CAIE A Level Biology 9700 · Gas exchange
A student looks at transverse sections of a human trachea and a bronchiole. The trachea wall contains C-shaped rings of cartilage and a layer of smooth muscle. The bronchiole wall contains a relatively thick layer of smooth muscle and no cartilage.
Explain how the differences in the distribution of cartilage and smooth muscle in the walls of the trachea and bronchioles are related to the functions of these structures.
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.
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