What are tropic movements? Explain them with examples.
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Solution
Movement in living organisms
Living organisms live in an environment where they have to respond to external stimuli like temperature, water, light, food, predators, chemicals, etc. Movement can be either in the direction of the stimulus or away from the stimulus.
Animals have different characteristics that help them in movement. They have locomotory organs, endocrine systems, and nervous systems which help them respond to external stimuli. They are reversible.
Plants lack locomotory organs, endocrine systems, and nervous systems. They respond to external stimuli slowly and gradually. This type of response is usually irreversible. They are termed tropic or nastic movements.
A movement towards the direction of stimuli is termed positive tropism whereas movement away from the stimuli in the opposite direction is termed negative tropism.
Tropic movements:
Tropic movements are the type of movements exhibited by plants. These are dependent on the direction of the external stimulus. Tropic movements involve the growth of plants.
Examples- phototropism (response to light), geotropism (response to gravitational pull), chemotropism (response to chemicals), thigmotropism (response to contact with objects), thermotropism (response to temperature), and hydrotropism (response to water).
1.The above image shows phototropism in a sunflower plant. The stem of the plant show growth in the direction of sunlight. This is called positive phototropism. On the other hand, the roots grow in the direction away from sunlight. This is called negative phototropism.
2. The above image shows thigmotropism. This phenomenon is observed in certain plants with weak stems which require support to grow upright. Examples- Grapevine and Cucurbita plants. The tendrils of the stem, on contact with a support, twine around it and provides the weak stems with support for growth.
