Skip to content
Myclass24

Site, biochemical events, end product, and fate of nitrogen fixation.

GeneralClass 12AllAnswered 27 Mar 2026
Answer

Site:Root nodules of leguminous plants

Biochemical Events:

  1. Enzyme:Nitrogenase (Mo-Fe protein complex) catalyzes N₂ reduction
  2. Nitrogen binding: N₂ binds to Mo-Fe component
  3. Sequential reduction: NADPH provides hydrogen atoms:
    • N₂ → N₂H₂ (dimide)
    • N₂H₂ → N₂H₄ (hydrazine)
    • N₂H₄ → 2NH₃ (ammonia)
  4. Energy requirement: 16 ATP per N₂ fixed (derived from host respiration)

Overall Reaction:N₂ + 8e⁻ + 8H⁺ + 16ATP → 2NH₃ + H₂ + 16ADP + 16Pᵢ

End Product:Ammonia (NH₃)

Fate of Ammonia:

  • Ammonia is protonated to ammonium (NH₄⁺) in soil
  • Ammonium ions are toxic to plants, so they are rapidly assimilated into amino acids via:
    • Reductive amination (glutamate dehydrogenase pathway)
    • Transamination reactions
  • Amino acids are incorporated into proteins, nucleotides, and other nitrogen-containing compounds

Suggested Q&A

General · Class 12