Question

Thigmonastic movement is observed in
A. Crocus and tulip
B. Chlamydomonas and volvox
C. Ulothrix and cladophora
D. Drosera and dionaea

Answer 1

Hint: The phenomenon of changing the position is called movement. Generally, movement is done in response to certain kinds of stimuli like light, touch,etc. Various organisms can respond to various types of stimulus. Let us look into the type of movement shown by the given species to find the correct answer.

Complete answer:
Let us first know the movements observed in the given species-
> Crocus and tulip- opening of flower in crocus and tulip is in response to change in temperature. This type of movement is called thermonasty. Thermonasty is a nastic movement and thus non-directional.
> Chlamydomonas and volvox- in chlamydomonas and volvox, light acts as the external stimulus bringing about the movement. This movement of a part of an organism in response to light is called phototaxis. Positive phototaxis movement is observed when diffused light is present and negative phototaxis movement is exhibited in presence of intense light.
> Ulothrix and cladophora- zoospores of ulothrix and cladophora also show phototaxis movement.
> Drosera and dionaea- insectivorous plant’s leaves like Drosera ad dionaea exhibit thigmonastic movement. Thigmonasty is the movement shown by some plants and fungus brought about by external stimuli like touch or vibration. It is also a nastic movement. In the given species, the tentacles may show variation in movements when they come in contact with insects.

Based on the above discussion, the correct answer is (D)- Drosera and dionaea.

Note:
> Nastic movement is the response of parts of plants which is independent of the external stimulus direction.
> It is noteworthy to mention that thigmonasty and thigmotropism are not the same. Thigmonasty is the non-directional movement in response to touch or vibration whereas, thigmotropism is the directional response to touch stimulus.
> Thigmonastic movement is also known as seismonastic movement.