Which process is the assimilation of atmospheric nitrogen by soil bacteria and its release for plant use on the death of the bacteria?

• A. Nitrification
• B. Nitrogen Fixation
• C. Denitrification
• D. Nitrogen Assimilation

Answer: (B)

Nitrogen fixation is the process by which atmospheric nitrogen (N2) is converted into a form that organisms can use, typically ammonia (NH3) or ammonium (NH4+), by certain soil bacteria (such as free-living bacteria or Rhizobium in legume nodules) using the enzyme nitrogenase. This captured nitrogen then becomes available to plants, which can take up ammonium or nitrate after further soil processes. The note about release for plant use upon the death of the bacteria fits into the broader nitrogen cycle: when the fixing bacteria die, their organic nitrogen is mineralized by other microbes, releasing ammonium back into the soil for plant uptake and continuing the cycle through nitrification and other steps.

So, this scenario best reflects nitrogen fixation because it starts with converting inert atmospheric N2 into a usable form mediated by bacteria. Nitrification involves oxidation of ammonium to nitrate; denitrification reduces nitrate back to gaseous N2; nitrogen assimilation is the uptake of inorganic nitrogen by plants and incorporation into organic matter, not the initial capture of atmospheric nitrogen.