OCR A Level Biology Paper 3, Unified Biology (H420/03), from June 2025 is the synoptic paper: 70 marks in 1 hour 30 minutes, drawing on all six modules with a heavy practical and data element. The question paper, mark scheme and examiners’ report are on the OCR past papers page.
What the paper tested
Plant and animal responses took 15 marks, with a 6-mark question identifying muscle tissues from photomicrographs and a question on antibodies at the neuromuscular junction. Manipulating genomes took 13, including a 6-mark discussion of gene editing against established gene therapy. Nucleic acids (7 marks, including DNA extraction and post-transcriptional regulation), communicable disease (7), analysis and evaluation (11 together) and transport in plants and exchange surfaces in Question 1 made up the rest. Microscopy (PAG 1), chromatography and electrophoresis (PAG 6) and transport across membranes (PAG 8) were the practicals in play.
Start with the plant and animal responses written quiz, the manipulating genomes written quiz and the nucleic acids written quiz.
Where students lost marks
3(a) Identifying muscle tissue from photomicrographs (6 marks)
This is a levels-marked question and the marks were for the quality of the evidence, not just the identifications. Many students could not access the first level because they named the tissues without any supporting evidence or terminology. Where students wrote ‘uninucleate’ or ‘multinucleate’ they often did not say whether they meant the cell or the tissue. Learn the three tissues as a table of features (striations, branching, intercalated discs, nuclei per cell, spindle shape) and write the evidence before the conclusion.
6(b) Gene editing versus gene therapy (6 marks)
The gene-editing information was new to most students, and the best answers combined it with what they knew about gene therapy: a more permanent treatment, fewer immune responses, the possibility of treating conditions caused by dominant alleles. The ethical issues most students raised were risk, religious objection and cosmetic use, but few developed them enough for the top level. In a ‘discuss’ question, each issue needs a sentence of explanation, not a label.
3(c)(ii) Antibodies at the neuromuscular junction (2 marks)
Fewer than half the cohort scored a mark. Students said ‘less depolarisation’ or ‘less calcium released’, but the marks required the location: less depolarisation of the muscle cell membrane, so fewer calcium ions released from the sarcoplasmic reticulum. In an unfamiliar context, the technical terms are what separate a one-mark answer from two.
4(b) Post-transcriptional regulation (2 marks)
Most students gained one mark for splicing out introns; fewer mentioned joining exons. The errors were referring to the lac operon or histone modification (which are transcriptional), ‘removing introns from DNA’, ‘extrons’, and using ‘splice’ to mean ‘remove’.
4(c)(ii) Improving a DNA extraction method (1 mark)
Only some students scored. The expected answer was to add protease to break down the histones; ‘protease to break down proteins’ without saying which proteins was not enough. Adding salt to help precipitation or keeping the sample cold were also accepted.
1(b)(ii), 2(a)(i), 5(c) and 7(a)(i)
Several one-mark parts were marked hard by the examiners: stating a limitation of a surface-area calculation, describing a feature of DNA, explaining an analysis step and suggesting a reason in an evaluation. These are the marks that separate grades on Paper 3, and they come from reading the data carefully rather than from recall.
How to use this paper
Sit it timed, 1 hour 30 minutes. It is shorter than Papers 1 and 2 but the questions are denser, so practise pacing.
Mark it and read the examiners’ comments on the two 6-mark questions especially. Both were marked by levels, and the report explains what moved an answer from one level to the next.
For the practical skills, the PAG 1, PAG 6 and PAG 8 question sets are the right follow-up.
Convert your mark with the OCR grade boundaries.
Questions and examiners’ comments are summarised from OCR’s published question paper, mark scheme and report for H420/03 June 2025, © OCR.