Plants take in this nutrient when they perform photosynthesis. An animal eats the plant and uses its carbohydrates for energy. The animal releases the nutrient back into the atmosphere during respiration.

Plants take in carbon dioxide during photosynthesis and use its carbon to make carbohydrates. When an animal eats the plant, that carbon enters the animal; respiration releases some of it back into the atmosphere as carbon dioxide. This describes the carbon cycle, not the nitrogen or phosphorus cycles.

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