Question

what roles do bacteria play in the nitrogen cycle? select all that apply. they convert nitrogen gas to ammonia and ammonium. they transform nitrate into nitrogen gas. they convert nitrate into ammonia. they change ammonium into nitrates and nitrites

Explanation:

1. Nitrogen - fixing bacteria convert atmospheric nitrogen gas ($N_2$) into ammonia ($NH_3$) and ammonium ($NH_4^+$).
2. Denitrifying bacteria transform nitrate ($NO_3^-$) into nitrogen gas ($N_2$).
3. Nitrate - reducing bacteria can convert nitrate ($NO_3^-$) into ammonia ($NH_3$).
4. Nitrifying bacteria change ammonium ($NH_4^+$) into nitrites ($NO_2^-$) and then into nitrates ($NO_3^-$).

Answer:

They convert nitrogen gas to ammonia and ammonium, They transform nitrate into nitrogen gas, They convert nitrate into ammonia, They change ammonium into nitrates and nitrites