CAIE A Level Biology 9700 · Gas exchange
A student views transverse sections of the wall of two airways: one from the trachea and one from a bronchiole. The student notes that the tracheal wall contains prominent C-shaped pieces of cartilage and a relatively thin layer of smooth muscle. In contrast, the bronchiole wall has no cartilage but a thick layer of smooth muscle.
Explain the functional advantage of these structural differences between the trachea and the bronchiole.
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.