CAIE A Level Biology 9700 · Control and coordination
A student investigates the effect of auxin on cell elongation in maize coleoptiles. When coleoptile segments are placed in a buffer solution containing auxin, the pH of the solution drops over time. Explain the mechanism by which auxin causes cell wall acidification and how this leads to cell elongation.
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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