Question

A young dicot seedling (e.g., soyabean) is laid horizontally on a surface and is subjected to gravity stimulus. The shoot bends in upward direction and the root bends in downwards direction. Which out of the following is the possible reason for this movement ?
A. Redistribution of auxins throughout the seedlings is responsible for the stimulatory unequal growth in shoots and roots.
B. Redistribution of cytokinins throughout the seddling is respondible for the stimulatory unequal growth in roots and shoots.
C. Redistribution of auxins in roots and cytokinins in shoots is responsible for stimulatory unequal growth.
D. Redistribution of auxins in shoots and cytokininis in roots is responsible for stimulatory unequal growth.

Answer 1

Correct Answer - a
Auxins play a paramount role in the various tropic movements shown by plants such as phototropism and gravitropism. Photoropism is the movement in response to light. The shoot tip is responsible for the directional movement in response to sunlight, as tip is the area where auxins are synthesised. The part of the shoot tip which receives direct sunlight will have the least amount of auxin. more auxin present on the shaded side promotes more cell division and elongation, causing the plant to bend towards sunlight. Gravitropism is the movement in response to gravity. Roots bend downwards in response to gravity due to the regulated transport of auxins called as poalr auxin transport.