# Explain how changes in temperature affect the rate of an enzyme-catalysed reaction, including the molecular basis for the optimum temperature.

> IB DP Biology Higher Level (2023 syllabus) — C1.1 Enzymes and metabolism · Explain · 4 marks

## Mark scheme (4 marks)

1. Increasing temperature increases the kinetic energy of molecules, leading to more frequent collisions between enzyme and substrate, increasing the rate of reaction.
2. At the optimum temperature, the rate of reaction is at its maximum because the increase in collision frequency outweighs any thermal disruption of enzyme structure.
3. Above the optimum temperature, hydrogen bonds and other non-covalent interactions maintaining tertiary structure are disrupted / broken, causing the active site to change shape (denaturation).
4. The altered active site can no longer form an enzyme-substrate complex effectively, so the reaction rate falls / the enzyme loses catalytic activity.

## Key terms

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

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-changes-in-temperature-affect-35c9df98) · Published by Druglandscape Ltd.