IGCSE Biology glossary
Enzyme
Biology editorial review is supported by the named review panel. Reviewer participation may vary by guide. Checked against Cambridge IGCSE Biology 0610 (2026–2028); last reviewed August 2026.
Definition
A protein that functions as a biological catalyst. It speeds up a chemical reaction without being changed or used up by the reaction.
What to include in an exam answer
Both halves are needed for full marks: 'protein' and 'catalyst'. Questions then test the lock-and-key model: substrate shape is complementary to the active site (never say 'same shape as the active site'. Complementary is the key term).
Example in context
Asked what an enzyme does to a reaction: 'The enzyme acts as a biological catalyst, lowering the energy needed so the reaction speeds up, without the enzyme being used up.'
Related syllabus topic
Enzymes