Photosynthesis and cellular respiration are the same chemical reactions headed in opposite directions. Photosynthesis takes carbon dioxide and water and produces carbohydrates and oxygen. Cellular respiration takes carbohydrates and oxygen and produces carbon dioxide and water. Respiration is the exothermic reaction. Photosynthesis requires the input of energy from the sun in order to proceed. In the economy of ecology, why are both reactions necessary? How did the cycling of solar energy through the biosphere begin? How can it be best maintained today?
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