# Explain why proteins must be chemically digested before they can be used by the body, and describe the role of gastric juice in this process.

> Cambridge International IGCSE Biology (0610) — 7.4 Chemical digestion · Explain · 4 marks

## Mark scheme (4 marks)

1. Proteins are large / insoluble molecules that cannot be absorbed through the wall of the intestine
2. Chemical digestion breaks proteins down into amino acids (smaller, soluble molecules) so they can be absorbed
3. Gastric juice contains protease enzymes (pepsin) which break down protein
4. Hydrochloric acid in gastric juice provides an optimum (acidic) pH for pepsin / protease activity AND/OR kills harmful microorganisms in food

## Key terms

- [gastric juice](https://www.gradenine.co.uk/glossary/gastric-juice)

## Related

- [Revision notes for Cambridge International IGCSE Biology (0610)](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-proteins-must-be-chemically-9de1ea23) · Published by Druglandscape Ltd.