The nitrogen cycleनाइट्रोजन चक्र
NCERT Fig 13.15 · interactive diagram
Parts and their functions
- Atmospheric nitrogen (N₂) (वायुमंडलीय नाइट्रोजन (N₂)) — The largest reservoir (78% of air) but unreactive — most organisms cannot use it directly.
- Nitrogen fixation (नाइट्रोजन स्थिरीकरण) — Rhizobium in legume root nodules and free-living Azotobacter in soil turn N₂ into ammonia. Industrially: Haber–Bosch process.
- Lightning (तड़ित) — Fixes a small amount of nitrogen as nitrogen oxides, which rain brings to the soil.
- Legume with root nodules (मूल-ग्रंथिकाओं वाला फलीदार पौधा) — Pea, gram, beans — nodules house Rhizobium, so these crops enrich the soil.
- Ammonia (NH₃) (अमोनिया (NH₃)) — Product of fixation and of ammonification.
- Nitrite (NO₂⁻) (नाइट्राइट (NO₂⁻)) — Made from ammonia by Nitrosomonas.
- Nitrate (NO₃⁻) (नाइट्रेट (NO₃⁻)) — Made from nitrite by Nitrobacter; the main form plants absorb.
- Nitrification (नाइट्रीकरण) — Nitrosomonas: NH₃ → NO₂⁻; Nitrobacter: NO₂⁻ → NO₃⁻.
- Assimilation (स्वांगीकरण) — Plants absorb nitrate and ammonium to make proteins and nucleic acids; animals get nitrogen by eating plants.
- Animals (जंतु) — Use plant proteins; their wastes and dead bodies return nitrogen to the soil.
- Ammonification (अमोनीकरण) — Decomposers (bacteria, fungi) turn nitrogen in dead matter and wastes back into ammonia.
- Denitrification (विनाइट्रीकरण) — Pseudomonas turns nitrates back into N₂ gas, completing the cycle.
Original diagram drawn by Simple Learning Hub, based on NCERT Fig 13.15. Report a mistake