Describe how white blood cells protect the body against pathogens, including the roles of both phagocytes and lymphocytes.

Cambridge International IGCSE Biology (0610) — 9.4 Blood · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

Phagocytes such as macrophages and neutrophils engulf pathogens by phagocytosis, forming a phagosome. Inside the phagosome they release enzymes that digest and break down the engulfed microbe. Lymphocytes, mainly B‑cells, recognise specific antigens on pathogens and produce antibodies. These antibodies bind to the antigens on the pathogen surface, causing the pathogens to clump together (agglutination) or marking them for destruction, thereby rendering them harmless.

Examiner tips

  • Use the exact terms "phagocytosis", "enzymes", "antibodies", "antigens" and "agglutination".
  • Show the two main cell types (phagocytes and lymphocytes) and their distinct actions.
  • Keep each point short and directly linked to the mark scheme.

Common mistakes

  • Confusing phagocytes with lymphocytes or vice versa.
  • Using vague terms like "kill" instead of "digest" or "clump together".
  • Omitting the specific role of antibodies or the antigen‑specific nature of the response.

Mark scheme (4 marks)

  1. Phagocytes engulf pathogens by phagocytosis
  2. Phagocytes release enzymes to digest / break down the engulfed pathogen
  3. Lymphocytes produce antibodies that are specific to the antigen on the pathogen
  4. Antibodies bind to antigens on pathogens, causing them to clump together / rendering them harmless

Key terms in this question

phagocyte · lymphocyte

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