Question

What is the percentage of photosynthetically active radiation (PAR) in the incident solar radiation.
A. 100%
B. 50%
C. 1-5%
D. 2-10%

Answer 1

Hint: As we know that Photosynthetically Active Radiation (PAR) is the spectral range of the solar radiation. It is utilized by photosynthetic organisms in the process of photosynthesis. The main source of radiation is sun and many rays are emitted by the sun and few of them reach the plant which are very useful and are known as Photosynthetically active radiation.

Complete answer:
Solar radiation absorbed by the plants for photosynthesis is known as photosynthetically active radiation and the wavelength of it lies between the range of 400-700 nm( nanometer).
Sun is the main source of light radiation as it emits a number of rays (Cosmic rays, Gamma rays, X-rays, Ultra violet rays, Visible rays, etc.) and the visible light spectrum of visible rays has the wavelength 400-700 nm.
There are very few rays which are absorbed or can reach the plant i.e. visible rays and they are not harmful for living organisms.
Chlorophyll is the main component present in plants for light absorption other than chlorophyll Carotene, Xanthophylls, etc. are also present for absorption of light. Both blue and red light is absorbed by chlorophyll.
To make photosynthesis process more efficient Light harvesting complex (LHC) have hundreds of pigments which absorb different wavelengths of light.
The LHC consists of photosystem I and II. Photosystem I shows absorption peak at 700nm and Photosystem II shows absorption peak at 680nm.
PAR is required for growth of plants as a higher amount of PAR leads to the growth of plants by photosynthesis. Approximately 50% of visible light or visible rays are reached to the plant which are emitted by the sun.

Hence, the correct answer is option (B) i.e. 50%.

Note: Chlorophyll a and Chlorophyll b are most important photosynthetic pigments present in plants for light absorption and both of these show different absorption patterns. Photosystem I is also known as P700 and Photosystem II is also known as P680. The wavelength of PAR lies between the range 400-700nm.