MadSci Network: Botany

Re: Why does blue light quicken the reaction for Photsynthesis?

Date: Thu Aug 5 12:50:57 1999
Posted By: Maggie Guo, Grad student, Plant Physiologu and Molecular Biology Program, Dept.of Plant Biology, UIUC
Area of science: Botany
ID: 932402680.Bt


Visible light ( from wavelength 400nm to 700 nm ) emitted by the sun to the earth can be devided to several parts, in which blue and red light are mainly absorbed by plants. That's because light has both the characterastic of wave and particle, and when plants' chlorophyll absorbs light, the energy of light will excite the chlorophyll molecules from ground state to excited state. In visible light, blue light ( wavelength 430 nm ) contains the comparably high energy, which corresponds to the energy that excites chlorophyll to higher excited state; while the red light ( wavelength 660nm ) contains lower energy which can transfer cholophyll in to lower excited state. In higher excited state, the chlorophyll is not stable and will back to lower state by emitting some energy as heat. From the lower state, the excited chlorophyll will return to ground state by transferring its energy into photosynthesis reaction center for photochemistry reactions, that's photosynthesis.

So, the blue light will activate chlorophyll, but not quicken the reaction. But why does chlorophyll prefer blue and red light, not green light ( that's why we see the plants green )? I think it's due to the structure of pigment molecules of chlorophyll. Hope that this answered you question.

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