Required practicals · Biology
Biology required practicals
AQA sets 10 required practicals for Biology. This page covers the AQA specification only — not Edexcel, OCR or any other exam board — so check with your teacher which board you’re actually sitting before relying on it. (MarkMatch as a whole is AQA-only for now, too.)
Every practical below has a real method to know, but not everything is equally exam-critical — the greenbox under each one is what actually costs marks if you don’t know it; the grey box is useful context you don’t need to stress about memorising.
RP1
Microscopy
Prepare a slide of plant/animal cells and use a light microscope to observe, draw and measure them.
Equipment
Light microscope, Slide, coverslip, mounted needle, Onion/other plant tissue, Iodine or methylene blue stain, Pipette, scalpel, forceps
Method
- Cut a thin section of tissue (or peel a thin layer, e.g. onion epidermis).
- Place it flat in a drop of water or stain on a slide.
- Lower a coverslip at an angle using a mounted needle to avoid trapping air bubbles.
- Start on the LOWEST magnification objective lens to find and centre the specimen, then increase magnification.
- Produce a labelled scientific drawing; calculate the actual size of a structure using the magnification formula.
You definitely need to know
- I = A × M (Image size = Actual size × Magnification) — rearrange for whichever value is missing.
- Convert mm ↔ μm by ×1000 / ÷1000 BEFORE dividing — the single most common lost mark.
- Always start on low power, not high power, to locate the specimen first.
- A stain (e.g. iodine or methylene blue) is added because it increases the contrast between structures (e.g. the nucleus) and the rest of the cell, making them visible under the microscope — "increases contrast" is the specific creditable idea; "so you can see it better" alone restates the question rather than answering it.
- A scientific drawing has FOUR independently creditable features, any two of which answer a "state two features" question: (1) a title stating what is shown, (2) clear, unbroken/continuous lines with no shading or colouring, (3) a scale line or the magnification stated, (4) label lines drawn with a ruler that do not cross.
Good to know — less essential
- Electron microscopes have far higher resolution than light microscopes but need a dead, vacuum-mounted sample — you won’t need to operate one, just compare the two (see the notes page for the full comparison table).
Common exam question types
- Calculate the magnification/actual size/image size given the other two values.
- Explain why the coverslip is lowered at an angle (avoids air bubbles obscuring the view).
- Suggest why low power is used first.
RP2Biology only
Culturing microorganisms
Use aseptic technique to investigate the effect of antiseptics/antibiotics on bacterial growth using agar plates.
Equipment
Agar plates, Bacterial culture + sterile inoculating loop, Bunsen burner, Paper discs soaked in antiseptic/antibiotic, Forceps, sticky tape
Method
- Sterilise the inoculating loop in a Bunsen flame before and after use.
- Spread the bacterial culture evenly across the agar using the loop, working near the Bunsen flame ("cone of protection").
- Place antiseptic-soaked paper discs on the agar using sterilised forceps, spaced apart.
- Tape the lid on (not sealed all round — allows gas exchange but stops contamination) and incubate at 25°C, not higher (school labs avoid 37°C to reduce risk of growing pathogens harmful to humans).
- After 48 hours, measure the diameter of the clear zone (no bacterial growth) around each disc.
| Independent | The antiseptic or antibiotic being tested (or its concentration) |
| Dependent | Diameter (or area) of the clear zone of inhibition around each disc |
| Control | Bacteria/agar plate type; Incubation temperature and time; Volume/concentration soaked into each disc; Spacing of the discs |
You definitely need to know
- Aseptic technique = sterilise equipment, work near a flame, tape (don’t seal) the lid, wash hands.
- A bigger clear zone around a disc = that antiseptic/antibiotic is more effective at inhibiting bacterial growth.
- Incubate at 25°C in school labs, not 37°C, to minimise the risk of growing pathogens that could infect humans.
- Area of the clear zone, not just diameter, is sometimes needed: A = πr².
Good to know — less essential
- This is Biology-only (not Combined Science Trilogy) — see practical-topics.ts tripleOnly flag.
Safety
Never open incubated plates once bacteria has grown — inspect through the lid.
Common exam question types
- Calculate the area of a clear zone from its diameter.
- Explain why the lid is taped, not sealed.
