Question

The positive response of the plants towards the gravitation is called
A. Phototropism
B. Geotropism
C. Hydrotropism
D. Chemotropism

Answer 1

Tropism can be explained as a response of plants against a particular stimulus.

Complete answer: 1. When a plant responds towards the stimulus it is called positive tropism and when a plant responds against that particular stimulus it is called negative tropism.
2. When light acts as a stimulus and plant respond against the light, it is called phototropism.
Photo means light and tropism means response towards the stimulus.
For example, the stem grows towards the sunlight and roots grow against sunlight.
So, for stem positive phototropism is seen and for roots, negative phototropism is seen.
3. When gravitation acts as a stimulus and plant respond against gravitational force, it is called geotropism. Geo means the study of gravitation and tropism means response towards the stimulus.
For example, roots grow towards the gravitation and stem grow against gravitation.
So, for roots, positive geotropism is seen and for stems, negative geotropism is seen.
4. When water acts as a stimulus and the plant responds against water, it is called hydrotropism.
Hydro means water and tropism means response towards the stimulus.
For example, roots grow towards the water of the soil and stem grow against the water of the soil.
So, for roots, positive hydrotropism is seen and for stems, negative hydrotropism is seen.
5. When any chemical compound acts as a stimulus and the plant respond against that chemical compound, it is called chemotropism.
Chemo means chemicals and tropism means response towards the stimulus.
For example, the development of a pollen tube towards the ovule.

So, the correct answer is “Option B”.

Note: The stimulus can be light, water, gravitation, chemical compound, touch, etc.
Tropism can be of two types – positive and negative.