# A person contracts a bacterial infection for the first time. Explain how B-lymphocytes respond to the antigens on the bacteria to protect the body from the infection.

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

> When a bacterial pathogen enters the body, the immune system mounts a specific response involving white blood cells. B-lymphocytes play a central role in this response by producing proteins that target the pathogen.

## Mark scheme (5 marks)

1. The bacteria carry antigens on their surface which are recognised as foreign / non-self
2. B-lymphocytes specific to that antigen are activated / the specific B-lymphocyte recognises the complementary antigen
3. The activated B-lymphocyte divides / multiplies to produce clones (clonal expansion)
4. The cloned B-lymphocytes produce large quantities of antibodies specific to that antigen
5. Memory B-lymphocytes / memory cells are produced that remain in the body so that the response is faster and greater if the same pathogen is encountered again

## Key terms

- [antigen](https://www.gradenine.co.uk/glossary/antigen)
- [B-lymphocyte](https://www.gradenine.co.uk/glossary/b-lymphocyte)

## 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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Source: [GradeNine](https://www.gradenine.co.uk/q/a-person-contracts-a-bacterial-infection-899ab3ae) · Published by Druglandscape Ltd.