Which process converts atmospheric nitrogen into a form usable by living organisms?

Which process converts atmospheric nitrogen into a form usable by living organisms?

• A. Nitrogen fixation
• B. Photosynthesis
• C. Evaporation
• D. Denitrification

Answer: (A)

The ability to make nitrogen usable by living things comes from nitrogen fixation. Atmospheric nitrogen (N2) is abundant but very stable and not directly usable by most organisms. Nitrogen fixation breaks that strong N≡N bond and converts nitrogen gas into ammonia (NH3) or ammonium (NH4+), forms that can be taken up by plants and incorporated into proteins, nucleic acids, and other vital molecules. This can occur through certain soil bacteria and cyanobacteria, often living in symbiosis with plants, or through industrial processes. Photosynthesis uses light energy to convert carbon dioxide and water into sugars, not to fix nitrogen. Evaporation is a water cycle process involving liquid water turning into vapor. Denitrification converts fixed nitrogen back into gaseous N2, returning it to the atmosphere rather than making nitrogen available for organisms in the first place.

The ability to make nitrogen usable by living things comes from nitrogen fixation. Atmospheric nitrogen (N2) is abundant but very stable and not directly usable by most organisms. Nitrogen fixation breaks that strong N≡N bond and converts nitrogen gas into ammonia (NH3) or ammonium (NH4+), forms that can be taken up by plants and incorporated into proteins, nucleic acids, and other vital molecules. This can occur through certain soil bacteria and cyanobacteria, often living in symbiosis with plants, or through industrial processes.

Photosynthesis uses light energy to convert carbon dioxide and water into sugars, not to fix nitrogen. Evaporation is a water cycle process involving liquid water turning into vapor. Denitrification converts fixed nitrogen back into gaseous N2, returning it to the atmosphere rather than making nitrogen available for organisms in the first place.