Describe the role of the immune system in defending the body against a pathogen that has entered the body for the first time.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
When a pathogen enters the body for the first time, the immune system mounts a response to destroy it and provides protection against future infections by the same pathogen.
Model answer (5 marks)
White blood cells recognise the pathogen through receptors on their surface that bind to specific antigens on the pathogen. Lymphocytes then produce antibodies that are complementary to these antigens. Phagocytes such as macrophages ingest and digest the pathogen by phagocytosis, using enzymes to break it down. Antibodies neutralise the pathogen directly or cause agglutination, clumping pathogens together to make them easier to destroy. After the infection, memory cells persist, so that if the same pathogen re‑enters the body, antibodies are produced more rapidly and effectively.
Examiner tips
- Use the exact terms: receptors, antigens, lymphocytes, antibodies, phagocytes, phagocytosis, agglutination, memory cells.
- Show the sequence: detection → antibody production → phagocytosis → neutralisation/agglutination → memory.
- Keep each point brief but complete – 1 mark each.
- Mention that antibodies are specific to the antigen.
Common mistakes
- Confusing antibodies with T‑cell receptors; antibodies are produced by B‑cells. Forgetting to mention memory cells or describing them as ‘long‑lasting’ rather than ‘memory cells’. Using vague phrases like ‘immune response’ without detailing the specific mechanisms.
Mark scheme (5 marks)
- White blood cells detect the pathogen using receptors on their cell surface to identify antigens on the pathogen
- Lymphocytes release antibodies that are complementary/specific to the antigen on the pathogen
- Phagocytes ingest and digest the pathogen using enzymes (phagocytosis)
- Antibodies neutralise the pathogen / clump pathogens together (agglutination) making them easier to destroy
- Memory cells remain after the infection so that if the same pathogen enters the body again, antibodies are produced more quickly
Related
- All WJEC A-Level Biology (Wales) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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