Explain how the human body uses both non-specific defences and the specific immune response to prevent and destroy a bacterial pathogen that enters the body through a skin wound for the first time.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A person cuts their finger and bacteria enter the body through the broken skin.
Model answer (5 marks)
Blood clotting forms a clot over the wound, creating a mechanical barrier that stops further bacteria from entering.
White blood cells recognise bacterial antigens and are attracted to the site.
Phagocytes, such as neutrophils and macrophages, engulf the bacteria and digest them by phagocytosis.
Lymphocytes (B‑cells) produce antibodies that bind specifically to the bacterial antigens, neutralising or marking the bacteria for destruction.
Memory B‑cells persist after the infection, so if the same bacteria invade again, antibodies are produced more rapidly.
White blood cells recognise bacterial antigens and are attracted to the site.
Phagocytes, such as neutrophils and macrophages, engulf the bacteria and digest them by phagocytosis.
Lymphocytes (B‑cells) produce antibodies that bind specifically to the bacterial antigens, neutralising or marking the bacteria for destruction.
Memory B‑cells persist after the infection, so if the same bacteria invade again, antibodies are produced more rapidly.
Examiner tips
- Mention clotting as a mechanical barrier first. Show the sequence: detection → phagocytosis → antibody production → memory. Use terms: antigens, phagocytes, antibodies, memory cells.
Common mistakes
- Confusing clotting with immune cells. Failing to name phagocytes or antibodies. Omitting the memory cell component.
Mark scheme (5 marks)
- Blood clotting seals the wound, acting as a mechanical barrier to prevent more microorganisms from entering.
- White blood cells detect antigens on the surface of the bacteria.
- Phagocytes engulf and digest the bacteria (phagocytosis).
- Lymphocytes produce specific antibodies that bind to the antigens on the bacteria to neutralise / destroy them.
- Memory cells remain after the infection so that if the same bacteria enter again, antibodies are produced more quickly.
Key terms in this question
non-specific defence · immune response
Related
- All WJEC A-Level Biology (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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