- Explain why 25°C is used instead of body temperature.
- Suggest a control/comparison needed (e.g. a disc soaked in water only).
RP3
Osmosis
Investigate the effect of a range of concentrations of sugar (or salt) solution on the mass of plant tissue, to find osmosis by mass change.
Equipment
Potato (or similar) cut into equal cylinders, A range of sugar solution concentrations (incl. distilled water), Boiling tubes, Balance, ruler, cork borer, scalpel
Method
- Cut equal-sized cylinders of potato using a cork borer; trim to the same length with a scalpel and ruler.
- Blot each cylinder dry and record its starting mass.
- Place one cylinder into each concentration of sugar solution; leave for a set time (e.g. 24 hours).
- Remove, blot dry again, and record the final mass.
- Calculate percentage change in mass for each concentration: (final − initial) ÷ initial × 100.
- Plot percentage change in mass against concentration.
| Independent | Concentration of the sugar solution |
| Dependent | Percentage change in mass of the potato cylinder |
| Control | Size/mass of the cylinders; Time left in the solution; Temperature; Type/variety of potato |
You definitely need to know
- Percentage change (not raw mass change) is required — cylinders start at slightly different masses.
- Blotting dry before EACH weighing is essential (surface water would inflate the mass reading).
- Where mass increase = decrease crosses zero, that concentration matches the potato’s own solute concentration (water potential) — a classic "estimate from the graph" question.
- Osmosis is the movement of water from a dilute (high water potential) to a concentrated (low water potential) solution through a partially permeable membrane.
Common exam question types
- Calculate percentage change in mass from raw data.
- Explain the mass change at a named concentration in terms of water movement.
- Read off/estimate the concentration at which there is no net change in mass.
- Identify a control variable and explain why it must be controlled.
RP4
Food tests
Use qualitative reagent tests to identify the presence of starch, sugars, proteins and lipids in food samples.
Equipment
Food samples (ground/dissolved), Iodine solution, Benedict’s solution + water bath, Biuret solution (or sodium hydroxide + copper sulfate), Ethanol + water
Method
- Starch: add a few drops of iodine solution directly to the sample — blue-black = starch present.
- Sugars (reducing sugars): add Benedict’s solution, heat in a water bath at 75°C+ — brick-red precipitate = sugar present (stays blue if none).
- Protein: add biuret solution (or NaOH then a few drops of copper sulfate) at room temperature — purple/lilac = protein present.
- Lipids: shake the sample with ethanol, then pour into water — a cloudy white emulsion = lipid present.
You definitely need to know
- Iodine test result colours: orange-brown → blue-black (positive).
- Benedict’s test needs HEATING; biuret and iodine tests do not.
- Benedict’s colour change sequence with increasing sugar concentration: blue → green → yellow → orange → brick-red.
- The emulsion test result (cloudy/milky white) is a physical change, not a colour change — easy to phrase wrong.
Safety
Ethanol is flammable — keep away from the Bunsen flame during the emulsion test.
Common exam question types
- State the positive result colour for a named test.
- Describe the method for a named test.
- Explain why Benedict’s solution must be heated but biuret does not need to be.
- Given a table of colours across foods, identify which nutrients are present.
RP5
Enzymes and pH
Investigate the effect of pH on the rate of reaction of amylase enzyme breaking down starch.
Equipment
Amylase solution, Starch solution, Buffer solutions at different pH values, Spotting tile, Iodine solution, Stopwatch, water bath
Method
- Mix amylase, starch solution and a buffer of a chosen pH in a test tube; start the stopwatch.
- Every 10-30 seconds, use a pipette to take a drop of the mixture and place it in a fresh well of the spotting tile with iodine already in it.
- Repeat sampling until the iodine no longer turns blue-black — i.e. the starch has been completely broken down.
- Record the time taken; repeat at each pH value, keeping temperature and concentrations constant (e.g. using a water bath).
- Calculate rate = 1 ÷ time for each pH and plot rate against pH.
| Independent | pH of the buffer |
| Dependent | Time taken for starch to disappear (or 1/time = rate) |
| Control | Temperature; Concentration/volume of amylase and starch; Sampling interval |
You definitely need to know
- The end point is when iodine STAYS orange-brown (no blue-black) — starch is gone.
