CAIE A Level Biology 9700 · Transport in mammals
A student observes a capillary network in a living hamster's cheek pouch under a microscope. They note that the capillary walls are extremely thin (only one cell thick), the lumen is very narrow, and the blood flow is slow compared to that in arteries. Explain how the structure of capillaries is adapted to allow efficient exchange of substances between the blood and tissue fluid.
5 marks, so the mark scheme is looking for about 5 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
Written by Markquill to follow the Cambridge International syllabus. Markquill is independent and is not affiliated with or endorsed by Cambridge International.