5 Steps in Nitrogen cycle Simplified with video Steps in nitrogen cycle (easy to understand) 8 minutes Nitrogen cycle: Definition? 5 Steps in Nitrogen cycle. simplified step by step Why N2 is important? Why N2 is the most limiting nutrient?

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Easy to
understand

2. Nitrogen cycle: Definition?
Nitrogen cycle is the cyclic movement of nitrogen (N2) between
atmosphere, organisms and soil.
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N2

3. 5 Steps in Nitrogen cycle
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Step 2
Step 3
Step 4
Step 5
Step 1

4. Why N2 is important?
Nitrogen is an essential element required for the synthesis of bio-
molecules like proteins, DNA, vitamins, chlorophyll, alkaloids etc.
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Protein
Amino acids
DNA
Nitrogenous bases Chlorophyll-a
Pigments

5. Why N2 is the most limiting nutrient?
•Atmospheric N2 is extremely stable, unreactive, inert with triple
covalent bond between nitrogen atoms.
•Plants and animals cannot use atmospheric N2. So it should be
converted to some other usable forms such as nitrates (NO3
-)
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N2 gas is inert
941 kj/mol
Atmospheric Nitrogen
(79%)

6. Step 1
Step 2
Step 3
Step 4
Step 5
Step 1: Nitrogen Fixation
Nitrogen fixation: atmospheric N2 → NH3 (Ammonia)
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7. Step 1: Nitrogen Fixation
3 Methods of Nitrogen Fixation
2.Non-biological N2 fixation
by lightning, volcanic
eruptions etc.
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3. Industrial Nitrogen fixation
Haber Bosch process
1. Biological Nitrogen Fixation (BNF)

8. Step 1: Biological Nitrogen fixation ( BNF)
1. Biological nitrogen fixation (BNF): conversion of atmospheric N2 to ammonia (NH3)
2. carried out by prokaryotes called as nitrogen fixers or diazotrophs. 70% of natural nitrogen
fixation.
3. Rhizobium in root nodules of leguminous plants, blue green algae like Anabaena and lichens
like Collema.
4. high energy requiring process & N2 fixers uses 16 moles of ATP to fix each molecule of
Nitrogen (N2)
N2 + 8 H+ + 8 e−+ 16 ATP → 2 NH3 + H2 +16 ADP +16 Pi
BNF
(70% of
NF)
Symbiotic prokaryotes like Rhizobium
Free living like Azotobacter
16 moles of ATP to fix each molecule of Nitrogen (N2)
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9. Step 2: Nitrification
Nitrosomonas Nitrobacter
Nitrite bacteria
Nitrosomonas
Nitrosospira
Nitrosococcus
Nitrate bacteria
Nitrobacter
Nitrifying bacteria
NH3
Ammonia
NO2
-
Nitrite
NO3
-
Nitrate
Step 2
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10. Step 3: Nitrate Assimilation by Plants
Now soil nitrates (NO3
-) formed by nitrification can be taken up by the
plants for the synthesis of amino acids, DNA, pigments etc. This is
known as nitrate assimilation.
NO3
-
Soil
NO3
-
nitrate
NO3
-
NO3
-
NO3
-
Biomolecules
(DNA, protein ,
pigments)
Food chain
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11. Step 4: Ammonification
organic nitrogen (amino acids, DNA etc) in plant and animal tissues is
converted to ammonia (NH3).
Death of organism
Organic Nitrogen (DNA,
protein etc) in tissues
NH3
ammonia
decomposers
excretion
Biomolecules
(DNA, protein ,
pigments)
soil
ammonification
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12. Step 5: Denitrification
It is the conversion of soil nitrate (NO3
-) to N2
NO3
- NO2
- NON2
Anammox (anaerobic ammonia oxidation)
It is the conversion of ammonia (NH3) to N2 using nitrite as the electron
acceptor under anoxic condition.
NH4
+ + NO2
- N2 + 2H2O
Denitrifying bacteria
Bacillus, Paracoccus
Soil NO3
-
Nitrate
NO2
-
Nitrite
NO N2
Atmosphere
N2
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