A student cuts their hand and bacteria enter the body through the wound. Explain how T-lymphocytes and B-lymphocytes work together to destroy the bacteria.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
When the skin is broken, pathogens can enter the body and trigger an immune response involving several types of white blood cell.
Model answer (5 marks)
Bacteria have antigens on their surface, which are unique chemicals that the immune system recognises as foreign.
T‑lymphocytes recognise these antigens presented by antigen‑presenting cells and become activated.
Activated T‑lymphocytes then stimulate B‑lymphocytes.
B‑lymphocytes differentiate into plasma cells that produce antibodies specific to the bacterial antigens.
The antibodies bind to the antigens on the bacteria, marking them for destruction and neutralising the pathogen.
During this response, memory T and B cells are formed, so if the same bacteria enter again the immune response is faster and produces a larger quantity of antibodies.
T‑lymphocytes recognise these antigens presented by antigen‑presenting cells and become activated.
Activated T‑lymphocytes then stimulate B‑lymphocytes.
B‑lymphocytes differentiate into plasma cells that produce antibodies specific to the bacterial antigens.
The antibodies bind to the antigens on the bacteria, marking them for destruction and neutralising the pathogen.
During this response, memory T and B cells are formed, so if the same bacteria enter again the immune response is faster and produces a larger quantity of antibodies.
Examiner tips
- Use the exact terms – antigens, T‑lymphocytes, B‑lymphocytes, antibodies, memory cells
- Show the sequence: antigen → T‑cell activation → B‑cell stimulation → antibody production → marking for destruction
- Mention the role of memory cells for a faster future response
Common mistakes
- Confusing T‑cells with B‑cells as the main antibody producers
- Omitting the step where T‑cells activate B‑cells
- Failing to mention memory cells or the speed/quantity advantage of a secondary response
Mark scheme (5 marks)
- Bacteria have antigens on their surface / antigens are unique chemicals on the surface of the bacteria
- T-lymphocytes detect / recognise the foreign antigens and activate B-lymphocytes
- B-lymphocytes produce antibodies specific to the antigen on the bacteria
- Antibodies bind to the antigens on the bacteria, marking / clumping them for destruction / neutralising them
- Memory cells are produced so that if the same bacteria enter again, the response is faster / greater quantity of antibodies is produced more quickly
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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