Describe how the human body uses non-specific defences and the specific immune response to protect itself when a pathogen enters through a cut in the skin.

WJEC A-Level Biology (Wales) — 3.1 Photosynthesis · Describe · 5 marks · View as Markdown

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

Model answer (5 marks)

Non‑specific mechanical barrier: blood clotting seals the wound to prevent pathogens entering
Phagocytes engulf and ingest pathogens and digest them using enzymes (phagocytosis)
Lymphocytes detect antigens on the pathogen surface and release complementary antibodies
Antibodies bind to antigens on the pathogen, neutralising it or causing agglutination so the pathogen is destroyed
Memory cells remain after infection so that if the same pathogen enters the body again, the response is faster and the pathogen is killed more quickly

Examiner tips

  • Use the exact terminology (e.g. phagocytosis, antibodies, memory cells)
  • Show the sequence from mechanical barrier to adaptive response
  • Keep each point concise and separate with line breaks

Common mistakes

  • Confusing mechanical barrier with chemical barrier
  • Mixing up phagocytes with lymphocytes
  • Omitting the role of memory cells

Mark scheme (5 marks)

  1. Non-specific mechanical barrier: blood clotting seals the wound to prevent pathogens entering
  2. Phagocytes engulf / ingest pathogens and digest them using enzymes (phagocytosis)
  3. Lymphocytes detect antigens on the pathogen surface and release complementary antibodies
  4. Antibodies bind to antigens on the pathogen, neutralising it / causing agglutination so the pathogen is destroyed
  5. Memory cells remain after infection so that if the same pathogen enters the body again, the response is faster / pathogen is killed more quickly

Key terms in this question

non-specific defence

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