Carbon is the building block of life. Carbon is present in all living organisms; the human body is approximately eighteen percent carbon by weight. In plants, carbon dioxide is essential in the formation of carbohydrates; through the process of photosynthesis the energy of the sun is stored in the bonds of the sugar molecules. The synthesis of these complex compounds from simpler substances, involves the utilization of energy stored by photosynthesis, is called anabolism. After anabolism catabolism takes place releasing stored energy by the oxidative destruction of organic compounds, producing water and carbon dioxide. This continuing synthesis and degradation involving carbon dioxide is known as the carbon cycle. The carbon cycle is the single most important process to biological life.