# Explain why enzymes are described as specific, and describe what happens to enzyme activity when the substrate concentration is increased from a very low level.

> Edexcel GCSE Biology (1BI0) — 1.4 Enzymes · Explain · 4 marks

> Enzymes are biological catalysts that speed up chemical reactions in living organisms. Each enzyme catalyses only one type of reaction.

## Mark scheme (4 marks)

1. Enzymes are specific because each enzyme has an active site with a unique/complementary shape
2. Only a substrate with a complementary shape can fit into / bind to the active site
3. As substrate concentration increases from a low level, the rate of reaction increases
4. Rate of reaction levels off / reaches a maximum because all active sites are occupied / enzyme molecules become the limiting factor

## Key terms

- [enzyme](https://www.gradenine.co.uk/glossary/enzyme)
- [substrate](https://www.gradenine.co.uk/glossary/substrate)
- [substrate concentration](https://www.gradenine.co.uk/glossary/substrate-concentration)
- [specific](https://www.gradenine.co.uk/glossary/specific)

## Related

- [Revision notes for Edexcel GCSE Biology (1BI0)](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-4dafd13d) · Published by Druglandscape Ltd.