Question

Which of the following describes the movements of tentacles in Drosera?
A) Photonastic
B) Thermonastic
C) Thigmonastic
D) None of the above

Answer 1

Hint:The word nastic means non-directional movement in responses to stimuli like photo (light), thermo (temperature), thigmo (touch).

Complete answer:
1) Photonasty is a nastic movement in response to a change in light intensity. The stimulus in photonastic movement is light. Many petals of flowers like: Dandelion flower, Moonflower, flower of Cestrum Open in the daylight and close in the evening in response to the intensity of light. This is a growth movement in plants and an example of Photonastic movement.
2)Thermonasty can be described as the tendency in certain plant species like: Rhododendron species, Phryma Leptostachya. In these species, the plant responds to temperature changes (by developing a cellular force or growth on one side of an axis to change the form or position of the axis). The movements of the tentacles of Drosera are influenced by temperature changes as well, therefore it is a thermonastic plant species.
3) Lastly, Thigmonasty is the response of a plant to the stimulus of touch or vibration. These movements are generally linked with the changes in turgor pressure within the cells, instead of the slower movements of plants caused by plant growth. Notable examples include the Touch-me-not plant and Venus Fly-trap.
As the Drosera species only respond to the changes in temperature they are thermonastic in nature.

Additional information:There are various other nastic movements in plants like Nyctinasty: movements at night or in the dark, Chemonasty: response to chemicals or nutrients, Hydronasty: response to water, Seismonasty: response to shock, Geonasty: response to gravity.

Thus, the correct answer is option B (Thermonastic).

Note:Thermonasty (non-directional response to temperature) is not to be confused with thermotropism, which is a directional response in plants to temperature.