Explain how the body responds to a pathogen the first time it enters the body. Include in your answer the roles of lymphocytes and antibodies.

AQA A-Level Biology (7402) — 3.2.4 Cell Recognition and the Immune System · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

Lymphocytes recognise foreign antigens on the pathogen’s surface.
Lymphocytes that match the antigen produce specific antibodies.
The antibodies bind to the antigens, marking the pathogen for destruction.
Because the correct lymphocyte must be found and multiplied, the response is slow on first exposure.
After the infection is cleared, memory lymphocytes remain to give a faster response on re‑exposure.

Examiner tips

  • Use the term ‘lymphocytes’ and ‘antibodies’ explicitly. Explain the sequence: detection → antibody production → binding. Mention the delay and the generation of memory cells. Keep the answer concise to fit the 5‑mark limit.

Common mistakes

  • Confusing T‑cells with B‑cells or not specifying antibody binding. Omitting the slow response or memory cell formation. Using vague terms like ‘immune cells’ instead of ‘lymphocytes’.

Mark scheme (5 marks)

  1. Lymphocytes detect antigens on the surface of the pathogen (that are foreign / not recognised as self)
  2. Lymphocytes produce antibodies that are specific / complementary to that antigen
  3. Antibodies bind to / attach to the antigens on the pathogen
  4. The response is slow / takes time on first exposure because the correct lymphocyte must be found and multiply
  5. Memory lymphocytes / memory cells are produced that remain in the body after the infection is cleared

Key terms in this question

lymphocytes · antibodies

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