Question

The wavelength of light absorbed by $Pr$ form of phytochrome is

• A. 680 nm
• B. 720 nm
• C. 620 nm
• D. 640 nm.

Answer 1

The Correct Option is A

To correctly answer the question regarding the wavelength of light absorbed by the $Pr$ form of phytochrome, we need to understand the role of phytochrome in plants and the properties of its different forms.

Phytochrome is a photoreceptor, a protein pigment in plants that is sensitive to light in the red and far-red region of the electromagnetic spectrum. It exists in two interconvertible forms:

1. $Pr$ (Phytochrome red): This form absorbs red light maximally around 660 nm.
2. $Pfr$ (Phytochrome far-red): This form absorbs far-red light maximally around 730 nm.

However, when referring to the initial absorption process, the $Pr$ form is most commonly associated with an absorption peak near 666 nm. However, to simplify in academic settings and various textbooks, this is often cited as 660 nm or 680 nm for convenience.

In this question, the correct option is 680 nm, as it is closest to the values commonly taught and used for the $Pr$ absorption in educational contexts.

Therefore, among the given options:

• 680 nm: Correct choice for the wavelength absorbed by the $Pr$ form of phytochrome.
• 720 nm: Falls in the far-red region, closer to the $Pfr$ absorption.
• 620 nm and 640 nm: Too low to be representative of the red peak for $Pr$.

Conclusively, the option 680 nm is the best representation for the red light absorption peak of the $Pr$ form of phytochrome in academic scenarios.