Question

If a plant uses 6 percent PAR, then percentage of I.S.R. plant use is ______.

Answer 1

Hint: Photosynthetically active radiation is abbreviated as PAR and I.S.R. stands for Incident solar radiation.The word ‘photo’ means light and ‘synthesis’ means production i.e. combining with the help of light. It occurs in chloroplasts which are present in all the green parts of a plant including stem, green leaves and sepals. Two reactants i.e. carbon dioxide and water are involved in photosynthesis reaction and products formed are two i.e. glucose and oxygen.

Complete answer:
We know that plants use light energy to make carbohydrates from ${ CO }_{ 2 }$ and water. This process is known as Photosynthesis. The general empirical equation for photosynthesis is given as –
\[{\text{C}}{{\text{O}}_2}{\text{ + }}{{\text{H}}_2}{\text{O }}\xrightarrow{{{\text{Light}}}}{\text{ [C}}{{\text{H}}_2}{\text{O] + }}{{\text{O}}_2}\]
From this equation, it is clear that light energy is essential for photosynthesis to take place. The one and only source of light on earth is the Sun. Plants harness light energy from the Sun to make carbohydrates.
Photosynthetically Active Radiation (PAR) is the amount of light available for the plants to carry out photosynthesis. ISR stands for incident solar radiation. Out of the total ISR which is available from the sun, only 50% is light which can be used for photosynthesis.
Hence, if PAR is 6%, ISR will be twice i.e. 12%.

Additional Information: The quality, intensity and duration of exposure of light are important factors which affect the rate and the process of photosynthesis. Photosynthesis occurs in visible light only which has a wavelength of 400-700 nanometres. This light is easily and efficiently absorbed by plants. Rate of production of ADP and NADPH is directly affected by the intensity of light.

Note: After a certain threshold point, if the intensity of light goes in increasing, chlorophyll breaks down and stops functioning thus, further photosynthesis cannot occur.