation reached before cooling, so the salt does not decompose or trap impurities.AQA
Poles of a magnet: A permanent magnet has fixed north and south poles, but a magnetic material has no fixed poles to repel.AQA
Political and economic barriers to change: Considerations such as government priorities, international agreements, public unpopularity, the cost of renewable technology or of closing fossil fuel plants…AQA
Political and social factors: Limits that include government priorities, public habits and the time taken to build new infrastructure.AQA
Pollen grains: The male gametes, produced in the anther of the stamen, each containing a male nucleus and carried by wind or insects to the stigma.AQA
Polydactyly: Having extra fingers or toes, caused by a dominant allele so that one copy of the allele is sufficient for the condition to be expressed.AQA
Polygenic: Controlled by multiple genes, often with environmental influence, so features show continuous variation rather than simple dominant or recessive categories.AQA
Polygenic inheritance: Most characteristics are controlled by multiple genes rather than one gene, which is called polygenic inheritance.AQA
polymer: A very large covalent molecule built from many small repeating units called monomers.AQA
Polymers: Covalently bonded substances that have very large molecules, in which many identical small units are joined by strong covalent bonds.AQA
Polymers and everyday materials: Alkenes produced by cracking are used to make polymers, solvents, lubricants and detergents, linking crude oil to everyday materials.AQA
Polymers and monomers: Large molecules built from many small monomer units joined by covalent bonds.AQA
Polymers as useful materials: Alkenes are used to produce polymers, such as poly(ethene) from ethene, which is used for carrier bags and bottles.AQA
Poor vehicle condition: A condition strictly limited to the vehicle's brakes or tyres, where worn brakes reduce the braking force and worn or under-inflated tyres have poor grip.AQA
Pop sound: The sound heard when hydrogen burns rapidly with oxygen from the air, showing a positive test.AQA
Population: One species in a habitat, as distinguished from a community of all the populations of all species there.AQA
Population change over time: Evolution is a change in the inherited characteristics of a population over time, not a change in an individual bacterium.AQA
Population cycles and limiting factors: Prey numbers may fall, then predator numbers may fall as food becomes scarce, giving a cyclical relationship, with the effect depending on factors such as…AQA
Population size: The number of individuals, which falls when a pathogen causes many individuals to become ill or die.AQA
Populations and communities: A population is all the organisms of one species in a habitat, while a community is all the populations of different species living and interacting in a…AQA
Portability and energy density in transport: Transport needs portable, energy-dense fuels, so petrol, diesel and jet fuel dominate, with battery electric vehicles and hydrogen increasingly used.AQA
Position of equilibrium: Where the equilibrium sits, shifting to oppose a temperature change and changing the relative amounts of substances present at the new equilibrium.AQA
Positive correlation: A relationship where y increases as x increases, shown by points trending upwards on a scatter diagram.AQA
Positive ion: The ion in the base, alkali or carbonate that determines the first part of the salt name and comes from the base, alkali or carbonate.AQA
Positive ion formation by metal atoms: When metals react with other substances the metal atoms form positive ions.AQA
Positive ions: Formed when metals lose outer electrons, for example Na → Na⁺ + e⁻.AQA
Potable water: Water that is safe to drink, with acceptable levels of dissolved substances and microbes, but not necessarily pure in the chemical sense.AQA
Potency: The ability of meristem cells to differentiate into any type of plant cell, retained throughout the life of the plant.AQA
Potential difference: The electrical 'push' on each branch; in a parallel circuit it is the same across each component and equal to the supply value.AQA
Potential difference across components and branches: In a series circuit the cell potential difference is shared between the components, while the potential difference across each parallel branch equals the…AQA
Potential difference and current: Power depends on both the potential difference across a device and the current through it, as summarised by P = VI.AQA
Potential difference as energy per unit charge: Potential difference is energy transferred per unit charge, measured in volts.AQA
Potential difference in parallel branches: Each branch has the same potential difference across it, equal to the supply potential difference.AQA
Potential difference shared in series: The supply potential difference is shared between components, so the individual values sum to the supply value.AQA
Potential divider circuits: The LDR is connected in series with a fixed resistor across a supply, and the output voltage is taken across one of them.AQA
Potential dividers: In a potential divider, the changing resistance of the LDR changes the potential difference across it, which can switch a device on or off.AQA
Potential energy: Energy of a particle due to its position and the forces between particles.AQA
Potometer measurements: A potometer can estimate water uptake by a leafy shoot, and the distance moved by an air bubble along a capillary tube can be converted into a volume using…AQA
Power: Equals potential difference multiplied by current, measured in watts, and shows that a component transfers more energy each second when potential difference…AQA
Power as the rate of energy transfer: Power is given by P in the equation E = P t, measured in watts (W), where 1 W = 1 J/s.AQA
Power rating: A value on an appliance label that tells you how quickly electrical energy is transferred from the mains into useful stores.AQA
Powers of ten: The 10ⁿ part of standard form, whose index is positive for large numbers and negative for small ones.AQA
Practical and lifestyle barriers: Limits that include living in a rented flat where insulation cannot be installed, or a rural area with no bus service.AQA
Practical applications of half-life: This lets scientists date rocks and trace medical isotopes.AQA
Practical circuit applications: Domestic appliances are connected in parallel so each receives the full mains potential difference and can be switched independently.AQA
Practical consequences of circuit arrangement: Removing one lamp stops the whole series circuit, whereas in parallel the other branches keep working.AQA
Practical graph-reading skills: Draw a straight line that touches the curve at the chosen time and continues equally on both sides, then choose two well-separated points on that tangent and…AQA
Practical measurement of density: Finding mass with a balance and volume by displacement or by measuring dimensions.AQA
Practical measurement skills: To find e, measure the stretched length and subtract the original unstretched length, using consistent units.AQA
Practical plotting method: Place the magnet on paper and put a small plotting compass near one pole, then mark the direction the compass needle points.AQA
Practical timing and precision: Measuring or recording the duration of a current with a stopwatch or timer, reading to an appropriate precision.AQA
Precipitate: A fine white solid suspended in the liquid, formed when carbon dioxide reacts with calcium hydroxide and making the limewater milky or cloudy.AQA
Precipitation of carbonates and sediment formation: Carbonates precipitated out of solution, forming sediments on the sea bed.AQA
Precision and repeatability of measurements: A small range relative to the mean indicates precise, repeatable measurements, while a large range warns that technique or apparatus may need checking.AQA
Preclinical testing: Laboratory studies on cells and tissues and tests on animals that happen before any human exposure to assess efficacy, toxicity and safe dosage.AQA
Predation and its effect on prey populations: A new predator is a biotic factor, and predation reduces prey numbers, after which predators may compete and plants the prey ate may grow more.AQA
Predator: A consumer that kills and eats other animals.AQA
Predator cycle: The repeating rise and fall of predator numbers, which lags behind the prey cycle because breeding and survival respond to prey availability.AQA
Predator-prey population cycles: Graphs often show peaks and troughs, with the predator peak lagging behind the prey peak.AQA
Predator–prey relationships: A relationship in which a predator eats other organisms, transferring energy from prey to predator and reducing the number of prey.AQA
Predicting count rate from half-life: The expected count rate after one or more half-lives is found by halving the starting value that many times.AQA
Predicting direction of equilibrium shift: Increasing pressure shifts equilibrium towards the side with fewer gas molecules, and decreasing pressure shifts it towards the side with more gas molecules.AQA
Predicting electrode products: Identify the ions present, compare their ease of discharge at each electrode, then name the products formed.AQA
Predicting ion charges from group number: Ion charges can be deduced from group number alone for these groups, without writing full electron configurations.AQA
Predicting pollutants from fuel composition: Knowing the elements present lets you predict the combustion products and the pollutants released, for example sulfur in a fuel can lead to sulfur dioxide.AQA
predicting products of electrolysis: Identify the ions from the formula, then apply charge attraction to name the element formed at each electrode.AQA
Prediction and evidence in science: This shows how a model can be tested by prediction and subsequent evidence.AQA
Preservation and decay: The organism must usually be buried quickly, and soft parts normally decay before preservation, so hard parts are most commonly fossilised.AQA
Preservation in amber, tar and ice: Decay is prevented, so even soft parts may survive almost unchanged.AQA
Preservation in sedimentary rock: A trace survives when the sediment sets before the trace is destroyed, and is later exposed by erosion or quarrying.AQA
Pressure: Caused by the force of molecular collisions acting on the container walls per unit area.AQA
Pressure–temperature relationship at constant volume: At constant volume, the pressure of a fixed mass of gas increases as its temperature increases, and decreases as it cools.AQA
Pressure, volume and temperature relationships: For a fixed mass of gas at constant volume, pressure is directly proportional to absolute temperature in kelvin.AQA
Prevention: A way to reduce cost, for example anti-smoking campaigns or sugar reduction, linked to lower future spending.AQA
Prevention and control of disease: Control methods include preventing mosquitoes from breeding and using mosquito nets to avoid being bitten, which reduce the spread of malaria.AQA
Prevention and health: A person cannot always control risk, but changing habits can reduce it, for example stopping smoking lowers heart disease risk over time.AQA
Prevention by reducing multiple risk factors: Reducing several risk factors together can lower risk more than changing just one.AQA
Prevention of resistant strains spreading in populations: Completing the course keeps killing susceptible bacteria and reduces the chance that resistant survivors multiply and spread.AQA
Probability: The chance that a particular genotype or phenotype appears in one offspring, calculated from the equally likely gamete combinations.AQA
Problem solving: Rearranging gives force = work done ÷ distance or distance = work done ÷ force, and the distance must be the displacement along the force direction.AQA
Processing: Converting extracted material into a usable form, for example crushing and heating limestone, reducing metal ores or fractionally distilling crude oil.AQA
Producer: The organism that all food chains begin with, which synthesises molecules and is usually a green plant or alga making glucose by photosynthesis.AQA
Producers: Photosynthetic organisms that synthesise their own organic nutrients from inorganic raw materials using light energy.AQA
Product formed: The quantity of a product formed, which may be measured in grams, cm³ of gas or moles.AQA
Product prediction patterns: Applying the pattern for the reaction type, such as acid with metal carbonate giving salt, water and carbon dioxide.AQA
Production of genetically identical cells: The overall cell cycle produces two genetically identical daughter cells.AQA
Production of H⁺(aq) ions and acidic properties: Complete ionisation produces a high concentration of H⁺(aq) ions, leading to a low pH and vigorous reactions with metals.AQA
Production of true-breeding populations: After many generations all or nearly all offspring show the desired characteristic, so the population is described as true-breeding for that feature.AQA
Products: The names of the substances formed, written on the right of the arrow and separated by plus signs where there is more than one.AQA
Products of cracking: shorter alkanes and alkenes: A valid cracking equation produces a shorter alkane and an alkene, so the products must include a C=C-containing molecule.AQA
Profit: The difference between income from increased yield and the cost of providing enhanced conditions, such as heating, lighting or CO₂ enrichment.AQA
Progesterone: Secreted by the corpus luteum after ovulation, it maintains the uterus lining and inhibits FSH and LH.AQA
Projection: A prediction based on stated assumptions rather than a measured fact, shown where a graph shows a projection.AQA
Prokaryotes and eukaryotes compared: Prokaryotic cells such as bacteria are much smaller and have no nucleus, their genetic material being a single loop of DNA free in the cytoplasm.AQA
Prokaryotic and eukaryotic cells: Prokaryotic cells lack a membrane-bound nucleus, while eukaryotic cells have a nucleus.AQA
Prokaryotic cell: A bacterial cell that is much smaller in comparison, with cytoplasm and a cell membrane surrounded by a cell wall, and genetic material not enclosed in a…AQA
Prokaryotic cell structure: A cell with no nucleus and no membrane-bound organelles, whose genetic material is a single circular DNA molecule free in the cytoplasm.AQA
prokaryotic cells: Cells, such as bacteria, that have no nucleus and hold their DNA free in the cytoplasm.AQA
prop-: Prefix used in the names of alkanes to indicate three carbon atoms.AQA
Properties and purity of recycled materials: The properties required of the final product determine how pure or how well sorted the recycled metal must be.AQA
Properties of solids, liquids and gases: A solid has a definite shape and volume, a liquid has a definite volume but takes the shape of its container, and a gas has neither definite shape nor…AQA
Properties of substances: Each substance in a mixture keeps its own properties, and separation depends on a property such as solubility or boiling point.AQA
Proportion: A comparison of a part with the whole, written as a fraction, decimal or percentage rather than with a colon.AQA
Proportional reasoning: A simple model in which a factor that increases the frequency of successful collisions by a given factor increases the rate by roughly the same factor when…AQA
Proportional reasoning with squared terms: Because speed is squared, doubling speed multiplies kinetic energy by four for the same mass.AQA
Proportionality: A straight line through the origin on a rate against 1 ÷ distance² graph shows rate is proportional to light intensity.AQA
Proportions of gases by volume: The atmospheric proportions are proportions by volume, and for gases this is effectively the same as the proportion by number of molecules.AQA
Proportions of nitrogen and oxygen: Nitrogen makes up about four-fifths of the atmosphere and oxygen about one-fifth, quoted as approximate rather than fixed.AQA
Proteases: Produced in the stomach, the pancreas and the small intestine, they catalyse the breakdown of proteins to amino acids.AQA
Protecting treatment equipment: Screening traps large solids and grit removal takes out dense particles, so that pumps, valves and downstream equipment are not blocked, damaged or eroded.AQA
Protection: Keeping an existing rare habitat intact by limiting damaging human activities such as building, drainage, ploughing and pollution.AQA
Protective role of mucus: The stomach wall secretes mucus, which protects the lining from damage by acid and enzymes.AQA
Protein: A molecule made when amino acids are joined together in the order coded for by a gene.AQA
Protein structure and shape: Enzymes are made of protein, and the shape of the active site is complementary to the shape of its substrate.AQA
Protein synthesis: The building of proteins from amino acids, which is limited when nitrate ions are deficient, so growth is reduced and leaves may become yellow.AQA
Protist diseases: Malaria is caused by protist pathogens, not by a virus or bacterium, and antibiotics that target bacteria are not effective against it.AQA
proton: The name given to the smaller particles, each having the same amount of positive charge, into which the positive charge of any nucleus could be subdivided.AQA
Proton number and element identity: All atoms of a particular element have the same number of protons, and atoms of different elements have different numbers of protons.AQA
Proton transfer: The mechanism occurring in acid-base neutralisation, where an acid donates a hydrogen ion (H⁺) to a base.AQA
Protons: All atoms of a particular element have the same number of these, and their number is the atomic number.AQA
Protons and electrons: In an atom the number of electrons is equal to the number of protons in the nucleus.AQA
Protons, neutrons and electrons: A neutral atom has equal numbers of protons and electrons, and losing electrons leaves more protons than electrons, producing an overall positive charge.AQA
Protons, neutrons and electrons as sub-atomic particles: Protons are positively charged, neutrons have no charge, and electrons are negatively charged and surround the nucleus.AQA
Provisional nature of scientific knowledge: Scientific models are provisional and may be replaced when further evidence is obtained.AQA
Puberty: The stage when the reproductive system becomes functional, triggered by hormones from the pituitary gland which stimulate the gonads.AQA
Public health and treatment failure: The resistant strain spreads because people are not immune to it and there is no effective treatment.AQA
Publication: Makes methods, data and conclusions available so other scientists can examine the study.AQA
pulmonary artery: Carries deoxygenated blood to the lungs, showing that artery means direction, not oxygen content.AQA
pulmonary vein: The exception among veins, carrying oxygenated blood from the lungs to the left atrium.AQA
Punnett square: A diagram showing the four equally likely fertilisation outcomes for a single gene cross, such as AA, Aa, Aa and aa.AQA
Punnett square diagram: A diagram used to construct a genetic cross, with one parent's alleles across the top and the other's down the side.AQA
Pure compound: Contains only one compound, and may contain different types of atom chemically bonded together in a fixed ratio.AQA
Pure metals: Metals whose atoms are arranged in layers, which allows them to be bent and shaped, but which are too soft for many uses.AQA
Pure substance: A substance that produces a single spot in every solvent system because it has one fixed composition and one R_f value.AQA
pure water: Water that contains only H₂O molecules and nothing else, so it has a fixed boiling point of 100 °C at standard pressure and no dissolved ions.AQA
Purity and melting or boiling point evidence: A pure substance melts or boils sharply at one temperature, while an impure sample melts or boils over a range.AQA
Purity and single spots: A pure compound produces a single spot in all solvents, while a mixture may separate into different spots depending on the solvent.AQA

