Explain how the immune system and the lymphatic system are integrated in the body's response to a bacterial infection.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Lymphatic vessels transport interstitial fluid as lymph into lymph nodes, where immune cells are concentrated and pathogens can be intercepted.
Macrophages and dendritic cells in the nodes engulf bacteria by phagocytosis and present bacterial antigens to lymphocytes, especially T cells.
B lymphocytes in the nodes are activated by the presented antigen, proliferate and differentiate into plasma cells that secrete antibodies specific to the bacterial antigen.
The activated lymphocytes and antibodies are then released into the lymphatic system, which drains into the bloodstream, providing a systemic immune response.
Macrophages and dendritic cells in the nodes engulf bacteria by phagocytosis and present bacterial antigens to lymphocytes, especially T cells.
B lymphocytes in the nodes are activated by the presented antigen, proliferate and differentiate into plasma cells that secrete antibodies specific to the bacterial antigen.
The activated lymphocytes and antibodies are then released into the lymphatic system, which drains into the bloodstream, providing a systemic immune response.
Examiner tips
- Use the word "interstitial fluid" and "lymph" to show understanding of lymphatic transport. Mention macrophages/dendritic cells and antigen presentation to link innate and adaptive immunity. Show the sequence: activation → differentiation → antibody secretion → systemic spread. Keep the answer concise, 4‑point structure matching the scheme.
Common mistakes
- Confusing lymphatic vessels with blood vessels; forgetting that lymph drains into the bloodstream. Omitting the role of macrophages/dendritic cells in antigen presentation. Failing to state that B cells become plasma cells that secrete antibodies.
Mark scheme (4 marks)
- Lymphatic vessels carry interstitial fluid (as lymph) through lymph nodes, where immune cells are concentrated / where pathogens can be intercepted.
- Macrophages / dendritic cells in lymph nodes engulf bacteria by phagocytosis and present antigens to lymphocytes / T cells.
- B lymphocytes in lymph nodes are activated and differentiate into plasma cells that secrete antibodies specific to the bacterial antigen.
- Lymphocytes proliferate within lymph nodes and are distributed via the lymphatic system back into the bloodstream / circulatory system, providing a systemic immune response.
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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