How nitrogen-containing substances are made available to and are used by living organisms.

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How nitrogen-containing substances are made available to and are used by living organisms.

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Nitrogen is taken up by living organisms in the soil for the purpose of manufacturing proteins, nucleic acids and other nitrogen-containing compound. However, a vast minority of living organisms can use up the nitrogen gas directly, plants are only capable of absorbing the nitrogen-containing substances as nitrate ions, which are taken up from the soil via active transport. And so nitrogen enters the ecosystem through the absorption by plants and so theses plants are then eaten and digested by animals.

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For nitrogen gas from the surrounding atmosphere to be available for living organisms, especially plants it needs to be nitrified down to nitrate ions. There are specific organisms in the soil that feed on ammonium-containing compounds which release ammonia which then forms ammonium ions in the soil. The next stage is nitrification which is where ammonium ions in the soil are converted into nitrite ions with the aid of nitrifying bacteria, and then the nitrite ions are then converted into nitrate ions. It is an oxidation reaction and so energy is released in this stage.

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