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.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Influenza is caused by a virus that can mutate rapidly, producing new strains. Each new strain carries different antigens on its surface.
Model answer (5 marks)
White blood cells recognise the surface antigens of the influenza virus.
White blood cells then produce antibodies that are complementary to those antigens.
The antibodies bind to the virus, neutralising or destroying it.
During the first infection memory cells are created and remain in the body.
On a second infection with the same strain, memory cells trigger a rapid, stronger antibody response, clearing the virus before serious illness develops.
White blood cells then produce antibodies that are complementary to those antigens.
The antibodies bind to the virus, neutralising or destroying it.
During the first infection memory cells are created and remain in the body.
On a second infection with the same strain, memory cells trigger a rapid, stronger antibody response, clearing the virus before serious illness develops.
Examiner tips
- Use the exact terms: white blood cells, antibodies, memory cells; explain the sequence; mention ‘rapid’ and ‘stronger’ response for second exposure.
- Show the link between memory cells and reduced severity; avoid vague statements like ‘immune system helps’.
Common mistakes
- Confusing antibodies with T‑cells; not mentioning memory cells; saying the virus is ‘killed’ instead of ‘neutralised’ or ‘destroyed’.
Mark scheme (5 marks)
- White blood cells detect the antigens on the surface of the influenza virus
- White blood cells produce antibodies that are specific/complementary to the antigens on the influenza virus
- The antibodies bind to / attack the antigens on the virus, destroying or neutralising the virus
- Memory cells are produced during the first infection that remain in the body long-term
- 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
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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