of light. Six molecules of carbon dioxidecombine with six molecules of water to form one molecule of glucose (sugar).The glucose molecule consists of six atoms of carbon, twelve of hydrogen, andsix of oxygen. Six oxygen molecules, consisting of two oxygen atoms each, arealso produced and are discharged into the atmosphere unless the plant needsenergy to live. In that case, the oxygen combines with the glucose immediately,releasing six molecules of carbon dioxide and six of water for each molecule ofglucose (Beggott 25-32). The carbon cycle is then completed as the plantobtains the energy that was stored by the glucose. The length of time requiredto complete the cycle varies. In plants without an immediate need for energy,the chemical processes continue in a variety of ways. By reducing the hydrogenand oxygen content of most of the sugar molecules by one water molecule andcombining them to form large molecules, plants produce substances such as starch, inulin , and fats and store them for future use. Regardless of whether thestored food is used later by the plant or consumed by some other organism, themolecules will ultimately be digested and oxidized, and carbon dioxide and waterwill be discharged. Other molecules of sugar undergo a series of chemicalchanges and are finally combined with nitrogen compounds to form proteinsubstances, which are then used to build tissues (WWW 2). Although protein substances may pass from organism to organism, eventuallythese too are oxidized and form carbon dioxide and water as cells wear out andare broken down, or as the organisms die. In either case, a new set oforganisms, ranging from fungi to the large scavengers, use the waste products ortissues for food, digesting and oxidizing the substances for energy release (WWW1). At various times in the Earth's history, some plant and animal tissues havebeen protected by erosion and sedimentation from the natural agents ofdecomposition and converted ...
