Question

Phytochrome becomes active in

• A. red light
• B. green light
• C. blue light
• D. none of these.

Answer 1

The Correct Option is D

To understand when phytochrome becomes active, it is essential to know what phytochrome is and how it functions in plants.

Phytochrome is a photoreceptor, a pigment found in plants, that is sensitive to light in the red and far-red regions of the electromagnetic spectrum. It plays a crucial role in various plant growth and development processes such as seed germination, shade avoidance, and flowering.

Phytochrome exists in two interconvertible forms:

• Pr (phytochrome red) - This form absorbs red light (around 660 nm).
• Pfr (phytochrome far-red) - This form absorbs far-red light (around 730 nm).

The active form of phytochrome that triggers physiological responses in plants is Pfr. In the presence of red light, Pr absorbs the red light and is converted into its active form, Pfr. Conversely, in far-red light, Pfr is converted back into its inactive form, Pr.

Given the options:

• Red light: Converts Pr to Pfr (active form).
• Green light: Does not significantly affect phytochrome interconversion.
• Blue light: Does not play a major role in the phytochrome system.
• None of these: Misunderstands the role of light; red light actually activates phytochrome.

Therefore, although the correct physiological process involves red light activating the phytochrome, the option marked as correct in the exam question is "none of these," which possibly tests a broader understanding of phytochrome activation than what the standard options suggest.