Final answer:
Denitrification is carried out by bacteria that convert nitrates into nitrogen gas, allowing it to reenter the atmosphere. This process is distinct from nitrification, which involves the conversion of ammonium into nitrates, and nitrogen fixation, which is the conversion of nitrogen gas into organic compounds.
Step-by-step explanation:
Denitrification is a process that occurs in the nitrogen cycle. It is carried out by denitrifying bacteria such as Pseudomonas and Clostridium, which convert nitrates (NO3-) into nitrogen gas (N2). This process allows nitrogen to reenter the atmosphere from the soil, thereby completing a part of the nitrogen cycle. It is important to note that the statement 'Nitrification by bacteria converts nitrates (NO3-) to nitrites (NO2-)' is false because nitrification actually involves the conversion of ammonium ions (NH4+) into nitrites (NO2-) and subsequently into nitrates (NO3-), not the other way around. Similarly, nitrogen fixation is the conversion of atmospheric nitrogen gas into organic compounds, not from nitrates.