# Explain how the body's defence mechanisms prevent pathogens from entering the bloodstream when a person breathes in air containing pathogens.

> Edexcel GCSE Biology (1BI0) — 5.2 Pathogens and immunity · Explain · 4 marks

> The respiratory tract contains several physical and chemical defences that work together to prevent pathogens from reaching the lungs and entering the bloodstream.

## Mark scheme (4 marks)

1. Mucus is produced in the respiratory tract / airways which traps pathogens / prevents them passing further into the body
2. Cilia (on ciliated epithelial cells) waft / move the mucus (containing trapped pathogens) upward / toward the throat so it can be swallowed or expelled
3. Hydrochloric acid in the stomach kills pathogens that have been swallowed / destroys pathogens in the swallowed mucus
4. These defences work together / are non-specific barriers to prevent pathogens reaching the bloodstream / prevent an infection developing

## Key terms

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

## 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-how-the-body-s-defence-mechanisms-091db727) · Published by Druglandscape Ltd.