OCR A-Level Biology A (H420): complete guide to the six modules and the exams

OCR A-Level Biology A (specification H420) is a two-year linear course assessed by three written papers at the end of Year 13. There is no coursework grade; practical work is reported separately as the Practical Endorsement. This page is the index: below is a module-by-module map of the six content areas, the exam structure, and how to study each one.

The six OCR Biology A modules

The specification splits the subject content into six teaching modules. Module 1 is a set of practical skills that runs through everything; modules 2 to 6 carry the examinable subject content, building from molecules and cells up to whole organisms, populations and ecosystems.

Module 1 Development of practical skills in biology

Not taught as a separate block. It defines the planning, implementing, analysing and evaluating skills assessed on paper (about 15 percent of marks) and through the Practical Endorsement (PAG1 to PAG12). Microscopy, dilutions, data handling and evaluating methods recur across every paper.

Module 2 Foundations in biology

The molecular and cellular foundation: cell structure and microscopy, biological molecules (water, carbohydrates, lipids, proteins and nucleic acids), enzymes, DNA replication and the genetic code, the cell cycle and mitosis, meiosis, stem cells and cell organisation. Start here; everything later assumes it.

Module 3 Exchange and transport

Surface-area-to-volume ratio and exchange surfaces, gas exchange in mammals, fish and insects, transport in animals (the heart, the cardiac cycle, blood vessels, tissue fluid and haemoglobin), and transport in plants (xylem, the cohesion-tension theory and phloem translocation).

Module 4 Biodiversity, evolution and disease

Communicable diseases and pathogens, the immune response and vaccination, antibiotics and resistance, measuring biodiversity and sampling, Simpson's index, classification and phylogeny, and evolution by natural selection.

Module 5 Communication, homeostasis and energy

Homeostasis and negative feedback, excretion and the liver, the kidney and osmoregulation, neuronal communication (the nerve impulse and synapses), hormonal communication and blood-glucose control, plant and animal responses, photosynthesis and respiration.

Module 6 Genetics, evolution and ecosystems

Cellular control and gene expression, patterns of inheritance (monohybrid, dihybrid, sex linkage and the chi-squared test), the Hardy-Weinberg principle and speciation, manipulating genomes (sequencing, PCR, gene editing and DNA profiling), cloning and biotechnology, and ecosystems, energy transfer and sustainability.

Exam structure

OCR A-Level Biology A is assessed by three written papers, all sat at the end of the course. A calculator is allowed in every paper.

• Paper 1 Biological processes (H420/01) covers modules 1, 2, 3 and 5. 2 hours 15 minutes, 100 marks, 37 percent of the A-Level. Section A is 15 marks of multiple choice; Section B is 85 marks of structured, data and extended-response questions.
• Paper 2 Biological diversity (H420/02) covers modules 1, 2, 4 and 6. 2 hours 15 minutes, 100 marks, 37 percent. Same structure as Paper 1.
• Paper 3 Unified biology (H420/03) is synoptic across all six modules. 1 hour 30 minutes, 70 marks, 26 percent. Structured and extended-response questions that deliberately link topics from different modules.

At least 10 percent of marks assess maths skills, and around 15 percent assess practical skills drawn from the PAGs. The longest extended responses are marked with Level-of-Response descriptors that reward a sustained, logically linked line of reasoning, not just correct points.

How to study OCR Biology A

Biology rewards precise factual mastery plus the ability to apply it to unfamiliar contexts.

1. Work from the specification statements. Each numbered point (for example 2.1.4 enzymes) is a checklist; questions are written from them. Turn each statement into a flashcard.
2. Learn definitions exactly. Mark schemes award marks for precise wording (for example "condensation reaction", "glycosidic bond", "counter-current exchange", "negative feedback").
3. Master the biochemical tests and PAG methods. The food tests (Benedict's, iodine, emulsion, biuret), microscopy and calibration, dissection, chromatography and serial dilutions appear repeatedly across all three papers.
4. Drill application, data and Level-of-Response questions. Paper 3 especially rewards linking topics across modules. Practise extended responses weekly from the start of Year 13.
5. Separate the maths. Drill magnification, Simpson's index, the chi-squared test and the t-test until they are automatic, because they are easy marks under time pressure.

Module 2 dot points

For specification-statement-level coverage of Module 2 Foundations in biology, each topic has its own focused answer page with worked exam questions and cross-links:

• Cell structure and microscopy - organelles, the secretory pathway, prokaryotes, and magnification and resolution.
• Enzymes - active sites, the induced-fit model, inhibition, and the factors affecting rate.
• DNA replication and the genetic code - semi-conservative replication and the triplet code.

Browse the full set at /a-level-ocr/biology/syllabus.

For the official specification

OCR publishes the full specification (H420), past papers, mark schemes and the practical handbook at ocr.org.uk. Always revise from the current specification and OCR's own past papers, because the question style and the Level-of-Response mark schemes are board-specific.