# Explain how a rise in temperature above an enzyme's optimum affects the rate of reaction. In your answer, refer to the active site and enzyme-substrate complexes.

> WJEC A-Level Biology (Wales) — 1.3 Cell membranes and transport · Explain · 5 marks

> Enzymes are biological catalysts that control chemical reactions within cells. Each enzyme has an active site with a specific shape that is complementary to its substrate.

## Mark scheme (5 marks)

1. Above the optimum temperature, the enzyme becomes denatured
2. The shape of the active site changes (permanently)
3. The substrate can no longer fit into the active site
4. Fewer / no enzyme-substrate complexes can form
5. Therefore the rate of reaction decreases

## Key terms

- [active site](https://www.gradenine.co.uk/glossary/active-site)
- [enzyme-substrate complex](https://www.gradenine.co.uk/glossary/enzyme-substrate-complex)

## 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-a-rise-in-temperature-1a2a1f63) · Published by Druglandscape Ltd.