Question

Percentage of photosynthetically active radiation (PAR) in the incident solar radiation is?
A) 1-5%
B) 2-10 %
C) Less than 50%
D) Approx. 100%

Answer 1

Hint:Light can be split into various types of radiation, ranging from the invisible ultra violet, to the visible wavelengths, and then the infra-red range of the spectrum. The range of wavelengths used by plants for photosynthesis is called photosynthetically active radiation.

Complete answer:
>PAR ranges between 400-700nm. These are the light rays used by the chlorophyll pigments in green plants to produce carbohydrates from carbon dioxide and water during photosynthesis.
>Option A is too low a figure, nowhere close to the actual number. A is incorrect.
>Green plants absorb about 2-10% of the PAR, which is not the same as saying that photosynthetically active radiation is only 2-10%. Option B is not correct.
>Of all the radiation in the electromagnetic spectrum that enters through the upper reaches of the atmosphere, the photosynthetically active radiation forms around 50% of these. Option C is the correct answer.
>For Option D to be correct, the entire electromagnetic spectrum would be required. However green plants use a range that comes close to the visible light spectrum. They do not use the very short or very long wavelengths. Option D is therefore incorrect.

Hence the correct answer is option ‘C’.

Note:The electromagnetic spectrum can be divided into various categories. Some of these are visible light which ranges between 380 to 900nm; X rays which are very short wavelengths below that of the UV range, and have very high energy; and microwaves which are another type that we are familiar with, and of longer wavelengths than the far red end.