# 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 quickly.

> AQA A-Level Biology (7402) — 3.2.4 Cell Recognition and the Immune System · Explain · 5 marks

## Mark scheme (5 marks)

1. Phagocytes engulf and destroy the pathogen (by phagocytosis)
2. Lymphocytes produce antibodies that are complementary to / specific to the antigen on the pathogen
3. Memory cells are produced during the first infection
4. On second infection, memory cells recognise the same antigen and respond more quickly / rapidly
5. More antibodies are produced more rapidly so the pathogen is destroyed before symptoms develop / the person does not become ill

## Key terms

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

## Related

- [Revision notes for AQA A-Level Biology (7402)](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-immune-system-responds-cd590c11) · Published by Druglandscape Ltd.