Question

Movement of plant part in response to touch is
A. Seismonasty
B. Thigmonasty
C. Nutation
D. None of the above

Answer 1

Hint: In the insectivorous plant’s leaves like Drosera, Dionaea the tentacles show variation in movements on coming in contact with an insect. The stimulus touch of an insect is transmitted to the entire leaf and all the tentacles bend over the insect.

Complete answer:
The movement of a plant part in response to an external stimulus in which the direction of response is not determined by the direction of stimulus is known as Nastic movement. It is also known as Nasties.
The stimuli may be classified as light, heat, touch or contact, etc. Nastic movement is not a directional movement of the plant part with response to the stimulus.The movement can be due to changes in turgor or changes in growth. Decrease in turgor pressure causes shrinkage while increase in turgor pressure brings about swelling.
Thigmonasty movement:-The non-directional movement of a plant in response to the contact of an object is called Thigmonasty movement.
In the insectivorous plant’s leaves like Drosera, Dionaea the tentacles show variation in movements on coming in contact with an insect. The stimulus touch of an insect is transmitted to the entire leaf and all the tentacles bend over the insect.

Hence the correct answer is option ‘B’.

Note:Nastic movements differ from tropic movements in that the direction of tropic responses depends on the direction of the stimulus, whereas the direction of nastic movements is independent of the stimulus's position. The tropic movement is a growth movement but nastic movement may or may not be a growth movement.