Nitrogen cycle check: Identify the false statement about nitrogen fixation and related processes in ecosystems. Full question: Nitrogen is fixed in ecosystems in the following ways. Which statement below is <em>false</em>? Choose the correct option.

Difficulty: Easy

Symbiotic bacteria in legume nodules fix N₂ into ammonia using nitrogenase.
Free-living cyanobacteria and soil bacteria can fix atmospheric N₂.
Lightning converts N₂ to oxides of nitrogen that become nitrates in rainwater.
Nitrification converts nitrate (NO₃⁻) to ammonia (NH₃/NH₄⁺) by Nitrosomonas and Nitrobacter.
Denitrification returns nitrate/nitrite to N₂ gas under anaerobic conditions.

Correct Answer: Nitrification converts nitrate (NO₃⁻) to ammonia (NH₃/NH₄⁺) by Nitrosomonas and Nitrobacter.

Explanation:

Concept
The nitrogen cycle includes fixation (N₂ → NH₃/NH₄⁺), nitrification (NH₃/NH₄⁺ → NO₂⁻ → NO₃⁻), assimilation (into amino acids), and denitrification (NO₃⁻/NO₂⁻ → N₂).

Why option D is false
Nitrification does not convert nitrate to ammonia; instead, it converts ammonia to nitrite (by Nitrosomonas) and then to nitrate (by Nitrobacter). The reverse (NO₃⁻ → NH₄⁺) would be assimilatory/dissimilatory nitrate reduction, not nitrification.

Verification
Other options accurately describe nitrogen fixation, abiotic fixation by lightning, and denitrification.

Final Answer
Nitrification converts nitrate (NO₃⁻) to ammonia (NH₃/NH₄⁺) by Nitrosomonas and Nitrobacter. (This statement is false.)

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Nitrogen cycle check: Identify the false statement about nitrogen fixation and related processes in ecosystems. Full question: Nitrogen is fixed in ecosystems in the following ways. Which statement below is <em>false</em>? Choose the correct option.

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