Formation of Carbohydrates by Photosynthesis

Carbohydrates are formed in green plants by photosynthesis, which is the chemical combination, or fixation, of carbon dioxide and water by utilization of energy from the absorption of visible light. The overall result is the reduction of carbon dioxide to carbohydrate and the formation of oxygen  

If the carbohydrate formed is cellulose, then the reaction in effect is the reverse of the burning of wood, and obviously requires considerable energy input. 

Because of its vital character to life as we know it, photosynthesis has been investigated intensively and the general features of the process are now rather well understood. The principal deficiencies in our knowledge include just how the light absorbed by the plants is converted to chemical energy and the details of how the many complex enzyme-induced reactions involved take place. 

One photoprocess reduces nicotinamide adenine dinucleotide phosphate (NADP ) to NADPH. These dinucleotides, shown below, differ from NAD and NADH (Section 15-6C) in having a phosphate group at C2 of one of the ribose units. The oxidized form, NADP , behaves like NAD and receives the equivalent of H e at C4 of the nicotinamide ring to form NADPH  

The other important photoreaction is oxidation of water to oxygen by the reaction  

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