Methodology

This list is based on analysis of Pearson Edexcel International A-Level Biology past papers (2019–2024), examiner reports, mark schemes and specification. Topics are ranked by frequency and mark allocation.

Top 10 most frequently tested topics

1. Genetics and inheritance

Evidence: Inheritance patterns, genetic diagrams, gene expression. Significant mark allocation.

Covers: monohybrid and dihybrid crosses; codominance; multiple alleles; gene linkage; epistasis; genetic variation.

2. Enzymes and enzyme kinetics

Evidence: Appears in almost every series. Examiner reports note enzyme-substrate complex and V_max confusion.

Covers: enzyme action; active site; lock-and-key; initial rate; V_max; effect of temperature and pH; inhibitors.

3. Cell structure and membranes

Evidence: Organelles, magnification, membrane structure. Examiner reports note terminology errors.

Covers: ultrastructure; magnification calculations; membrane structure; fluid mosaic; transport across membranes.

4. Protein synthesis and gene expression

Evidence: Transcription, translation, mutations. Examiner reports note mutation = nucleotide change; tRNA anticodon confusion.

Covers: DNA replication; transcription; translation; mRNA, tRNA; mutations; regulation.

5. Respiration and energy

Evidence: Aerobic respiration, glycolysis, Krebs cycle. Core topic.

Covers: glycolysis; link reaction; Krebs cycle; oxidative phosphorylation; respiratory quotient.

6. Photosynthesis

Evidence: Light-dependent and light-independent reactions. Examiner reports note chloroplast structure.

Covers: chloroplast structure; light-dependent; light-independent; factors affecting rate.

7. Transport in plants and animals

Evidence: Translocation; heart, circulation, blood. Appears regularly.

Covers: translocation; mass flow; heart structure; cardiac cycle; blood vessels; tissue fluid.

8. Immune system

Evidence: B lymphocytes, T lymphocytes, antibodies. Examiner reports note terminology.

Covers: non-specific and specific immunity; B and T cells; antibodies; vaccination.

9. Homeostasis and kidneys

Evidence: Osmoregulation, nephron structure. Examiner reports note excretion vs egestion.

Covers: kidney structure; nephron; ultrafiltration; reabsorption; osmoregulation.

10. Classification and evolution

Evidence: Phylogeny, species, natural selection. Appears in extended content.

Covers: classification; phylogeny; evidence for evolution; natural selection; speciation.

Revision priority

Focus on genetics, enzymes and protein synthesis first. Combine with common mistakes to avoid repeated errors.

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Sources: Edexcel past papers 2019–2024, examiner reports, specification.