# Explain how the immune system responds when a pathogen enters the body for the first time and why a second infection by the same pathogen is dealt with more rapidly.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 5.3 Immune response · Explain · 5 marks

> When a pathogen enters the body, the immune system mounts a specific response involving white blood cells. If the same pathogen enters the body again, the immune response is faster and stronger.

## Mark scheme (5 marks)

1. The pathogen has antigens on its surface that are recognised as foreign
2. B-lymphocytes produce antibodies specific to that antigen
3. The antibodies bind to / destroy the pathogen, neutralising it or marking it for destruction
4. Memory cells are produced during the first infection
5. On second infection, memory cells rapidly produce large quantities of the correct antibodies, so the pathogen is destroyed before symptoms develop

## Related

- [Revision notes for Edexcel A-Level Biology A: Salters-Nuffield (9BN0)](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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