Science 20F The Carbon Cycle Carbon is the key element for living things. Each year, about 50 to 70 billion tonnes of carbon from inorganic carbon dioxide are recycled into more complex organic substances. This is done through photosynthesis. Photosynthesis Chemical Process Carbon dioxide + water + light energy CO2 + H2O + light sugar + oxygen C6H12O6 + O2 Balanced Photosynthesis Equation: Some of the organic carbon is released back to the environment through cellular respiration as carbon dioxide. (opposite to photosynthesis) Cellular Respiration Chemical Process Glucose + oxygen water + carbon dioxide C6H12O6 + O2 H2O + CO2 Balanced Cellular Respiration Equation: Carbon cycle: The matter cycle in which, through the processes of photosynthesis, digestion, cellular respiration, decomposition, and combustion, carbon atoms move from an inorganic form in the air, water, or soil, to an organic form in living things, and then back to an inorganic form; all organic compounds contain carbon. Carbon Cycle Delay Under certain conditions the decay process is delayed and the organic mater may be converted into rock or fossil fuels such as coal, petroleum, and natural gas. Carbon can be found in three main reservoirs (storage areas): Atmosphere – smallest reservoir of carbon dioxide. Oceans – Tremendous amount of inorganic carbon is held as dissolved carbon dioxide in the oceans, where it is available to algae and other water plants for photosynthesis. Earth’s Crust – limestone (Calcium Carbonate; CaCO3) is made from the discarded shells and bones of living things discarded in the oceans. This sedimentary rock comprises the largest reservoir of inorganic carbon. Bogs and areas of ocean floors contain organic carbon stored as a result of decaying aquatic animals and plants trapped by sediment. Carbon Dioxide increases due to Human Influence Humans have released carbon from organic reservoirs faster than would normally occur, by mining and burning fossil fuels trapped in Earth’s crust, and by burning forests. By clearing away vegetation for farming, the lack of vegetation reduces the amount of carbon dioxide removed from the atmosphere. As a result, the amount of carbon dioxide in the atmosphere is rising.