CAIE A Level Biology 9700 · Gas exchange
A student examines a photomicrograph of a mammalian lung. She observes that the walls of the alveoli are lined with a very thin layer of squamous epithelial cells. Describe how the structure of the squamous 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.