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Auxin and root growth response
Figure 6 shows the stationary apparatus A and slowly rotating apparatus B. The student left both sets of apparatus in a dark cupboard for 24 hours.
Figure 7 shows the seedling from apparatus A at the start and the source drawing after 24 hours.
Auxin is a plant hormone. Explain how auxin causes the results in apparatus A.
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Marking points
- 1 Identifies an uneven auxin distribution, with more auxin on the lower side.
- 2 Explains that the lower side grows less/slower than the upper side, producing the bend.
Full-mark answer
Gravity causes auxin to collect on the lower side of the root. In a root, this higher auxin concentration inhibits growth, so the lower side grows more slowly than the upper side and the root bends downward.
Why this answer loses marks
Auxin makes the lower side of the root grow faster.
In roots, more auxin inhibits elongation on the lower side, so the upper side grows faster.