Explain how the immune system responds when a pathogen enters the body for the first time and produces antibodies to destroy it.

Edexcel GCSE Biology (1BI0) — 5.2 Pathogens and immunity · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

The pathogen carries antigens on its surface.
B‑lymphocytes recognise and are activated by the specific antigen.
Activated B‑lymphocytes produce antibodies that are specific to that antigen.
The antibodies bind to the antigens, triggering destruction or neutralisation of the pathogen. The response is slower on first exposure because no memory cells are yet present.

Examiner tips

  • Use the word "recognise" to show antigen–cell interaction. Mention that antibodies are produced by B‑lymphocytes. Explain that the first response is slower due to lack of memory cells. Keep the answer concise – 4 points only.

Common mistakes

  • Forgetting to mention the role of B‑lymphocytes. Describing T‑cells instead of B‑cells. Claiming the response is fast on first exposure. Using vague terms like "immune cells" without specifying B‑lymphocytes.

Mark scheme (4 marks)

  1. The pathogen carries antigens on its surface
  2. B-lymphocytes are activated / respond to the specific antigen
  3. B-lymphocytes produce antibodies specific to that antigen
  4. Antibodies bind to the antigens, triggering destruction / neutralisation of the pathogen, and the response is slower on first exposure (no memory cells yet)

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