Biology B A-Level
Biology B A-Level glossary
45 key terms for Biology B A-Level, A to Z, each linked to the topic pages that use it.
45 terms found. Open a term to try a short memory check.
C
- Calcium ions
- Form calcium pectate with pectin, and this cements the middle lamella between adjacent plant cell walls.Pearson Edexcel
- Catalysis and activation energy
- Enzymes are biological catalysts that lower the activation energy needed for a reaction and are unchanged at the end.Pearson Edexcel
- Cell theory
- A unifying concept stating that cells are a fundamental unit of structure, function and organisation in all living organisms.Pearson Edexcel
- Condensation
- A reaction joining two monosaccharides, releasing water and forming a glycosidic bond.Pearson Edexcel
- Condensation reaction
- A reaction in which amino acid monomers join, releasing a water molecule and forming a peptide bond between the carboxyl group of one and the amine group of…Pearson Edexcel
D
- Dipole
- Water is a dipole because oxygen is slightly negative and hydrogen slightly positive, so hydrogen bonds form between molecules.Pearson Edexcel
- Disaccharides
- Sugars containing two monosaccharide units joined by a glycosidic bond.Pearson Edexcel
E
- Early embryonic development
- The development of the embryo from the zygote, which divides by mitosis to a morula and forms a blastocyst with an inner cell mass and trophoblast.Pearson Edexcel
- Embryo sac
- Formed when one surviving haploid megaspore undergoes mitosis to produce eight nuclei, including the egg cell and two polar nuclei.Pearson Edexcel
- Enzyme specificity and induced fit
- The active site's shape and chemistry complement a particular substrate, and the induced fit hypothesis states that the active site moulds slightly around the…Pearson Edexcel
- Ethical implications of medical interventions
- Evaluating untested drugs during epidemics involves weighing potential benefits against risks, consent and equity.Pearson Edexcel
F
- Factors affecting rate of enzyme activity
- Rate rises with temperature until denaturation, has an optimum pH, and increases with substrate or enzyme concentration until a plateau when the other factor…Pearson Edexcel
- Fertilisation
- The events from the first contact between the gametes to the fusion of the haploid nuclei.Pearson Edexcel
G
- Gametogenesis
- The processes of oogenesis and spermatogenesis, producing the gametes involved in sexual reproduction in mammals.Pearson Edexcel
- Gel electrophoresis
- A technique that separates DNA fragments by size and charge, giving banding patterns that distinguish species and reveal relationships.Pearson Edexcel
- Gene mutation
- Illustrated by base deletions, insertions and substitutions, which can alter the amino acid sequence, as in sickle cell anaemia in humans.Pearson Edexcel
- Generative nucleus
- Divides by mitosis to produce two haploid male nuclei (gametes) that travel down the pollen tube to enter the embryo sac.Pearson Edexcel
H
- Hierarchical classification
- A system consisting of a hierarchy of domain, kingdom, phylum, class, order, family, genus and species, each level nested inside the one above.Pearson Edexcel
- High specific heat capacity
- A large energy change causes only a small temperature change, stabilising organism temperature and aquatic habitats.Pearson Edexcel
- Hydrolysis
- A reaction that adds water and splits a glycosidic bond, reversing condensation.Pearson Edexcel
L
- Limitations of the species definition
- The definition of a species as a group of organisms with similar characteristics that interbreed to produce fertile offspring fails for asexual organisms,…Pearson Edexcel
- Lipid roles
- Lipids store energy because their hydrocarbon chains are reduced and release much energy when oxidised, and they are waterproof and provide thermal insulation.Pearson Edexcel
M
- Magnesium ions
- A structural component of chlorophyll, so deficiency reduces photosynthesis and causes chlorosis.Pearson Edexcel
- Monosaccharides
- Single sugar units, which join to form disaccharides and polysaccharides.Pearson Edexcel
N
- Nitrate ions
- Provide nitrogen used to synthesise amino acids, which are polymerised into proteins, and for the bases of DNA, supporting replication and cell division.Pearson Edexcel
- Nucleoid
- A prokaryotic structure of unbound circular DNA, without a nuclear envelope.Pearson Edexcel
- Nucleotide
- Composed of a pentose sugar, a phosphate group, and a nitrogenous base; phosphodiester bonds link them into a sugar-phosphate backbone.Pearson Edexcel
P
- Peptide bond
- The link formed between the carboxyl group of one amino acid and the amine group of another during a condensation reaction.Pearson Edexcel
- Phosphate ions
- Incorporated into ADP and ATP, which transfer energy in cellular reactions.Pearson Edexcel
- Phospholipid structure
- Phospholipids contain glycerol, two fatty acids and a phosphate group, with a hydrophilic phosphate head and hydrophobic fatty acid tails.Pearson Edexcel
- Polar solvent
- Water dissolves ions and polar molecules, allowing transport in blood or sap and providing a medium for reactions.Pearson Edexcel
- Pollen grain
- Formed when a haploid microspore divides by mitosis to produce a generative nucleus and a tube nucleus inside a protective wall.Pearson Edexcel
- Protein structure and function
- Enzymes are globular proteins whose polypeptide chains fold so that hydrophilic groups face outwards and hydrophobic groups cluster inside, producing a…Pearson Edexcel
Q
- Quaternary structure
- The level of protein structure that involves multiple polypeptide subunits.Pearson Edexcel
R
- Resolution
- The ability to distinguish two close points as separate, achieved using light and electron microscopy.Pearson Edexcel
S
- Saturated and unsaturated fatty acids
- Saturated lipids have no carbon-carbon double bonds in their fatty acid chains, while unsaturated lipids have at least one, producing kinks.Pearson Edexcel
- Semi-conservative DNA replication
- DNA helicase breaks hydrogen bonds, DNA polymerase joins adjacent nucleotides, and DNA ligase joins fragments.Pearson Edexcel
- Staining
- A process that adds contrast to specimens in microscopy to distinguish specific organelles and structures.Pearson Edexcel
- Surface tension
- Hydrogen bonding produces this at the surface, which supports small organisms and contributes to capillary action.Pearson Edexcel
T
- Tertiary structure
- The overall 3D folding of a protein, stabilised by ionic, hydrogen and disulfide bonds between R groups.Pearson Edexcel
- Transcription
- In the nucleus, RNA polymerase builds a single-stranded mRNA molecule with a ribose sugar-phosphate backbone, complementary to the anti-sense DNA strand.Pearson Edexcel
- Treatment and prevention of viral diseases
- Viruses are not living cells, so antivirals must target virus replication rather than cell metabolism, and because established infection is difficult to…Pearson Edexcel
- Triglyceride synthesis
- A triglyceride is synthesised from one glycerol and three fatty acids, with each condensation reaction forming an ester bond and releasing water.Pearson Edexcel
- Tube nucleus
- Controls pollen tube growth, directing secretion of hydrolytic enzymes that digest style tissue to reach the embryo sac.Pearson Edexcel
V
- Viral structure and classification
- Classification of viruses is based on structure and nucleic acid types, as illustrated by λ phage (DNA), tobacco mosaic virus and Ebola (RNA) and human…Pearson Edexcel
Where these terms come from
Each definition is one we publish on a Biology B A-Level 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 Biology B revision or the glossary for every subject.
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