Describe how the body responds when a pathogen enters the bloodstream for the first time, and explain why a second infection by the same pathogen is overcome more quickly.

Cambridge International IGCSE Biology (0610) — 10.1 Diseases and immunity · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

1. White blood cells (lymphocytes) recognise the pathogen’s antigens and produce specific antibodies.
2. The antibodies are complementary to the antigen on that particular pathogen.
3. After the first infection, memory cells are generated and remain in the bloodstream.
4. On a second exposure, the memory cells recognise the antigen and produce antibodies more quickly and in larger amounts, so the infection is cleared faster.

Examiner tips

  • Use the word "recognise" to show understanding of antigen–antibody specificity. Mention memory cells explicitly – this is a key point. Show the sequence: first infection → antibody production → memory cell formation → faster response on second infection.
  • common_mistakes
  • :
  • Confusing antibodies with white blood cells; they are produced by lymphocytes. Omitting the role of memory cells. Using vague terms like "immune response" without specifying antibodies and memory cells.

Mark scheme (4 marks)

  1. White blood cells (lymphocytes) produce antibodies in response to the pathogen's antigens
  2. Antibodies are complementary / specific to the antigen on that particular pathogen
  3. Memory cells are produced after the first infection and remain in the blood
  4. On second exposure, memory cells recognise the antigen and produce antibodies more quickly / in greater quantity

Key terms in this question

pathogen

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