Methodology

This list is based on analysis of Cambridge IGCSE Combined Science 0653 past papers (2019–2025), examiner reports and mark schemes. Combined Science draws from Biology, Chemistry and Physics; topics are ranked by frequency across the papers.

Top 10 most frequently tested topics

1. Cell structure and magnification (Biology)

Evidence: Examiner reports note cell magnification and structure errors. Appears in Biology MC and structured questions.

Covers: cell structure; magnification calculations; organelles.

2. Enzymes (Biology)

Evidence: Enzyme action, temperature, pH. Examiner reports highlight enzyme-related confusion.

Covers: enzyme action; effect of temperature and pH; denaturation.

3. Movement in and out of cells (Biology)

Evidence: Diffusion, osmosis. Examiner reports note osmosis experiment errors.

Covers: diffusion; osmosis; active transport.

4. Electrolysis (Chemistry)

Evidence: Examiner reports repeatedly note electrolysis errors. Products at electrodes.

Covers: electrolysis of aqueous solutions; products; electrolysis rules.

5. Acids, bases and salts (Chemistry)

Evidence: Neutralisation, pH, salt preparation. Core chemistry.

Covers: acids and bases; neutralisation; salt preparation; pH.

6. Stoichiometry and mole (Chemistry)

Evidence: Mole calculations appear across chemistry questions.

Covers: mole concept; reacting masses; calculations.

7. Electricity and circuits (Physics)

Evidence: Current, voltage, resistance; Ohm’s law. Examiner reports note circuit errors.

Covers: series and parallel; Ohm’s law; circuit calculations.

8. Forces and motion (Physics)

Evidence: Resultant force, acceleration. Examiner reports note constant motion confusion.

Covers: force; acceleration; Newton’s laws; graphs.

9. Biological molecules and nutrition (Biology)

Evidence: Proteins, carbohydrates; diet. Examiner reports note protein composition errors.

Covers: carbohydrates, proteins, fats; balanced diet; digestion.

10. Energy and energy resources (Physics)

Evidence: Energy transfers, efficiency. Appears in physics sections.

Covers: energy types; conservation; efficiency; power.

Revision priority

Enzymes, electrolysis and cell structure appear frequently and cause examiner-reported errors. See common mistakes.

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Sources: Cambridge past papers 2019–2025, examiner reports, syllabus.

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