Answer: NO3- back to N2 gas (by bacteria in anaerobic conditions).
- A Converts atmospheric N2 gas into ammonia (NH3) directly
- B Converts ammonia (NH3) into nitrate (NO3-) ions
- C NO3- back to N2 gas (by bacteria in anaerobic conditions)
- D Converts organic nitrogen compounds into ammonia (NH3)
Correct answer: C. NO3- back to N2 gas (by bacteria in anaerobic conditions)
Explanation: Denitrification: anaerobic bacteria (Pseudomonas, Paracoccus) convert NO3- back to N2 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.