Answer: It converts atmospheric N2 to NH3; requires anaerobic conditions and ATP.
- A It converts nitrate ions back into ammonia within specialized root cells
- B It converts atmospheric N2 to NH3; requires anaerobic conditions and ATP
- C It oxidizes ammonia into nitrite ions during the nitrification process
- D It breaks down amino acids into ammonia during microbial decomposition
Correct answer: B. It converts atmospheric N2 to NH3; requires anaerobic conditions and ATP
Explanation: Nitrogenase is the enzyme complex that reduces N2 to NH3 (N2 + 8H+ + 8e- + 16ATP → 2NH3 + H2 + 16ADP + 16Pi). It is irreversibly inhibited by O2. Legume nodules maintain low O2 using leghemoglobin.
Atmospheric N₂ is fixed into ammonia by nitrogen-fixing bacteria (protected from oxygen by leghaemoglobin in root nodules), converted to nitrate via nitrification for plant uptake, and eventually returned to the atmosphere as N₂ via denitrification, completing the cycle.
Concept context
Essential mineral elements, their roles and deficiency symptoms. Nitrogen fixation and soil nutrition.