Question

Percentage of photosynthetically active radiation (PAR) that is captured by plants in synthesis of organic matter is?
A. 50-70%
B. 30-40%
C. 80-100%
D. 2-10%

Answer 1

Photosynthetically active radiation (PAR) is light of wavelengths 400-700 nm and is the part of the light spectrum used by plants for photosynthesis. The rate at which energy is converted into organic substances by photoautotrophs is known as primary productivity.

Complete Answer:
- Most solar energy occurs at wavelengths which is not apt for photosynthesis. Ninety-eight to ninety-nine percent of solar energy reaching the Earth is reflected from leaves and other surfaces and absorbed by other molecules, which convert it to heat. Only one to two percent is available to be captured by plants.

- The rate at which plants photosynthesize depends on various factors such as, the amount of light reaching the leaves, and the availability of water, and other nutrients such as nitrogen and phosphorus. The measurement of the rate at which organisms convert light energy (or inorganic chemical energy) to the chemical energy of organic compounds is called primary productivity.

- Hence, the total amount of energy assimilated by plants in an ecosystem during photosynthesis varies among environments. This is known as the gross primary productivity. Productivity is also measured by an increase in biomass. It is used to refer to the weight of all living organisms in an area and is measured in grams or metric tons. Only 2-10% of the PAR is captured by plants for the synthesis of organic matter.

- PAR measurement is used in forestry, agriculture, and oceanography. For a productive farmland, adequate PAR is required, so PAR is used to evaluate agricultural investment potential. PAR sensors positioned at various levels of the forest canopy to measure the pattern of PAR availability and utilization. Photosynthetic rate and related parameters can be measured without destroying the plant using a photosynthesis system. These instruments measure PAR and sometimes control PAR at a pre-set intensity. PAR measurements can also be used to calculate the euphotic depth in the ocean.

Hence, the correct option id D, “2-10%”.

Note: Much of the energy assimilated by plants through photosynthesis is not stored as organic material but instead is used during cellular respiration. Organic compounds such as carbohydrates, proteins, and fats are broken down, or oxidized, to provide energy for the metabolic need of the cell.