# Explain how the immune system responds when a pathogen enters the body for the first time and produces a faster response if the same pathogen enters the body a second time.

> Pearson Edexcel A-Level Biology A (9BI0) — 5.3 Immune response · Explain · 5 marks

> The human immune system can recognise and destroy pathogens. It also has the ability to respond more rapidly to pathogens that have been encountered before.

## Mark scheme (5 marks)

1. Pathogens carry antigens on their surface that are recognised as foreign / trigger an immune response
2. B-lymphocytes produce antibodies specific to that antigen
3. Antibodies bind to / destroy / neutralise the pathogen, removing it from the body
4. Memory cells are produced during the first infection that remain in the body long-term
5. On second exposure to the same pathogen, memory cells rapidly produce large quantities of the correct antibodies, destroying the pathogen before symptoms develop

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](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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