# Explain how temperature affects the rate of an enzyme-controlled reaction, including what happens both below and above the enzyme's optimum temperature.

> WJEC A-Level Biology (Wales) — 1.4 Biological reactions and enzymes · Explain · 5 marks

## Mark scheme (5 marks)

1. As temperature increases up to the optimum, the rate of reaction increases
2. Because molecules have more kinetic energy, so move faster and collide more frequently / more successfully
3. More enzyme-substrate complexes form (at or below the optimum)
4. Above the optimum temperature the enzyme is denatured / the shape of the active site changes permanently
5. The substrate can no longer fit into the active site, so no enzyme-substrate complexes can form and the rate of reaction decreases

## Key terms

- [optimum temperature](https://www.gradenine.co.uk/glossary/optimum-temperature)

## Related

- [Revision notes for WJEC A-Level Biology (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-temperature-affects-the-rate-11d723f7) · Published by Druglandscape Ltd.