PART – 2, CHAPTER 2, CONTROL AND COORDINATION, BIOLOGY, CLASS 10

CONTROL AND COORDINATION IN PLANTS

The plants do not have a nervous system and sense organs like eyes, ears, or nose, etc., like the animals, but they can still sense things. The plants can sense the presence of stimuli like light, gravity, chemicals, water, and touch, etc., and respond to them. The plants can sense things like light, gravity, chemicals, water, and touch, etc., by the action of hormones in them. The stimuli like light, gravity, chemicals, water, and touch, etc., are called environmental changes. So, we can also say that the plants coordinate their behaviour against environmental changes by using hormones. The hormones in plants do not act the same way as in animals. The hormones in plants coordinate their behaviour by affecting the growth of a plant. And the effect on growth of the plant can result in the movement of a part of the plant like shoot (stem) or root, etc.

Animals use both nervous system and hormones for coordination of their activities. Plants have no nervous system, so plants use only hormones for coordination. Thus, the reaction (or response) of plants to different stimuli like light, gravity, chemical substances, water, and touch etc., is due to the effect of hormones. Please note that animals can respond quickly because they have a nervous system. Plants cannot respond quickly because they have no nervous system. The plants respond to various stimuli very slowly by growing. So, in most of the cases, the response of a plant to a stimulus cannot be observed immediately. It usually takes a considerable time to observe the effect of a stimulus on a plant.

From the above discussion we conclude that the function of control and coordination in plants is performed by the chemical substances called plant hormones.

Please note that the plant hormones are also called phytohormones (‘phyto’ means ‘plant’). Before we discuss the various types of plant hormones, we should know the meanings of ‘dormancy’ and ‘breaking of dormancy’. A resting, inactive condition in which metabolism almost stops is called dormancy. The seed of a plant is inactive or dormant. It has dormancy. A seed must have certain conditions like water, warmth, air and hormones to break dormancy and germinate to form a seedling (which then grows into a plant). Another part of a plant having dormancy is the bud. The bud is a young, undeveloped shoot of a plant which on breaking dormancy can form a branch, a leaf or a flower depending on its position in the plant. The breaking of dormancy of a bud also requires certain plant hormones. Keeping these points in mind, we will now discuss the various types of plant hormones.