CAIE A Level Biology 9700 · Gas exchange
A student is studying the gas exchange system of a mammal. They observe that the alveoli are lined with a very thin layer of cells and are surrounded by a dense network of capillaries.
Describe how the structure of the alveolar epithelium and the associated capillaries are adapted to facilitate efficient gas exchange between alveolar air and blood.
4 marks, so the mark scheme is looking for about 4 separate creditworthy points. Making the same point twice in different words earns it once.
Describe means: Say what happens or what something is like, in order and with detail. You are not being asked why. If there is data, quote it: name the trend, then give figures with units at the points where it changes.
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