Question

(a) Explain the different types of movements shown in plant with examples.
(b) Explain the term 'response to stimuli' with a suitable example.​

Answer 1

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Ans-A-There are five types of Nastic movements in plants:-

• Seismonastic Movement: This type of movement is caused by the mechanical stimuli like shock, touch or contact, fast moving wind, rain drops, etc.
• Photonasty Movement:The non directional movement of a plant part in response to light is called photonasty . Example : Dandelion flower opens the petals in bright. during the daytime .
• Thermonastic movement: Such movements in plants occur due to the change in temperature. Flowers of a plant open with the rise in temperature and close with a drop in temperature. Sometimes Thermonastic movement is associated with Photonastic movements also.Examples are: Dandelion flower, Moonflower, flower of Cestrum Nocturnum etc.
• Nyctinastic movement:Nyctinasty is the circadian rhythmic nastic movement of higher plants in response to the onset of darkness, or a plant "sleeping". Nyctinastic movements are associated with diurnal light and temperature changes and controlled by the circadian clock and the light receptor phytochrome.example, are nyctinastic, as they close their leaves up each evening and open them again in the morning. Flowers may also open in the morning after closing for the night.
• Thigmonasty movement:Thigmonastic movement is also called as seismonastic movement. It is the nastic response of a plant or fungus to tactile stimuli. This movement is seen in carnivorous plants such as Dionaea and Drosera in response to the touch of an insect that may serve as a meal for that plant.Example is the shutting of a venus fly trap. The drooping of leaflets of Mimosa pudica when touched is also a thigmonastic movement.

Ans-B- A tropism is a response that an organism makes to a stimulus. An example of a common tropism in plants is phototropism (or light response). Plants grow towards light sources, and if the direction of light is changed, the plant will also change its direction of growth to accommodate for survival.

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