# Describe the role of cilia and mucus in protecting the gas exchange system from damage caused by pathogens and particles in inhaled air.

> Pearson Edexcel International GCSE Biology (4BI1) — 2.9 Gas exchange: humans · Describe · 4 marks

## Mark scheme (4 marks)

1. Goblet cells / lining of the trachea and bronchi produce mucus
2. Mucus traps pathogens / dust / particles / microorganisms
3. Cilia beat / move rhythmically
4. Cilia move the mucus (with trapped particles / pathogens) towards the throat / mouth to be swallowed or expelled

## Key terms

- [cilia](https://www.gradenine.co.uk/glossary/cilia)
- [mucus](https://www.gradenine.co.uk/glossary/mucus)
- [pathogens](https://www.gradenine.co.uk/glossary/pathogens)

## Related

- [Revision notes for Pearson Edexcel International GCSE Biology (4BI1)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" 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/describe-the-role-of-cilia-and-98c06d50) · Published by Druglandscape Ltd.