# Explain how the human body defends itself against pathogens before they enter the body and after they have entered the body.

> Eduqas A-Level Biology — 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 nose / blood clotting sealing wounds)
2. Named non-specific chemical barrier (e.g. stomach acid / mucus / tears)
3. Phagocytes engulf / ingest and digest pathogens (phagocytosis) once inside the body
4. Lymphocytes produce antibodies that bind to specific antigens on the pathogen to neutralise it
5. Memory cells remain after infection so that if the same pathogen enters the body again, it can be destroyed more quickly

## Related

- [Revision notes for Eduqas A-Level Biology](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-169cd1da) · Published by Druglandscape Ltd.