Explain how the human body uses non-specific defence systems to prevent pathogens from entering, and describe what happens when a pathogen successfully enters the body and is detected by white blood cells.

Eduqas A-Level Biology — 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)

1. Skin acts as a physical barrier, preventing pathogen entry by covering the body.
2. Stomach acid is a chemical barrier that kills or inactivates ingested pathogens.
3. White blood cells recognise pathogens via receptors that bind to antigens on the pathogen surface.
4. Phagocytes engulf the pathogen and digest it with enzymes in a process called phagocytosis.
5. Lymphocytes produce antibodies that are complementary to the pathogen’s antigens, neutralising or disabling the pathogen.

Examiner tips

  • Use the exact terminology (e.g. phagocytosis, antibodies).
  • Show the sequence: barrier → detection → phagocytosis → antibody production.
  • Include both physical and chemical barriers.
  • Mention receptors on white blood cells.

Mark scheme (5 marks)

  1. A non-specific physical/mechanical barrier is named and its function stated (e.g. skin acts as a physical barrier to prevent pathogen entry; hairs in the nose trap pathogens; blood clotting seals wounds)
  2. A chemical barrier is named and its function stated (e.g. stomach acid / mucus / tears kill or trap pathogens)
  3. White blood cells detect pathogens using receptors to identify antigens on the pathogen's surface
  4. Phagocytes engulf (ingest) and digest the pathogen using enzymes (phagocytosis)
  5. Lymphocytes produce antibodies that are specific/complementary to the pathogen's antigens and neutralise / disable the pathogen

Key terms in this question

non-specific defence system

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