Explain how phagocytes and lymphocytes work together to destroy a pathogen that has entered the body for the first time. Include in your answer what happens after the infection has been cleared.

WJEC A-Level Biology (Wales) — 3.1 Photosynthesis · 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 the pathogen’s surface antigens via specific receptors and secrete antibodies.
Antibodies bind to the antigens, neutralising the pathogen and causing agglutination.
The antibody‑pathogen complexes activate phagocytes.
Phagocytes engulf the pathogen in a phagosome and digest it with enzymes (phagocytosis).
After clearance, some lymphocytes become memory cells, enabling a faster response on re‑exposure.

Examiner tips

  • Use the exact sequence: detection → antibody release → agglutination → phagocyte activation → phagocytosis → memory cell formation.
  • Mention both antibody functions (neutralisation & agglutination) and the role of memory cells.
  • Keep answer concise, 5 points total.
  • Use UK spelling (phagocytosis).

Common mistakes

  • Confusing lymphocytes with phagocytes as the main destroyer.
  • Omitting the role of memory cells or describing them incorrectly.

Mark scheme (5 marks)

  1. Lymphocytes detect the antigen on the pathogen's surface (using receptors) and release antibodies
  2. Antibodies bind to the antigens on the pathogen to neutralise it / clump pathogens together (agglutination)
  3. Lymphocytes activate phagocytes
  4. Phagocytes engulf (ingest) and digest the pathogen using enzymes (phagocytosis)
  5. After the infection, memory cells remain so the body can respond more quickly if the same pathogen is encountered again

Key terms in this question

phagocyte · lymphocyte

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