- Rate = 1 ÷ time is the standard way AQA wants this expressed, not raw time alone.
- Enzyme activity rises to an optimum pH then falls sharply either side — link this to the enzyme’s active site changing shape (denaturing) at extreme pH.
- A water bath is used to keep TEMPERATURE constant — a very common "control variable" answer that’s easy to muddle with pH itself.
Common exam question types
- Explain the shape of a rate-against-pH graph in terms of enzyme structure (denaturation, active site).
- Explain why sampling continues until iodine stays orange-brown.
- Identify and justify a control variable.
- Suggest an improvement to make results more reliable (e.g. shorter sampling intervals, repeats).
RP6
Photosynthesis and light intensity
Investigate the effect of light intensity on the rate of photosynthesis using pondweed (e.g. Elodea/Cabomba).
Equipment
Pondweed, Lamp, Ruler, Beaker, sodium hydrogencarbonate solution (extra CO₂), Stopwatch
Method
- Cut the pondweed stem underwater and set it up in sodium hydrogencarbonate solution with the cut end near the surface.
- Position a lamp at a set distance from the beaker.
- Count the number of bubbles of oxygen released in one minute (or measure the volume of gas collected in a capillary tube/gas syringe).
- Repeat at several different lamp distances, calculating 1/distance² to represent light intensity.
- Plot rate of bubbling against light intensity (1/distance²).
| Independent | Light intensity (distance of the lamp) |
| Dependent | Rate of oxygen production (bubbles/min or gas volume) |
| Control | Temperature (a water bath or heat-absorbing glass tank of water between lamp and beaker, to stop the lamp’s heat itself changing rate); CO₂ concentration; Species/length of pondweed |
You definitely need to know
- Light intensity ∝ 1/distance² (the inverse square law) — you must be able to calculate this, not just distance itself.
- A heat-absorbing water bath/tank is placed between lamp and plant so the lamp’s HEAT isn’t a confounding variable — a very commonly tested control.
- As light intensity increases, rate of photosynthesis increases then plateaus once another factor (CO₂ or temperature) becomes limiting.
- Counting bubbles is a valid but less accurate method than measuring gas volume — expect a question on limitations.
Common exam question types
- Calculate light intensity using 1/d² given a distance.
- Explain why a water bath/heat filter is used between lamp and plant.
- Explain the shape of the rate-vs-light-intensity graph using limiting factors.
- Evaluate the reliability of counting bubbles as a method.
RP7
Reaction time
Measure human reaction time using the ruler-drop method.
Equipment
Ruler, A partner to drop it
Method
- One person holds a ruler vertically, zero end level with the top of the test subject’s open finger and thumb.
- The ruler is dropped without warning; the subject catches it as fast as possible.
- Record the distance (cm) the ruler fell before being caught.
- Repeat several times (e.g. 5+) and calculate a mean, ignoring anomalous results.
- Optionally repeat with a variable that might affect reaction time (e.g. caffeine, distraction) and compare means.
| Independent | The factor being tested (e.g. caffeine intake, a distraction, dominant vs non-dominant hand) — varies by investigation; the base method alone has no fixed independent variable |
| Dependent | Reaction distance/time (mean of several repeats, excluding anomalies) |
| Control | Same person dropping and catching the ruler each time; Same ruler/apparatus; Same warning/no-warning routine before each drop |
You definitely need to know
- A shorter distance caught = a FASTER reaction time (this trips people up under exam pressure — smaller number is better here).
- Repeats and a calculated mean (excluding anomalies) are needed for reliability — expect a "why repeat" question.
- This is a nervous-system reflex-style question: stimulus (ruler falling, seen) → receptor (eye) → coordinator (CNS/brain) → effector (muscles in the hand) → response (catching).
Common exam question types
- Calculate a mean reaction distance, identifying and excluding an anomaly.
- Explain why the test is repeated.
- Describe the pathway from stimulus to response using correct terms (receptor, coordinator, effector).
- Suggest a variable that could be investigated and how the method would change.
RP8Biology only
Plant growth (light and gravity)
Investigate the effect of light or gravity on the growth of germinating seedlings (tropisms).
