THE MAXIMUM EFFICIENCY OF PHOTOSYNTHESIS

Within the ideal assumptions: (1) two Photosystems for photosynthetic fixation of CO2, (2) all solar photons with lambda less-than-or-equal-to 700 nm are absorbed, (3) the photon requirement is 8 for each CO2 molecule fixed and O2 molecule evolved and (4) the principal stable product of photosynthesis is d-glucose, the theoretical maximum efficiency of conversion of light to stored chemical energy in green-plant type (oxygen-evolving) photosynthesis in bright sunlight is calculated to be 13.0%. Thermodynamic arguments are presented which indicate that a photosynthetic system with one Photosystem would be highly unlikely to be able to drive each electron from water to evolve O2 and reduce CO2. The practical maximum efficiency of photosynthesis under optimum conditions is estimated to be 8-9%.