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 false? Choose the correct option.
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ASymbiotic bacteria in legume nodules fix N₂ into ammonia using nitrogenase.
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BFree-living cyanobacteria and soil bacteria can fix atmospheric N₂.
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CLightning converts N₂ to oxides of nitrogen that become nitrates in rainwater.
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DNitrification converts nitrate (NO₃⁻) to ammonia (NH₃/NH₄⁺) by Nitrosomonas and Nitrobacter.
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EDenitrification returns nitrate/nitrite to N₂ gas under anaerobic conditions.
Answer
Correct Answer: Nitrification converts nitrate (NO₃⁻) to ammonia (NH₃/NH₄⁺) by Nitrosomonas and Nitrobacter.
Explanation
ConceptThe 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 falseNitrification 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.
VerificationOther options accurately describe nitrogen fixation, abiotic fixation by lightning, and denitrification.
Final AnswerNitrification converts nitrate (NO₃⁻) to ammonia (NH₃/NH₄⁺) by Nitrosomonas and Nitrobacter. (This statement is false.)