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Photosynthesis 



I. Introduction 



The surface of the earth continually receives radiant energy from the 

 sun. This may be dissipated as heat or used to drive the syntheses of 

 new molecules. These new molecules, in turn, can serve as sources of 

 energy for later reactions and syntheses. The primary synthesis of new 

 compounds driven by radiant energy is called photosynthesis. It is 

 catalyzed by colored pigments found in many plants. Photosynthesis 

 occurs in all green plants, including all of the higher plants and some of 

 the algae. In addition, many other unicellular forms carry out photo- 

 synthesis. The blue-green algae and bacteria of a variety of colors all 

 photosynthesize. There is also a genus of one-celled animals, called 

 euglena, which contain a green-pigmented organelle capable of cata- 

 lyzing photosynthesis. (In fact, some taxonomists prefer to call euglena 

 a plant.) 



All living processes, other than photosynthesis, involve the degrada- 

 tion of chemical energy to heat energy. Eventually, all sources of 

 chemical energy would be consumed and life on earth would stop if 

 photosynthesis did not occur. This process of building up of the 

 chemical energy available to living organisms is continuously driven 



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