CAIE A Level Biology 9700 · Gas exchange
A student examines a stained section of the tracheal wall under a light microscope. Two types of cells are clearly visible: ciliated epithelial cells and goblet cells.
Describe the roles of these two cell types in maintaining the health of the gas exchange system.
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.