Question

What is called the movement of plants towards gravity?
A. Chemotropism
B. Geotropism
C. Hydrotropism
D. Phototropism

Answer 1

Hint: Plant movement of the plant body or an organ or material within the plant body are free or spontaneous. These movements are known as plant movement. The movements are brought about by various aspects or in response to the number of external impulses.

Complete answer:
Plant growth movements which take place in relation to some directional external impulse is known as movement. These types of movement are induced by some external force or external stimuli. it results in positional movement of the plant. This type of movement of the plant is known as tropic movement and the phenomenon is known as tropism. The stimuli or the impulse is an external force and the reaction of the plant to the stimuli can be negative or positive. In the case of a positive stimuli, the response of the plant will be towards the stimuli and in negative response it would be away from the stimulus

The different types of stimuli that work to produce tropism are response to temperature, humidity, chemicals, electric field, source of gases, water, magnetic field, response to light etc. The plants may also respond to touch or contact.

> Option B: The coordinated process of differential growth or response to the gravity pulling by a plant is known as geotropism or gravitropism. Plants grow towards the direction of gravity pull and the stems of the plant show negative stimuli and grow upwards in the opposite direction. The differential in the roots of the plant growing towards the gravity involves changes in the cell expansion. The gravity sensed in the root tip which is then relayed to the elongation zone so that growth direction can be maintained. The growth responses cause changes in the orientation and allows the roots to grow in the same direction as that of the gravity. Roots bend in response to gravity due to a regulated movement of the auxin plant hormone. Auxin is also known as polar auxin transport. The stems respond as a negative stimulus to geotropism orienting its position to maximize sunlight contact.

> Option A: Chemotropism is the growth of organisms that is affected by the presence of chemical stimulus in the external environment of the plant. Changes in the chemical gradient may show a negative or positive stimulus by the plant. The roots may grow towards useful minerals or grow away from harmful chemicals.

> Option C: Hydrotropism is the response of a plant which is determined by a stimulus or gradient in water concentration. The root cap sensing water sends a signal to the elongation part of the root which then moves towards the area of water concentration. This helps the roots to find water in the ground.

> Option D: The movement of an organism towards or away from light stimulus is referred to as a phototropism.

Hence, the correct answer is option (B).

Note: A tropism can be described as a biological event which indicates the growth or movement due to the presence of an environmental stimuli. The movement of the plant towards the response of gravity pull is known as geotropism. THe roots of the plant show positive stimuli as they grow in the direction of gravity and the stem reflects negative stimuli as it grows in the opposite direction.