Which step in the nitrogen cycle involves soil bacteria converting atmospheric nitrogen gas (N2) into plant-available ammonia (NH3)?
Answer and explanation
Correct answer: C. Nitrogen fixation
- Step 1: Atmospheric nitrogen has a strong triple covalent bond that plants cannot break directly. Step 2. Specialized diazotrophic bacteria (e.g., Rhizobium, Frankia, Azotobacter) perform nitrogen fixation, reducing N2 to ammonia. Answer: Nitrogen fixation. Why not the others: Nitrification oxidizes ammonia into nitrite and nitrate; denitrification reduces nitrate back to N2 gas.
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