Describe the nitrogen cycle

5.1.9 · Biology › Ecology & Ecosystems

HOW kaam karta hai — paanch core processes

Ise ek loop ki tarah socho. Hum $N_{2}$ → usable → living things → wapas $N_{2}$ ki taraf badhte hain.

1. Nitrogen Fixation ( $N_{2} \to N H_{3} / N H_{4}^{+}$ )

Kaun: Nitrogen-fixing bacteria (jaise Rhizobium legume root nodules mein; Azotobacter soil mein free-living; aur cyanobacteria bhi).
Kaise: Yeh enzyme nitrogenase use karte hain $N_{2}$ ko ammonia mein reduce karne ke liye: $N_{2} + 8 H^{+} + 8 e^{-} + 16 A T P \to 2 N H_{3} + H_{2} + 16 A D P + 16 P_{i}$
WHY itna zyada ATP? $N \equiv N$ todna energetically bahut mushkil hai — 16 ATP is "brute-force" energy cost hai.
Non-biological fixation: Lightning itni energy deti hai ki $N_{2}$ aur $O_{2}$ nitrogen oxides mein combine ho jaate hain, jo baarish ke saath nitrate ban ke neeche aate hain.

2. Nitrification ( $N H_{4}^{+} \to N O_{2}^{-} \to N O_{3}^{-}$ )

Step A: Nitrosomonas : $N H_{4}^{+} \to N O_{2}^{-}$ (ammonium → nitrite)
Step B: Nitrobacter : $N O_{2}^{-} \to N O_{3}^{-}$ (nitrite → nitrate)
Yeh aerobic bacteria hain (oxygen chahiye — oxidation!).

3. Assimilation (life mein uptake)

Plant roots ==nitrate ( $N O_{3}^{-}$ )== aur ammonium absorb karti hain, phir amino acids → proteins aur nucleotides → DNA/RNA banati hain.
Animals apna nitrogen plants khaa ke (ya doosre animals khaa ke) lete hain. Isliye tum protein khaate ho.

4. Ammonification / Decomposition (organic N $\to N H_{4}^{+}$ )

Kaun: Decomposer bacteria aur fungi.
Dead organisms, urea, aur faeces → toot kar → $N H_{4}^{+}$ soil mein wapas.

5. Denitrification ( $N O_{3}^{-} \to N_{2}$ )

Kaun: Denitrifying bacteria (jaise Pseudomonas), jo anaerobic hote hain (waterlogged, oxygen-poor soils mein kaam karte hain).
$2 N O_{3}^{-} \to N_{2} + ...$ (nitrate reduce hokar wapas nitrogen gas banta hai).

Common mistakes (Steel-man + fix)

Recall Feynman: ek 12-saal ke bacche ko explain karo

Hawa nitrogen se bhari hai, lekin yeh ek super-strong "box" ( $N_{2}$ ) mein locked hai jise plants khol nahi sakti. Kuch special tiny bacteria hi akele woh "chaabi" (ek enzyme) rakhte hain jo box khol sake aur nitrogen ko "food dust" (ammonium/nitrate) mein badal sake jise plants apni roots se choos sakti hain. Plants protein banati hain, animals plants khaate hain, sab kuch marta hai, doosre bacteria bodies ko tod ke nitrogen wapas soil mein daal dete hain. Aakhir mein, kuch bacteria nitrogen ko wapas strong "box" mein band karke aasman mein bhej dete hain. Yeh chakkar hamesha chalata rehta hai!

Flashcards

Plants seedha atmospheric

N_{2}

kyun use nahi kar sakti?

N \equiv N

triple bond bahut zyada strong hai; sirf nitrogenase wale bacteria (ya lightning) ise tod sakte hain.

Nitrogen fixation kya hai aur kaun karta hai?

N_{2}

ka ammonia/ammonium mein conversion; nitrogen-fixing bacteria jaise Rhizobium, Azotobacter, aur lightning karte hain.

Nitrification kya hai aur kaun se bacteria?

N H_{4}^{+} \to N O_{2}^{-}

ka oxidation (Nitrosomonas) phir

N O_{2}^{-} \to N O_{3}^{-}

(Nitrobacter); aerobic.

Plants kaun si form ka nitrogen sabse acha absorb karti hain?

Nitrate,

N O_{3}^{-}

(ammonium bhi).

Ammonification kya hai aur kaun karta hai?

Decomposers (bacteria/fungi) dead organisms aur waste ko tod ke ammonium (

N H_{4}^{+}

) release karte hain.

Denitrification kya hai aur iske conditions kya hain?

Anaerobic bacteria (jaise Pseudomonas) nitrate ko wapas

N_{2}

gas mein reduce karte hain, waterlogged/oxygen-poor soil mein.

Denitrification poore cycle ke liye kyun important hai?

Yeh nitrogen ko atmospheric

N_{2}

reservoir mein wapas bhejta hai, loop close karta hai.

Fixation mein 16 ATP kyun use hota hai?

N_{2}

ka bahut strong triple bond todne ke liye badi energy input chahiye.

Animals nitrogen kaise obtain karte hain?

Plants ya doosre animals khaa ke (unke proteins consume karke).

Nitrification oxidation hai ya reduction?

Oxidation (electrons remove hote hain, oxygen add hoti hai). Denitrification reduction hai.

Connections

Ecology & Ecosystems
Decomposers and Decay
Carbon Cycle (compare: doosra biogeochemical cycle)
Proteins and Amino Acids
Bacteria and Microorganisms
Fertilisers and Eutrophication
Symbiosis (Rhizobium and Legumes)

WHAT hai nitrogen cycle?