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(a) What is meant by positive tropism and negative tropism? Explain with examples.(b) Define thigmotropism. Give one example of thigmotropism.(c) What is the difference between thigmotropism and thigmonasty? Name one plant which exhibits thigmotropism and one plant which exhibits thigmonasty. What behaviour (or responses) of these plants make you think that they exhibit thigmotropism and thigmonasty respectively?
(a) Positive tropism- If the movement of the response is towards the stimulus, it is known as positive tropism.
Example- The movement of roots towards the pull of gravity. Negative tropism- If the movement of the response is in the direction opposite to the stimulus, it is known as negative tropism. Example- The movement of plant stem opposite to the direction of gravitational pull.
(b) Thigmotropism- It is the directional movement of plant parts in response to touch. Example- The movement of tendrils of climbing plants towards the things they happen to touch.
(c) The difference between Thigmotropism and Thigmonasty are-
| Thigmotropism | Thigmonasty |
1. It is a directional movement of plant parts in response to touch. | 1. It is a non-directional movement of plant parts in response to touch. |
2. Example: Bitter gourd. | 2. Example: Mimosa pudica. |
Bitter gourd exhibits thigmotropism as its tendrils show directional movement on touching. On the other hand, Mimosa pudica exhibits thigmonasty as its leaflets show non-directional movement in response to touch.
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