Question

The stimulus of plant due to certain chemicals is known as,
A. Phototropism
B. Chemotropism
C. Geotropism
D. None of the above

Answer 1

Stimulus is something that causes a reaction, especially interest, excitement or energy. For plants, here stimulus is when the stimuli like the things which put the change upon the plant as an object. These stimuli could be light, water, chemicals, etc.

Complete answer:
Phototropism is a directional response that allows plants to grow towards, or in some cases, away from a source of light. The sensing of light in the environment is important to plants. It can be crucial for competition and survival of the plant.
Chemotropism is defined as the growth of the organisms navigated by chemical stimulus from the outside of the organism. It has been observed in bacteria, plants and fungi. A chemical gradient can influence the growth of the organism in a positive or negative way. Positive growth is characterised by growing towards a stimulus and negative growth is growing away from the stimulus. Chemotropism is slightly different from Chemotaxis, the major difference being that chemotropism is related to growth whereas chemotaxis is related to locomotion.
Geotropism can be defined as the growth of a plant or immovable animal in response to the force of gravity. An example of geotropism is the roots of a plant growing down straight into the ground.

Hence, the correct answer is option (B). Chemotropism.

Note:
Chemotaxis is defined as the movement of an organism in response to a chemical stimulus. Somatic cells, bacteria and other single-cell or multicellular organisms are some which direct their movements according to certain chemicals in their environment.