Q

Q = I × t: The equation linking charge flow to current and time, rearranged to t = Q ÷ I when charge flow and current are known.AQA
Quadrat: A square frame of known area used to sample organisms in a small, defined area, with counts repeated to reduce the effect of chance.AQA
Qualitative food tests: Tests that show whether a nutrient is present, not its exact concentration, although Benedict’s colour can indicate relative amounts of reducing sugar.AQA
Qualitative reagents: Substances used to test for a range of carbohydrates, lipids and proteins, showing whether a food molecule is present rather than its exact concentration.AQA
Qualitative resistance behaviour: Adding resistors in parallel decreases the total resistance, and the combined resistance is always less than the resistance of the smallest individual resistor.AQA
Qualitative test: A test that shows the presence of an alkene but does not identify which alkene.AQA
Quantification of resource use: Use of water, resources, energy sources and production of some wastes can be fairly easily quantified.AQA
Quantitative calculation using supplied data: Add the energies of all bonds broken in the reactants, add the energies of all bonds made in the products, then subtract: energy transferred = energy of bonds…AQA
Quantitative circuit calculations: Substituting values into Q = I t, and its rearrangements, to calculate charge flow, current or time.AQA
Quantitative energy calculations: Each store's energy is calculated in joules using the correct equation, such as E = mgh for gravitational potential energy.AQA
Quantitative problem solving: Identify the two known quantities, substitute values with units, then rearrange and calculate to find the unknown quantity.AQA
Quantity of reactant used: Always found by subtracting the final reading from the initial reading, regardless of when the interval starts.AQA

