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.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
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.
Model answer (5 marks)
Memory cells recognise the specific antigen on the influenza virus
Memory cells divide and multiply rapidly, faster than the primary response
Large quantities of specific antibodies are produced quickly
Antibodies bind to the antigens on the virus, destroying the pathogens before they can multiply to high enough levels to cause illness
The immune response overcomes the infection before symptoms develop, so the person remains immune
Memory cells divide and multiply rapidly, faster than the primary response
Large quantities of specific antibodies are produced quickly
Antibodies bind to the antigens on the virus, destroying the pathogens before they can multiply to high enough levels to cause illness
The immune response overcomes the infection before symptoms develop, so the person remains immune
Examiner tips
- Use the exact terms: memory cells, antigen, antibodies, rapid division, early clearance
- Show the sequence: recognition → rapid proliferation → antibody production → pathogen destruction
- Mention that the response is faster and stronger than the first exposure
Common mistakes
- Confusing memory cells with plasma cells; not stating the rapid division Failing to explain that antibodies bind to the virus and prevent symptom development
Mark scheme (5 marks)
- Memory cells recognise the specific antigen on the influenza virus
- Memory cells divide / multiply rapidly (faster than the first response)
- Large quantities of specific antibodies are produced quickly
- Antibodies bind to the antigens on the virus / pathogens are destroyed before they can multiply to high enough levels to cause illness
- The immune response overcomes the infection before symptoms develop / the person becomes immune
Key terms in this question
memory cells · B-lymphocyte · antigen
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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