Nitrogen Cycles - Home - KSU Faculty Member websites

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Transcript Nitrogen Cycles - Home - KSU Faculty Member websites

Nitrogen Cycles
• All life requires nitrogen
compounds to form
proteins and nucleic
• Air is major reservoir of
nitrogen (~ 78%).
• Even though air is a large
source of N2, most living
things cannot use this
form, and it must be
converted to other forms
• There are several modes
of N2fixation that convert
N2into NH3, NO2, or NO3
Forms of Nitrogen
Inorganic nitrogen:
• NH3=Ammonia
• NH4+=Ammonium
• NO3-=Nitrate
• NO2-=Nitrite
• all nutrients, but toxic at high levels
Organic nitrogen
• Livings organisms and their proteins, nucleic
acids, urea, and other nitrogenous molecules.
• Atmospheric nitrogen is almost
chemically inert under normal
• Lavoisier named it “Azote”; meaning
“without life”.
• The N≡N triple bond, however, is
very stable, with a bond energy of
930 kJ/mol
Nitrogen Fixation
• “Nitrogen Fixation” is the process that causes
the strong two-atom nitrogen molecules
found in the atmosphere to break apart so
they can combine with other atoms.
• Nitrogen gets “fixed” when it is combined
with oxygen or hydrogen
• Nitrogen fixation is the process that converts
N2into either: NH3,NO3-,or NO2 - (usable
There are three ways that nitrogen
gets “fixed”!
(a) Atmospheric Fixation
(b) