JWBS121-c02 JWBS121-Razeghifard Printer: Yet to Come July 30, 2013 8:16 Trim: 6.125in × 9.25in CHAPTER 2 Oxygenic Photosynthesis DMITRIY SHEVELA, LARS OLOF BJ ¨ ORN, and GOVINDJEE 2.1 INTRODUCTION 2.1.1 Importance of Photosynthesis: Why Study Photosynthesis? In a general sense the term photosynthesis is synthesis of chemical compounds by the use of light. In the more restricted sense, as we shall use it here, it stands for the process by which plants, algae, cyanobacteria, and phototrophic bacteria convert light energy to chemical forms of energy. Most photosynthesis is coupled to assimilation of carbon in the form of carbon dioxide or bicarbonate ions, but there exists also assimilation of CO 2 that is not coupled to photosynthesis, as well as photosynthesis that is not coupled to assimilation of carbon. All life on Earth, with some exceptions, is completely dependent on photosynthe- sis. Most organisms that do not live directly by photosynthesis depend on the organic compounds formed by photosynthesis and, in many cases, also on the molecular oxy- gen formed by the most important type of photosynthesis, oxygenic photosynthesis. Even much of the energy fueling the ecosystems at deep-water hydrothermal vents depends on photosynthesis, since it is made available to organisms using molecular oxygen of photosynthetic origin. In addition, photosynthesis is biologically impor- tant in a number of more indirect ways. The stratospheric ozone layer protecting the biosphere from dangerous ultraviolet radiation from the sun is formed from photosynthesis-derived oxygen by a photochemical process. The photosynthetic as- similation of CO 2 , and associated processes such as formation of carbonate shells by aquatic organisms, has (so far) helped to maintain the climate of our planet in a life-sustainable state. For basic descriptions of photosynthesis, see Rabinowitch [1] and Blankenship [2], and for reviews on all aspects of Advances in Photosynthesis and Respiration Including Bioenergy and Other Processes, see many volumes at the following web site: http://www.springer.com/series/5599. Natural and Artificial Photosynthesis: Solar Power as an Energy Source, First Edition. Edited by Reza Razeghifard. © 2013 John Wiley & Sons, Inc. Published 2013 by John Wiley & Sons, Inc. 13