# A person is infected with a new strain of influenza (flu) virus for the first time. Explain how the immune system responds to this infection and why the person is unlikely to become seriously ill if they are infected with the same strain of flu virus again in the future.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 6 Immunity, Infection and Forensics · Explain · 5 marks

> Influenza is caused by a virus that can mutate rapidly, producing new strains. Each new strain carries different antigens on its surface.

## Mark scheme (5 marks)

1. White blood cells detect the antigens on the surface of the influenza virus
2. White blood cells produce antibodies that are specific/complementary to the antigens on the influenza virus
3. The antibodies bind to / attack the antigens on the virus, destroying or neutralising the virus
4. Memory cells are produced during the first infection that remain in the body long-term
5. On second exposure to the same strain, memory cells allow a faster and greater antibody response so the virus is destroyed before the person becomes seriously ill

## 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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