Class 11 Biology Photosynthesis In Higher Plants Factors affecting photosynthesis

Factors affecting photosynthesis

  • Photosynthesis is under the influence of several factors, both internal and external.
  • The plant factors include the number, size, age and orientation of leaves, mesophyll cells and chloroplasts, internal CO2 concentration and the amount of chlorophyll.
  • The external factors would include the availability of sunlight, temperature, CO2 concentration and water.
  • When several factors affect any biochemical process, Blackman’s law of limiting factors comes into effect, which states that “If a chemical process is affected by more than one factor, then its rate will be determined by the factor which is nearest to its minimal value: it is the factor which directly affects the process if its quantity is changed.”

External factors

  • Light
  • There is a linear relationship between incident light and CO2 fixation rates at low light intensities.
  • At higher light intensities, gradually the rate does not show further increase as other factors become limiting.
  • Increase in incident light beyond a point causes the breakdown of chlorophyll and a decrease in photosynthesis.
  • Carbon dioxide concentration
  • The concentration of CO2 is very low in the atmosphere.
  • The C3 and C4 plants respond differently to CO2
  • At low light conditions, neither C3 nor C4 group responds to high CO2 conditions, whereas at high light intensities, both C3 and C4 plants show increase in the rates of photosynthesis.
  • C4 plants show saturation at about 360 μlL-1, whereas C3 responds to increased CO2 concentration and saturation is seen only beyond 450 μlL-1.
  • Temperature
  • The dark reactions being enzymatic are more sensitive to temperature than light reaction.
  • The C4 plants respond to higher temperatures and show higher rate of photosynthesis, whereas C3 plants have a much lower temperature optimum.
  • Tropical plants have a higher temperature optimum than the plants adapted to temperate climates.
  • Water
  • Water stress causes the stomata to close hence reducing the CO2
  • Besides, water stress also makes leaves wilt, thus, reducing the surface area of the leaves and their metabolic activity as well.


Fig. Factors affecting photosynthesis

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