Question

why is denitrification necessary for the nitrogen cycle to function properly?
a denitrification converts excess nitrate into nitrogen gas, allowing for the nitrogen cycle to continue.
b denitrification produces nitrate, which is the form of nitrogen that plants assimilate through their roots.
c denitrification undoes many steps of the nitrogen cycle so there is not any excess nitrogen in the atmosphere.
d denitrification converts nitrogen gas to ammonia, thereby bringing nitrogen into the soil for plants.

Explanation:

Denitrification is a process in the nitrogen - cycle where nitrate ($NO_3^-$) is converted into nitrogen gas ($N_2$) by bacteria. This returns nitrogen to the atmosphere, completing the cycle. Option B is incorrect as denitrification consumes nitrate, not produces it. Option C is wrong because denitrification is a part of the cycle, not something that undoes it. Option D is incorrect as the conversion of nitrogen gas to ammonia is nitrogen - fixation, not denitrification.

Answer:

A. Denitrification converts excess nitrate into nitrogen gas, allowing for the nitrogen cycle to continue.