Explain5 marksStandard
An oxygen molecule enters the human gas exchange system through the trachea. Explain how the structures of the airways and the alveoli are adapted to enable efficient gas exchange between the air and the blood.
CAIE A Level Biology 9700 · Gas exchange
Gas exchange: explain question
How this question is marked
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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