Explain the role of auxins in tropisms/ tropic responses.

Answer:

a)Phototropism; light stimulus causes auxins to migrate to the darker sided; higher concentration of auxins on the darker side stimulates faster growth than the lit side; hence the shoot tip bends/ curves to the source of light;
b)Geotropism/ gravitotropism; gravity causes auxins to migrate to the lower side of the seedling; higher concentration of auxins on the lower side of the shoot stimulates faster growth than the upper side; hence the shoot tip/ plumule bends/ curves upwards; higher concentration of auxins on the lower side of the root inhibits growth than on the upper side; hence the shoot tip curves/ bends downwards;
c)Thigmotropism/ haptotropism; contact causes the auxins to migrate away from the point of contact in the shoot; higher concentration of auxins on the outer side stimulates faster growth than the point of contact; thus the stem/ tendril coils around the support structure;

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