A person contracts a bacterial infection for the first time. Explain how B-lymphocytes respond to the antigens on the bacteria to protect the body from the infection.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
When a bacterial pathogen enters the body, the immune system mounts a specific response involving white blood cells. B-lymphocytes play a central role in this response by producing proteins that target the pathogen.
Model answer (5 marks)
1. Bacteria display antigens on their surface that are recognised as foreign by the immune system.
2. B‑lymphocytes that have receptors complementary to those antigens recognise and bind the antigen.
3. The antigen‑bound B‑lymphocyte is activated and undergoes clonal expansion, producing many identical cells.
4. The clones differentiate into plasma cells that secrete large amounts of antibodies specific to the bacterial antigen.
5. Some activated B‑lymphocytes become memory cells, remaining in the body to give a faster, stronger response on re‑exposure.
2. B‑lymphocytes that have receptors complementary to those antigens recognise and bind the antigen.
3. The antigen‑bound B‑lymphocyte is activated and undergoes clonal expansion, producing many identical cells.
4. The clones differentiate into plasma cells that secrete large amounts of antibodies specific to the bacterial antigen.
5. Some activated B‑lymphocytes become memory cells, remaining in the body to give a faster, stronger response on re‑exposure.
Examiner tips
- Use the exact sequence of events: recognition, activation, clonal expansion, antibody production, memory formation. Show the word ‘specific’ when describing B‑cell receptors and antibodies. Keep each point short but complete – 1 mark each.
- common_mistakes
- :
- Confusing T‑cell with B‑cell actions. Omitting the step of clonal expansion. Using vague terms like ‘immune response’ instead of specific B‑cell actions.
Mark scheme (5 marks)
- The bacteria carry antigens on their surface which are recognised as foreign / non-self
- B-lymphocytes specific to that antigen are activated / the specific B-lymphocyte recognises the complementary antigen
- The activated B-lymphocyte divides / multiplies to produce clones (clonal expansion)
- The cloned B-lymphocytes produce large quantities of antibodies specific to that antigen
- Memory B-lymphocytes / memory cells are produced that remain in the body so that the response is faster and greater if the same pathogen is encountered again
Key terms in this question
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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