The plant hormones (or phytohormones) regulate many functions in plants. The various functions in plants which are regulated by the plant hormones (or phytohormones) are:
1. Germination of seeds (or Breaking the dormancy of seeds),
2. Growth of root, stem and leaves,
3. Movement of stomata (or stomatal movement) in leaves,
4. Flowering of plants,
5. Ripening of fruits, and
6. Phototropism, geotropism, chemotropism, hydrotropism, thigmotropism and nastic movements.
Let us answer some questions now.
Sample Problem 1:
Which of the following is a plant hormone?
(a) Insulin (b) Thyroxine
(c) Oestrogen (d) Cytokinin
Sample Problem 2:
How do auxins promote the growth of a tendril around a support?
When the tip of a tendril touches a support, then the auxins (plant hormones) present in its tip move to that side of tip which is away from the support. Auxins promote growth. So, due to more auxins in it, the side of tendril away from the support grows faster (and becomes longer) than the side which is an if contact with the support, and makes the tendril curve (or bend) towards the support. This ‘curving’ tendril can then encircle the support and wind around it.
Sample Problem 3:
How is the movement of the leaves of the sensitive plant different from the movement of a shoot towards light?
The main differences between the movement of the leaves of a sensitive plant and the movement
Movement of leaves of sensitive plant
Movement of a shoot towards light
1. It is a nastic movement which does not depend on the direction of stimulus applied
2. The stimulus is ‘touch’.
3. It is caused by the sudden loss of water
from the swellings at the base of leaves
4. It is not a growth movement.
1. It is a tropic movement which depends on the direction of stimulus applied.
2. The stimulus is ‘light’.
3. It is caused by the unequal growth on the two sides of the shoot.
4. It is a growth movement.
Sample Problem 4:
What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?
The movement in the leaves of a sensitive plant takes place due to the sudden loss of water ii the pad-like swellings (called pulvini) at the base of all the leaves. The loss of water makes the pulvini limp leading to drooping and folding of leaves. On the other hand, the movement in our legs takes place when the leg muscles pull on the leg bones.