Question

When we touch the leaves of a touch-me-not plant, they bend down. This is an example of
A. Thigmotropism
B. Thigmonasty
C. Phototropism
D. Geotropism

Answer 1

Hint:
There are several movements of organisms according to the movement of sun and direction of
earth. These movements are referred to as tropism. Plant movements include their movements toward light, opening and closing of flowers, growth of roots in search of water and nutrients. Inflorescence, fruits, and shoots are capable of moving by sensing the changes in an environment, thereby adjusting their position, function, and behavior accordingly

Complete answer:
The touch me not plant exhibits thigmotropism. Thigmotropism means the directional response of a
plant organ to touch or physical contact with a solid object. The directional response is generally caused by the induction of some pattern of differential growth. This phenomenon is clearly illustrated by climbing tendrils of some plants such as sweet peas.Thigmotropism helps climbing plants to direct their pattern of growth around an object that they are in contact with. Auxin and ethylene help to facilitate the growth process.
Thigmonasty is also known as seismonasty. It is the nastic movement of a plant or fungus to touch or
vibration. Conspicuous examples of thigmonasty include many species of the leguminous subfamily,
mimosoideae. Phototropism is a well known movement of plants. They always grow towards the sun. Sunlight is required for the process of photosynthesis. The plants utilize light energy to prepare carbohydrates. Geotropism refers to the movements along the earth. Some plants such as rhizomes of ginger are positive towards geotropism.
So, the correct answer is “Option A”.

Note:
The difference between thigmonasty & thigmotropism is that thigmonasty is a form of nastic
movement by plants or fungus in response to touch whereas thigmotropism is the directional
response of plants when it is not in thigmonasty