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Photosynthesis Chlorophyll wavelength absorption

  1. May 2, 2010 #1
    Why do the chlorophyll in land plants absorb primarily in the blue and red wavelengths, http://en.wikipedia.org/wiki/File:Solar_Spectrum.png" [Broken]? Isn't more energy available in 500nm green light vs 700nm red light? [tex]E =\frac{hc}{\lambda}[/tex]
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. May 2, 2010 #2


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    I suppose the only answer possible is "Because the mechanism that was evolved requires it."

    Total energy is less important here than whether a single photon has sufficient energy to cause the ionization/charge-separation which is the first step in photosynthesis.
    And that single photon doesn't have enough energy in itself either; it takes four photons to cause a reaction, while the energy is 'stored' in the manganese ion cluster of Photosystem II.

    It's all a very intricate system, and it's somewhat telling that nature has only evolved this once; it's essentially the same PS2 in all green things.

    Perhaps, for instance, a lower-energy photon would not cause a large enough charge separation, and the electron would too easily return back to the chlorophyll.
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