Malaria is a communicable disease caused by a protist spread by mosquitoes. Describe how the human body's immune system responds after the Plasmodium pathogen enters the bloodstream for the first time, and explain why a second infection with the same pathogen would be dealt with more quickly.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
White blood cells recognise the Plasmodium parasite in the blood by receptors that bind to antigens on its surface.
Lymphocytes then release antibodies that are complementary to those antigens; the antibodies bind and neutralise the parasite.
Phagocytes such as macrophages engulf and digest the parasite by phagocytosis.
After the first infection, memory B‑cells and T‑cells remain in the body.
On a second infection these memory cells rapidly divide and produce the same specific antibodies, so the parasite is destroyed before it can cause disease.
Lymphocytes then release antibodies that are complementary to those antigens; the antibodies bind and neutralise the parasite.
Phagocytes such as macrophages engulf and digest the parasite by phagocytosis.
After the first infection, memory B‑cells and T‑cells remain in the body.
On a second infection these memory cells rapidly divide and produce the same specific antibodies, so the parasite is destroyed before it can cause disease.
Examiner tips
- Use the correct terminology – receptors, antigens, antibodies, phagocytosis, memory cells.
- Show the sequence: detection → antibody release → phagocytosis → memory cell formation.
- Explain the speed‑up on re‑infection by citing memory cell proliferation and antibody production.
- Keep the answer concise – 5 marks, so one point per bullet.
Common mistakes
- Confusing antibodies with T‑cell receptors; they are produced by B‑cells.
- Omitting the role of phagocytes or memory cells.
- Using vague terms like "immune response" without specifying mechanisms.
Mark scheme (5 marks)
- White blood cells detect the Plasmodium pathogen using receptors that identify antigens on its surface
- Lymphocytes release antibodies that are complementary / specific to the Plasmodium antigen, which bind to the antigen and neutralise the pathogen
- Phagocytes engulf / ingest and digest the pathogen using enzymes (phagocytosis)
- After the first infection, memory cells remain in the body
- On second infection, memory cells rapidly divide and produce the correct antibodies more quickly, so the pathogen is destroyed before it causes disease
Key terms in this question
communicable disease · protist
Related
- All WJEC A-Level Biology (Wales) revision notes →
- How to answer a "Describe and Explain" question →
- Decode the mark scheme abbreviations →
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