AQA A Level Biology Paper 3 (7402/3) from June 2025 is the synoptic paper: 78 marks in 2 hours, with Section A built around practical and data questions from any part of the specification and Section B the 25-mark essay. The question paper, mark scheme and examiners’ report are on the AQA past papers page, and all the essay resources are on the Paper 3 essay page.
What the paper tested
Section A had six questions worth 53 marks. Question 1 was bacterial growth with a log-scale calculation; Question 2 the nephron, blood water potential and a 5-mark evaluation of a rat study on kidney damage; Question 3 populations, mark-release-recapture and species identification; Question 4 proteins, antibodies and a 3-mark evaluation of an immune-response study; Question 5 Hardy–Weinberg and gene expression in the context of cleft lip and palate; and Question 6 gas exchange, lung fibrosis and a 4-mark evaluation of two drug trials. Nearly 17 marks were for considering margins of error, accuracy and the validity of conclusions, which is the Paper 3 signature.
The essay
The two titles were ‘The importance of condensation and hydrolysis reactions in biological systems’ and ‘The importance of responses to changes in the internal and external environment of organisms’. Students split evenly between them, and the examiners said the first was answered less well.
On condensation and hydrolysis, the common fault was writing long descriptions of a topic with the reaction mentioned only at the end, a page on synaptic transmission that finishes with ‘acetylcholine is hydrolysed’, for example. The AO2 part, saying why the reaction matters in that system, was often missing or wrong. The examiners also listed errors they saw repeatedly: hydrogen bonds being ‘hydrolysed’, water being hydrolysed, reduced coenzymes formed by condensation, and myosin binding to actin by condensation. Topics that worked well included DNA replication, ATP, digestion, protein synthesis and the immune system.
On responses to change, the recurring fault was describing a process without first saying what the change was and what the response was. Where students did frame each paragraph as change, detection, response, the examiners gave credit, and the immune system, photosynthesis, receptors and control of heart rate were well handled.
Our guide to choosing topic areas and the example essay show how to structure paragraphs so that every one earns AO2 credit.
Where students lost marks in Section A
4.4 Why further investigation was needed (3 marks)
The lowest-scoring part of the paper. The question told students not to refer to statistical tests, repeats or sample size, and many did anyway, reeling off ‘no stats test’, ‘small sample’, ‘other factors’. Others suggested what the scientists should do next rather than why they reached their decision, or wrote about testing in humans or in males, which had nothing to do with the study. Answer the question in front of you, using the information in it.
5.1 Why Hardy–Weinberg could not be used (2 marks)
About 15% scored both marks. The data gave numbers of affected babies, not allele frequencies, and the examiners wanted students to see that the conditions for the equation were not met in this context. Many instead wrote that they did not know whether the allele was dominant or recessive, or confused the situation with mark-release-recapture. The {a('/tutoring-blog/hardy-weinberg-calculations-a-level-biology','Hardy–Weinberg explainer')} covers what the equation assumes.
2.3 Evaluating a rat study (5 marks)
Fewer than 1% of students scored all five marks. The weakest points were interpreting P < 0.01 correctly (some did not know that < means ‘less than’; many wrote ‘the results are significant’ with no qualification), and recognising that 160-day-old rats are adults so the study did cover adulthood. ‘Small sample size’ scored only when it was followed by ‘so not representative’.
2.1 Nephron table (2 marks)
About 20% scored both marks. Ticks appeared in every combination, and the most common omission was that water is reabsorbed from the filtrate in the proximal convoluted tubule, not only in the collecting duct. The {a('/tutoring-blog/aqa-a-level-biology-kidney-quiz','kidney quiz')} is a quick check on this.
3.3 Mark-release-recapture (2 marks)
Just under a third scored two marks, which surprised the examiners. The usual error was using the wrong total for the second sample. The formula is on the {a('/tutoring-blog/aqa-a-level-biology-populations-ecosystems-quiz','populations in ecosystems quiz')} page.
1.2 Log scales (2 marks)
About a third scored two marks. The question said to use the 10x button to convert from log10; many used the log button instead, or just read the difference in log values off the graph and gave that as the answer.
How to use this paper
Do Section A timed (about 70 minutes) and the essay separately, planned for 5 minutes and written in 40.
Mark Section A against the scheme and read the examiners’ comment on each part. The theme of this paper is ‘use the information you were given’; rote evaluation phrases scored badly.
Mark your essay against the levels descriptors, then compare it with the example essay. Write a second plan for the title you did not choose.
The handling data and required practical question sets are the right follow-up for Section A.
Questions and examiners’ comments are summarised from AQA’s published question paper, mark scheme and report for 7402/3 June 2025, © AQA. Figures quoted are AQA’s.