In the Northern Hemisphere winter, when few land plants are growing and many are decaying, atmospheric carbon dioxide concentrations climb. The movement of carbon from reservoir to reservoir is known as the carbon cycle. The cycle incorporates molecules from carbon dioxide and glucose. Plants take in carbon dioxide from the atmosphere, and change it into glucose, a compound that animals can use to produce ATP, the energy required to function. During the spring, when plants begin growing again, concentrations drop. Carbon can be stored in a variety of reservoirs, including plants and animals, which is why they are considered carbon life forms. The fast carbon cycle is so tightly tied to plant life that the growing season can be seen by the way carbon dioxide fluctuates in the atmosphere. How the products of the light reactions, ATP and NADPH, are used to fix carbon into sugars in the second stage of photosynthesis. The process is a large-scale example of LeChatelier's Principle. carbon dioxide + water + sunlight -> carbohydrate + oxygen ... Because of the role of CO2 in climate, feedbacks in the carbon cycle act to maintain global temperatures within certain bounds so that the climate never gets too hot or too cold to support life on Earth. Plants can kind glucose via photosynthesis, and the carbon atoms wanted for glucose are derived from the carbon dioxide current within the ambiance (air), which is an especially small proportion, 0.039%. Earth system models predict that increases in atmospheric and soil dryness will reduce photosynthesis in the Amazon rainforest, with large implications for the global carbon cycle. In Crassulacean acid metabolism (CAM), time isolates functioning RuBisCO (and the other Calvin cycle enzymes) from high oxygen concentrations produced by photosynthesis, in that O 2 is evolved during the day, and allowed to dissipate then, while at night atmospheric CO 2 is taken up and stored as malic or other acids. This process is known as photosynthesis. It is as if the Earth is breathing. Carbon is used by plants to build leaves and stems, which are then digested by animals and used for cellular growth.