CAIE A Level Biology 9700 · Gas exchange
A student observes transverse sections of the trachea and a bronchiole under a light microscope. In the trachea, the wall contains C-shaped rings of cartilage and a layer of smooth muscle. In the bronchiole, no cartilage is visible, but the wall contains a relatively thick layer of smooth muscle. Explain how the difference in distribution of cartilage and smooth muscle between these two structures is related to their functions.
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.