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Last updated date: 29th Nov 2023
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MVSAT Dec 2023

Plants convert light into chemical energy with a photosynthetic efficiency of
A. 35-41%
B. 20-35%
C. 6-20%
D. 3-6%

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Hint: Photosynthesis is the primary determinant of crop yield, and the efficiency with which the crop absorbs light and transforms it to biomass during the growing season is a crucial determinant of final yield, be it biomass or grain.

Complete Answer:
- The energy efficiency of photosynthesis is the ratio of energy stored to energy consumed by light.
- Chemical energy retained is the difference between that found in gaseous oxygen and organic compound products and that of water , carbon dioxide and other reactants. The amount of energy stored can only be calculated because many goods are manufactured and they vary depending on plant species and environmental conditions.
Plants typically transform light into chemical energy with a photosynthetic efficiency of 3–6 percent.
- Unconverted absorbed light is dissipated mainly as heat, with a small fraction (1–2 percent) re-emitted as chlorophyll fluorescence at longer (redder) wavelengths. This enables the light reaction of photosynthesis to be determined using chlorophyll fluorometers.
- The photosynthetic efficiency of individual plants varies with the frequency of light being converted, the light intensity, the temperature and the proportion of carbon dioxide in the atmosphere, and can range from 0.1 to 8 per cent.
- By contrast, solar panels transform light into electrical energy with an efficiency of approximately 6–20 per cent for mass-produced panels and more than 40 per cent for laboratory deviants.The effectiveness of both light and dark reactions can be calculated, but the relationship between the two can be complex.
- For example, ATP and NADPH energy molecules formed by light reactions can be used for carbon fixation or photorespiration in C3 plants. Electrons can also flow to other electron sinks. For this reason, it is not rare for authors to distinguish between work conducted under non-photorespiratory conditions and under photorespiratory conditions.

Thus the correct answer is option(D) 3-6%.

Note: Photosynthesis in plants requires a series of steps and reactions that use solar energy, water and carbon dioxide to create organic compounds and oxygen. There are two major reactions: energy-transduction reactions (commonly referred to as light reactions) and carbon-fixing reactions (commonly referred to as dark reactions).