Explain5 marksStandard
Explain how the movement of potassium ions into and out of guard cells controls the opening and closing of stomata. In your answer, refer to the role of abscisic acid (ABA) and calcium ions during water stress.
CAIE A Level Biology 9700 · Homeostasis
Homeostasis: 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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