CAIE A Level Biology 9700 · Gas exchange
A student examines a stained section of lung tissue under a light microscope. They observe thin-walled alveoli lined with a single layer of flattened cells, and numerous capillaries in close contact with the alveoli.
Describe how the structure of the alveolar epithelium is adapted for efficient gas exchange.
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.
Written by Markquill to follow the Cambridge International syllabus. Markquill is independent and is not affiliated with or endorsed by Cambridge International.