# Explain how the human body defends itself against pathogens before they enter the body and how the immune system responds once a pathogen has entered the body.

> WJEC A-Level Biology (Wales) — 3.4 Population size and ecosystems · Explain · 5 marks

## Mark scheme (5 marks)

1. Named non-specific physical/mechanical barrier (e.g. skin / hairs in the nose / blood clotting sealing a wound)
2. Named non-specific chemical barrier (e.g. stomach acid / mucus / tears)
3. Phagocytes engulf/ingest and digest pathogens (phagocytosis)
4. Lymphocytes produce antibodies that bind to antigens on the pathogen to neutralise it
5. Memory cells remain after infection so that if the same pathogen enters the body again, the response is faster/more rapid

## Related

- [Revision notes for WJEC A-Level Biology (Wales)](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-human-body-defends-df54c0a1) · Published by Druglandscape Ltd.