Question

Some flowers (e.g., Oxalis) open in the morning and close during evening because of
A. Photonasty
B. Phototropism
C. Phototaxis
D. Nyctinasty

Answer 1

Hint: The first movement of the plant starts in the morning, thus in response to “photo i,e to the light” but it closes at night, thus reacting to changing intensity of light.

Complete Answer:
A. Photonasty: Photo nasty is the property of plants to react to words changing light intensity certain plants respond to light by growing in a specific direction with much more force and this property is used by plants to manipulate the axis of the plant example being light sensitive flowers like morning glory.
B. Phototropism: Phototropism is the property of the plant to react to light stimulus. This is done with the help of a plant hormone, auxins which helps the cells of the plant are more elongated when away from the light source. A sunflower turning its face towards sunlight is an example of phototropism.
C. Phototaxis: Phototaxis is the kind of taxes which involves the movement of the entire organism towards or away from a light source euglena is an example of phototaxis while Cockroaches move away from light with which is another example of phototaxis.
D. Nyctinasty: Sensitivity of plants towards darkness by movement towards the dark or night is called nyctinasty. The word Nastic means the movement of parts of plants in a repetitive rhythmic way folding of leaves that night is an example of nyctinasty.

Hence the correct answer is option ‘A’.

: 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.
Types of Nastic movements in plants:
1) Seismonastic Movement
2) Photonasty Movement
3) Thermonastic movement
4) Nyctinastic movement
5) Thigmonasty movement

Note:
1. In the Mimosa pudica plant, when we touch the leaves of the plant they fold up. Here the stimulus is touch.
2. In a dandelion flower, the opening up of the petals of this flower in the morning in bright light and closing in the evening when light fades.