In the nitrogen cycle, nitrifying bacteria primarily convert which substance to which product?

• A. Organic nitrogen (proteins) to ammonia (NH$N_3$)
• B. Nitrogen gas (N$N_2$) to ammonia (NH$N_3$)
• C. Ammonia (NH$N_3$) to nitrate (NO$N_3$${-}^{\mathrm{}}$)
• D. Nitrate (NO$N_3$${-}^{\mathrm{}}$) to nitrogen gas (N$N_2$)

Answer: (C)

Verified step by step guidance

1. Understand the role of nitrifying bacteria in the nitrogen cycle: these bacteria are involved in the oxidation of nitrogen compounds, transforming them from one form to another.
2. Identify the starting substrate for nitrifying bacteria: they do not convert organic nitrogen or nitrogen gas directly, but rather act on ammonia (NH\_3).
3. Recognize the two-step process of nitrification: first, ammonia-oxidizing bacteria convert ammonia (NH\_3) to nitrite (NO\_2\^-), and then nitrite-oxidizing bacteria convert nitrite to nitrate (NO\_3\^-).
4. Focus on the overall conversion attributed to nitrifying bacteria: the key product formed from ammonia is nitrate (NO\_3\^-), which is a more oxidized and bioavailable form of nitrogen for plants.
5. Conclude that nitrifying bacteria primarily convert ammonia (NH\_3) to nitrate (NO\_3\^-), completing the nitrification process in the nitrogen cycle.