CAIE A Level Biology 9700 · Control and coordination
A student investigated the effect of auxin on stem elongation in tomato seedlings. The table below shows the mean increase in stem length after 24 hours for segments treated with auxin and untreated controls.
| Treatment | Mean increase in stem length (mm) |
|---|---|
| Control (distilled water) | 2.1 |
| Auxin (1 mg/L) | 8.7 |
Outline the mechanism by which auxin stimulates cell elongation in plant stems. Use the data in the table to support your answer.
4 marks, so the mark scheme is looking for about 4 separate creditworthy points. Making the same point twice in different words earns it once.
Outline means: Give the main points briefly. Less detail than describe, but every key step has to be there. One short line per step, in order. The marks are for coverage, not depth.
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