Chlamydia is a communicable disease caused by a bacterium. Explain how the human body attempts to defend itself against a chlamydia infection, including both non-specific defences and the specific immune response.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Non‑specific defences:
1. The skin, mucus and stomach acid act as barriers, preventing chlamydia from entering the body.
Specific immune response:
2. White blood cells recognise chlamydia by its surface antigens.
3. Lymphocytes then produce antibodies that are complementary to those antigens.
4. Phagocytes engulf, ingest and digest the bacterium (phagocytosis).
5. Memory cells persist after the infection, so that if chlamydia re‑enters, antibodies are produced more rapidly.
1. The skin, mucus and stomach acid act as barriers, preventing chlamydia from entering the body.
Specific immune response:
2. White blood cells recognise chlamydia by its surface antigens.
3. Lymphocytes then produce antibodies that are complementary to those antigens.
4. Phagocytes engulf, ingest and digest the bacterium (phagocytosis).
5. Memory cells persist after the infection, so that if chlamydia re‑enters, antibodies are produced more rapidly.
Examiner tips
- Use the word "non‑specific" for the first part and "specific" for the second.
- Show the sequence: barrier → antigen detection → antibody production → phagocytosis → memory cells.
- Include key terms: skin, mucus, stomach acid, antigens, lymphocytes, antibodies, phagocytes, memory cells.
Common mistakes
- Mixing up non‑specific and specific defences; e.g. describing antibodies as a non‑specific defence.
- Omitting the role of memory cells or phagocytosis.
- Using vague language such as "the immune system" without specifying the mechanisms.
Mark scheme (5 marks)
- Non-specific defence: skin / mucus / stomach acid acts as a barrier to prevent pathogens entering the body
- White blood cells detect the chlamydia bacterium using antigens on its surface
- Lymphocytes produce antibodies that are specific / complementary to the chlamydia antigens
- Phagocytes engulf / ingest and digest the bacterium (phagocytosis)
- Memory cells remain after infection so that if chlamydia enters the body again, antibodies are produced more quickly
Key terms in this question
Related
- All WJEC A-Level Biology (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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