Question

What is a tropic movement?
A. The directional growth movements of plants
B. The directional growth movements of plants due to external stimuli
C. The directional growth movements of plants due to internal stimuli
D. The random growth movements of plants due to external stimuli.

Answer 1

Plants are not able to move from one place to another like animals as they lack specific locomotory structures. But plants can show various types of movements in response to specific
stimuli from their surroundings.

Complete answer: Plants can respond to the external stimuli around them and show some sort
of growth either towards the stimuli or against them. This movement shown by plants is called tropic movements. Know that it differs from sudden movements shown by animals as the tropic movements shown by plants are slow and gradual. Plants can’t move from one place to another even by tropic movements.
-Based on the external stimuli, tropic movements are of several types. Examples of tropic movements are geotropism, phototropism, chemotropism, hydrotropism, thigmotropism, etc. It can be positive when the movement is towards the direction of the stimulus and negative when the movement is against the stimuli direction.
-In geotropism, the plant shows movement towards the gravitational stimuli. Roots show positive
geotropism as it grows towards the earth while shoot shows negative geotropism. Positive phototropism is shown by shoot tips as they grow towards the sunlight.
-Root tip shows negative phototropism. Plant movements in response to external chemical stimuli is called chemotropism. Roots may grow towards the water and are called positive hydrotropism.
Hence, the correct answer is Option B

Note: The tropic movements shown by the plants are of great use to the plants. Positive
Phototropism helps plants to absorb more sunlight and perform photosynthesis for food production.
Positive geotropism by roots helps the plant to stay firm and stable, attached to the earth. Positive
hydrotropism of roots helps plants to absorb more water and minerals from the soil.