AQA GCSE Required Practicals: The Ones You Have to Memorise (and How)

Quick answer: AQA GCSE Science has 21 required practicals in Combined Science (7 biology, 6 chemistry, 8 physics) and 28 across the separate sciences, and questions about them make up at least 15% of your written-exam marks. You are not marked on doing the experiment - you are marked on recalling the method, naming the variables, explaining why each step matters, and spotting the errors, so revise those four things for every practical rather than re-watching a demo.

I sit Cambridge IGCSE, not AQA - but here is what nobody tells you: the science practicals overlap so heavily that when I first read the AQA list, I had already done half of them. Osmosis with potato cylinders, the food tests, pondweed and light intensity - same experiments, same trap questions. So the recall answers below are the ones examiners reward whichever board you are on.

The mistake I made early was treating practicals as the "fun" lessons and revising them last, the night before. They are not a footnote. On an AQA paper they are a guaranteed block of marks - and unlike an unseen essay question, the answers barely change year to year.

Why 15% of your marks live here

AQA does not do coursework or a separate practical exam. Instead, the specification promises that at least 15% of the total marks in your written papers come from questions that draw on the required practicals - a lot of marks hanging on a fixed, known list.

They are also the most predictable marks on the paper: the examiner can only ask about method, variables, results and evaluation, and those buckets repeat for every practical - so once you know the pattern you can revise any of the 21 (or 28) in about ten minutes each.

The four things examiners ask about every practical

Whatever the experiment, the questions come from the same four places - so a revision sheet that answers all four has the practical covered.

• Method - the apparatus and the order of steps. Watch for the one step that is easy to forget (blotting the potato dry, flaming the loop, using a water bath not a naked flame).
• Variables - the independent variable (what you change), the dependent variable (what you measure), and the control variables (what you keep the same to make it a fair test). Naming all three correctly is worth easy marks and most students only name two.
• Results - how you process the data: repeats and a mean, a line graph with the independent variable on the x-axis, and often a calculation.
• Evaluation - the sources of error and one realistic improvement. "Human reaction time when starting the stopwatch" and "repeat and take a mean" are the safe answers.

Worked example: the osmosis practical, revised properly

This is RP3 in Biology and the most examined practical, so learn it as your template - written the way a mark scheme wants it.

1. The method. Cut potato cylinders with a cork borer and trim them to the same length. Blot each one dry and record its starting mass. Place each in a different sucrose concentration (say 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 mol per dm3) for a set time, then remove, blot dry again, and record the final mass.

1. Name the variables. Independent variable = concentration of the sucrose solution. Dependent variable = percentage change in mass. Control variables = temperature, time left in solution, volume of solution, and the size and surface area of the potato cylinders.

1. Do the calculation. You do not compare raw masses - you calculate percentage change in mass = (final mass - initial mass) / initial mass x 100. Say a cylinder in distilled water went from 4.2 g to 4.6 g: that is (4.6 - 4.2) / 4.2 x 100 = +9.5%. One in the 1.0 mol per dm3 solution went from 4.0 g to 3.4 g: that is (3.4 - 4.0) / 4.0 x 100 = -15%. Positive means water moved in by osmosis; negative means water moved out.

1. Read the graph. Plot concentration on the x-axis and percentage change on the y-axis, then draw a line of best fit. The point where the line crosses zero (no change in mass) tells you the concentration where the solution outside equals the cell contents inside - the water potentials are equal, so there is no net osmosis.

1. The two marks people drop. Why percentage change, not raw mass change? The cylinders start at slightly different masses, so percentage makes the comparison fair. Why blot the potato dry? Surface water adds mass that has nothing to do with osmosis.

If any step of that felt shaky, paste the practical into /explain, set your board to AQA, and ask it to walk you through the variables and the calculation line by line.

The recall questions that catch people out

The one-liners examiners love, with the answer they want.

• Osmosis - why repeat at each concentration and take a mean? To reduce the effect of random error and make results more reliable.
• Microbiology (Biology only) - why pass the inoculating loop through a flame? To sterilise it and kill unwanted microorganisms, so you only grow the culture you want.
• Microbiology - why incubate at 25 degrees C in school, not 37? To reduce the risk of growing harmful pathogens that thrive at human body temperature.
• Enzymes and pH - why use a water bath instead of heating with a Bunsen? To keep the temperature constant and even, so temperature is controlled and does not affect the rate.
• Photosynthesis with pondweed - why place a beaker of water between the lamp and the plant? It absorbs heat from the lamp so that light intensity, not temperature, is the only variable changing.
• Microscopy - the magnification formula? Magnification = image size / actual size (and remember 1 mm = 1000 micrometres when your units do not match).

Notice the pattern: nearly every "why" answer is really "so it stays a fair test" or "so it is safe." See that, and you can reason out answers you never revised.

How to revise all of them without burning out

Do not re-read your practical booklet - that is recognition, not recall. Make one index card per practical with four boxes (method, variables, results, evaluation), then close it and rebuild it from memory.

Turn the recall one-liners above into a deck on /flashcards so the "why" answers come back automatically under pressure. When you can write a full method from memory, test it: type your answer to a six-mark practical question into /grade and let it mark against the AQA style, so you see exactly which marking points you missed. Any theory that still will not stick - water potential, the inverse-square light law - drop into /explain to be re-taught at your level.

Test yourself

1. In the osmosis practical, a potato cylinder's mass changes from 5.0 g to 4.4 g. Calculate the percentage change in mass.
2. Name the independent, dependent and one control variable for the effect of light intensity on the rate of photosynthesis.
3. Give one reason results are more reliable when you repeat readings and take a mean.

Quick answers: (1) (4.4 - 5.0) / 5.0 x 100 = -12%. (2) Independent = light intensity (distance of lamp); dependent = number of oxygen bubbles per minute; control = temperature, carbon dioxide concentration, or the same piece of pondweed. (3) It reduces the effect of random error, giving a more reliable mean.

Want a full set in your board's style? Generate a practicals paper on /mock-exam or re-teach any weak spot on /explain.

FAQ

How many required practicals are there in AQA GCSE Science? 21 for Combined Science (7 biology, 6 chemistry, 8 physics) and 28 in total if you take the three separate sciences: 10 biology, 8 chemistry and 10 physics.

Do I have to memorise every practical? Yes - the exam can question any of them, and there is no formula sheet for methods. But it is only four things per practical (method, variables, results, evaluation), which is far less than it sounds.

Are the required practicals the same for Combined and Triple? Combined Science shares most of them; the separate sciences add extra ones such as the microbiology culturing and rate-of-decay practicals in Biology, and titration and ion tests in Chemistry.

What is the difference between accuracy and precision? Accuracy is how close a reading is to the true value; precision is how close repeated readings are to each other. Reliability - getting consistent results when you repeat - is why the mark scheme rewards repeats and a mean.

In short: Learn each AQA required practical as four fixed boxes - method, variables, results, evaluation - and you turn 15% of your science marks into some of the most predictable points on the whole paper.