GCSE biology required practicals: AQA checklist and revision guide

There are 10 required practicals in the AQA GCSE Biology specification, and every single one of them can appear on your exam. You will not be asked to physically carry out the experiment in the exam hall, but you will be expected to describe the method, identify variables, interpret results, and draw conclusions as if you had done it yourself.

Required practicals make up a significant chunk of marks across both papers. AQA designs questions that test whether you genuinely understand the science behind the practical, not just whether you memorised a set of steps. This guide lists all 10 practicals, explains what the exam expects for each one, and gives you a checklist to track your revision.

The table below lists every required practical on the AQA GCSE Biology specification, grouped by the paper they fall under. Each practical is tied to a specific topic area, and exam questions will usually appear within that topic's section of the paper.

For every required practical, you should be able to answer four things from memory: The method (step by step), the variables (independent, dependent, and control), the expected results, and the conclusion you can draw. Below is a brief breakdown of each one.

You place a specimen on a slide, add a drop of water and a stain such as iodine, then lower a coverslip to avoid air bubbles. Start on the lowest magnification and focus, then switch to higher magnification. You need to be able to calculate total magnification (eyepiece lens multiplied by objective lens) and use the formula: Real size = image size divided by magnification. Exam questions often ask you to label a biological drawing or calculate the actual size of a cell from a photomicrograph.

Agar plates are inoculated with bacteria, then paper discs soaked in different antiseptics or antibiotics are placed on the surface. After incubation at 25 degrees C (not higher in school labs, to prevent growth of harmful pathogens), you measure the clear zones around each disc. A larger clear zone means the substance is more effective at killing bacteria. You need to calculate the area of the clear zone using the formula pi r squared, where r is the radius of the zone minus the radius of the disc. Aseptic technique is essential – the exam loves asking why you sterilise equipment, tape the lid rather than seal it, and incubate at a controlled temperature.

Cylinders of potato are cut to equal lengths and placed in sugar solutions of different concentrations. After a set time, you remove them, blot dry, and measure the change in mass. The independent variable is the concentration of the sugar solution, the dependent variable is the percentage change in mass, and control variables include the volume of solution, size of potato cylinder, temperature, and time left in the solution. In dilute solutions the potato gains mass (water enters by osmosis), and in concentrated solutions it loses mass (water leaves). The point where there is no change in mass indicates that the solution is isotonic – the same concentration as the cell contents.

There are four food tests to know. Benedict's reagent turns from blue to green, yellow, orange, or brick red when heated with reducing sugars. Iodine solution turns from brown-orange to blue-black in the presence of starch. Biuret reagent turns from blue to purple when protein is present. The ethanol emulsion test involves dissolving the food in ethanol, then adding water – a cloudy white layer indicates lipids. Exam questions may present results in a table and ask you to identify which nutrients are present in an unknown food sample.

Amylase breaks down starch into sugars. You set up test tubes with amylase and starch at different pH values using buffer solutions, then test samples with iodine at regular intervals. When the iodine no longer turns blue-black, all the starch has been digested. The time taken for starch to be fully broken down is your dependent variable. Amylase works fastest at its optimum pH (around pH 7) and is denatured at extreme pH values. Be ready to explain denaturation – the active site changes shape so the substrate can no longer fit, and this is a permanent change.

An aquatic plant such as pondweed is placed in water under a lamp. You count the bubbles of oxygen produced per minute at different distances from the lamp. Moving the lamp closer increases light intensity and increases the rate of photosynthesis – up to a point, after which another factor (carbon dioxide or temperature) becomes limiting. Light intensity follows an inverse square law, so if you halve the distance you quadruple the light intensity. Exam questions frequently ask you to plot or interpret a graph showing rate against light intensity, or to explain why the graph plateaus.

The simplest version uses a ruler drop test. One person holds a ruler vertically and drops it without warning. The other person catches it, and the distance the ruler falls is recorded. A shorter drop distance means a faster reaction time. You can investigate the effect of factors such as caffeine, practice, distraction, or time of day. Control variables include the hand position, the same ruler, and the same person catching. Repeated measurements and calculating a mean are important for reliability. Exam questions often ask you to identify anomalous results from a data table or explain how the investigation could be made more valid.

Seedlings are grown in different conditions to observe phototropism (growth towards light) or gravitropism (growth in response to gravity). A clinostat can be used to eliminate the effect of gravity. The hormone auxin causes cell elongation – it moves to the shaded side of a shoot, causing uneven growth that bends the shoot towards the light. Exam questions may ask you to explain the results using auxin redistribution or to design an experiment to test the effect of light direction on plant growth.

You use quadrats and transects to measure the distribution and abundance of organisms in a habitat. A quadrat is placed randomly (using random number coordinates) and you count the organisms inside. Repeat this many times and calculate a mean to estimate the population in the whole area. A transect is a line along which quadrats are placed at regular intervals to show how a population changes across a habitat. Exam questions often ask you to calculate the estimated total population by multiplying the mean per quadrat by the total number of quadrats that would fit in the area, or to explain why random sampling reduces bias.

Fresh milk is mixed with lipase and a pH indicator such as phenolphthalein or cresol red. As lipase breaks down the fat in milk, it produces fatty acids that lower the pH, causing the indicator to change colour. You measure how long the colour change takes at different temperatures. Higher temperatures speed up the reaction (up to the point where lipase is denatured). This practical tests your understanding of enzymes, decomposition, and the effect of temperature on biological processes. The independent variable is temperature, the dependent variable is the time taken for the colour change, and control variables include the volume of milk, volume of lipase, and concentration of lipase.

AQA tends to ask the same types of questions about required practicals year after year. Knowing these patterns means you can prepare your answers in advance.

Describe the method questions ask you to list the steps in order. Be specific – name the equipment, state the quantities, and explain how you would take measurements. Vague answers like "test the substance" score zero.

Identify the variables questions expect you to name the independent variable (what you change), the dependent variable (what you measure), and at least two control variables (what you keep the same). You should also state how you would control each one.

Explain the results questions require you to use scientific knowledge to explain why the results turned out as they did. For example, explaining that a potato gained mass in a dilute solution because water moved into the cells by osmosis, from a region of higher water potential to a region of lower water potential.

Evaluate the method questions ask you to identify weaknesses and suggest improvements. Common improvements include repeating the experiment and calculating a mean, using more data points, using a more precise measuring instrument, or controlling a variable that was not controlled in the original method.

Six-mark extended response questions sometimes focus entirely on a required practical. These need a logical structure – describe the method, explain the science, and link your answer to the context of the question.

Reading through the method is not enough. Required practicals test whether you can think like a scientist, not whether you can recite a recipe.

For each practical, write out the method from memory. Then check it against your notes or a Cognito video. Pay attention to the steps you forgot or got wrong – those are the ones that would cost you marks.

Practise drawing results tables with the correct headings, units, and number of columns. AQA frequently asks you to draw or complete a table, and marks are awarded for correct column headings with units, consistent decimal places, and the independent variable in the left column.

Work through past paper questions on each practical. AQA recycles similar question styles, so the more past papers you complete, the more familiar the wording becomes. After answering each question, check the mark scheme carefully and note any marking points you missed.

Sketch the graphs you would expect for each practical. For osmosis, you should be able to draw a line showing percentage change in mass against concentration. For photosynthesis, you should be able to draw a curve that rises and then plateaus. Labelling the axes correctly and plotting accurately are worth marks on their own.