R

R = V ÷ I: The equation defining resistance, where V is the potential difference across the component in volts and I is the current through it in amperes.AQA
R_f as a ratio: A value comparing how far a dissolved substance travels with how far the solvent front travels, having no units and always between 0 and 1.AQA
R_f calculation: The distance travelled by the substance divided by the distance travelled by the solvent front, then rounded to a sensible number of significant figures.AQA
R_f value: Calculated using distance moved by substance divided by distance moved by solvent front, measured from the start line, with no units and always between 0 and 1.AQA
R_f values: Calculated using the distance travelled by the substance divided by the distance travelled by the solvent front.AQA
R_f values and solvents: Different compounds have different R_f values in different solvents, so a compound can have different R_f values in different solvents.AQA
radio: The group with the longest wavelength and lowest frequency, going from long to short wavelength before microwave.AQA
Radio waves: Transverse electromagnetic waves with the longest wavelength and lowest frequency in the electromagnetic spectrum, used for television and radio communications.AQA
Radioactive contamination: Radioactive material gets onto or into an object or person, so the source travels with them and keeps exposing them until removed or decayed.AQA
Radioactive decay: A random process in which an unstable nucleus gives out radiation as it changes to become more stable.AQA
Radioactive waste and storage: Nuclear fuel gives low carbon emissions in operation but leaves radioactive waste needing long-term safe storage.AQA
Radioactive waste management: Nuclear fuel produces radioactive waste needing long-term safe storage, though operation releases little carbon dioxide.AQA
Random and systematic error: Repeating a measurement and taking a mean reduces the effect of random variation, but a systematic offset such as a zero error shifts all results and is not…AQA
Random and systematic sampling: Placing quadrats randomly, such as by using a random number generator to select coordinates, or along a transect at regular intervals.AQA
Random molecular motion: Gas molecules move continuously, randomly and in straight lines between collisions with each other or with the container walls.AQA
Random motion of particles: The movement that drives diffusion, with particles spreading out until they reach a uniform concentration.AQA
Random nature of radioactive decay: You cannot predict when any particular unstable nucleus will decay, nor which nucleus in a sample will decay next.AQA
Random process: You cannot predict when a particular nucleus will decay, nor which nucleus in a sample will decay next.AQA
Random sampling: Placing quadrats randomly, for example using random numbers as coordinates, avoids bias and makes the sample more representative of the whole habitat.AQA
Random selection and bias reduction: Number every individual, then use a random number generator to pick participants, giving every member an equal chance of selection.AQA
random variation: Variation between repeats that means are used to smooth out.AQA
Randomness of individual decay events: You cannot predict which nucleus decays next or exactly when, so individual decays are chance events.AQA
Range: Found by subtracting the smallest reading from the largest reading.AQA
Range as a measure of spread: Describes how far apart the smallest and largest readings are, found by subtracting the smallest reading from the largest.AQA
Ranking and ordering: Placing several metals from most to least vigorous using all the comparisons, ensuring the final order is consistent with every observation.AQA
Rapid burial and decay prevention: Quick burial in sediment limits decay and scavenging, so hard parts remain.AQA
Rarefaction: A region where particles are spread further apart, with lower pressure and density.AQA
Rate: A compound measure that compares a quantity with time, such as volume of blood passing a point each second.AQA
Rate calculations: Quantify how quickly a reactant is used up or a product is formed, found by dividing the amount changed by the time taken.AQA
Rate graphs and gradients: Plotting volume against time, where a steeper initial gradient on a volume–time graph means a faster rate.AQA
Rate of change: Speed is the rate of change of distance, linking how far an object travels to how long it moves for.AQA
Rate of change of velocity: Acceleration is defined as the rate of change of velocity.AQA
Rate of cooling of a building: How quickly energy is transferred from the warmer interior of a building to the cooler outside through its walls.AQA
Rate of diffusion: The number of particles crossing per unit time, which rises when a larger surface area provides more space for particles to diffuse across at the same time.AQA
Rate of energy transfer: The watt tells you how quickly energy is transferred or work is done, so a higher power means more energy transferred each second.AQA
Rate of energy transfer by conduction: Increases with greater temperature difference and greater cross-sectional area, and decreases with greater thickness.AQA
Rate of flow of charge: The size of the electric current, so current equals charge flow divided by time.AQA
Rate of photosynthesis: A measure that depends on light intensity, carbon dioxide concentration and temperature, and is raised by increasing a factor until another becomes limiting.AQA
Rate of reaction: A quantity that depends on the frequency of successful collisions, so a factor that increases this frequency increases it.AQA
Rate of reaction and end-point timing: The time from mixing to the first yellow-brown result is recorded for each pH, and rate can be compared using rate = 1 ÷ time.AQA
Rate of resource use versus rate of replacement: A resource such as fresh water or wood is renewable only if the rate of use stays below the rate of replacement.AQA
Rate of transpiration: A compound measure that compares a volume of water lost with a time taken, calculated as volume of water lost ÷ time taken.AQA
Rate of water uptake: Calculated as change in mass or volume divided by time taken, giving units such as g/min, g/h, cm³/min or cm³/h.AQA
Ratio: A way of comparing parts with parts, such as the numbers of each genotype or phenotype in a genetic cross.AQA
Ratio and calculation skills: R_f is calculated by dividing the distance moved by the substance by the distance moved by the solvent.AQA
Raw materials and manufacturing: The stages of extracting and processing raw materials, and manufacturing and packaging.AQA
Reactant classification: Deciding whether the named reactants are an acid and a base or alkali before predicting products.AQA
Reactant used or product formed: The quantity measured to follow a reaction, such as the loss in mass of a reaction mixture or the volume of gas collected.AQA
Reactants: The names of the starting substances, written on the left of the arrow and separated by a plus sign where there is more than one.AQA
Reactants and products: Glucose is the reactant and lactic acid is the product in the anaerobic respiration equation for muscles.AQA
Reacting ratios: The ratio in which substances react, which a balanced equation is used to show.AQA
Reaction profile: A graph of energy on the vertical axis against progress of reaction on the horizontal axis, starting at the reactant energy level and ending at the product…AQA
Reaction profiles: These are used to show the relative energies of reactants and products.AQA
Reaction time: The interval between seeing a hazard and braking, which is not fixed and depends on the driver's state and surroundings.AQA
Reaction time and nervous coordination: A shorter reaction time can be linked to faster impulse transmission or more efficient coordination when interpreting data about nervous function.AQA
Reactions of metals with chlorine: The alkali metals react when heated to form white metal chlorides.AQA
Reactions of metals with oxygen: The first three alkali metals burn in air to form metal oxides, and the reaction becomes more vigorous down the group.AQA
Reactions of metals with water: These reactions produce a metal hydroxide and hydrogen, and the hydroxide makes the solution alkaline.AQA
Reactivity and ease of discharge: At the cathode, hydrogen is produced if the metal is more reactive than hydrogen; at the anode, oxygen is produced unless halide ions are present, in which…AQA
Reactivity and electronic structure: Reactivity decreases down the group because the outer shell is further from the nucleus and shielded by more inner shells, so attraction for an incoming…AQA
Reactivity and extraction method: Carbon can reduce oxides of metals below carbon in the series, while metals above carbon need electrolysis instead, and the more reactive the metal the more…AQA
Reactivity linked to tendency to form positive ions: The reactivity of a metal is related to its tendency to form positive ions.AQA
Reactivity of carbon with oxygen at high temperature: The oxygen produced reacts with the hot carbon anode to form carbon dioxide, so the carbon anode is gradually burned away.AQA
Reactivity of Group 1 metals: A property that increases from lithium to sodium to potassium, so elements lower down react even more vigorously with water.AQA
Reactivity series: The order of the named metals from potassium > sodium > lithium > calcium > magnesium > zinc > iron > copper, built by comparing their reactions with water or…AQA
Reactivity series and carbon reduction: Electrolysis is used when the metal is too reactive to be extracted by reduction with carbon, because carbon cannot displace a more reactive metal from its…AQA
Reactivity series and selective discharge: The relative reactivity of the elements involved determines which ions are discharged, with the less reactive element discharged at the cathode.AQA
Reactivity series and the position of hydrogen: The metal must be more reactive than hydrogen for the reaction to occur, so metals such as copper, silver and gold do not react with dilute acids.AQA
Reactivity trends: The increasing number of inner shells down a group explains trends in reactivity, even though the type of reaction is similar.AQA
Reactivity trends down Group 1: Reactivity increases down the group because the outer electron is lost more easily, so reactions with water become more vigorous.AQA
Reading and interpreting graphs: Moving confidently between a graph and the numbers it represents, by reading the axes and units, locating the required point, and stating the value with its…AQA
Reagents and colour changes: Benedict’s solution, iodine solution and Biuret reagent each give a starting colour and a positive colour change when the nutrient they detect is present.AQA
real size: The actual size of the object, found by dividing image size by magnification, and smaller than the image size when magnification is greater than 1.AQA
Rearrangement of atoms: During a chemical reaction, bonds break and new bonds form, but the atoms themselves are simply rearranged.AQA
Rearranging: Changing the equation so that distance moved by substance equals R_f multiplied by distance moved by solvent.AQA
Rearranging and applying equations: Rearranged, V = P ÷ I and I = P ÷ V, which lets you find an unknown when the other two quantities are known.AQA
Rearranging and using equations: The relationship concentration = mass ÷ volume is rearranged so that mass = concentration × volume before substituting.AQA
Rearranging equations: Writing the equation in another form, such as L = E ÷ m to give the energy needed per kilogram, or m = E ÷ L to give the mass.AQA
Rearranging formulae: Changing the subject of the equation to give v = s ÷ t or t = s ÷ v when the unknown is speed or time.AQA
Rearranging the charge equation: Changing Q = I t into t = Q ÷ I so that time can be found when charge and current are known.AQA
Rearranging to s = W ÷ F: Used in calculations to find s when work done and force are known.AQA
Receiver aerial: When radio waves are absorbed by it, they create an alternating current with the same frequency as the radio wave itself.AQA
Receptor: A specialised cell or structure that detects the stimulus and converts it into an electrical impulse in a neurone.AQA
Receptors: Components that detect changes in the water concentration of the internal environment and send this information to a coordination centre.AQA
Receptors and effectors: Receptors detect changes in temperature and send information to coordination centres, while effectors, such as muscles or glands, bring about responses that…AQA
Receptors, coordination centres and effectors: Each controlled factor has receptors that detect deviation, a coordination centre such as the brain or pancreas, and effectors such as muscles or glands that…AQA
recessive: Describes an allele whose characteristic is only expressed in the phenotype when two copies are present, because a dominant allele masks it in a heterozygote.AQA
Recessive allele: An allele that is only expressed if two copies are present, therefore no dominant allele present.AQA
Recessive alleles: Alleles that are expressed only when two copies are present.AQA
Recessive disorder: A disorder that only appears when both alleles are recessive, for example cystic fibrosis.AQA
Recessive disorder alleles: Versions of a gene that cause the condition only when two copies are inherited, one from each parent.AQA
reciprocal relationship: Period and frequency describe the same repeating event from opposite viewpoints, so T = 1 / f and rearranging gives f = 1 / T.AQA
Recognising repeating units: Identifying the repeating unit shown in brackets with a subscript n, indicating many identical units joined together.AQA
Recognition and interpretation of diagrams: Identifying the repeating unit, counting bonds per atom, and noting whether layers or a rigid three-dimensional network are present.AQA
Recoil and explosions: An initially stationary object separates into parts moving in opposite directions, keeping the total momentum at zero.AQA
Recombinant DNA formation: The isolated gene is inserted into the vector, forming a recombinant molecule before delivery.AQA
Rectification: The use of a diode to convert alternating current into direct current.AQA
Recurring chemical properties: Chemical properties repeat, with Group 1 metals reacting vigorously with water and Group 7 halogens reacting with metals to form salts.AQA
Recurring physical properties: Melting point, boiling point, density and state at room temperature change gradually across a period and repeat in a pattern down a group.AQA
recycled: Materials in the living world are passed along food chains and returned to the environment so they provide the building blocks for future organisms.AQA
Recycling: Collecting and reprocessing materials, such as melting used aluminium cans into new ones.AQA
Recycling and material choice: Each packaging material has its own extraction, processing and disposal impacts, and glass can be recycled many times while plastic film may not be recycled.AQA
Recycling and reuse: Reduce the volume sent to landfill and lower pollution risk.AQA
Recycling of matter in ecosystems: The chemicals in ecosystems are continually cycling through the natural world, being recycled between the living and non-living parts rather than being lost.AQA
Red blood cells: Carry oxygen, as haemoglobin binds oxygen in the lungs to form oxyhaemoglobin and releases it in tissues where respiration is occurring.AQA
Redox reactions: Reactions in which oxidation, the loss of electrons, and reduction, the gain of electrons, happen simultaneously.AQA
Reduced dependence: Having many interconnections in a food web rather than a single critical link, so species rely less on any one other species.AQA
Reduced genetic variation: A result of selective breeding using a small number of closely related parents, meaning a breed may be less able to resist new diseases or environmental…AQA
Reducing agent: The species that loses electrons and is itself oxidised.AQA
Reducing random error: Repeating the timing several times and calculating a mean time to reduce the effect of random errors in reaction time.AQA
Reducing reaction-time error: When timing oscillations, time several cycles and divide by the number of cycles to reduce reaction-time error.AQA
Reducing sugars, starch and protein: Each test is specific to one nutrient, so identifying an unknown food requires separate tests for sugars, starch and protein.AQA
Reducing waste and conserving finite resources: Chemists use renewable feedstock, recycle metals and plastics, design biodegradable polymers, treat waste water and use atom economy to reduce waste and…AQA
Reduction: Extraction is a reduction process in which the metal compound loses oxygen or gains electrons, producing the metal.AQA
Reduction and oxidation: At the cathode positive ions gain electrons and are reduced, while at the anode negative ions lose electrons and are oxidised.AQA
Reduction as electron gain: Positively charged ions gain electrons at the cathode, and this electron gain is defined as reduction.AQA
Reduction at the cathode: At the negative electrode, positively charged ions gain electrons.AQA
Reduction in use: Buying and consuming less, for example choosing products with less packaging or keeping a phone longer.AQA
Reduction of atmospheric carbon dioxide over time: The removal of carbon dioxide from the atmosphere reduced its atmospheric concentration.AQA
Reduction of metal oxides by carbon: Carbon reduces a metal oxide when carbon is above the metal, as with zinc oxide but not aluminium oxide.AQA
Reflection: The wave bounces off a surface, and the proportion reflected depends on the substance and wavelength.AQA
Reflex action: An automatic and rapid response that does not involve the conscious part of the brain.AQA
Reflex arc: A pathway through the spinal cord that lets responses occur without conscious brain processing, making reactions fast and automatic.AQA
refracted ray: The ray drawn on the other side of the normal, continuing into the second medium after the wave crosses the boundary.AQA
Refraction: The wave changes direction at a boundary because its speed changes, and the change in speed, and so the bending, varies with wavelength.AQA
Regeneration: Restoring a degraded habitat through active management, for example rewetting a bog or clearing scrub from chalk grassland.AQA
Regular lattices: The atoms are arranged in a regular, repeating pattern called a lattice, rather than as separate molecules.AQA
Regular solid: An object whose volume is determined from its measured dimensions, for example V = length × width × height.AQA
Regulation and licensing: Regulators review the evidence from trials before a licence is granted, and the whole process is strictly regulated to protect participants and patients.AQA
Regulation of internal conditions: Keeping the internal conditions of a cell or organism within narrow limits to maintain optimum conditions for function.AQA
Relationship between bonding, structure and properties: The giant ionic lattice explains why ionic compounds have high melting and boiling points, conduct electricity when molten or dissolved, and often dissolve in…AQA
Relationship between current and field strength: Increasing the current strengthens the field, shown by a denser pattern.AQA
Relationship between current and resistance: Because the potential difference across each branch is the same as the power supply, the total current leaving the supply increases, so according to R = V / I…AQA
Relationship between energy change and wave frequency: The frequency of the emitted wave is related to the size of the energy change in the atom or nucleus.AQA
Relationship between force, mass and acceleration: For a given resultant force, a larger inertial mass produces a smaller acceleration, so velocity changes more slowly.AQA
Relationship between particle spacing and bulk properties: The spaces between particles and how they move explain bulk properties such as shape, volume and compressibility.AQA
Relationship between potential difference, current and power: Power equals potential difference multiplied by current, with power in watts, potential difference in volts and current in amperes.AQA
Relationship between speed, frequency and wavelength: Wave speed v is measured in metres per second, frequency f in hertz and wavelength λ in metres, and rearranged forms are f = v ÷ λ and λ = v ÷ f.AQA
Relationship between structure and properties: Solid ionic compounds do not conduct because their ions are held in fixed positions in the giant lattice and cannot move through the structure.AQA
Relative amount of products: The proportion of products at the new equilibrium, which increases when an endothermic forward reaction is heated and falls on cooling.AQA
Relative area: Judged by comparing estimated two-dimensional extents, for example using length × width for a rectangular structure.AQA
Relative atomic mass: A weighted mean of isotope masses that is not usually a whole number and is not the same as mass number.AQA
Relative atomic mass trend: Going down Group 0 it increases because atoms have more protons and neutrons.AQA
Relative charge: Each proton has a relative charge of 1⁺ and each electron has a relative charge of 1⁻.AQA
Relative energy transferred: Aerobic respiration transfers a relatively larger amount of energy per glucose molecule than anaerobic respiration.AQA
Relative formula mass: A value taken from the periodic table and summed correctly for compounds, used when converting a given mass to moles using n = m ÷ Mᵣ.AQA
Relative formula mass (Mr): A value calculated from the correct formula, used to convert between mass and moles.AQA
Relative mass: A proton and a neutron each have a relative mass of 1, whereas an electron has a relative mass of about 1/1836.AQA
Relative size: Judged by comparing estimated dimensions, such as length or diameter, of sub-cellular structures.AQA
Relay neurone: Located inside the spinal cord or brain and connects the sensory neurone to the motor neurone.AQA
Reliability: Improved when checking by peer review identifies errors, bias or unsupported conclusions in the findings.AQA
Reliability and output in electricity generation: Electricity generation needs resources that can drive turbines or photovoltaic cells, chosen for reliability, output and emissions.AQA
Reliability and repeatability of data: Repeating a measurement and calculating a mean reduces the effect of random variation on the reported value.AQA
Reliability, bias and data processing: Repeating samples to improve reliability, sampling randomly or systematically to reduce bias, and calculating a mean count or plotting a graph.AQA
Reliable: Describes results that are repeatable, so that a mean of repeats gives a more reliable value than a single measurement.AQA
Relights: The expected observation in oxygen, where the glowing splint relights because oxygen supports combustion.AQA
Religious and moral views: Some people object to embryonic sources because of beliefs that life begins at conception, so embryo research is wrong.AQA
remaining fraction: The amount left after n half-lives, found using (1/2)ⁿ because the process is repeated halving.AQA
Renewable: A correct term for an energy source used instead of coal or gas, as when generating electricity from solar or wind.AQA
Renewable energy resource: One that is being (or can be) replenished as it is used.AQA
Renewable fuels: Fuels such as biodiesel and bioethanol produced from crops that can be regrown.AQA
Renewable resource: A resource that is replaced at the same rate as it is used, so it will not run out.AQA
Renewable resources: Resources such as bio-fuel, wind, hydro-electricity, geothermal, tidal, solar and wave energy that are replenished naturally and will not run out.AQA
Repeat measurements and data quality: Repeat readings are taken, for example by adjusting a variable resistor or changing the number of cells, to check consistency and reduce the effect of random…AQA
Repeat readings: Taking measurements more than once and calculating a mean to reduce the effect of random error.AQA
Repeated breeding over generations: Breeding the chosen parents together, then breeding the offspring that show the desired characteristic together, continuing over many generations.AQA
repeating unit: The smallest section of the polymer chain that repeats many times.AQA
Repeating units and chain length: The units inside the brackets are joined many times, and the size of n affects the length of the polymer chain.AQA
Repeating units in polymers: Shown by drawing the two backbone atoms with a line between them and extending bonds through brackets with n outside.AQA
Repeats: Readings taken at each distance, with a mean calculated and anomalous results identified and excluded where appropriate.AQA
Replenishment: Whether the resource is being replaced while it is consumed, which is the criterion used to distinguish the two types.AQA
Representations of ionic compounds: A dot-and-cross diagram represents electron transfer and outer-shell electron configurations, while a ball-and-stick or space-filling model represents the…AQA
Representative sampling: Studying a subset of a population selected to represent the whole population, so that something about the whole population can be estimated.AQA
Representing bonds with lines in small molecules: Drawing the central atom, attaching each bonded atom with one line per shared pair, and adding any unbonded outer-shell electrons as dots if required.AQA
Representing data on a common scale: One common scale, such as a single axis or a consistent bar-chart scale, lets before-and-after values be compared directly.AQA
Representing energy changes graphically: A reaction profile is a graph of energy against reaction progress, with energy on the y-axis and progress on the x-axis.AQA
Representing ions with dots, crosses and charges: Each ion is drawn with a complete outer shell and its charge shown, commonly in square brackets, labelled with the compound name or formula and the ion charges.AQA
Representing molecules: A model or diagram uses spheres or letters for atoms and lines or sticks for covalent bonds in the molecule.AQA
Representing reactions with word and symbol equations: The reaction can be represented by a word equation and by a symbol equation, balancing atoms and including state symbols where required.AQA
Representing structures: Diagrams such as dot and cross, ball and stick or space-filling models, where charged particles rather than neutral atoms or molecules show an ionic compound.AQA
Reproductive isolation: Occurs when populations are separated so that they no longer interbreed and gene flow between them stops.AQA
Reproductive organs: The organs where meiosis occurs, such as the testes and ovaries in humans, or the anthers and ovaries in flowering plants.AQA
Repulsion between like charges: Because alpha particles are positive, the repulsion that deflected them shows the nucleus is positively charged, as a spread-out positive sphere could not…AQA
Required practical skills: Investigating how changes in concentration affect the rates of reactions by measuring the volume of a gas produced and by a change in colour or turbidity.AQA
residue: The excess solid left on the filter paper after the mixture is filtered.AQA
Resistance: Measured in ohms (Ω), it opposes the flow of electric current and is a key factor in determining the rate at which energy is transferred.AQA
Resistance and current: Components in parallel may have different resistances and therefore different currents, while their potential differences remain equal.AQA
Resistance and energy transfer: A larger current transfers more energy, raising the filament temperature, which increases the resistance of a filament lamp.AQA
Resistance and light intensity: The resistance of an LDR decreases as light intensity increases and increases as light intensity decreases.AQA
Resistance and temperature: In a metal, higher temperature makes the ions vibrate more strongly, which increases the number of collisions with the moving electrons and so increases…AQA
Resistance as the ratio of potential difference to current: Calculated using R = V ÷ I with the measured current and potential difference, giving resistance in ohms.AQA
Resistance as the sum of series resistances: The total resistance is the sum of the individual resistances.AQA
Resistant strain: Bacteria that are not affected by an antibiotic, produced by mutation, which survive and reproduce when the antibiotic is used.AQA
resolution: The ability to distinguish two close points, which is limited by the wavelength of the radiation used.AQA
Resolving power: The smallest distance at which two points can still be seen as separate.AQA
Resource evaluation: Considering a resource's availability, cost, reliability and environmental effects for each specific use.AQA
Respiration: A series of enzyme-controlled reactions that transfers chemical energy from glucose into a usable form in cells.AQA
Respiration as energy release: Some glucose is used in respiration to release energy for cell processes.AQA
Response to internal and external change: Operating in response to internal changes, such as blood glucose concentration, and external changes, such as air temperature.AQA
Resultant: What vectors give when combined, which depends on their directions, so two 5 N forces can give from 0 N to 10 N.AQA
Resultant force: At steady speed it is zero, because the driving force and the total resistive forces are equal in size and opposite in direction.AQA
Resultant force and acceleration: A resultant force acting on an object causes acceleration in the direction of that force, so force is the cause and acceleration the effect.AQA
Resultant force and deceleration: The resultant force is found by combining all forces acting along the line of motion, and negative acceleration is deceleration when the resultant force…AQA
Resultant force and motion: Zero resultant gives uniform velocity; non-zero resultant gives changing speed, direction or both.AQA
Reuse: Using an item again for the same or a new purpose, such as refilling a water bottle or passing on clothes.AQA
Reuse and disposal of materials: Reusing a plastic bag many times can lower its impact per use, while paper is biodegradable and recyclable but may produce methane if buried in landfill.AQA
Reuse versus recycling: Reuse keeps the item for the same purpose without changing it, while recycling reprocesses the material so it can be used again, often for a different product.AQA
Reverse bias: The connection in which the diode blocks current because its resistance is very high, so the current is negligible.AQA
Reverse osmosis: Forces salty water at high pressure through a partially permeable membrane that retains dissolved ions while water molecules pass through.AQA
Reverse reaction: The change that converts products back into reactants.AQA
Reversibility: Reversing a change of state restores the original properties, such as melting point, boiling point, density and appearance.AQA
Reversibility and the ⇌ symbol: A reversible reaction can proceed in both the forward and reverse directions, shown by the ⇌ symbol, meaning the forward and reverse reactions occur…AQA
Reversibility of chemical reactions: A reversible reaction can proceed in both directions, and its energy change depends on direction.AQA
Reversible reaction: A reaction in which the products can react to produce the original reactants.AQA
Reversible reactions and dynamic equilibrium: The system adjusts until the rates of the forward and reverse reactions are equal again, establishing a new equilibrium position.AQA
Reversible reactions and industrial processes: A reaction in which the forward and reverse reactions occur, such as the Haber process for ammonia, where equilibrium is reached when the rate of ammonia…AQA
Rf value: The distance moved relative to the solvent front, which can be compared with known values to help identify a substance.AQA
Ribosomes: Small structures found in the cytoplasm of animal, plant and bacterial cells where protein synthesis takes place.AQA
right atrium: The location of the group of cells that act as a pacemaker controlling the natural resting heart rate.AQA
Right ventricle: The chamber that receives deoxygenated blood from the right atrium and contracts to pump it to the lungs, where gas exchange takes place.AQA
Right-hand grip rule: Point the thumb of your right hand along the conventional current, and your curled fingers show the field direction.AQA
ripple tank: A practical arrangement in which wavelength is measured across several wavelengths and divided by the number of waves.AQA
Rising sea levels: A potential effect occurring as land ice melts and ocean water expands when warmed, threatening low-lying coasts and islands.AQA
Risk: Probability, not certainty: exposure raises the chance of cancer but does not guarantee it, and generally increases with dose and duration of exposure.AQA
Risk and benefit: Possible treatments must be weighed against risks such as transfer of viral infection when deciding whether to use stem cell treatment.AQA
Risk and probability in health: Having several factors increases the probability of disease without making it certain.AQA
Risk assessment and monitoring: Using a radiation monitor and following a risk assessment to confirm safe dose rates and reduce the dose received by people.AQA
Risk factor: Anything that raises the chance of developing a disease, but it is not a guarantee.AQA
Risk factors: Things that increase the probability of disease rather than causing it directly, such as obesity raising the chance of developing Type 2 diabetes.AQA
Risk factors and disease interaction: One disease can increase the risk or severity of another, for example diabetes can lead to poor wound healing and increased susceptibility to infection.AQA
Risk factors for mental illness: Long-term pain, disability, loss of independence, social isolation and uncertainty about the future, which place sustained stress on a person.AQA
Risk of side effects from antiviral treatment: A drug that blocks viral protein synthesis might also block human protein synthesis, causing side effects, and even when virus-specific enzymes or structures…AQA
Role of Alexander Fleming: He noticed a mould contaminating a culture plate of bacteria had killed the bacteria around it, identified the mould as Penicillium and named the substance…AQA
Role of chemistry in agriculture: Chemistry improves agricultural processes, for example the Haber process making ammonia for fertilisers to increase food production.AQA
Role of chemistry in industry: Chemistry improves industrial processes, for example using catalysts to increase rate and reduce energy demand.AQA
Role of cryolite in reducing energy costs: Cryolite is added to lower the melting point of the electrolyte, reducing the energy required and making the process more economical.AQA
Role of decomposers in nutrient return: Bacteria and fungi break down dead organisms and waste, releasing mineral ions and carbon compounds back into the environment so that producers can reuse them.AQA
Role of evidence in accepting scientific models: The theoretical calculations of Bohr agreed with experimental observations, so his adapted model was accepted.AQA
Role of experimental evidence: New experimental evidence can support, modify or contradict an existing model.AQA
Role of gaps and trends in models: He used the gaps and the trends in his table to predict the properties of undiscovered elements.AQA
Role of hydrochloric acid in defence: Gastric juice contains hydrochloric acid, which gives the stomach a low pH and kills many ingested microorganisms.AQA
Role of the immune system in clearing infection: When only symptom-relieving medicines are used, the immune system still has to destroy the pathogen.AQA
Role of vectors in gene transfer: A vector acts as a carrier to transfer the isolated gene into a host cell.AQA
Root hair cells: Root epidermal cells that may grow into these, increasing surface area for water and mineral ion uptake.AQA
Root-mean-square value: The stated 230 V is an alternating potential difference, and this value is the root-mean-square value, so the peak is higher, about 325 V.AQA
Ruler drop test: A partner holds a ruler vertically with the zero mark level with your open thumb and finger, then releases it without warning and you catch it as quickly as…AQA

