Question

Phytochrome is involved in
A. Phototropism
B. Photorespiration
C. Photoperiodism
D. Geotropism

Answer 1

Phytochrome is a pigment that changes structure when exposed to light. It produces photomorphogenesis by absorbing red and far-red light from the absorption spectrum. It's a series of morphological changes that occur in plants when they're exposed to various wavelengths of light.
In nature, the phytochrome pigment occurs in two reversible forms, the reversibility of which is determined by the wavelength of light available to the plants and absorbed by them. Continuous exposure to red light causes phytochrome to be converted and hence its levels to be reduced.

Complete answer:
Option A: Plants have photoreceptors that detect light and are called phytochromes. They are sensitive to light of red and far-red wavelengths. Many flowering plants use it to regulate photoperiodism. It's used to control flowering times depending on the length of the day and night.
So option A is correct.
Option B: "Photorespiration" is the reaction of RUBISCO with oxygen and the metabolic processing of the resultant -PG (phosphoglycolate). It's called so because it only happens in the light (mitochondrial respiration continues in the dark) and consumes oxygen while producing carbon dioxide, just like mitochondrial respiration.
So option B is not correct.
Option C: The physiological response of organisms to the length of night or a dark period is known as photoperiodism.It can be found in both plants and mammals. The developmental reactions of plants to the relative lengths of light and dark cycles are known as photoperiodism.
So option C is not correct.
Option D: Geotropism is defined as the growth of a plant or immobile animal in response to gravity's force. The roots of a plant growing down into the ground are an example of geotropism.
So option D is not correct.

So option A is the correct answer.

Note:
Because they require a continuous, unbroken crucial dark phase, short day plants are also known as long night plants. Flowering is impeded in such plants if it is interrupted by even a flash of light or red light of 660 nm in this continuous darkness. Long-day plants, on the other hand, require a shorter amount of darkness than a critical dark period.Even if the dark period is exposed to light, the flowering process is unaffected. Instead, it encourages blossoming.