14 December 2007
Ron Milo
Department of Systems Biology
HMS
The sun's spectrum harvested through photosynthesis is the primary source of energy for life on earth. Plants, green algae and cyanobacteria—the major primary producers on earth—utilize reaction centers that operate at wavelengths of 680 and 700 nm. Why were these wavelengths "chosen" in evolution? We analyze the efficiency of light conversion into chemical energy as a function of hypothetical reaction center absorption wavelengths given the sun's spectrum and the thermodynamic and kinetic cost associated with charge separation. We find that when taking into account the empirical charge separation cost the range 680-720 nm maximizes the efficiency. This finding suggests that the wavelengths of photosystem I and II are optimized for the utilization of the sun's spectrum.