Class 10 Science Short Notes 2026-27

6.2 COORDINATION IN PLANTS

In animals the work of control and coordination is shared between the nervous system and the endocrine system. Plants possess neither nerves nor muscles, and yet they clearly respond to changes in their surroundings. The leaves of the touch-me-not plant fold within seconds when they are touched, while a germinating seed always sends its root downwards and its shoot upwards whichever way the seed happens to be lying. The first kind of movement is rapid and does not depend on growth; the second is gradual and results from growth taking place more on one side than the other.

Movements that depend on the direction of a stimulus and are brought about by growth are known as tropic movements. They may be directed towards the stimulus or away from it. Stems usually bend towards the source of light and roots bend away from it; this is called phototropism. Roots grow downwards in response to gravity, a response known as geotropism, while the response to water and to chemicals is called hydrotropism and chemotropism respectively.

Growth in plants is regulated by chemical substances called plant hormones. Among these, auxin promotes elongation of cells, gibberellins help the stem to grow, cytokinins promote cell division and abscisic acid has an inhibitory effect on growth.