Explain how increasing temperature affects the rate of an enzyme-controlled reaction, both below and above the enzyme's optimum temperature.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Enzymes are biological catalysts that speed up metabolic reactions in living cells. The rate at which an enzyme works is affected by temperature.
Model answer (5 marks)
Below the optimum temperature, increasing temperature increases the rate of the enzyme‑controlled reaction because molecules have more kinetic energy, move faster and collide more frequently, leading to more enzyme‑substrate complexes and a higher rate of product formation. Above the optimum temperature the enzyme becomes denatured; the shape of the active site changes permanently so the substrate can no longer fit, no enzyme‑substrate complexes form and the rate of reaction decreases.
Examiner tips
- Use the word ‘optimum’ to show you understand the temperature range.
- Explain both the kinetic energy effect and the denaturation effect.
- Show the cause–effect chain: temperature → kinetic energy/denaturation → complex formation → rate.
Common mistakes
- Confusing ‘denaturation’ with ‘inactivation’ without explaining the active‑site change.
- Failing to mention that the rate increases *before* the optimum, not just that it ‘increases’ in general.
- Using vague terms like ‘hot’ or ‘cold’ instead of ‘below’ and ‘above’ the optimum.
Mark scheme (5 marks)
- Below the optimum, increasing temperature increases the rate of reaction
- Because molecules have more kinetic energy so move faster / collide more frequently
- More enzyme-substrate complexes form (below/at the optimum)
- Above the optimum temperature the enzyme becomes denatured
- Because the shape of the active site changes permanently, so the substrate can no longer fit / no enzyme-substrate complexes can form, decreasing the rate of reaction
Key terms in this question
Related
- All Eduqas A-Level Biology revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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