12 photosynthesis - part 02 - Nature of Light

 

12 photosynthesis - part 02 - Nature of Light


Nature of Light :

  • Form of energy. 
  • Travels as stream of tiny particles called photons. 
  • A photon contains a quantum of light. 
  • Has different wavelengths having different colors.
  • Electromagnetic radiation with wavelengths ranging from 390nm to 730nm. This part of the spectrum is called the Visible light. 
  • It lies between wavelengths of ultraviolet and infra-red.








Absorption and Action spectrum : 


  • Pigments absorb light quanta or photons and transfer the absorbed energy to chlorophyll a. 
  • The amount of light absorbed at each wavelength can be shown in the form of a graph. 
  • It shows different curves at different wavelengths. 
  • Such a curve which shows the amount of light absorbed at each wavelength is termed as Absorption spectrum.
  • The absorption spectrum of chlorophyll a and b clearly shows that more light energy is absorbed at 
  1. blue
  2. violet and
  3. red wavelengths of the visible spectrum. 
  • The relative rate of photosynthesis at different wavelengths indicates close relationship with absorption spectrum of chlorophyll a and b. 
  • This curve that shows the rate of photosynthesis at different wavelengths is called Action
    Spectrum.
  • Action spectrum of photosynthesis differs from the absorption spectrum. 
  • There is quite a lot of photosynthetic activity even in parts of the spectrum where chlorophyll a absorb little light. 
  • This infers that the light energy absorbed by other pigments (yellow and orange carotenoids and also other forms of chlorophyll) is transferred to chlorophyll a.

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