Explain how the human body uses antibodies to destroy a pathogen after it has entered the bloodstream.

WJEC A-Level Biology (Wales) — 3.4 Population size and ecosystems · Explain · 5 marks · View as Markdown

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

When a pathogen enters the human body, the immune system produces antibodies as part of the specific defence response.

Model answer (5 marks)

White blood cells (lymphocytes) recognise antigens on the surface of the invading pathogen. The lymphocytes then produce antibodies that are complementary to those antigens. The antibodies bind to the pathogen’s surface, which can lead to agglutination or neutralisation of the pathogen, making it easier for other immune cells to destroy it. After the infection, memory cells remain, so if the same pathogen enters again, antibodies are produced more rapidly.

Examiner tips

  • Use the exact terms – lymphocytes, antibodies, antigens, agglutination, memory cells
  • Show the sequence: detection → antibody production → binding → destruction
  • Mention that antibodies make the pathogen easier to destroy

Common mistakes

  • Confusing antibodies with T‑cells or B‑cells
  • Omitting the role of memory cells
  • Using vague phrases like ‘immune response’ instead of specific steps

Mark scheme (5 marks)

  1. White blood cells / lymphocytes detect antigens on the surface of the pathogen
  2. Lymphocytes release / produce complementary antibodies specific to that antigen
  3. Antibodies bind to the antigens on the surface of the pathogen
  4. Antibodies clump pathogens together (agglutination) / neutralise the pathogen, making it easier to destroy
  5. Memory cells remain after infection so that if the same pathogen enters the body again, antibodies are produced more quickly

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