Answer: NO 3 - back to N 2 gas (by bacteria in anaerobic conditions).
- A Converts atmospheric N<sub>2</sub> gas into ammonia (NH<sub>3</sub>) directly
- B Converts ammonia (NH<sub>3</sub>) into nitrate (NO<sub>3</sub><sup>-</sup>) ions
- C NO<sub>3</sub><sup>-</sup> back to N<sub>2</sub> gas (by bacteria in anaerobic conditions)
- D Converts organic nitrogen compounds into ammonia (NH<sub>3</sub>)
Correct answer: C. NO<sub>3</sub><sup>-</sup> back to N<sub>2</sub> gas (by bacteria in anaerobic conditions)
Explanation: Denitrification: anaerobic bacteria (Pseudomonas, Paracoccus) convert NO<sub>3</sub><sup>-</sup> back to N<sub>2</sub> gas, returning nitrogen to the atmosphere.
Energy pyramid showing a simple food chain (producer to herbivore to carnivore) with energy decreasing roughly tenfold at each trophic level.
Concept context
Ecosystems, food chains, energy flow, nutrient cycles, biodiversity, and conservation.