nitrogen cycle

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nitrogen cycle Circulation of nitrogen through plants and animals in the biosphere. Plants obtain nitrogen compounds for producing essential proteins through assimilation. Nitrogen-fixing bacteria in the soil or plant root nodules take free nitrogen from the soil and air to form the nitrogen compounds (nitrates) used by plants in assimilation (see nitrogen fixation). Herbivores obtain their nitrogen from the plants, and carnivores obtain nitrogen by eating herbivores (see food chain). Saprophytes decompose the tissue of all the organisms concerned and the nitrogen is released back into the cycle.

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