Activity 7.2 NCERT class 10 Science Control and Coordination
Procedure: Activity 7.2 asks us to put a plant towards a source of light and see what happens to the growth of its shoot and root.
Explanation: Plants does not have a nervous system or nerve fibres, they show response towards change in the environment chemically.
Shoot exposed to light form auxin. Auxin now diffuses to the unexposed part of the shoot.
Auxin has growth promoting characteristic in stems. It induces growth in the unexposed parts. As a result, the plant bends toward the light.
Auxin has an inhibitory action on the root. As a result, root bends away from the light.
- plant stem grows toward the light. We call this phenomenon as positive phototropism.
- Plant root grows away from the light.
We can understand this observation by analysing the needs of the plant also. A shoot of the plant needs light, so they like to grow in the direction of light. Root need water and mineral from the soil. So they try to move away from the sun.
This phenomenon is called Phototropism.