# Explain why enzymes are described as biological catalysts, and explain how a change in pH can prevent an enzyme from carrying out its function.

> Pearson Edexcel International GCSE Biology (4BI1) — 2.3 Biological molecules · Explain · 4 marks

## Mark scheme (4 marks)

1. Enzymes increase the rate of reactions in living organisms
2. Enzymes are not used up / remain unchanged after the reaction
3. The shape of the active site changes / is altered at extreme pH
4. The substrate can no longer fit the active site / enzyme-substrate complex cannot form, so the enzyme cannot function

## Key terms

- [enzyme](https://www.gradenine.co.uk/glossary/enzyme)
- [biological catalyst](https://www.gradenine.co.uk/glossary/biological-catalyst)

## Related

- [Revision notes for Pearson Edexcel International GCSE Biology (4BI1)](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-why-enzymes-are-described-as-88ea12fd) · Published by Druglandscape Ltd.