Answer: Nitrogen fixation (converting N2 to NH3 by bacteria).
- A Denitrification converting nitrate back into atmospheric nitrogen gas
- B Nitrogen fixation (converting N2 to NH3 by bacteria)
- C Nitrification converting ammonia into nitrite and then nitrate
- D Ammonification converting organic nitrogen into ammonia
Correct answer: B. Nitrogen fixation (converting N2 to NH3 by bacteria)
Explanation: Nitrogen fixation: Rhizobium (symbiotic) and Azotobacter (free-living) convert N2 gas to NH3. This is the main biological entry of N2 into ecosystems.
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.