Question

Why do the stems and roots of a plant show unilateral growth towards light and gravity of the earth respectively?

Answer 1

• Tropism is the growth movement of a plant in the direction of an external stimulus.
• The movement of a plant and their parts in response to light is called phototropism.
• The shoots of the plant grow towards the sunlight, but the roots of the plant grow or move away from the sunlight.
• When the growth of a plant or a part of a plant is towards the stimulus, it is called positive and when it is away from the stimulus, it is called negative.
• Hence, the shoots exhibit positive phototropism, and the roots exhibit negative phototropism.
• The movement of a plant and their parts in response to the force of gravity is called geotropism.
• The shoots of a plant grow above the soil, that is, against the force of gravity, while the roots grow in the soil towards the force of gravity.
• Thus, shoots exhibit negative geotropism and the roots exhibit positive geotropism.
• Hence, we can conclude that stems grow in the direction of light and exhibit positive phototropism and roots grow in the direction of gravitational force and exhibit positive geotropism.