Answer: Converting dead organic matter (proteins) back to ammonia by decomposers.
- A Converting atmospheric N<sub>2</sub> gas directly into ammonia by nitrogenase
- B Converting dead organic matter (proteins) back to ammonia by decomposers
- C Oxidizing ammonia stepwise into nitrite and then nitrate
- D Direct uptake of ammonia ions through plant root hairs
Correct answer: B. Converting dead organic matter (proteins) back to ammonia by decomposers
Explanation: Ammonification is the decomposition of organic nitrogen (from dead organisms and waste) back to NH<sub>3</sub>/NH4+ by putrefying bacteria and fungi. It is part of the nitrogen cycle that returns organic nitrogen to the soil.
Atmospheric N₂ is fixed into ammonia by nitrogen-fixing bacteria (protected from oxygen by leghaemoglobin in root nodules), converted to nitrate via nitrification for plant uptake, and eventually returned to the atmosphere as N₂ via denitrification, completing the cycle.
Concept context
Essential mineral elements, their roles and deficiency symptoms. Nitrogen fixation and soil nutrition.