Question

Denitrifying bacteria are part of which biogeochemical cycle?

Answer 1

Denitrifying bacteria are part of the nitrogen cycle.

Explanation:

Nitrogen, `N_2`, makes up `79.8 %` of the atmosphere. `N_2` can not be used by most living organisms, but nitrogen is essential to living organism in order to make DNA, RNA and proteins necessary for life.

Nitrifying bacteria are able to remove nitrogen from the atmosphere changing `N_2` into nitrites, `NO_2^(-)`. These nitrites can be changed into nitrates, `NO_3^(-)`. Nitrates are high energy ions that can be used by plants to make plant proteins which are used by animals.

Denitrifying bacteria reverse the process breaking down the nitrites. The nitrogen-fixing bacteria have used energy to fix the nitrogen into nitrite compounds Denitrifying bacteria get the energy back out of the nitrite compounds to fuel their life process.

(Note nitrogen compounds are unstable and have a lot of chemical energy stored inside of them. Think nitroglycerine. TNT. making nitrogen compounds requires energy, breaking nitrogen compounds releases energy.