Question
What are the factors which affect photosynthesis? Explain.
✓
Answer
Light: There is a linear relationship between incident light and $CO _2$ fixation rates at low light intensities. At higher light intensities, gradually the rate does not show further increase as other factors become limiting. What is interesting to note is that light saturation occurs at 10 per cent of the full sunlight. Hence, except for plants in shade or in dense forests, light is rarely a limiting factor in nature. Increase in incident light beyond a point causes the breakdown of chlorophyll and a decrease in photosynthesis. Carbon dioxide Concentration: Carbon dioxide is the major limiting factor for photosynthesis. The concentration of $CO _2$ is very low in the atmosphere (between 0.03 and 0.04 percent). Increase in concentration upto 0.05 percent can cause an increase in $CO _2$ fixation rates; beyond this the levels can become damaging over longer periods.
The $C_3$ and $C_4$ plants respond differently to $CO _2$ concentrations. At low light conditions neither group responds to
The $C _3$ and $C _4$ plants respond differently to $CO _2$ concentrations. At low light conditions neither group responds to high $CO _2$ conditions. At high light intensities, both $C _3$ and $C _4$ plants show increase in the rates of photosynthesis. What is important to note is that $C _4$ the plants show saturation at about $360 \mu IL ^{-1}$ while $C _3$ responds to increased $CO _2$ concentration and saturation is seen only beyond $450 \mu IL ^{-1}$. Thus, current availability of $CO _2$ levels is limiting to the $C _3$ plants. The fact that $C _3$ plants respond to higher $CO _2$ concentration by showing increased rates of photosynthesis leading to higher productivity has been used for some greenhouse crops such as tomatoes and bell pepper. They are allowed to grow in carbon dioxide enriched atmosphere that leads to higher yields.
Temperature: The dark reactions being enzymatic are temperature controlled Though the light reactions are also temperature sensitive they are affected to a much lesser extent. The plants respond to higher temperatures and show higher rate of photosynthesis while $C_3$ plants have a much lower temperature optimum.
The temperature optimum for photosynthesis of different plants also depends on the habitat that they are adapted to. Tropical plants have a higher temperature optimum than the plants adapted to temperate climates.
Water: Even though water is one of the reactants in the light reaction, the effect of water as a factor is more through its effect on the plant, rather than directly on photosynthesis. Water stress causes the stomata to close hence reducing the $CO _2$ availability. Besides, water stress also makes leaves wilt, thus, reducing the surface area of the leaves and their metabolic activity as well.
The $C_3$ and $C_4$ plants respond differently to $CO _2$ concentrations. At low light conditions neither group responds to
The $C _3$ and $C _4$ plants respond differently to $CO _2$ concentrations. At low light conditions neither group responds to high $CO _2$ conditions. At high light intensities, both $C _3$ and $C _4$ plants show increase in the rates of photosynthesis. What is important to note is that $C _4$ the plants show saturation at about $360 \mu IL ^{-1}$ while $C _3$ responds to increased $CO _2$ concentration and saturation is seen only beyond $450 \mu IL ^{-1}$. Thus, current availability of $CO _2$ levels is limiting to the $C _3$ plants. The fact that $C _3$ plants respond to higher $CO _2$ concentration by showing increased rates of photosynthesis leading to higher productivity has been used for some greenhouse crops such as tomatoes and bell pepper. They are allowed to grow in carbon dioxide enriched atmosphere that leads to higher yields.
Temperature: The dark reactions being enzymatic are temperature controlled Though the light reactions are also temperature sensitive they are affected to a much lesser extent. The plants respond to higher temperatures and show higher rate of photosynthesis while $C_3$ plants have a much lower temperature optimum.
The temperature optimum for photosynthesis of different plants also depends on the habitat that they are adapted to. Tropical plants have a higher temperature optimum than the plants adapted to temperate climates.
Water: Even though water is one of the reactants in the light reaction, the effect of water as a factor is more through its effect on the plant, rather than directly on photosynthesis. Water stress causes the stomata to close hence reducing the $CO _2$ availability. Besides, water stress also makes leaves wilt, thus, reducing the surface area of the leaves and their metabolic activity as well.
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