Blue light is absorbed not only by chlorophyll, but also by carotenoids, and some carotenoids are not in the chloroplasts; further, carotenes and xanthophylls make up the carotenoids. Carotenes do not transfer absorbed energy efficiently to chlorophyll, and thus some part of absorbed blue light is not going to photosynthesis. On the other hand, all of red light is absorbed by chlorophylls and used effectively.
For the process of photosynthesis, light is abosorbed by Photosystem II which are membrane bound. Photosystem II aborbs infrared and red light (540nm-630nm) and it is for this reason that photosynthesis is highest under red light. Though blue light maybe absorbed the highest it does not activate photosynthesis, red light is.
Blue light is absorbed not only by chlorophyll, but
also by carotenoids, and some carotenoids are not in the chloroplasts;
further, carotenes and xanthophylls make up the carotenoids.. and
Carotenes do not transfer absorbed energy efficiently to chlorophyll, and
thus some part of absorbed light in the blue is not going to
photosynthesis. On the other hand, all of red light is absorbed by
chlorophylls and used effectively.
Answer through email to me by
Prof. (Emiritus) Govindjee
Biochemistry, Biophysics and Plant
Biology,University of Illinois, 265 Morrill Hall,MC-116, 505 South Goodwin
Avenue, Urbana,IL 61801-3707, USA;
although both be absorbed, blue light have much more energy (high frequency, see Planck Law), that lead the chlorophyll to S2 excitation state . This state there is no photochemistry, and need to dissipation as heat, being low eficiency, when compared with red light, which lead chlorophyll to S1 excitation state , used to photochemistry in the photosystems!
I hope to be help!!!
From how to why: might seem strange, but evolution had a strong effect on red bands selection. Like all life, plants first evolved in the ocean where blue and green penetrate much less than red. Chlorophyll was the right pigment for the job and chloroplast have got an extra-long memory. Still now artificial photosynthesis uses Chl for genearting e-
Besides non-chlorophyll light absorption and lower efficiencie of carotenoids there seems to be an other effect for plants and under low light conditions. The quantum yields of PSII and PSI seem to be more balanced under red light (averaged over 600-700 nm) then under blue light (averaged over 400-500 nm). In the absence of any alternative and cyclic electron flows, any imbalance of photosystem I+II excitation (i.e. ratio 1) will translate to overall reductions in overall linear electron flow. But this is likely modulated by the spectral light distribution during growth, which influences stochiometry of photsystems and by the extent of state transitions.
Moreover, under high light intensities UV/blue light is likely to induce stronger photoinhibition than red light, because quantum efficiency for photoinhibition is higher for UV/blue wavelengths.
Lower efficiency of blue light may be due to
1. Non-chlorophyll absorption.
2. Blue light produces S2 excited state of chlorophyll (no photosynthetic efficiency), which transfers exciton to S1 (red light) (photosynthetically active) state.t This transition is one of the path in relaxation of S2 excited state. Hence, lower efficiency.
3. Blue light inhibits photosynthesis by physiological processes as protective mechanism.
Rate of blue light absorption is higher because of higher exctinction coefficient of blue light band or Soret band.
What effect would their be on photosynthesis if green light was missing?
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