Light Conversion in Photosynthetic Organisms

The sun is the ultimate source of free energy that drives all of the processes in living cells. The radiant energy of the sun is captured and converted to chemical energy by photosynthesis. The flux of carbon through the biosphere begins with photosynthesis. Photosynthetic organisms produce carbohydrates and molecular oxygen from carbon dioxide and water: 6H₂O + 6CO₂ + light → (CH₂O)6 pedice + 6O₂ (1.1) The carbohydrates produced by photosynthesis serve as the energy source for other non-photosynthetic (heterotrophic) organisms. In this process, carbohydrates are recycled to carbon dioxide and water by the combined action of cellular catabolic processes.

The fixation of carbon dioxide into sugars requires free energy in the form of ATP and reducing power in the form of NADPH. The light reactions of photosynthesis respond to this need: the visible component of solar radiation is captured and its energy is converted into ATP and NADPH through a complex series of redox reactions and membrane-mediated energy conversions.