Exergy analyses of the biochemical processes of photosynthesis

This paper gives the exergy analyses of the main biochemical processes of photosynthesis in green plants. In the light reactions, photosystem I, photosystem II, and ATP-synthesis are found to operate at exergy efficiencies of 50%, 68% and 81%, respectively, so that 48% of the exergy of directly utilised solar photons is converted to biochemical energy carriers. Subsequently, in the dark reactions, glucose is synthesised from CO2 at an exergy efficiency of 85%. When including the wasteful effect of photorespiration, the overall exergy efficiency of the photosynthesis of glucose is determined at 31–34%, with most of the exergy losses occurring during the initial conversion of the photon energy.

Keywords: exergy analysis, thermodynamics, second-law, exergy efficiency, biochemical processes, living cell, photosynthesis, solar photons, Calvin cycle, chloroplast, glucose, photorespiration