IB Biology SL 3.2.1 Capillary Adaptations Question Bank
Practise IB Biology SL 3.2.1 by linking thin, permeable capillary walls, narrow lumens and dense branching to rapid tissue exchange.
- Syllabus
- First assessment 2025
- Course
- Biology SL
- Level
- SL
Exam points
- Explain how thin, permeable capillary walls shorten diffusion distance for tissue exchange.
- Relate narrow lumens and dense branching to surface area, flow and oxygen delivery.
B3.2.1—Capillary adaptations question 1
[Maximum number: 3]
Explain how the structure of capillaries relates to their functions.
Complete correct answer:
Capillary walls are thin or one cell thick for better diffusion. Capillaries have a small diameter or narrow lumen so they fit into small spaces between cells. Their small diameter gives a greater surface area for molecular exchange. Pores between cells in the walls allow plasma to leak out and allow phagocytes or immune components to enter tissues. Only one red blood cell passes at a time, allowing efficient oxygen uptake.
Marking guidance:
Do not accept "membranes" for the thin-wall point. Award up to 3 marks. Official markscheme page 7.
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