Use of apparatus and techniques — OCR A-Level Biology

This statement requires you to choose suitable apparatus and record quantitative measurements of mass, time, volume, temperature, length and pH. For each quantity you select equipment with an appropriate range and resolution: a top-pan or analytical balance for mass, a stopwatch or datalogger for time, a measuring cylinder, burette or pipette for volume, a thermometer or temperature probe for temperature, a ruler, callipers or graticule for length, and a pH meter or indicator for pH. You then read the instrument correctly, record the value with its unit and an appropriate number of significant figures, and note uncertainty. Assessment uses practical-based multiple-choice questions testing apparatus choice, correct reading and unit handling.

Choosing appropriate instrumentation means matching the instrument to the quantity being measured and the precision required. A colorimeter records the absorbance or transmission of light through a coloured solution, so it quantifies colour change objectively rather than by eye; it is calibrated with a blank or distilled water before use and a suitable filter is selected. A potometer records the rate of water uptake by a shoot as a proxy for transpiration rate; a bubble of air moves along a capillary scale as the shoot takes up water, and the distance moved in a set time is recorded. Both instruments give quantitative data, reducing subjective judgement. The choice depends on what is being measured: colour intensity for a colorimeter, water uptake for a potometer.

This practical technique requires you to select and correctly use laboratory glassware — such as graduated pipettes, burettes, volumetric pipettes, measuring cylinders and volumetric flasks — across a range of experimental procedures, and specifically to carry out serial dilutions. A serial dilution is a stepwise series in which each dilution is made from the previous one, giving a geometric fall in concentration. For example, to make a 1:10 series you transfer a fixed volume of stock into a known final volume, mix thoroughly, then take the same fixed volume from that tube into the next, repeating along the series. Correct glassware choice matters: a volumetric pipette delivers one accurate fixed volume, a measuring cylinder suits approximate volumes, and a volumetric flask makes up to a single calibrated volume.

This technique requires you to set up and use a light microscope correctly at both low power and high power, and to use an eyepiece graticule for measurement. Begin on low power to locate and focus the specimen, using the coarse focus, then switch to the high-power objective and refocus with the fine focus only. The eyepiece graticule is a scale in the eyepiece that must be calibrated for each objective using a stage micrometer of known scale; the calibration factor converts graticule units into actual lengths. Because the magnification changes between objectives, the graticule must be recalibrated at each power. Measurements are then taken by counting graticule divisions across the specimen and multiplying by the calibration factor, giving a real size in micrometres.

Scientific drawing is a transferable practical skill: you observe a specimen, then produce a clear, accurate representation that another biologist could interpret. Work with a sharp pencil on plain paper, draw large enough to show detail, and use continuous single lines rather than sketching or shading. Keep proportions faithful to what you observe rather than making the specimen look tidy. Labels are written outside the drawing with straight, unbroken leader lines that touch the structure named and do not cross. Annotations go beyond naming: they record observations such as colour, texture, relative size or a measured dimension. Add a title stating what is drawn and, where relevant, the magnification or scale. Drawings are assessed on accuracy of shape and proportion, clarity of line, correct labelling and the quality of annotations, so plan space before starting.

Qualitative reagents give a visible change when a particular biological molecule is present, so they confirm identity rather than measure amount. Benedict's reagent, heated with a reducing sugar such as glucose, turns from blue to a brick-red precipitate of copper(I) oxide; a non-reducing sugar such as sucrose needs prior hydrolysis with dilute acid, then neutralisation, before it gives that result. Iodine in potassium iodide solution turns blue-black with starch. Biuret reagent turns from blue to purple or lilac when peptide bonds are present, so it detects protein. Emulsion tests with ethanol and water give a cloudy white emulsion with lipids. Each test needs the correct sample volume, reagent excess and, for Benedict's, a water bath at around 70–80 °C. Controls and replicates support a valid conclusion.

Chromatography and electrophoresis both separate compounds by movement, but by different mechanisms. In paper or thin layer chromatography a sample is spotted on the stationary phase and a solvent moves up by capillary action; compounds partition between stationary and mobile phases and travel different distances according to solubility and affinity. The Rf value is the distance travelled by the compound divided by the distance travelled by the solvent front, and it is compared with known standards. In electrophoresis, charged molecules such as amino acids or proteins migrate through a gel under an applied voltage; the direction depends on charge and the rate on charge and size. Buffer maintains pH so charge is controlled. Both methods separate a mixture so components can be identified.

