ChemPhotoSyn_2_ - 2 0 - )/ 8 N A h where the first 3...

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Extracted from: "Photosynthetic Efficiency" W. Gebhardt, Radiation & Environmental Biophysics , 1986, 25, 275-288. We define the chemical efficiency as follows: η ch = G°(-CH 2 0 -) / 8 N A h ν 0 η th where N A is Avogadro's number. The free energy of one carbohydrate unit -CH 2 0- is G O = 477 kJ.]]]]]]] Its synthesis needs 8 photons, of which 4 are absorbed in each photosystem. But as shown in Sect. 2 only a fraction η th of this quantum energy is available. η th The thermodynamic efficiency depends only on the radiation "temperature" and the geometry of the incident rays relative to the leaf surface. η th ~ 0.73 and thus the η ch can be estimated to be 0.46 (Note: Includes second law losses too.) η c h = 0.46 We can finally write the total efficiency in the form: η = η s η R η P G°(-CH
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Unformatted text preview: 2 0 - )/ 8 N A h where the first 3 factors give the fraction of incident photons effectively used in photosynthesis. P is the trapping efficiency of the photoexcitation by the reaction centers. P ~ 0.8. R , is the reflectivity factor. R ~ 0.8. S , is the spectral efficiency, i.e. the fraction of light with sufficient energy. s ~0.33. Using the values given above we obtain the overall efficiency as: 0.1 which may be achieved under favorable conditions, although experimentally the efficiency is closer to 0.07. The details of how each factor above was evaluated is given in the full paper. Recall the half reactions we are talking about: CO 2 + 4e- C + 2O = 2H 2 O O 2 + 4e-+ 4H +...
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This note was uploaded on 01/16/2012 for the course ENVIRON 404 taught by Professor Rasmussen during the Fall '11 term at University of Michigan.

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ChemPhotoSyn_2_ - 2 0 - )/ 8 N A h where the first 3...

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