# A person is infected with influenza virus for the first time. Some B-lymphocytes that respond to the influenza antigens survive as memory cells. Years later, the same person is exposed to the same strain of influenza. Explain why this second exposure rarely results in the person becoming ill.

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

> Memory cells are long-lived B-lymphocytes that remain in the body after an initial immune response. They can be rapidly activated upon re-exposure to the same antigen.

## Mark scheme (5 marks)

1. Memory cells recognise the specific antigen on the influenza virus
2. Memory cells divide / multiply rapidly (faster than the first response)
3. Large quantities of specific antibodies are produced quickly
4. Antibodies bind to the antigens on the virus / pathogens are destroyed before they can multiply to high enough levels to cause illness
5. The immune response overcomes the infection before symptoms develop / the person becomes immune

## Key terms

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

## 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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Source: [GradeNine](https://www.gradenine.co.uk/q/a-person-is-infected-with-influenza-ae352f22) · Published by Druglandscape Ltd.