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Question
Give an account of factors which affect photosynthesis.
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Solution
Photosynthesis is affected by both internal (plant) and external factors.The plant factors include the number, size, age and orientation of leaves, mesophyll cells and chloroplasts, internal O2 concentration and amount of chlorophyll. The plant factors are dependent on the genetic predisposition and the growth of the plant.The external factors include the availability of sunlight, temperature, CO2 concentration and water.- Light: It is an essential factor for photosynthesis. It affects the rate of photosynthesis as:
- Light intensity: There is a linear relationship between incident light and CO2 fixation at low light intensities. At higher light intensities, gradually the rate does not show further increase as other factors become limiting. The light saturation occurs at 10 percent of the total sunlight available to plants. Increase in the incident light beyond a point causes the breakdown of chlorophyll and thus resulting in the decrease in photosynthesis. Hence, except for plants in shade or in dense forests, light rarely become a limiting factor.
- Light quality: Light between 400-700 nm wavelengths constitute the photosynthetically active radiation (PAR). Maximum photosynthesis takes place in red and blue light of the visible spectrum and minimum photosynthesis takes place in the green light.
- Duration of light: Light duration does not affect the rate of photosynthesis, but it affects the overall photosynthesis.
- Carbon Dioxide Concentration: It is a major limiting factor influencing the rate of photosynthesis. The concentration of CO2 is very low in the atmosphere which is far below the requirement for optimum photosynthesis. Increase in concentration up to 0.05 percent can cause an increase in the rate of photosynthesis. But beyond this level, it becomes damaging over longer periods.
- Temperature: Photosynthesis can take place over a wide range of temperatures. The light reactions are temperature sensitive, but they are affected to a much lesser extent. The dark reactions being enzymatic are temperature controlled. Again, the temperature optimum for photosynthesis also depends on the habitat the plants are adapted to. The C4 plants respond to higher temperatures and they show the higher rate of photosynthesis, while C3 plants have much lower temperature optimum.
- Water: Water is one of the raw materials utilized for the process of photosynthesis. The photosynthetic process utilizes less than 1% of the water absorbed by a plant; hence it is rarely a limiting factor in photosynthesis. Water stress causes the stomata to close, hence reducing the CO2 availability as gaseous exchange could not occur. Also, water stress makes leaves wilt, thus reducing the surface area of the leaves and the metabolic activity reduces as well. Thus, the effect of water as a factor is more through its effect on the plant, rather than directly on photosynthesis.
The plant factors include the number, size, age and orientation of leaves, mesophyll cells and chloroplasts, internal O2 concentration and amount of chlorophyll. The plant factors are dependent on the genetic predisposition and the growth of the plant.
The external factors include the availability of sunlight, temperature, CO2 concentration and water.
- Light: It is an essential factor for photosynthesis. It affects the rate of photosynthesis as:
- Light intensity: There is a linear relationship between incident light and CO2 fixation at low light intensities. At higher light intensities, gradually the rate does not show further increase as other factors become limiting. The light saturation occurs at 10 percent of the total sunlight available to plants. Increase in the incident light beyond a point causes the breakdown of chlorophyll and thus resulting in the decrease in photosynthesis. Hence, except for plants in shade or in dense forests, light rarely become a limiting factor.
- Light quality: Light between 400-700 nm wavelengths constitute the photosynthetically active radiation (PAR). Maximum photosynthesis takes place in red and blue light of the visible spectrum and minimum photosynthesis takes place in the green light.
- Duration of light: Light duration does not affect the rate of photosynthesis, but it affects the overall photosynthesis.
- Carbon Dioxide Concentration: It is a major limiting factor influencing the rate of photosynthesis. The concentration of CO2 is very low in the atmosphere which is far below the requirement for optimum photosynthesis. Increase in concentration up to 0.05 percent can cause an increase in the rate of photosynthesis. But beyond this level, it becomes damaging over longer periods.
- Temperature: Photosynthesis can take place over a wide range of temperatures. The light reactions are temperature sensitive, but they are affected to a much lesser extent. The dark reactions being enzymatic are temperature controlled. Again, the temperature optimum for photosynthesis also depends on the habitat the plants are adapted to. The C4 plants respond to higher temperatures and they show the higher rate of photosynthesis, while C3 plants have much lower temperature optimum.
- Water: Water is one of the raw materials utilized for the process of photosynthesis. The photosynthetic process utilizes less than 1% of the water absorbed by a plant; hence it is rarely a limiting factor in photosynthesis. Water stress causes the stomata to close, hence reducing the CO2 availability as gaseous exchange could not occur. Also, water stress makes leaves wilt, thus reducing the surface area of the leaves and the metabolic activity reduces as well. Thus, the effect of water as a factor is more through its effect on the plant, rather than directly on photosynthesis.
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