S

Safe domestic electricity supply: A step-down transformer decreases the potential difference to a much lower, safe domestic value before electricity reaches homes.AQA
Safety: The drug does not cause unacceptable harm, which testing and trials check before it is used.AQA
Salicin: A compound contained in willow bark that the body converts into a pain-relieving substance.AQA
Salt formation and naming from the parent acid: The salt formed depends on the acid used: hydrochloric acid gives chloride salts, sulfuric acid gives sulfate salts, and nitric acid gives nitrate salts.AQA
Salt formula: Deduced by balancing the charge on the positive ion from the base, alkali or carbonate with the charge on the negative ion from the acid.AQA
Salt naming from acids and bases: Salt names combine the metal or ammonium ion with the acid anion, for example sodium nitrate from sodium hydroxide and nitric acid.AQA
Salt nomenclature: Naming the salt requires identifying both the positive ion from the base, alkali or carbonate and the negative ion from the acid.AQA
Salt production: A salt and water are formed when an acid reacts with an alkali or base, and a salt, water and carbon dioxide are formed with a metal carbonate.AQA
Salt water: Water whose dissolved ions must be removed by distillation or reverse osmosis, both energy-intensive.AQA
Sample size and reliability: A sample must be large enough, because larger samples generally give more reliable estimates of risk.AQA
Sampling and estimation: Counting a common species in quadrats rather than every organism, then scaling the mean count up to the whole habitat area.AQA
Satellite communications: Sending signals to and from satellites, because microwaves can pass easily through the Earth's atmosphere and are not strongly absorbed by it.AQA
Saturated: Every carbon forms four single covalent bonds, so no more atoms can add without substitution.AQA
Saturated fatty acid: A fatty acid with only single carbon-carbon bonds.AQA
Saturated hydrocarbons: Molecules in which every carbon is joined by single bonds only, so the molecule is saturated.AQA
Scalar: A quantity that has magnitude only, without direction.AQA
Scalar quantities: Quantities for which direction is not specified, as with speed, which gives magnitude only.AQA
Scalar quantity: A quantity for which direction is not needed, as when distance is read from a description or a distance-time graph.AQA
Scale: The size and reach of change, which is global and long-term and affects atmosphere, oceans, ice, land and living things.AQA
Scale and axis labelling: A sensible scale fills the grid, and each axis is labelled with quantity and unit, for example 'change in mass / g'.AQA
Scale and size of atomic structure: The radius of a nucleus is less than 1/10 000 of the radius of an atom, so the atom is mostly empty space.AQA
Scale and size of atoms: Atoms are very small, having a radius of about 0.1 nm, which is 1 x 10⁻¹⁰ m.AQA
Scale and size of cells: Cells vary greatly in size, so biologists use a common unit, the micrometre, to compare them.AQA
Scale and size of the nucleus: The radius of a nucleus is less than 1/10 000 of that of the atom, roughly 1 x 10⁻¹⁴ m.AQA
Scale bar: A printed bar on a microscope image whose measured length divided by its stated length gives the magnification.AQA
Scale diagram: A vector diagram of the journey in which the straight-line length and the angle of the displacement are measured.AQA
Scale interpretation: Determining what one square represents by multiplying the time interval per square by the velocity interval per square.AQA
Scale selection: Choosing a consistent scale for each axis using equal intervals such as 1, 2, 5 or 10 units per major grid square, so the data fills most of the grid.AQA
Scale selection and grid use: Choose a scale so the data spans most of the grid, and label each axis with quantity and unit.AQA
Scaling amounts in chemical reactions: The same ratio applies whatever the actual amounts, so amounts can be scaled up or down in direct proportion.AQA
Science and society: The idea that science can identify environmental issues arising from the use of energy resources but does not always have the power to deal with them.AQA
Scientific and technical limits: Limits that include the intermittent output of wind and solar power, so storage or backup supply is needed.AQA
Scientific explanation: Linking a pattern to scientific ideas such as evaporation or diffusion of water vapour.AQA
Scientific method: Science is self-correcting: a model survives only while evidence fits, and new data can overturn an accepted idea.AQA
scientific model: A simplified picture used to explain observations and predict behaviour, not a fixed truth.AQA
Scientific models and their revision: Evolutionary trees are revised over time rather than being fixed because new evidence may emerge.AQA
Scientific uncertainty and hypotheses: Because the evidence is incomplete, scientists cannot be certain how life began and explanations remain hypotheses supported by indirect evidence.AQA
Screening: Passes the water through bars or meshes that trap large solids, protecting pumps, valves and downstream equipment from blockage and damage.AQA
Sealed sources and containment: Storing sources in labelled lead-lined containers and containing the source so it cannot spread.AQA
Secondary response: A rapid response on re-exposure in which the correct antibodies are produced in large amounts before symptoms develop, preventing infection.AQA
Secondary sex characteristics: Physical features that develop during puberty but are not directly involved in reproduction, unlike primary sex characteristics.AQA
Secondary sexual characteristics: Features developed during puberty that testosterone also controls.AQA
Secondary tumours: Tumours formed where malignant cells settle in other parts of the body after spreading in the blood.AQA
Sedimentary rock formation: Layers of mud, sand or silt bury dead organisms and harden over long periods.AQA
Sedimentary rocks: Rocks such as limestone that contain carbon as calcium carbonate, CaCO₃, formed when carbonate compounds precipitated or were incorporated into sediments.AQA
Sedimentation: A physical separation step in which suspended solid particles denser than water settle under gravity in large tanks where the water moves slowly.AQA
Selecting relevant data from a scenario: Identifying the start and end of the acceleration phase so the correct time interval is chosen from the question rather than a total journey time.AQA
Selection from a mixed population: Choosing parents with the desired characteristic from a mixed population in which individuals vary.AQA
Selective and abbreviated LCA: A study that covers only some stages, materials or impact categories rather than a full life cycle assessment.AQA
Selectivity of antiviral drugs: Antiviral drugs must be selective for virus-specific features, but many antiviral targets are similar to human cell processes, so damage to body tissues is a…AQA
Sensing and control: The changing output voltage can drive a switching circuit, such as a transistor, to turn a lamp on when it gets dark.AQA
Sensing and control circuits: An LDR is useful as a light sensor in circuits such as automatic street lights, burglar alarms and light meters.AQA
Sensor components in circuits: A thermistor's resistance decreases as temperature increases, while an LDR's resistance decreases as light intensity increases.AQA
Sensory neurone: Carries impulses from receptors to the central nervous system and has a cell body positioned alongside the spinal cord.AQA
Separation and identification: Comparing R_f values with known values or reference spots identifies substances, and counting spots judges purity.AQA
Separation and processing of scrap: The amount of separation required depends on the material being recycled and on the properties required of the final product.AQA
Separation of compounds: Compounds can only be separated into elements by chemical reactions, not by physical separation techniques.AQA
Separation of mixtures: Paper chromatography separates mixtures because each component distributes differently between two phases, so the components separate into distinct spots at…AQA
Separation techniques: Physical processes such as filtration, crystallisation, simple distillation, fractional distillation and chromatography separate mixtures without chemical…AQA
Separation techniques based on physical differences: Components of a mixture can be separated by physical methods such as filtration or distillation because no chemical bonds are broken.AQA
Separation versus purification: Choosing a technique to separate a mixture, and where purification is also asked for, mentioning how purity could be checked, such as by melting point.AQA
Series: The same current flows through each resistor and the potential differences add to give the supply potential difference.AQA
Series and parallel circuit behaviour: In a series circuit the current is the same at every point, while in parallel branches the current splits and recombines.AQA
Series and parallel connections: In a series circuit the same current passes through every component in a single loop, while in a parallel circuit current splits between branches that rejoin…AQA
Series and parallel connections of meters: The ammeter must be in series and the voltmeter in parallel, not the reverse, for valid measurements.AQA
series circuit: A dc circuit with one continuous path, so the same current flows through every component and the supply potential difference is shared between them.AQA
Series circuit rules: In a series circuit there is only one path for charge to flow, so there is the same current through each component.AQA
Series circuits: A single closed loop with only one path, so charge cannot leave or accumulate.AQA
Series connection: Components sit one after another along a single loop, so the same current passes through each in turn.AQA
Series resistance addition: For resistors in series, the equivalent resistance is the sum of the individual resistances: R_eq = R₁ + R₂ + R₃.AQA
Sewage sludge: The settled solid organic material that sinks to the bottom of the tank and is drawn off from there.AQA
Sex chromosomes: The pair of chromosomes that in males are not the same: one is a large X chromosome and the other is a much smaller Y chromosome, written XY.AQA
sexual contact: One route by which HIV is spread, along with exchange of body fluids such as blood.AQA
Sexual reproduction and inheritance: In sexual reproduction there is mixing of genetic information which leads to variety in the offspring.AQA
Sexually transmitted infections: Infections that spermicides do not protect against, so a condom is still required for that purpose.AQA
Shared characteristics: Features that members of a group have in common, so that members of a genus share more features than members of a class.AQA
Shared electron pairs: A pair of electrons in which each atom contributes at least one electron, and the pair is attracted to the nuclei of both bonded atoms.AQA
Sharing of potential difference between series components: The total potential difference of the supply is shared between the components, so the p.d.s across the components add up to the supply p.d.AQA
Sharp versus range melting and boiling: A pure substance melts and boils at a specific temperature, while an impure sample melts and boils over a range of temperatures rather than sharply.AQA
Shell diagrams: A representation of electronic structure drawn as a diagram with a nucleus and shells carrying dots or crosses.AQA
Shielding: Absorbing material such as lead reduces the dose received by absorbing X-rays.AQA
Shivering: Involves rapid muscle contraction, which requires more energy and therefore raises the rate of aerobic respiration.AQA
Short diffusion path: A thin membrane means particles have a shorter distance to travel between two regions, so they cross it quickly.AQA
Short wavelength radiation: Radiation from the Sun, including visible light and ultraviolet, which passes through the atmosphere and is absorbed by the Earth's surface.AQA
shorthand: A representation that avoids drawing thousands of atoms and lets chemists see the repeating pattern clearly.AQA
SI base unit: The unit in which time is measured is the second (s), which is the SI base unit.AQA
SI units: Consistent units that must be checked before calculating energy changes.AQA
SI units and conversion: Units must be consistent, with distance in metres, time in seconds and speed in metres per second, converting first before substituting.AQA
SI units and unit conversion: Converting units first, such as kJ to J, then substituting, then calculating, and giving the unit J with your answer.AQA
Sign conventions: Applied consistently so that a negative value indicates motion in the opposite direction to the positive direction.AQA
Sign conventions for motion in opposite directions: Areas below the time axis represent negative displacement, so subtract them when finding overall displacement.AQA
Sign conventions in calculations: A rise in temperature gives a positive value and a fall gives a negative value, so heating gives a positive ∆θ while cooling releases energy and gives a…AQA
Significant figures: The count of meaningful digits in a value, starting from the first non-zero digit.AQA
Significant figures and units: Estimated answers are rounded to one or two significant figures and given correct units such as m/s, m/s² and N.AQA
Simple distillation: Evaporating a solvent by heating, condensing the vapour, and collecting the distillate while the dissolved solute remains.AQA
Simple molecular substances: Substances such as fullerenes, which have weak forces between separate molecules and so relatively low melting points compared with giant covalent carbon…AQA
Simple ratio: Compares the expected numbers of different outcomes, such as 3:1 for a monohybrid cross between two heterozygotes or 1:1 for sex inheritance.AQA
Simple sugars: Small, soluble molecules that can be absorbed across the wall of the small intestine.AQA
Simple whole number ratio: What the numbers of moles are converted to, after dividing each by the smallest number of moles, to give the balancing numbers.AQA
Simplest whole-number ratios: The ion ratio reduced to its simplest whole-number form by dividing all parts by their highest common factor.AQA
Single covalent bond: One shared pair of electrons, shown as a line in a displayed formula.AQA
Single, double and triple covalent bonds: Bonds formed from one shared pair, two shared pairs or three shared pairs, as in hydrogen, oxygen and nitrogen respectively.AQA
Sink: Parts of the plant that use or store sugars, such as growing shoots, roots, fruits and storage organs.AQA
Sister chromatids: Two identical copies of each chromosome, held together at a centromere.AQA
Slope of the tangent: Used as a measure of the rate of reaction at that specific time.AQA
Sloping section: A part of the graph showing a temperature change in a single state, where the gradient depends on the mass, specific heat capacity and rate of energy transfer.AQA
Small intestine: The site where absorption happens mainly, having adaptations such as a large surface area, a thin wall and a rich blood supply.AQA
Smoke: Tiny solid particles and unburnt carbon from incomplete combustion of fuels, which can cause breathing problems, reduce visibility and deposit as soot.AQA
Social issues: These include reducing suffering, supporting families, the availability of screening and the effect on people already living with the disorder.AQA
Soft iron core: A core that increases field strength because the iron becomes magnetised and adds to the field.AQA
Soil moisture meter: Equipment used to measure moisture, alongside drying a soil sample to constant mass and calculating percentage water loss.AQA
Soil pH: A measure of acidity or alkalinity, usually on a scale from 0 to 14, with most plants growing best between pH 6 and pH 7.AQA
Solenoid: A wire shaped into a coil, which increases the strength of the magnetic field created by a current through the wire.AQA
Solenoid as an electromagnet: The ends behave as north and south poles, with field lines outside running from the north end to the south end.AQA
Solid-sphere model: The earliest scientific model of the atom, in which atoms were imagined as tiny spheres that could not be divided.AQA
Solubility and attraction: Each substance has its own balance of solubility and attraction, so a component very soluble in the solvent and only weakly attracted to the paper travels far…AQA
Solubility limit: The point the dissolved salt exceeds as solvent is removed or the solution is cooled, causing it to precipitate out of solution.AQA
Solubility of carbon dioxide in water: Carbon dioxide from the atmosphere dissolved in the ocean water.AQA
Solvents: Substances that dissolve other substances, for example in paints and dry cleaning.AQA
Soot: Solid carbon particles produced by the incomplete combustion of fuels when the oxygen supply is limited.AQA
Sound: A wave travelling through a medium, so its speed depends on the medium and on temperature rather than being a universal constant.AQA
Sound as a longitudinal wave: Sound travelling through air is longitudinal, with air particles vibrating back and forth along the same line as the sound travels.AQA
Source: The leaves, where sugars are made by photosynthesis and loaded into the phloem.AQA
Source selection: Choosing a source whose radiation has the property the task needs, such as beta for thickness monitoring, alpha for a smoke detector and gamma for…AQA
Sources of potential difference: A source such as a cell or battery is needed to make charge flow, and it does work on the charge, transferring energy to it and causing it to move.AQA
Specialisation: The process by which a cell develops specific structures or features suited to a particular function.AQA
Specialised: Describes cells in multicellular organisms that become adapted for particular jobs.AQA
Specialised cell: A cell with structures and organelles suited to its job, such as many mitochondria in muscle cells or a long axon in nerve cells.AQA
Specialised plant cells: Cells that have elongated and become specialised to form new tissues such as xylem, phloem, epidermis and palisade mesophyll.AQA
