How to answer "Explain" questions
Explain means: Say how or WHY something happens — give the reasons, linked with causal words.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
AO2 (apply knowledge) — the most common mid-tariff command word. · Also phrased as: give reasons, account for, why
What the examiner is looking for
- Every point must carry a REASON — use "because", "so", "this causes", "which means".
- Link cause to effect: X happens because of Y, which leads to Z.
- Use correct terminology and the relevant science.
How to structure your answer
- For each mark, make a point AND justify it (point → because → consequence).
- A 6-marker usually needs ~6 linked points across the whole chain of reasoning.
- Keep the logic in order so the examiner can follow the causal chain.
Worked example
Q: Explain why the rate of an enzyme-controlled reaction falls above the optimum temperature. (3 marks)
Model answer: Above the optimum, the higher temperature gives the enzyme molecules more energy so bonds holding the tertiary structure break [1]. The active site changes shape / denatures [1], so the substrate no longer fits and fewer enzyme–substrate complexes form, lowering the rate [1].
Common mistakes
- Describing instead of explaining — listing what happens with no "because".
- Saying an enzyme "dies" (enzymes are not alive — they denature).
- Stopping halfway down the causal chain and losing the final mark.
Practise it
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