Question

Explain response of plant parts to light with the help of a diagram.

Answer 1

Response of Plant Parts to Light (Phototropism)

1. Definition: The growth movement of a plant part in response to light is called phototropism.
2. Shoot: The shoot grows towards the light, so it shows positive phototropism.
3. Root: The root grows away from the light, so it shows negative phototropism.
4. Mechanism: Auxin is made at the tip of the shoot. When light falls on one side only, the auxin moves towards the shaded side. The cells on the shaded side receive more auxin and elongate more than the cells on the lighted side. The shoot therefore bends towards the light.
5. Experiment: A potted plant is kept inside a cardboard box that has a hole on one side, and light is allowed to enter only through this hole. After a few days, the shoot is found bent towards the hole, while the roots grow downwards into the soil, away from the light.