Speciation and reproductive isolation: Populations so different that they can no longer interbreed to produce fertile offspring are different species, so natural selection may form a new species.AQA
Species: A group of organisms that can interbreed to produce fertile offspring, so extinction means no breeding population remains.AQA
Species distribution: Which organisms can survive and where they are found in a water body, affected by oxygen level because different species tolerate different concentrations.AQA
Specific heat capacity: The value found by measuring how much energy is transferred to a material and the resulting temperature rise, then using ΔE = mcΔθ.AQA
Specific immune response: Antibody production is a specific, adaptive response, unlike phagocytosis, which is non-specific.AQA
Specific latent heat: The energy needed to change the state of one kilogram of a substance without changing its temperature, measured in joules per kilogram, J/kg.AQA
Specific latent heat of fusion: The value used for melting and freezing, giving the energy needed to change the state of one kilogram with no temperature change.AQA
Specific latent heat of vaporisation: The value used for boiling and condensing, giving the energy needed to change the state of one kilogram with no temperature change.AQA
Specificity of antibodies: Antibodies for one antigen will not bind another, so the response is specific.AQA
Spectator ions: Ions that remain unchanged in a chemical equation, such as the chloride ions in a metal-acid reaction.AQA
Speed: The distance travelled per unit time, a scalar quantity so direction is not required, measured in metres per second (m/s).AQA
Speed = distance ÷ time: The calculation whose answer is a scalar with units such as m/s, and no direction needs to be stated.AQA
speed = frequency × wavelength: The equation used to calculate the speed of the ripples, with the unit included, for example m/s.AQA
Speed equation: Speed = distance ÷ time can be used with 330 m/s to calculate a distance or time, for example the distance to a lightning strike.AQA
Speed of light and speed of sound: Light travels much faster than sound, so seeing the blocks gives a near-instant start signal for the stopwatch.AQA
Speed of sound in air: A typical value for the speed of sound in air is 330 m/s, which is typical rather than exact.AQA
Speed, distance and time relationships: Using speed = distance ÷ time, rearranged as time = distance ÷ speed, to estimate a time or distance.AQA
Sperm cell: Has a tail for swimming, many mitochondria to release energy for movement, and an acrosome containing enzymes that digest the egg cell membrane.AQA
Sperm production: The process stimulated by testosterone as its primary function.AQA
Spermicidal agents: Chemical contraceptives placed in the vagina before intercourse that kill sperm or disable them by reducing their motility.AQA
sphere model: A historical stage, not the modern view, in which atoms were treated as the smallest possible particles with no internal structure.AQA
Spinal cord: A coordination centre that carries information and coordinates rapid reflex actions.AQA
Spindle fibres: Structures that attach to the chromosomes and pull the sister chromatids apart.AQA
Spongy mesophyll: Tissue below the palisade layer in a leaf whose rounded cells are loosely arranged, leaving many large air spaces between them.AQA
Spread in the blood: Malignant cells enter the blood and travel to different parts of the body.AQA
Spring constant: A measure of stiffness in newtons per metre (N/m), where a large value means a stiff spring needing a large force for a small extension.AQA
Spring constant and stiffness: The spring constant k measures stiffness in newtons per metre.AQA
spring constant, k: A measure of the stiffness of a spring or elastic object, measured in newtons per metre, N/m.AQA
Spring-balance: Also called a newtonmeter, it measures weight directly by the extension of a calibrated spring.AQA
Square brackets: Used around each ion in the diagram, with the charge placed outside the bracket.AQA
Stability: The ability of an ecosystem to resist or recover from change, such as disease, drought or the removal of one species.AQA
Stability of internal conditions: Thyroxine concentration in the blood is kept within a narrow range, preventing it drifting too high or too low.AQA
Stable community: One where all the species and environmental factors are in balance so that population sizes remain fairly constant.AQA
Stable outer electron arrangement: What atoms react to achieve, typically eight electrons, or two for the first shell.AQA
Standard circuit symbols: Recognised symbols used for each component, such as a cell, lamp, resistor, ammeter and voltmeter, joined by straight lines representing connecting wires.AQA
Standard form: A way of expressing numbers that, with correct symbols and units, is used when substituting values into an equation.AQA
Standard form and powers of ten: A size is written as A × 10ⁿ, where A is between 1 and 10, so the powers n can be compared.AQA
Standard of living and consumption: An increase in the standard of living means that increasingly more resources are used and more waste is produced.AQA
Standard symbols: Agreed symbols used in circuit diagrams so any physicist or engineer can read them.AQA
Starch: The storage polysaccharide in plants, found in leaves, roots, tubers and seeds, which is compact, insoluble and easily hydrolysed back to glucose.AQA
State symbols: Letters in brackets added to every formula in equations for the reactions you study, showing whether a substance is (s), (l), (g) or (aq).AQA
States of matter: Small-molecule substances are usually gases or liquids at room temperature, and some are solids with a low melting point.AQA
Statins: Widely used to reduce blood cholesterol levels, which slows down the rate of fatty material deposit.AQA
Stationary: Shown on a distance–time graph by a horizontal line, meaning the object is not moving.AQA
Stationary object: An object whose velocity is zero, so it has zero momentum.AQA
Stationary objects: When the resultant force is zero, an object that is stationary stays stationary.AQA
Stationary phase: The fixed phase, for example the water held in paper or a solid coating on a plate.AQA
stationary wave: Produced on a string by a vibration generator attached to it, with nodes and antinodes allowing wavelength to be measured.AQA
Statistical predictability of large samples: A large sample shows a steady pattern because many nuclei are present, so the proportion decaying per unit time is stable.AQA
Steady speed and constant velocity: A vehicle travelling at steady speed has constant velocity, so its acceleration is zero.AQA
Steam cracking: Mixes the hydrocarbon feedstock with steam and heats it strongly, without a catalyst.AQA
Steeper tangent: Indicates a faster rate at that time, while a shallower tangent indicates a slower rate.AQA
Stem cell: An undifferentiated cell of an organism capable of giving rise to many more cells of the same type, and from which certain other cells can arise from…AQA
Stem cell biology: Unspecialised cells that can divide and differentiate into other cell types, making them useful in medicine.AQA
Stem cell treatment: A possible future or experimental therapy that aims to replace lost cells, but is not yet a routine cure.AQA
Stem cells: A few animal cells, such as some in bone marrow, remain unspecialised and can still divide and differentiate to replace worn-out cells.AQA
Stents: Used to keep the coronary arteries open.AQA
Step-down transformer: A transformer near towns that lowers the potential difference to safer domestic values such as 230 V.AQA
Step-down transformers: These reduce potential difference to safe domestic levels for consumers.AQA
Step-up transformer: A transformer near a power station that raises the potential difference to very high values.AQA
Step-up transformers: These increase the potential difference from the power station to the transmission cables.AQA
Stepped line: A stepped dividing line running below boron and down through silicon, arsenic and tellurium that roughly divides metals from non-metals.AQA
sterilisation: A permanent, surgical method of contraception that prevents sperm and egg meeting, intended to be irreversible and giving no protection against sexually…AQA
Sterilising: Killing or inactivating microorganisms so the water is safe to drink, carried out after screening and filtration.AQA
Sterilising agents: Chlorine, ozone or ultraviolet light are used for potable water to kill or inactivate microorganisms.AQA
STI protection: Only barrier methods such as condoms also reduce the risk of sexually transmitted infections, whereas hormonal methods do not protect against them.AQA
Stimulus: A detectable change in the internal or external environment, such as a change in temperature, light intensity or pressure.AQA
Stimulus and response: A stimulus is a change detected by receptors, and a response is what effectors carry out after the central nervous system coordinates it.AQA
Stoichiometric amounts: The amounts that react completely, which the equation alone gives, without rate or yield.AQA
Stoichiometric coefficients: The large numbers in front of formulae that tell you the ratio in which particles react and are produced.AQA
stoichiometry: The balancing numbers in the chemical equation, by which the bond energy of a molecule must be multiplied.AQA
Stoichiometry from balanced equations: The stoichiometric coefficients of a balanced symbol equation are used to find the moles of the unknown substance.AQA
Stomata and gas exchange: Tiny pores, each surrounded by two guard cells, that open to allow carbon dioxide in for photosynthesis and close to reduce water loss.AQA
Stopping distance: The sum of the distance the vehicle travels during the driver's reaction time and the distance it travels under the braking force.AQA
straight line: A straight line means constant speed, while a horizontal line means the object is stationary.AQA
Strength of correlation: Described as strong or weak according to how closely the points lie to a single trend.AQA
Strengths and limitations of models: Every model has limits, such as particles not being solid spheres and rays ignoring diffraction, so a model is used to explain data and then one way it is…AQA
Stress and life situations: Long-term stress is linked to raised blood pressure and poorer mental health, and life situations such as poor housing, low income, pollution or limited…AQA
strong: Describes an acid that ionises completely in aqueous solution.AQA
Strong acids: Acids that ionise completely in water, while weak acids ionise partially, but both produce H⁺ ions.AQA
Strong covalent bonds: Bonds that link all of the atoms in these structures to other atoms and must be overcome to melt or boil the substances.AQA
Strong intramolecular covalent bonds: The atoms within each molecule are held together strongly by covalent bonds.AQA
Structural adaptation: A body part, such as thick fur or spines, that helps an organism survive in the conditions where it normally lives.AQA
Structural formulae: Show the arrangement of atoms without drawing every bond.AQA
Structural support and osmosis: The wall strengthens the cell and prevents it from bursting when it takes in water by osmosis.AQA
Structure and bonding: Ionic compounds form giant lattices of alternating positive and negative ions held by strong electrostatic attraction, and in the solid state these ions…AQA
Structure and formula relationships: Whichever representation is used, the molecule is unchanged, with the same atoms joined in the same order.AQA
Structure and function: Roots absorb water and mineral ions from the soil, the stem contains vascular tissue and holds the leaves up, and leaves absorb light and carbon dioxide and…AQA
Structure and function of root hair cells: A long, thin extension increases surface area for absorption, and many mitochondria release the energy needed for active transport.AQA
Structure and function relationships: Each structural feature of a cell is linked to the function it enables, so the shape and internal structures suit a particular job.AQA
Structure and properties: To explain a property, the structural feature responsible is named first and then linked to the property.AQA
Structure and properties of alloys: Atoms of different sizes distort the regular layers so they cannot slide as easily, making the alloy harder.AQA
Structure and properties of diamond: A rigid three-dimensional network of strong covalent bonds makes diamond very hard and gives it a very high melting point.AQA
Structure and properties of ionic compounds: The regular arrangement of ions and the strong forces between them explain the high melting point of sodium chloride.AQA
Structure of the atom: The nuclear model has a tiny, dense, positively charged nucleus at the centre, surrounded by mostly empty space in which electrons orbit.AQA
Structure related to function: The key idea that features such as many chloroplasts and a position near the upper surface maximise light absorption for photosynthesis.AQA
Structure-property relationships: Strong covalent bonds within a layer need much energy to break, while weak forces between layers let them slide, so graphite has a very high melting point but…AQA
Structure–property relationships: The strong electrostatic forces throughout the giant lattice explain the high melting point of sodium chloride.AQA
sub-cellular structures: Organelles inside cells, such as mitochondria, ribosomes, the internal membranes of chloroplasts and the details of the nucleus, that electron microscopy has…AQA
Subatomic particle charges: Protons are positively charged, neutrons are neutral and electrons are negatively charged.AQA
Subatomic particle properties: Protons and neutrons each have a relative mass of 1, while electrons have a relative mass of about 1/1836, which is negligible.AQA
Subatomic particles: Protons and neutrons are found in the nucleus and give an atom almost all of its mass, while electrons occupy energy levels around the nucleus.AQA
Subatomic particles and relative mass and charge: The neutron has a relative mass of about 1 and a relative charge of 0.AQA
Subscript: A multiplier that sits inside a formula and multiplies only the atom or group immediately before it.AQA
Subscripts: The small numbers inside a formula, such as the ₂ in H₂, which show atoms within a particle and are fixed by the substance.AQA
Substances in the body: Harmful substances introduced and retained in the body, such as asbestos fibres or tar accumulated in the lungs, that act as risk factors.AQA
Success rates: The overall chance of a live birth, which is not high because each cycle has only a modest chance of resulting in a live birth.AQA
Successive wave features: Equivalent points on consecutive waves, such as two successive crests or two successive troughs, used to read wavelength.AQA
Sugars: The small molecules from which carbohydrates are synthesised, with many sugar units joining by condensation to form polysaccharides such as starch or glycogen.AQA
sulfates: The salts formed from sulfuric acid, which gives its name to the salt produced with the solid reactant.AQA
Sulfur dioxide: An acidic gas formed when sulfur impurities in fuels burn, which dissolves in rainwater to form acid rain.AQA
Sulfur impurities in fuels: Sulfur compounds are present in some fuels as an impurity rather than as the main fuel component, especially in coal and crude-oil fractions.AQA
Supports combustion: The reason a glowing splint relights in oxygen, as the gas is an oxidising agent and allows the wood to burn more vigorously.AQA
Surface area: Finger-like projections, alveoli, filaments and lamellae, root hair cells, and broad leaves all increase this so that diffusion is maximised.AQA
Surface area to volume ratio: A comparison of area with volume that predicts how easily an organism exchanges materials, showing why small, thin structures exchange materials effectively.AQA
Surface area to volume ratio and exchange surfaces: A larger surface area over which diffusion can occur increases the rate.AQA
Survival and homeostasis: Coordination allows rapid, appropriate reactions that help humans survive, maintain internal conditions and function.AQA
Susceptibility: A raised chance of particular cancers due to inherited alleles, which does not guarantee the disease because risk is probabilistic.AQA
Susceptibility to disease: Breeds may share similar alleles that give poor resistance to disease, so a single pathogen can affect many individuals.AQA
Sustainable development: Development that meets the needs of current generations without compromising the ability of future generations to meet their own needs.AQA
Symbol equation: Replaces names with formulae, for example CH₄ + 2O₂ → CO₂ + 2H₂O, and must be balanced so every element has equal atom counts on both sides.AQA
Symptom relief versus pathogen destruction: Medicines may treat symptoms such as pain or fever without killing the pathogen, so the immune system must still clear it.AQA
Synthesis and breakdown: Metabolism includes synthesis reactions that build larger molecules from smaller ones and breakdown reactions that break molecules down.AQA
Synthesis of large molecules: Chemical reactions that build larger molecules from smaller ones, using energy transferred by respiration.AQA
Synthesis reactions: Reactions that build larger molecules, such as joining glucose to form glycogen or amino acids to form proteins.AQA
Synthetic carbon compounds: Compounds manufactured by humans, for example poly(ethene) from ethene and aspirin from salicylic acid.AQA
Synthetic products: Products such as synthetic rubber, polyester, nylon and synthetic fertilisers that are made by chemical processes, often from crude oil, and can replace…AQA
Systematic checking and fault finding: Comparing the built circuit with the diagram component by component, confirming each symbol matches the real component, and testing that switches control the…AQA
Systems and system boundaries: A system is an object or group of objects, and its boundary should always be stated.AQA

