A student cuts their finger and bacteria enter the wound. Explain how the immune system responds to destroy these bacteria.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
When the skin is broken, pathogens such as bacteria can enter the body and trigger an immune response.
Model answer (5 marks)
White blood cells, mainly phagocytes, recognise and engulf the bacteria by phagocytosis, digesting them inside lysosomes.
Lymphocytes detect bacterial antigens on the surface of the pathogen.
These lymphocytes then produce specific antibodies that bind to the antigens.
The bound antibodies cause the bacteria to agglutinate or are marked for destruction by phagocytes.
Memory cells are formed, so if the same bacteria re‑enter, antibodies are produced faster and in larger amounts.
Lymphocytes detect bacterial antigens on the surface of the pathogen.
These lymphocytes then produce specific antibodies that bind to the antigens.
The bound antibodies cause the bacteria to agglutinate or are marked for destruction by phagocytes.
Memory cells are formed, so if the same bacteria re‑enter, antibodies are produced faster and in larger amounts.
Examiner tips
- Use the exact terms – phagocytes, lymphocytes, antibodies, memory cells. Show the sequence: phagocytosis → antigen recognition → antibody production → agglutination/marking → memory cell formation. Keep each point brief but complete to hit all five marks.
Common mistakes
- Mixing up phagocytes with lymphocytes; they are different cell types. Forgetting to mention memory cells or the speed/quantity advantage they provide.
Mark scheme (5 marks)
- White blood cells / phagocytes engulf and digest (ingest) the bacteria by phagocytosis
- Lymphocytes recognise antigens on the surface of the bacteria
- Lymphocytes produce specific antibodies that bind to / complement the antigens on the bacteria
- Antibodies cause the bacteria to clump together (agglutinate) or neutralise / mark them for destruction by phagocytes
- Memory cells are produced so that if the same bacteria enter the body again, antibodies are produced more quickly / in greater quantities
Related
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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