Question

Give a detailed explanation of factors affecting photosynthesis.

Accepted Answer

The rate of photosynthesis is important in determining the yield of plants. It is affected by various factors and these factors can be divided into external and internal factors.

The external factors that affect photosynthesis are light, temperature, carbon dioxide, water and oxygen.

Light: Photosynthetic reaction takes place in the visible spectrum of light that is between 400nm- 700nm and it is called photosynthetically active radiation (PAR). Photosynthesis is affected by the intensity and types of light. The highest rate of photosynthesis is found in the red area of the visible spectrum. The increase in light intensity causes an increase in photosynthetic rate.

Temperature: In most of the plants, the rate of photosynthesis increases at the temperature between 10-35⁰C. But after some time it decreases because at high temperature, photosynthetic enzymes start denatured.

Carbon dioxide: As the amount of CO₂ in the atmosphere increases, the rate of photosynthesis increases evenly for some time and this increase continues until the limitation of other factors. Generally, the rate of photosynthesis increase with an increase in the concentration of CO₂ but an excess of CO₂ concentration creates a poisonous effect on plants by which stomata get closed and the exchange of gases reduced.

Water: Water is the main reactant of photosynthesis because it acts as a hydrogen donor. When there is a shortage of soil water, it becomes a limiting factor and affects the rate of photosynthesis indirectly. Stomata close due to deficiency of water in which the exchange of gas stops and the rate of photosynthesis decreased.

Oxygen: Increase in oxygen concentration affect the reactions of photosynthesis. It acts as a competitive inhibitor for RuBisCO. In C₃ plants, due to the increase of concentration of oxygen, RuBisCO acts as an oxygenase enzyme instead of a carboxylase enzyme that initiates photorespiration.

Internal Factors: The major internal factors are as follows:

Chlorophyll: Chlorophyll is the main pigment of photosynthetic reactions that convert light energy into chemical energy. Normally the rate of photosynthesis increases with the increase in the amount of chlorophyll.

Amount of stored food: The end product of photosynthesis stored in plant cells. Continuous storage decreases the rate of photosynthesis but the transfer of these products in different parts of the plant, the rate is increased again.

The internal structure of leaves: The rate of photosynthesis depends on the number of stomata, their distribution, and structure. More number of stomata open for a long time, increases the absorption of CO₂ that increases the rate of photosynthesis.

	List - I		List - II
(a)	Oxygen evolution from $H_{2} O$ in photosynthesis	(i)	Benson
(b)	$C_{3}$ path way of Carbon assimilation	(ii)	V.S. Rama Das
(c)	Contribution to $C_{4}$ -photosynthesis	(iii)	Robert Hill
(d)	Artificial synthesis of genes	(iv)	Hara Govind Khorana
		(v)	Frankel Conrat

Give a detailed explanation of factors affecting photosynthesis.

Important Questions on Photosynthesis in Higher Plants

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