T

Tangent: A straight line drawn so it touches the curve at the required time and has the same slope as the curve at that point.AQA
Target organ: The organ where a hormone produces an effect, having cells with receptors that the hormone binds to.AQA
target organs: Organs such as the liver and muscles to which hormones travel in the blood to regulate glucose uptake and storage.AQA
Technology driving biological discovery: Improved microscopy revealed subcellular structures such as mitochondria and ribosomes, and microscope development depended on advances in technology.AQA
TEM versus SEM: The transmission electron microscope passes electrons through a thin specimen to show internal structures, while the scanning electron microscope scans…AQA
Temperature: An abiotic factor measured with a thermometer, usually in degrees Celsius, that affects the rate of enzyme-controlled reactions and the distribution of…AQA
Temperature and energy: Temperature is a measure of the average kinetic energy of the molecules, not of the total kinetic energy or the speed of any single molecule.AQA
Temperature and reaction rate: Particles move faster, so collisions are more frequent and a greater proportion have energy greater than or equal to the activation energy.AQA
Temperature change: The difference between the final and initial temperatures of a system, calculated as ∆θ = θ_final − θ_initial and measured in degrees Celsius, °C.AQA
Temperature change as evidence: Measuring the temperature change of the surroundings, where an increase shows energy is being transferred out of the system.AQA
temperature change of the surroundings: The rise or fall in the temperature of the surroundings, which is the evidence used to distinguish between exothermic and endothermic reactions.AQA
Temperature change ΔT: Calculated as final temperature minus initial temperature, including sign.AQA
Temperature changes: These show whether energy is transferred to the surroundings, raising the temperature, or taken in from the surroundings, lowering the temperature.AQA
Temperature during a change of state: It stays constant because energy is used to overcome forces between particles rather than increase their kinetic energy.AQA
Temperature increase: A rise that means the average kinetic energy of the particles has increased.AQA
Temperature sensing and control: Thermistors are used in temperature sensors, thermostats and protection circuits.AQA
Temperature versus internal energy: Temperature measures the average kinetic energy of the particles, while internal energy is the total energy stored by all the particles.AQA
Temperature-dependent resistance: The resistance of a thermistor decreases as the temperature increases.AQA
Tension: The pulling force transmitted along a stretched string, rope or cable, acting towards the object at each end.AQA
Terminal velocity: A constant maximum speed reached when the drag force equals the weight and the resultant force is zero.AQA
Terrain: Uphill or rough ground increases resistance and reduces speed, while smooth, level ground allows faster movement.AQA
tesla: The unit of magnetic flux density, where 1 T equals 1 newton per ampere per metre.AQA
Testes: The gland responsible for producing testosterone, secreting it into the bloodstream.AQA
Testing and modifying drug molecules: Pharmaceutical chemists make many related compounds, test them for useful activity and modify structures to improve effectiveness and reduce side effects.AQA
Testosterone: The main male reproductive hormone produced by the testes, causing secondary sex characteristics such as voice deepening and facial hair growth.AQA
The continuous nature of the electromagnetic spectrum: There is no gap between adjacent groups because wavelength and frequency change smoothly.AQA
The genome as all genetic material: The entire genetic material of an organism, including all its genes.AQA
The logarithmic nature of the pH scale: Each unit change on the scale represents a tenfold change in hydrogen ion concentration.AQA
The menstrual cycle: A cycle of about 28 days in which an egg matures and is released, and the uterus lining thickens.AQA
The mole as a counting unit: Because atoms and molecules are too small to count individually, chemists measure chemical amount in moles, the counting unit for particles.AQA
The ohm: The unit of resistance, symbol Ω, where one ohm allows one ampere when one volt is applied.AQA
The periodic table: An organised reference used to check symbols, and in the exam it can be used if a symbol cannot be recalled.AQA
The pH scale: A numerical way to express the relative acidity or alkalinity of an aqueous solution, using whole numbers only in this specification.AQA
The reactivity series as an ordered model: Metals can be arranged in order of their reactivity in a reactivity series.AQA
The relationship R = V ÷ I: Resistance equals potential difference in volts divided by current in amperes.AQA
The role and limitations of scientific models: Simplified representations divide the world into grid boxes and use averaged values, so they cannot reproduce every local detail or every feedback.AQA
The very small scale of particles in chemistry: Atoms are far too small to see directly, and about 5 million atoms would fit across a 1 mm gap.AQA
The wave equation v = f λ: Wave speed is calculated using v = f λ, where v is speed in m/s, f is frequency in Hz and λ is wavelength in m.AQA
Theory and experiment in science: The theoretical calculations of Bohr agreed with experimental observations.AQA
Therapeutic cloning: An embryo is produced with the same genes as the patient, and its stem cells may be used for medical treatment.AQA
Thermal conductivity: Delocalised electrons gain kinetic energy at the hotter region and transfer energy by moving and colliding with other particles.AQA
Thermal conductivity of materials: A higher value means a faster rate of energy transfer, so the building cools more quickly; a lower value means slower transfer and slower cooling.AQA
Thermal decomposition: Breaking a compound down using heat, with energy supplied continuously for the decomposition to continue.AQA
Thermal energy and dissipation: Brake friction transfers energy to the thermal energy store of the brake discs and pads, while air resistance transfers energy to the thermal energy store of…AQA
Thermal energy stored: The energy that increases when a material's temperature rises, linked to the decrease of one energy store or work done.AQA
Thermal energy transfer: Energy spread out to the surroundings, for example in the brakes, tyres and air of a moving car, is dissipated in this form.AQA
Thermal image: Picture built by an infrared camera from the infrared emitted by objects, in which warmer regions appear brighter.AQA
Thermal store: The store that energy is transferred to or from when a system is heated or cooled.AQA
Thinking distance: The distance covered while a vehicle continues at its original speed during the reaction time, equal to speed multiplied by reaction time.AQA
Three-dimensional models: Show arrangement in space, but they can still misrepresent bond lengths, electron clouds and the scale of the structure.AQA
Three-domain system: A system in which bacteria are placed in their own domain, distinct from Archaea and Eukaryota based on biochemical differences.AQA
Three-figure bearing: A measured angle converted into this form when the question requires a bearing, for example 053° rather than 53°.AQA
Thyroid gland: A butterfly-shaped gland in the neck that is the source of thyroxine.AQA
Thyroxine: Secreted by the thyroid gland, it stimulates the basal metabolic rate, affecting how quickly cells respire, and aids growth and development.AQA
time: The duration for which a device operates or a charge flows, measured in seconds (s) and given the symbol t.AQA
Time as a measured interval: The duration over which the velocity changes, being the interval between the initial and final velocity readings rather than the total journey time unless the…AQA
Time in speed calculations: Time is the denominator in the speed equation, so a smaller time for the same distance means a greater speed.AQA
Time period: The time for one complete wave in seconds, linked to frequency by f = 1 ÷ T.AQA
Time taken: The total time for that change, used as the divisor when calculating the mean rate.AQA
Time, distance and shielding: Precautions that reduce the dose received by keeping exposure time as short as possible, increasing distance and placing appropriate shielding around the…AQA
Timescale of life: Simple life forms developed more than three billion years ago, and the process is gradual and cumulative over very long time periods.AQA
Timescale of millions of years: Fossils are the remains of organisms from millions of years ago, existing long before humans.AQA
Timescale of replacement: Whether a resource is replaced within a human timescale is asked to distinguish finite from renewable resources.AQA
Tiredness: Slows nerve processing and decision making, so the interval between seeing a hazard and braking increases.AQA
Tissue: A group of similar cells working together to carry out a shared function, such as muscle tissue or xylem tissue.AQA
Tissue culture: Growing a small piece of meristem tissue in sterile conditions on a nutrient medium, where it forms many genetically identical plantlets.AQA
Tissue damage: Ultraviolet waves, X-rays and gamma rays can have hazardous effects on human body tissue, with ultraviolet waves causing skin to age prematurely and…AQA
Tissue repair and replacement in adults: In adult animals, stem cells are found in tissues such as bone marrow and are used to replace cells that are worn out or damaged.AQA
Tissues: Groups of similar cells working together, such as a piece of heart or liver tissue, used to see how the drug affects them.AQA
Tobacco mosaic virus (TMV): A widespread plant pathogen affecting many species of plants, including tomatoes.AQA
Total distance and total time: The distances for all stages of a journey added together, and the times for all stages including any stationary periods added together.AQA
Total input energy: The energy supplied to the device before any transfer occurs.AQA
Total input energy transfer: The energy supplied to a device, which is the denominator in the efficiency equation and can be found by adding the useful and wasted energies.AQA
Total power input: The power supplied to a device, which is divided into useful power output and wasted power.AQA
Total resistance: In series it is the sum of the individual resistances, and for two resistors in parallel it is less than the smallest individual resistor.AQA
Total resistance and current in each circuit type: Adding a component in series increases the total resistance, reducing the current, whereas adding a branch in parallel increases the total current drawn.AQA
Total resistance and multiple paths: Adding a parallel branch decreases the total resistance because there are more paths for charge.AQA
Total resistance as the sum of individual resistances: The total resistance of the circuit is the sum of the individual resistances, so adding a component increases the total resistance and reduces the current.AQA
Total surface area: Very large in capillaries, which increases the rate of diffusion of substances.AQA
Toxic chemicals: Must not be released into soil, water or air; they are treated, neutralised, incinerated under controlled conditions or stored securely.AQA
Toxic chemicals and bioaccumulation: Pesticides, heavy metal ions and industrial solvents may poison organisms directly or accumulate along food chains.AQA
Toxicity: Asks whether the substance harms the body, for example by damaging the liver or kidneys.AQA
Toxin neutralisation: Binding to a toxin so that it cannot damage cells or tissues.AQA
Trace fossils: Preserved traces of organisms, such as footprints, burrows and rootlet traces, rather than the organism's body parts.AQA
Trace gases and variability: The remaining 1% is mostly argon, with small and variable amounts of carbon dioxide, water vapour and other noble gases.AQA
Trace gases in the early atmosphere: There may have been small proportions of methane and ammonia in the early atmosphere.AQA
Trade-offs between resource, energy and cost: Recognising that a method may reduce use of one resource while increasing use of another, such as energy or water.AQA
Transect: A line or belt across a habitat where quadrats are placed at regular intervals, revealing how distribution changes along an environmental gradient.AQA
Transfer from kinetic energy store to thermal energy store: Braking transfers energy from the vehicle's kinetic energy store to the thermal energy store of the brakes, so the brakes become hotter.AQA
Transfer through a vacuum: No medium is required, so energy can be transferred through a vacuum, as from the Sun to Earth.AQA
Transition state: The highest point on the curve, where bonds in the reactants are being broken and new bonds are forming.AQA
Translocation: The movement of dissolved sugars and other organic substances through the phloem from sources such as leaves to sinks such as roots, fruits and growing tips,…AQA
Transmission: The wave passes through the substance, and a substance may transmit some wavelengths well and absorb others.AQA
Transmission of pathogens: The measles virus is spread by inhalation of droplets from sneezes and coughs.AQA
Transmission routes: The ways a pathogen leaves one host, travels, and enters a new host, such as direct contact, water, air, food or a vector.AQA
Transmission routes in animals: Viruses spread through airborne droplets, direct contact or contaminated body fluids, bacteria through contaminated food or water, protists through vectors…AQA
Transmission routes in plants: Plant viruses spread through direct contact or contaminated tools, bacteria through wounds, water or vectors, and protists and fungi through spores carried by…AQA
Transmitting aerial: Where an alternating current generates radio waves, which then travel to a receiver.AQA
Transpiration: The loss of water vapour from plant leaves, mainly through stomata, creating a pull that draws water up the xylem from the roots.AQA
Transpiration and water loss: Water vapour is lost through the same stomata, and closing them reduces water loss but also restricts gas exchange.AQA
Transpiration stream: The movement of water through xylem, maintained by the pull from evaporation from leaves together with cohesion between water molecules.AQA
Transport: One of the uses of energy resources, including vehicles which mostly use fuels such as petrol, diesel or biofuels.AQA
Transport and distribution: Moving raw materials to a factory, finished goods to shops and waste to a disposal site, which must be counted at every stage.AQA
Transport in plants: Xylem carries water and dissolved mineral ions upward, while phloem translocates dissolved sugars and amino acids up and down the plant.AQA
Transport of substances: Water and dissolved mineral ions travel up from the roots through the stem to the leaves, while sugars made in the leaves are transported to growing regions,…AQA
Transport systems: A system that moves substances quickly to and from all cells.AQA
Transport systems in living organisms: Large organisms need specialised exchange surfaces and transport systems because diffusion alone would be too slow.AQA
Transverse: Describes waves whose oscillations are perpendicular to the direction of energy transfer.AQA
Transverse wave: A wave that transfers energy without transferring matter, and whose oscillations are perpendicular to the direction of energy travel.AQA
Transverse wave examples: Light, water surface waves and waves on a rope, in which the oscillations are perpendicular to the direction of energy transfer.AQA
Trapping pathogens: Hairs trap larger particles such as dust and some microorganisms, while mucus traps smaller particles and pathogens.AQA
Treatment strategies: Type 1 diabetes is treated with insulin injections, while Type 2 diabetes is commonly treated with a carbohydrate-controlled diet and an exercise regime,…AQA
Trend: A consistent change in the use of energy resources over time, such as a rising or falling share.AQA
Trends and patterns: The overall direction shown by data, for example as temperature increases the rate of transpiration increases.AQA
Trends in physical properties: Melting and boiling points rise as molecular size increases, because larger molecules need more energy to overcome their intermolecular forces.AQA
Trends in reactivity: Going down the group, reactivity increases because the outer electron is lost more easily.AQA
Trends in reactivity down a group: Reactivity decreases down the group because the outer shell is further from the nucleus and shielded by more inner shells, so the attraction for an incoming…AQA
Trends in the periodic table: The direction in which a property changes, such as reactivity increasing or melting point decreasing down Group 1.AQA
Triglyceride: The lipid molecule formed when one glycerol molecule reacts with three fatty acid molecules.AQA
Tubal ligation: A surgical method of female sterilisation that cuts, ties or blocks the oviducts so that the egg cannot travel from the ovary to the uterus and sperm cannot…AQA
Tumour: A mass of abnormal cells formed when cells divide repeatedly without responding to the usual controls.AQA
turgid: Describes a cell that has become firm because water entered by osmosis and the vacuole expanded.AQA
turgor pressure: Pressure maintained by the vacuole that keeps the cell firm and supports the plant.AQA
Turning effect of a force pair: The two opposite forces act at a distance from the axis, producing a turning effect (moment) that rotates the coil.AQA
Two-dimensional diagrams: Are quick to draw and show bonding, but they flatten a three-dimensional structure and can hide which atoms are in front.AQA
Type 1 diabetes: A disorder in which the pancreas fails to produce sufficient insulin, characterised by uncontrolled high blood glucose levels.AQA
Typical speeds of people: Approximate everyday values for a person walking at about 1.5 m/s, running at about 3 m/s and cycling at about 6 m/s.AQA
Typical speeds of transport: Approximate everyday values for transportation systems, such as a car on a motorway at roughly 30 m/s, a train at roughly 50 m/s and a plane at roughly 250 m/s.AQA
Typical values: Values such as iron at about 7.9 g/cm³ and water at about 1.0 g/cm³ that can be used to compare materials.AQA
Typical values for human motion: Standard values such as running at approximately 3 m/s, compared with walking at about 1.5 m/s.AQA
Typical values of speed: Approximate values used for estimates, such as about 6 m/s for cycling, rather than exact constants.AQA
Typical walking speed: About 1.5 m/s, meaning a walker covers roughly 1.5 metres each second.AQA

