Nitrifying bacteria participate in the nitrogen cycle mainly by which process?

• A. Reducing nitrate ($N_{\mathrm{O}}3$-) to nitrogen gas ($N_2$) under anaerobic conditions
• B. Oxidizing ammonia ($N_{\mathrm{H}}3$) to nitrite ($N_{\mathrm{O}}2$-) and then to nitrate ($N_{\mathrm{O}}3$-)
• C. Converting atmospheric nitrogen gas ($N_2$) into ammonia ($N_{\mathrm{H}}3$)
• D. Oxidizing ammonia ($N_2$) to nitrite ($N_{2}O$) and nitrate ($N_3$)

Answer: (B)

Verified step by step guidance

1. Understand the role of nitrifying bacteria in the nitrogen cycle, which involves transforming nitrogen compounds to forms usable by plants and other organisms.
2. Recall that nitrifying bacteria perform oxidation reactions, specifically converting ammonia (NH\3) into nitrite (NO\2\-) and then further oxidizing nitrite into nitrate (NO\3\-).
3. Recognize that this process is aerobic, meaning it requires oxygen, and is distinct from processes like denitrification, which reduce nitrate to nitrogen gas under anaerobic conditions.
4. Identify the key chemical transformations catalyzed by nitrifying bacteria: first, ammonia is oxidized to nitrite, and second, nitrite is oxidized to nitrate.
5. Summarize that nitrifying bacteria contribute to the nitrogen cycle mainly by oxidizing ammonia to nitrite and then to nitrate, facilitating nitrogen availability in ecosystems.