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Cycles for LifeAwake!—2009 | February
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The carbon and oxygen cycles involve two key processes—photosynthesis and respiration.a Photosynthesis uses sunlight, carbon dioxide, and water to produce carbohydrates and oxygen. Respiration, which occurs in animals and humans, combines carbohydrates and oxygen to produce energy, carbon dioxide, and water. Thus, the output of one cycle is the input of the other, and it all happens cleanly, efficiently, and quietly.
Oxygen
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Carbon dioxide
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Cycles for LifeAwake!—2009 | February
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a The cycles of various chemical elements may combine or overlap. Oxygen, for example, is present in carbon dioxide, carbohydrates, and water. Hence, it shares in both the carbon and the water cycles.
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