U

Ultraviolet light: Damages the genetic material of microorganisms so they cannot reproduce, adds no chemicals, and only works where the water is clear enough.AQA
Unadulterated and natural state: A substance that has had nothing added to it, so it is unadulterated and in its natural state.AQA
Unbalanced forces: When the resultant force is not zero, so the object accelerates in the direction of the resultant force.AQA
Uncertainty: Estimated from the spread, with a simple estimate being half the range.AQA
Uncertainty about a mean value: Estimated as half the range and written with a ± sign after the mean of the repeated measurements.AQA
Uncontrolled cell division: Mutations in genes that control cell division can lead to uncontrolled cell division and the formation of a cancer.AQA
Uncontrolled growth and division: Changes in cells lead to growth and division that is not regulated, producing a mass of abnormal cells.AQA
Uncontrolled high blood glucose levels: The characteristic state of type 1 diabetes, in which glucose is not removed from the blood efficiently after meals.AQA
Undifferentiated: Having not yet switched on the particular genes that give a cell its job, so having no special shape or chemistry for one task.AQA
Undisturbed position: The position of the medium when no wave passes, often drawn as the centre line on a graph.AQA
Unicellular: Describes an organism made of a single cell, such as a bacterium or Amoeba.AQA
Uniform acceleration: Acceleration that stays constant, which is the only condition under which the equation linking change in velocity to acceleration and distance applies.AQA
Uniform velocity: Both speed and direction are unchanged, so the object keeps moving at constant velocity.AQA
Unit consistency: Using consistent units such as cm³/s, dm³/min or m/s, converting all values to the same time unit before dividing.AQA
Unit consistency in calculations: Checking that distance and time units are consistent, converting km to m or minutes to seconds where necessary.AQA
Unit conversion: Converting between units such as millimetres, micrometres and metres so that image size and real size are in the same unit before dividing.AQA
Unit conversion and calculation accuracy: Convert units where necessary, such as minutes to seconds or kilojoules to joules, before calculating.AQA
Unit conversion and standard units: Convert milliamperes to amperes and kilovolts to volts before substituting into the equation, keeping potential difference in volts and current in amperes.AQA
Unit conversion between cm³ and dm³: A volume in cm³ must be divided by 1000 before use, because 1 dm³ equals 1000 cm³.AQA
Unit conversion between m/s and km/h: To compare values, convert to the same unit by multiplying m/s by 3.6 to get km/h, so 30 m/s is about 108 km/h.AQA
Unit conversion between nanometres and metres: A nanometre is one billionth of a metre, so convert nanometres to metres by multiplying by 1 x 10⁻⁹.AQA
Unit conversion in biology: Always convert to the same unit before comparing, using 1 µm = 1 × 10⁻⁶ m.AQA
Unit conversion in calculations: Units such as cm to m or kHz to Hz may need converting before values are substituted into the equation.AQA
Unit conversion to seconds: Changing a time given in minutes or other units into seconds before substitution, for example 2 minutes becomes 120 s and 0.5 minutes becomes 30 s.AQA
Units: Given as cm³/s or g/s, and kept consistent throughout a calculation by converting between units where necessary.AQA
Units and consistency: The symbol and unit must remain consistent with the question, and a change of 1 °C equals a change of 1 K so the same numerical value can be used in kelvin.AQA
Units and conversions: V is measured in volts, I in amperes and R in ohms, so convert mA to A and kΩ to Ω first, then substitute and give the answer with the correct unit.AQA
Units and dimensional consistency: Always include units (m/s) and show working.AQA
Units and measurement: Potential difference is measured in volts (V), current in amperes (A) and resistance in ohms (Ω), and values must be in the correct units before calculating.AQA
Units and symbols in electricity: The symbol for current is I and its unit is the ampere, symbol A, with 'amp' also accepted for ampere in written work.AQA
Units and unit conversion: Converting time to seconds and energy to joules before substituting into the equation, for example minutes to seconds or kilojoules to joules.AQA
Units mol/s: The unit attached to a rate calculated from mole data, meaning moles of reactant used or product formed each second.AQA
Units of mean rate: The units of quantity divided by the units of time, such as cm³/s, g/s or mol/s (Higher Tier).AQA
Units of power: Power is measured in watts, W, where one watt is one joule per second.AQA
Universal indicator: A mixture of dyes that changes colour gradually across the pH scale, showing whether a solution is strongly acidic, weakly acidic, neutral, weakly alkaline or…AQA
Universal scientific names: This universal naming system avoids confusion caused by common names and allows scientists worldwide to communicate clearly.AQA
Universal wave equation: All waves obey the wave equation, which links wave speed, frequency and wavelength as v = f λ.AQA
Unsaturated fatty acid: A fatty acid with at least one carbon-carbon double bond.AQA
Unsaturated hydrocarbons and the C=C double bond: Hydrocarbons containing a carbon–carbon double bond (C=C) are described as unsaturated, and this double bond makes them far more reactive than alkanes.AQA
Unwanted energy transfers: Transfers to the surroundings that should be identified and reduced, for example by insulating the container or using a lid.AQA
urea: A toxic substance made in the liver from the nitrogen of removed amino groups, which must be excreted rather than stored in the body.AQA
Use and operation during its lifetime: The stage covering everything that happens while the product is actually being used, including the energy it consumes and any fuel or electricity it needs.AQA
Use and storage of sugars: Transported sugars can be used immediately, for example in respiration or growth, or stored, often as starch.AQA
Use of molecular evidence in classification: Classification uses base sequences in ribosomal RNA, alongside visible features, to justify grouping.AQA
Use of standard SI units: Mass is used in kilograms and speed in metres per second before substituting into the equation.AQA
Use of vectors in genetic engineering: The gene is inserted into a vector, usually a bacterial plasmid, which carries it into the bacterium.AQA
Useful and wasted energy: A system change involves a transfer to the intended useful store and a dissipated transfer that is not useful.AQA
Useful energy and dissipation: Useful energy transfer is energy delivered to the intended store, while dissipated energy spreads into less useful stores, often warming the surroundings by…AQA
Useful output energy: The energy transferred to the intended store or form, such as light from a lamp or kinetic energy from a motor.AQA
Useful output energy transfer: The energy transferred usefully by a device, which is divided by the total input energy transfer to give efficiency.AQA
Useful power output: The power transferred usefully by a device, which is the numerator in the efficiency equation and is smaller than the total input.AQA
Useful products from GM: The genetically modified bacterium will produce human insulin, which can be harvested to treat diabetes.AQA
usefulness versus appearance: A characteristic is chosen either for usefulness or for appearance when deciding which variants become parents.AQA
Uses of half-life in dating and medicine: A fixed half-life for a given isotope allows dating and medical tracing.AQA
Using a simple model to explain observable properties: The simple model represents particles as small solid spheres, and closeness of particles is linked to the volume and shape observed.AQA
Using data to make and justify predictions: Predictions are made by identifying the trend, checking it across at least two known elements and extending it to the unknown element.AQA
Using data to make predictions: Identifying the direction of the trend, checking the pattern is consistent, then stating the property for the named element and justifying it using the outer…AQA
Using data to support judgements: Using the information provided, such as data on ore use, energy, cost or product quality, rather than unsupported opinion.AQA
Using data to test purity: Melting point and boiling point data can be used to distinguish pure substances from mixtures, since a sample melting sharply at the expected temperature is…AQA
Using equations and units: The relationship is mean rate of reaction = quantity of product formed ÷ time taken, and the answer carries a compound unit such as g/s or cm³/s.AQA
Using evidence: Quoting specific figures from the data to support each point you make and to support a conclusion.AQA
Using evidence to support conclusions about communities: Comparing data for two or more species and using the comparison to support a conclusion about their interaction.AQA
Using fractions and percentages to describe mixtures: The proportion of oxygen can be given as both a fraction and a percentage, for example one-fifth or about 20%, to make the value unambiguous.AQA
Using given information: Interpreting supplied information such as a table, key or list to assign an organism to a named group, giving the feature that supports the assignment.AQA
Using models to explain physical properties: These diagrams model differences in density, shape and volume: solids keep a fixed shape and volume, liquids take the shape of their container but keep a…AQA
Using R_eq with V = I × R: Once R_eq is known, the circuit behaves as one resistor, so I = V_supply ÷ R_eq gives the current through every component.AQA
Using the equation W = m × g: The relationship is written as W = m × g, where W is weight, m is mass and g is gravitational field strength.AQA
Using V = I × R to solve circuit problems: To calculate an unknown quantity, first identify what is known, then choose the relationship linking the known and unknown values.AQA
Using V = IR to solve series circuit problems: These rules let you calculate an unknown current, p.d.AQA
Uterus lining and implantation: The uterus lining is where an embryo can implant and continue developing, and hormones prepare it to receive the embryo.AQA

