CAIE A Level Biology 9700 · Control and coordination
An experiment investigates the effect of auxin on cell elongation in oat coleoptile segments. Segments are placed in a buffer solution at pH 7. Upon addition of auxin, the pH of the solution decreases to pH 5 within a few minutes, and the coleoptile segments begin to elongate.
Explain the mechanism by which auxin leads to this rapid elongation growth, including the role of cell wall acidification.
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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