12 Photosynthesis - part 10 - Factors affecting Photosynthesis

 

12 Photosynthesis - part 10 - Factors affecting Photosynthesis


Factors affecting Photosynthesis :

  • Like all other physiological processes, photosynthesis is also influenced by a number of factors.

A. External Factors :
Light :
  • It is an essential factor as it supplies the energy necessary for photosynthesis.
  • Both quality and intensity of light affect photosynthesis. 
  • Highest rate of photosynthesis takes place in the red rays and then come the blue rays. 
  • In a forest canopy the rate of photosynthesis decreases considerably in plants growing under the it.
  • In most of the plants, photosynthesisis maximum in bright diffused sunlight. 
  • It decreases in strong light and again slows down in the light of very low intensity. 
  • It has also been found that uninterrupted and continuous photosynthesis for relatively long periods of time may be sustained without any visible damage to the plant.

Carbon dioxide : 


  • The main source of CO2 in land plants is the atmosphere, which contains only 0.3% of the gas. 
  • Under normal conditionsof temperature and light, carbon dioxide acts as a limiting factor in photosynthesis. 
  • An increase in concentration of CO2 increases the photosynthesis. 
  • The increase in CO2 to about 1% is generally advantageous to most of the plants. 
  • Higher concentration of the gas has an inhibitory effect on photosynthesis.


Temperature : 

  • Like all other physiological processes, photosynthesis also needs a suitable temperature. 
  • In the presence of plenty of light and carbon dioxide, photosynthesis increases with the rise of temperature till it becomes maximum. 
  • After that there is a decrease or fall in the rate of the process.
  • The optimum temperature at which the photosynthesis is maximum is 25 – 30 degree Celsius.
  • Though in certain plants like Opuntia, photosynthesis takes place at as high as 55 degree Celsius . This is known as the maximum temperature. 
  • The temperature at which the process just starts is the minimum temperature.

Water : 

  • Being one of the raw material, water is also necessary for the photosynthetic process.
  • An increase in water content of the leaf results in the corresponding increase in the rate of photosynthesis. 
  • Thus the limiting effect of water is not direct but indirect. 
  • It is mainly due to the fact that it helps in maintaining the turgidity of the assimilatory cells and the proper hydration of their protoplasm.

B. Internal Factors : 

  • Though the presence of chlorophyll is essential for photosynthesis but the rate of photosynthesis is proportional to the quantity of chlorophyll present. 
  • It is because of the fact that chlorophyll merely acts as a biocatalyst and hence a small quantity is quite enough to maintain the large bulk of the reacting substances.
  • The final product in the photosynthesis reaction is sugar and its accumulation in the cells slow down the process of photosynthesis.
  • Factors which also affects the rate of photosynthesis are -
  1. Thickness of cuticle and epidermis of the leaf 
  2. Size and distribution of intercellular spaces 
  3. Distribution of the stomata 
  4. Development of chlorenchyma
  5. other tissues


Blackman’s law of limiting factors :

  • The Blackman’s law of limiting factors states that -when a process is conditioned as to its rapidity by a number of separate factors, the rate of the process is controlld by the pace of the “slowest factor”.
  • The slowest factor is that factor which is present in the lowest or minimum concentration in relation to others. 
  • The law of limiting factor can be explained by taking two external factors such as carbon dioxide and light. 
  • Suppose a plant photosynthesizing at a fixed light intensity sufficient to utilize 10mg of CO2 per hour only.
  • On increasing the CO2 concentration, the photosynthetic rate also goes on increasing. 
  • Now, if the CO2 concentration is further increased, no increase in the rate of photosynthesis. 
  • Thus in this case light becomes the limiting factor. 
  • Under such circumstances, the rate of photosynthesis can be increased only by increasing the light intensity.
  • This evidently shows that the photosynthetic rate responds to one factor alone at a time and there would be a sharp break in the curve and a plateau formed exactly at the point where another factor becomes limiting. 
  • If any one of the other factors which is kept constant (say, light) is increased, the photosynthetic rate increases again reaching and optimum where again another factor become limiting.

Significance of photosynthesis : 

  • This anabolic process uses inoganic substances and produces food for all life directly or indirectly. 
  • This process transforms solar energy into chemical energy.
  • The released by product O2 is necessary not only for aerobic respiration in living organisms but also used in forming protective ozone layer around earth. 
  • This process is also helping us in providing fossil fuels, coals, petroleum and natural gas.

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