Which of the following correctly lists a step in the nitrogen cycle?

• A. Glycolysis, where glucose is broken down into pyruvate
• B. Photosynthesis, where plants convert carbon dioxide into glucose
• C. Nitrification, where ammonia (\(NH_3\)) is converted to nitrites (\(NO_2^-\)) and then to nitrates (\(NO_3^-\))
• D. Transpiration, where water evaporates from plant leaves

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the nitrogen cycle, which is a biogeochemical process that transforms nitrogen into various chemical forms as it circulates among the atmosphere, soil, and living organisms.
2. Step 2: Recognize that nitrification is a key step in the nitrogen cycle. It involves the conversion of ammonia (\(NH_3\)) into nitrites (\(NO_2^-\)) and then into nitrates (\(NO_3^-\)) by specific bacteria.
3. Step 3: Differentiate nitrification from unrelated processes such as glycolysis (a metabolic pathway for glucose breakdown), photosynthesis (carbon fixation by plants), and transpiration (water evaporation from plant leaves). These processes are not part of the nitrogen cycle.
4. Step 4: Note that nitrification is carried out by two types of bacteria: ammonia-oxidizing bacteria (convert \(NH_3\) to \(NO_2^-\)) and nitrite-oxidizing bacteria (convert \(NO_2^-\) to \(NO_3^-\)).
5. Step 5: Conclude that nitrification is essential for making nitrogen available in forms that plants can absorb and use for growth, completing a critical step in the nitrogen cycle.