Equipment
Germinating seedlings (e.g. cress), Petri dish/pot, Black card or a rotating clinostat, Light source (for phototropism) or turntable placed on its side (for gravitropism)
Method
- Set up germinating seedlings so light or gravity is the only variable changing direction (e.g. a box with a hole letting light in from one side only, or seedlings pinned horizontally to test gravitropism).
- Include a control set-up with even light from all sides (or the normal vertical orientation for the gravity version).
- Leave for several days, keeping the seedlings watered.
- Observe and record the direction of growth of the shoot and/or root.
| Independent | Direction of the light source (phototropism version) or orientation relative to gravity (gravitropism version) |
| Dependent | Direction of growth of the shoot/root |
| Control | Same species/batch of seedlings; Watering, temperature and starting conditions; A comparison set-up with even light or normal vertical orientation |
You definitely need to know
- Shoots are positively phototropic (grow towards light) and negatively gravitropic (grow away from gravity/upwards).
- Roots are negatively phototropic and positively gravitropic (grow downwards).
- The cause is uneven distribution of the plant hormone auxin — auxin accumulates on the shaded/lower side, making cells elongate more there, bending the shoot/root.
- A control with even light or a normal vertical set-up is essential to show the response is due to the DIRECTIONAL stimulus, not growth itself.
Good to know — less essential
- This is Biology-only (not Combined Science Trilogy).
Common exam question types
- Explain the direction of growth observed in terms of auxin distribution.
- Explain why a control set-up is included.
- Describe how the experiment could be set up to test light OR gravity specifically.
RP9
Sampling a population
Use quadrats and, if needed, transects to determine the distribution and abundance of organisms in a habitat.
Equipment
Quadrat (known area, e.g. 0.25m²), Tape measure (for a transect), Random number generator/table
Method
- Mark out the study area; generate random coordinates (using random numbers, NOT by eye — avoids bias) to place the quadrat.
- Count/estimate percentage cover of the target species inside the quadrat.
- Repeat at many random points, then calculate a mean.
- To estimate total population: mean count per quadrat × (total area ÷ quadrat area).
- For a transect (e.g. across an environmental gradient): lay a tape measure in a line and sample at set intervals along it.
You definitely need to know
- Random placement (using random numbers) is essential to avoid sampling bias — a very common "explain why" question.
- Population estimate formula: mean number per quadrat × (total area ÷ area of one quadrat).
- A transect is used specifically to see how distribution CHANGES across a gradient (e.g. moving away from a hedge, up a shore).
- Percentage cover (not always a count) is used for things like grass that are hard to count individually.
Common exam question types
- Calculate an estimated population size from quadrat data.
- Explain why quadrat positions must be random.
- Explain when a transect would be more appropriate than random quadrats.
- Suggest how to improve the reliability of the estimate (more quadrats, larger sample area).
RP10Biology only
Rate of decay
Investigate the effect of temperature on the rate of decay of milk by measuring pH change over time.
Equipment
Fresh milk, Sodium carbonate solution + phenolphthalein indicator, Water baths at different temperatures, Pipette, test tubes, stopwatch
Method
- Add milk to a set volume of sodium carbonate solution and phenolphthalein indicator (bright pink when alkaline) in a test tube.
- Place in a water bath at a chosen temperature.
- Every set time interval, add a drop of milk (or sample) and time until the pink colour disappears (the mixture turns colourless/acidic) — this marks the milk has started to sour/decay.
- Repeat at several different temperatures, keeping volumes and indicator amount constant.
- Plot rate of decay (1/time) against temperature.
| Independent | Temperature of the water bath |
| Dependent | Time for the indicator to change colour (or 1/time = rate) |
| Control | Volume of milk added each time; Volume/concentration of sodium carbonate and indicator |
You definitely need to know
- The colour change (pink → colourless) happens because bacteria in the milk produce LACTIC ACID as they decompose it, neutralising the alkali.
- Rate generally increases with temperature up to an optimum (bacterial enzymes work faster), then falls as high temperatures denature the bacteria’s enzymes.
- This is Biology-only (not Combined Science Trilogy).
Common exam question types
- Explain why the indicator changes colour.
- Explain the shape of a rate-against-temperature graph, including why rate falls at high temperatures.
- Identify a variable that must be controlled and why.