How is atmospheric nitrogen made available for use in the human body?

Atmospheric nitrogen is converted into a usable form through a process called nitrogen fixation, primarily carried out by certain bacteria and archaea in the soil and water. These microorganisms transform nitrogen gas (N₂) into ammonia (NH₃) or related compounds, which can then be taken up by plants. Humans obtain nitrogen by consuming plant-based foods or animals that have eaten these plants, allowing the body to utilize nitrogen in the form of amino acids and nucleic acids necessary for various biological functions.