# Describe the role of enzymes in digestion and explain why a protease enzyme cannot break down starch.

> AQA A-Level Biology (7402) — 3.1.4 Proteins and Enzymes · Describe and Explain · 5 marks

## Mark scheme (5 marks)

1. Enzymes are biological catalysts
2. Enzymes break down large food molecules into smaller, soluble molecules (that can be absorbed)
3. Each enzyme has a specific active site with a complementary shape to its substrate
4. The active site of a protease is complementary to proteins (not starch)
5. Therefore starch cannot bind to / form an enzyme-substrate complex with protease, so it is not broken down

## Key terms

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

## Related

- [Revision notes for AQA A-Level Biology (7402)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and 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/describe-the-role-of-enzymes-in-02c457a1) · Published by Druglandscape Ltd.