CAIE A Level Biology 9700 · Control and coordination
In an experiment, segments of oat coleoptiles were placed in a solution containing auxin. The pH of the solution surrounding the cell walls was measured over time. Within minutes, the pH decreased from 7.0 to 5.5. After 30 minutes, the coleoptile segments had elongated significantly.
Explain how auxin causes this decrease in pH 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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