Describe the role of phagocytes and lymphocytes in destroying a pathogen that has entered the body.

Eduqas A-Level Biology — 3.2 Respiration · Describe · 5 marks · View as Markdown

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

Model answer (5 marks)

Phagocytes recognise and engulf the pathogen, forming a phagosome. The phagosome fuses with lysosomes where enzymes digest the pathogen.
White blood cells detect antigens on the pathogen surface. Lymphocytes then release antibodies that are specific to the antigen; the antibodies bind to the pathogen, neutralising it. Antibodies can also cause agglutination or, if the pathogen produces toxins, lymphocytes can release antitoxins to neutralise the toxins.

Examiner tips

  • Use the word "engulf" for phagocytes and "antibodies" for lymphocytes. Mention digestion by enzymes. Include both neutralisation and agglutination. Keep the answer concise and point‑wise.

Common mistakes

  • Confusing phagocytes with lymphocytes. Forgetting to mention enzyme digestion. Using vague terms like "destroy" without specifying mechanisms.

Mark scheme (5 marks)

  1. Phagocytes engulf/ingest the pathogen
  2. Phagocytes digest the pathogen using enzymes
  3. White blood cells detect antigens on the surface of the pathogen
  4. Lymphocytes release antibodies that are specific/complementary to the antigen and bind to it to neutralise the pathogen
  5. Lymphocytes can also release antitoxins to neutralise toxins produced by the pathogen OR antibodies cause agglutination making pathogens easier to destroy

Key terms in this question

phagocyte · lymphocyte

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