Explain how the immune system responds when a pathogen enters the body for the first time and produces a faster response if the same pathogen enters the body a second time.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
The human immune system can recognise and destroy pathogens. It also has the ability to respond more rapidly to pathogens that have been encountered before.
Model answer (5 marks)
Pathogens present antigens on their surface that are recognised as foreign, triggering an immune response.
B‑lymphocytes produce antibodies specific to that antigen.
The antibodies bind to, destroy or neutralise the pathogen, removing it from the body.
During the first infection, memory B‑cells are produced and remain in the body long‑term.
On a second exposure to the same pathogen, these memory cells rapidly produce large quantities of the correct antibodies, destroying the pathogen before symptoms develop.
B‑lymphocytes produce antibodies specific to that antigen.
The antibodies bind to, destroy or neutralise the pathogen, removing it from the body.
During the first infection, memory B‑cells are produced and remain in the body long‑term.
On a second exposure to the same pathogen, these memory cells rapidly produce large quantities of the correct antibodies, destroying the pathogen before symptoms develop.
Examiner tips
- Use the exact terms: antigens, B‑lymphocytes, antibodies, memory cells. Show the sequence: recognition → antibody production → pathogen removal → memory cell formation → rapid response on re‑exposure.
- Mention that the second response is faster and stronger, preventing symptoms.
Common mistakes
- Confusing T‑cells with B‑cells; only B‑cells produce antibodies. Forgetting to mention memory cells. Using vague phrases like "immune system" instead of specific components.
Mark scheme (5 marks)
- Pathogens carry antigens on their surface that are recognised as foreign / trigger an immune response
- B-lymphocytes produce antibodies specific to that antigen
- Antibodies bind to / destroy / neutralise the pathogen, removing it from the body
- Memory cells are produced during the first infection that remain in the body long-term
- On second exposure to the same pathogen, memory cells rapidly produce large quantities of the correct antibodies, destroying the pathogen before symptoms develop
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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