Richard Malkin
Krishna Niyogi

The synthesis of organic compounds from inorganic precursors requires energy and reducing power (low-potential electrons). For chemoautotrophic bacteria and the living communities dependent on their activity (e.g., in the fauna of deep sea vents), the ultimate source of this energy is chemical bonds. Such organisms are, however, a distinct minority. In nearly all biological systems, the synthesis of organic molecules is driven directly or indirectly by energy from the sun.
      The overall process whereby plants, algae, and prokaryotes directly use light energy to synthesize organic compounds is called photosynthesis. This process supports most autotrophic producers of organic material as well as the heterotrophic consumers they support. In addition to providing food, biomass, and fossil fuels, photosynthesis in plants produces as a byproduct the oxygen required for respiratory activity by all multicellular and many unicellular organisms.
      Photosynthesis encompasses both a complex series of reactions that involve light absorption, energy conversion, electron transfer, and a multistep enzymatic pathway that converts CO₂ and water into carbohydrates. This chapter will explore these life-sustaining processes in detail. Other topics frequently covered in discussions of photosynthesis are discussed elsewhere, such as sucrose and starch metabolism in Chapter 13 and photorespiration in Chapter 14.