In the nitrogen cycle diagram, which arrow represents the process carried out by denitrifying bacteria?

• A. Conversion of nitrite (NO_2^-) to nitrate (NO_3^-)
• B. Conversion of ammonia (NH_3) to nitrite (NO_2^-)
• C. Conversion of nitrate (NO_3^-) to nitrogen gas (N_2)
• D. Conversion of nitrogen gas (N_2) to ammonia (NH_3)

Answer: (C)

Verified step by step guidance

1. Understand the role of denitrifying bacteria in the nitrogen cycle: these bacteria convert nitrate (NO_3^-) into nitrogen gas (N_2), completing the cycle by returning nitrogen to the atmosphere.
2. Identify the chemical transformation associated with denitrification: it involves the reduction of nitrate (NO_3^-) to nitrogen gas (N_2), which is a key step in removing bioavailable nitrogen from the soil.
3. Review the other processes listed: conversion of nitrite (NO_2^-) to nitrate (NO_3^-) is nitrification, conversion of ammonia (NH_3) to nitrite (NO_2^-) is also part of nitrification, and conversion of nitrogen gas (N_2) to ammonia (NH_3) is nitrogen fixation.
4. Match the process carried out by denitrifying bacteria to the correct arrow in the nitrogen cycle diagram, which should show the transformation from nitrate (NO_3^-) to nitrogen gas (N_2).
5. Confirm that the arrow representing the conversion of nitrate (NO_3^-) to nitrogen gas (N_2) corresponds to the activity of denitrifying bacteria.