This practical technique requires you to plan and carry out measurements using living organisms so that both safety and ethics are satisfied. Safety means controlling biological, chemical and physical hazards: wear eye protection and gloves, disinfect surfaces, handle allergens and microorganisms aseptically, and dispose of waste correctly. Ethics means treating organisms with care and justifying their use: use the minimum number of organisms, choose the least sentient suitable species, avoid unnecessary pain or stress, keep conditions humane, and obtain approval where required. You must also ensure measurements are valid: control variables, use replicates, and record data accurately.

This technique requires you to measure a plant or animal response using appropriate apparatus and a controlled method. For a plant response you might measure phototropism or geotropism by recording the direction and angle of shoot or root growth over time, using a clinometer or protractor and ruler, with light or gravity as the controlled stimulus. For an animal response you might measure a reflex such as the response to a stimulus, recording reaction time with a ruler-drop or timing device, or measuring movement with a choice chamber. In both cases you must define the response, choose a measurable variable, control confounding variables such as temperature and light, take replicates, and record data in a suitable table. You should also consider the safety and ethical handling of the organism, and analyse the data to identify a trend.

Physiological functions are the normal jobs that cells, tissues, organs and organ systems carry out to keep an organism alive and functioning. Examples include gas exchange across a respiratory surface, absorption of nutrients in the gut, filtration and reabsorption in the kidney, conduction of impulses along neurones and contraction of muscle. When you investigate a physiological function practically, you link structure to the process: for instance, measuring heart or ventilation rate, or observing the effect of a variable on a living tissue. Interpret results in terms of the function being performed, not just the numbers recorded. Recognise that functions depend on transport, exchange and control, and that a change in one factor, such as temperature or substrate concentration, can alter the rate of the function.

This clause requires you to know and apply aseptic technique when working with microorganisms in both agar plates and broth. Aseptic technique keeps cultures pure and protects the worker and environment. Key actions: sterilise loops by flaming to red heat and allow cooling; flame the neck of bottles and tubes; lift lids rather than removing them fully; work close to a Bunsen flame with upward air currents; never place loops or lids on the bench; seal and incubate plates inverted at a suitable temperature; autoclave waste. For broth, flame the neck before and after transfer and keep the vessel angled. The distinction between agar plates (solid surface for colonies) and broth (liquid for suspension growth) matters when selecting the correct procedure.

This practical technique requires you to dissect an animal or plant organ while controlling biological and physical hazards. Before cutting, confirm the organ's identity and orientation, read the dissection instructions, and set out a clean board, the correct scalpel, scissors, forceps and mounted needle, plus eye protection where risk assessment requires it. Carry the scalpel with the blade covered and pointing down, cut away from your body and away from your fingers, and never cut towards a hand holding the specimen. Use forceps to steady tissue rather than fingers, make shallow controlled incisions, and pass instruments handle-first. Keep the workspace clear, dispose of sharps in the designated container and biological waste as your centre directs, and clean and store instruments afterwards. Safety is assessed by observing your conduct throughout, not by a written account alone.

Fieldwork sampling means choosing and applying a method that estimates a population or distribution without counting every individual. You should be able to use quadrats to sample sessile organisms, placing them randomly, for example by generating random coordinates within a grid, and to use a transect to record how distribution changes along an environmental gradient. For mobile animals, mark-release-recapture can be used, with the assumption that marked individuals mix randomly and are not affected by marking. You should also be able to use appropriate apparatus such as a pooter, sweep net or pitfall trap safely and record data systematically. Sampling is assessed by observing you carry out the technique and by the quality of the data you record, not by describing it in writing alone.

This practical technique covers three distinct ICT uses in biology. First, computer modelling: building a simulation of a biological system, such as a predator–prey model or a diffusion model, then changing variables to predict outcomes that would be slow or unsafe to test directly. Second, data logging: connecting sensors, for example a temperature probe or a pH electrode, to a logger that records readings at set intervals, giving continuous, objective data with fewer human reading errors. Third, software processing: entering raw readings into a spreadsheet or statistics package to calculate means, plot graphs and run tests. For each use, identify the purpose, the variable controlled or measured, and one limitation, such as a model's assumptions or a sensor's calibration drift.