Question

Phototropic and geotropic movements are linked to
a. Gibberellins
b. Cytokinins
c. Auxin
d. None of the above

Answer 1

A response to stimuli is called tropism in plants, where phototropic means stimuli to the cells to grow towards the light, while geotropism means, there is a stimulus to the cells which makes them move towards the ground or earth.

Complete answer:
- Phototropism is the movement of the plant cells, either toward or always from the sunlight.
- This phototropism mainly occurs with the help of a chemical or photo hormone of the plants called auxin, where this auxin helps plant cells to react to the light or sunlight and activates the auxin, this activated auxin makes the cells elongate which are far away from the light.
- This elongation of the cells results in the bending of the plant which is towards the light, hence it got the name phototropism.
- In plants, the shooting part shows positive phototropism, while the roots of plants show negative phototropism.
- In a similar way geotropism also occurs, where it is also regulated by the same plant hormone auxin.
- Where auxin stimulates the cells of the roots to grow towards the gravity of earth, and it helps to provide good mechanical support.
- Some cells of the roots and some cells of the shoot have an accumulation of auxin which makes them grow towards the gravity
- Generally, roots show positive geotropism, and shoot of plants shows negative geotropism.
- So this phototropism and geotropism make the plants grow in the proper direction, and auxin plays an important role in stimulating these movements in the plants.

Hence, the correct answer is option (C).

Note: Auxin the chemical which can be called photo hormone present in plants responsible for phototropism and geotropism while shoots of plants show positive phototropism and negative geotropism, and roots of plants show positive geotropism and negative phototropism.