Factors affecting photosynthesis
Nutrition in Plants of Class 7
All the factors which affect photosynthesis are divided into two main categories:
(a) External Factors:
There are number of factors which affect the process of photosynthesis thereby affecting the productivity of a plants. Each factor has three principal values i.e., minimum, optimum and maximum. Optimum means the process is taking place at its highest rate. Maximum value means beyond which the process is adversely affected. Important external factors are :
- Light,
- Temperature,
- Water, andCarbon dioxide
Light
In photosynthesis light is converted into chemical energy in the form of food. The rate of photosynthesis is affected by quality, intensity and duration of light. The chlorophyll absorbs mostly the blue and red regions of the spectrum.The green light has inhibitory effect. The low intensities of light increase the rate of photosynthesis while the higher intensities retard the rate of photosynthesis. Plants getting average light of 10-13 hours a day exhibit higher rate of photosynthesis.
Temperature
Temperature acts as a limiting factor under field conditions particularly on cool days. The influence of temperature on photosynthesis depends on both light intensity and availability of CO2.An increase in temperature above 30oC results in a fall in the rate of photosynthesis. Changes in temperature do not affect the light reactions of photosynthesis but markedly influence the rate of enzyme-mediated dark reactions.However, the effect of temperature on the rate of photosynthesis varies from plant to plant.
Water
Water deficiency may retard the rate of photosynthesis as it is one of the raw materials for the process. Under water deficient conditions stomata remain closed to reduce the transpiration thereby affecting the entry of CO2.
Carbon dioxide
Carbon dioxide is present in low concentration and forms about 0.032% of the atmosphere. It enters the leaves through stomata.The rate of photosynthesis increases with an increase in CO2 concentration up to a certain limit. Higher concentration of CO2 may prove toxic to plants.
(b) Internal Factors:
- Chlorophyll: Content is directly proportional to rate of photosynthesis. No photosynthesis occurs in etiolated cells. In variegated leaves it occurs only at places where chlorophyll is present.
- Protoplasmic factors: These affect the dark reaction of photosynthesis. The rate of photosynthesis is lowered when the temperature is above 30° C.
- Accumulation of carbohydrates: When the products of photosynthesis are accumulated in the same photosynthetic cell then the rate of photosynthesis is lowered.
(c) Significance of Photosynthesis:
Photosynthesis is a boon to the nature and to the human beings. It has following significances:
- Production of food material, for all the life forms.
- Atmospheric control and purification of air.
