Explain5 marksStandard
A person inhales a breath of air containing oxygen molecules. Describe the path taken by an oxygen molecule from the trachea to the blood, and explain how the structures along this path are adapted to facilitate gas exchange.
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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