Which best explains why plants and animals need nitrogen?

Nitrogen is important to all organisms because it forms the basis of many compounds necessary for life. However, living things cannot use N2 in its gaseous form in the atmosphere. Nitrogen gas found in air pockets within soil is converted into a form usable by plants through a process called nitrogen fixation.All plants and animals need nitrogen to make amino acids, proteins and DNA, but the nitrogen in the atmosphere is not in a form that they can use. ... When organisms die, their bodies decompose bringing the nitrogen into soil on land or into ocean water. Bacteria alter the nitrogen into a form that plants are able to use.

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