Without water, plants would not be able to trap the energy in light, and animals would not be able to process the energy in their food. The energy from the sun is not in a form that can be directly used by organisms. Organisms require energy in the form of chemical bonds. Carbon bonds are the form of most of the energy-containing molecules used by organisms. These bonds are formed when the carbon in CO 2 is reduced with an electron from water.
All organisms use the energy in chemical bonds to carryout the processes of life.
In organisms, this oxidation is performed on chemical bonds in a controlled manner called metabolism. Because reduction and oxidation must be performed efficiently, organisms have developed mechanisms to accomplish these tasks in a controlled manner. Organisms must also contain all their functions to maximize efficiency. These things require that organisms have structure and functions that are different from normal physical processes. Organisms use many elements to build their structures and functions.