V

V–I graph: For a fixed resistor at constant temperature, a straight line through the origin showing p.d.AQA
Vaccination: Introducing small quantities of dead or inactive forms of a pathogen into the body to stimulate the white blood cells to produce antibodies.AQA
Vaccination and immunity: Most young children are vaccinated against measles because it is a serious illness that can be fatal if complications arise.AQA
Vaccines: Medicines that stimulate immunity to prevent disease rather than treat an existing infection.AQA
Vacuole: The structure inside the white blood cell in which the pathogen is contained after the cell membrane surrounds it.AQA
Value judgements: Allocating numerical values to pollutant effects is less straightforward and requires value judgements about which impact matters most.AQA
valves: Folds of the inner lining in many veins that prevent backflow and keep blood moving towards the heart.AQA
variable resistor: Connected in series, it can change the total resistance and therefore control the current and the potential difference across a component.AQA
Variables and axes: Placing the independent variable on the x-axis and the dependent variable on the y-axis, with both axes labelled with the correct quantity and unit.AQA
Variables and axis convention: The independent variable goes on the x-axis and the dependent variable on the y-axis.AQA
Variables and fair testing: The independent variable, dependent variable and at least two control variables are identified, keeping all variables except the independent variable constant…AQA
Variant: A new allele that appears only when mutation alters a gene, so every variant has a mutational origin.AQA
variation: Differences between individuals that come from two sources working together: the genes they inherit and the environment they experience.AQA
Variation and approximate nature of atmospheric data: Carbon dioxide and water vapour concentrations vary with location, weather, season and human activity, so quoted values are approximate.AQA
Variation and mutation: Individuals within a population vary because of differences in their genes, often caused by mutation.AQA
Variation in offspring: The offspring of selected parents show variation in flower size or appearance, so only some are chosen to breed.AQA
Vascular bundles: Structures often formed by these tissues in the stem, with xylem towards the inside and phloem towards the outside.AQA
Vasectomy: A surgical method of male sterilisation that cuts, ties or blocks the vas deferens so that sperm cannot pass from the testes into the urethra.AQA
Vector: A quantity for which direction matters, so both magnitude and direction are needed to describe it fully.AQA
Vector direction and relative orientation: The rule shows relative orientation only, as the three directions are mutually perpendicular, rather than magnitude.AQA
Vector nature of forces: Every force has a direction and magnitude, so it is a vector.AQA
Vector quantity: A quantity for which both magnitude and direction are important, so an object moving in the opposite direction has negative momentum if the initial direction…AQA
Vector resolution using scale drawings: A single force can be resolved into two components acting at right angles to each other by drawing it to scale at the correct angle.AQA
Vectors and direction: A positive direction is chosen and opposing velocities are given negative signs before adding.AQA
Vectors and environmental spread: A vector is an organism that carries and transmits the pathogen, such as a mosquito carrying Plasmodium, whereas spores may be carried by wind or water.AQA
Vectors and transmission: The protists are transmitted to humans by the bite of an infected mosquito, which acts as a vector carrying the pathogen from one host to another.AQA
Vectors in genetics: A vector, usually a bacterial plasmid or a virus, is used to insert the gene into the required cells of the recipient organism.AQA
Veins: Vessels that return blood to the heart at low pressure, with thin walls and a wide lumen, and valves that prevent backflow.AQA
Velocity: A vector quantity, so it has size and direction and can be positive or negative depending on the chosen positive direction.AQA
Velocity as a vector: A quantity that includes both speed and direction, so a negative value means motion opposite to the chosen positive direction.AQA
Velocity of waves in different substances: The velocity depends on the substance, so the same wave can travel at different speeds in different materials.AQA
vena cava: The vessel through which deoxygenated blood returns from the body into the right atrium.AQA
vena cavae: The largest veins: the superior vena cava returns deoxygenated blood from the head and arms, and the inferior vena cava from the lower body, both emptying…AQA
Vertical height: The vertical change in position, not the distance moved along a slope, measured in metres.AQA
Viral disease and symptoms: Measles is a viral disease showing symptoms of fever and a red skin rash.AQA
Viral replication: Copying the viral genetic material and making viral protein coats inside a host cell, then releasing new virus particles.AQA
Viral replication inside host cells: Viruses reproduce inside host cells, so a drug that kills the virus must either enter the host cell or interfere with viral replication without harming the…AQA
Viruses: Non-cellular pathogens that are much smaller than cells and reproduce only inside host cells.AQA
viscosity: Resistance to flow that increases with increasing molecular size because stronger intermolecular forces resist sliding.AQA
Visible light: One of the groups, lying between infrared and ultraviolet, and ranging from red to violet.AQA
Volcanic activity: Intense volcanic activity released carbon dioxide, water vapour and nitrogen, forming an early atmosphere with little or no oxygen.AQA
Volcanic activity and outgassing: Intense volcanic activity released gases, including water vapour, carbon dioxide and nitrogen, that formed the early atmosphere.AQA
Volt: One joule per coulomb, so a 6 V battery transfers 6 J of energy to each coulomb of charge that passes through it.AQA
voltage: A name for the same quantity as potential difference, so either term earns credit in answers.AQA
Voltmeter: Connected in parallel with the component whose potential difference is being measured, because it must compare the two points across that component.AQA
Volume: Measured in cubic metres or cubic centimetres, and found using the rearranged form V = m / ρ when density is known.AQA
Vulnerability of small populations: Small populations are more vulnerable because they have less genetic variation and are more exposed to chance events.AQA

W

W = m × g: The equation used to calculate weight, in which m is the mass in kilograms and g is the gravitational field strength in newtons per kilogram.AQA
Waste management: Reduces pollution by choosing suitable disposal routes for waste.AQA
Waste management and landfill: Recycling processes used materials into new products instead of sending them to landfill, reducing the volume of waste buried.AQA
Waste management and pollution: Unless waste and chemical materials are properly handled, more pollution will be caused as waste escapes into air, water and land.AQA
Waste water: Water that carries organic matter, microbes and contaminants, needing screening, sedimentation, biological digestion of sludge and sterilisation.AQA
Waste water treatment: A sequence of physical and biological processes that removes organic matter and harmful microbes before release into the environment.AQA
Wasted: Energy that is not transferred to the intended useful store is often described as being this.AQA
Wasted energy: Energy not transferred usefully by a device, usually heating the device and surroundings, and reduced by a higher efficiency.AQA
Wasted power: The difference between total power input and useful power output, often as heating of surroundings.AQA
Water as a solvent and transport medium: Water is a solvent for metabolic reactions and is used in transport in organisms, for example in blood plasma and xylem.AQA
Water bath or electric heater: Used to control temperature, with the same temperature used for every pH so that temperature is not a confounding variable.AQA
Water pollution: Pollution can occur in water, from sewage, fertiliser or toxic chemicals, and each route harms organisms in a different way.AQA
Water pollution sources: Harmful substances enter rivers, lakes or groundwater from sewage, fertiliser or toxic chemicals.AQA
Water potential: A dilute solution has a higher water potential, meaning more free water molecules per unit volume, while a concentrated solution has a lower water potential.AQA
Watt: A power of one watt is an energy transfer of one joule per second.AQA
Wave equation: v = f λ, in which wavelength is the symbol λ and must be in metres when speed is in m/s and frequency is in Hz.AQA
Wave models of light and of sound: Models that represent light and sound as oscillations transferring energy, with light modelled as a ray or as a wave and sound as a longitudinal wave of…AQA
Wave properties and interactions with matter: How a wave interacts with matter explains why it is suitable for its application, for example microwaves pass through the atmosphere for satellite links.AQA
Wave speed: A quantity that depends on both frequency and wavelength through v = f × λ, and is not the same as frequency.AQA
Wavelength: A property of the radiation used by a microscope; electrons have a much shorter one than visible light, so the resolution of an electron microscope is much…AQA
Waxy cuticle: A covering on the upper epidermis that limits evaporation, reducing water loss.AQA
weak: Describes an acid that ionises partially, forming an equilibrium mixture with un-ionised molecules.AQA
Weak acid: An acid that is only partially ionised in aqueous solution, so a significant proportion of intact acid molecules remains.AQA
Weak intermolecular forces: Separate small molecules are attracted to one another only by weak intermolecular forces.AQA
Weakened immune system: Caused by a non-communicable disease or by treatment such as immunosuppressant drugs, making a person more likely to catch communicable diseases.AQA
Weather: Short-term and local conditions, as opposed to the long-term pattern over decades.AQA
Weight: Calculated using W = m × g, where m is the mass in kilograms and g is the gravitational field strength in newtons per kilogram.AQA
Weight, mass and gravitational field strength: Weight is the force of gravity on an object in newtons, mass is the amount of matter in kilograms, and gravitational field strength is in newtons per kilogram.AQA
Weighted mean: Calculated by multiplying each isotope mass by its abundance, adding the products, then dividing by the total abundance.AQA
White blood cell response: Phagocytes engulf and digest pathogens, while lymphocytes release antibodies and antitoxins.AQA
White blood cells: Defend the body, as some engulf pathogens by phagocytosis, while others produce antibodies that bind to antigens or antitoxins that neutralise toxins.AQA
White blood cells and lymphocytes: Antibodies are proteins produced by lymphocytes, which are a type of white blood cell.AQA
Whole-life-cycle comparison: In a life cycle assessment you compare impacts across the whole life cycle, using the same functional unit, such as one litre of drink delivered to a customer.AQA
Wide range indicator: An indicator that covers a broad pH interval and is used in the same way as universal indicator to estimate pH.AQA
Wildlife corridors: Features that link patches of habitat, allowing wildlife to move between them.AQA
Wind: Moving air whose speed varies with time and location, and which is measured with an anemometer.AQA
Wind direction: The compass bearing from which the wind blows, measured with a wind vane and recorded as a compass direction such as north-west.AQA
Wind intensity: The strength or speed of moving air, measured with an anemometer, often in metres per second (m/s).AQA
Word equation: Names the reactants and products of a chemical reaction, with an arrow showing the direction of change.AQA
Work: Energy transferred when a force causes an object to move through a distance, measured in joules, the same unit as energy.AQA
Work done: The energy transferred when a force moves an object through a distance along the force's line of action, measured in joules, J.AQA
Work done and energy: The equation P = W / t links power P in watts to work done W in joules and time t in seconds.AQA
Work done by a force: A stretching or compressing force does work because the point of application moves in the direction of the force.AQA
Work done by a friction force: The friction force between the brakes and the wheel does work against the vehicle's motion, and work done is force × distance.AQA
Work done by forces: A measure of energy transferred, equal to the force multiplied by the distance moved along the line of the force.AQA
Writing and balancing equations: Write word equations and balanced chemical equations for reactions, ensuring the number of atoms of each element is the same on both sides.AQA
Writing and balancing half-equations: The cathode half-equation 2H⁺ + 2e⁻ → H₂ is written so atoms and charge balance when hydrogen is discharged.AQA
Writing ionic charges with correct notation: Ion charges are written with the number before the sign, for example 2⁺ and 2⁻, and with the sign for single charges.AQA

X

Xylem: Carries water and dissolved mineral ions from the roots to the stem and leaves, and is made of dead, hollow cells joined end to end with lignified walls that…AQA
Xylem and phloem transport: Water is drawn up the xylem in a continuous column, while dissolved sugars move through the phloem from source to sink in either direction.AQA

Y

Y chromosome: Carries the sex-determining region with the gene that triggers male development, so its presence or absence determines sex.AQA
Yeast: Cells that carry out anaerobic respiration, converting glucose into ethanol and carbon dioxide.AQA
Yield: The amount of product obtained, which rises when heating favours an endothermic forward reaction.AQA

Z

Zero resultant force: Means no change in velocity, whether that velocity is zero or non-zero.AQA
Zygote: The cell formed by fertilisation, which is XX and female if an X sperm fertilises an egg and XY and male if a Y sperm does.AQA

Other terms

'Flight or fight': The preparation of the body for escaping danger or confronting it, brought about by adrenaline increasing the heart rate and boosting oxygen and glucose…AQA
3D and ball-and-stick models: Show the spatial arrangement of atoms and bonds, which is essential for visualising molecular shapes.AQA
ΔE = m c Δθ: The relationship where ΔE is energy transferred in joules, m is mass in kilograms, c is specific heat capacity in J/kg °C and Δθ is the temperature change in…AQA

Where these terms come from

Each definition is one we publish on a Combined Science GCSE topic page or study guide. Open a term to see how each exam board words it and which topic it belongs to. For the full course, go to Combined Science revision or the glossary for every subject.

Revise Combined Science with these terms

Create a free account to practise exam questions and get feedback on your answers.

Start free

A week of Premium from your first lesson · Then the free plan continues · No card, no charge

Combined Science topics

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

X

Y

Z

Other terms

Where these terms come from

Revise Combined Science with these terms

Cookies on MasteryMind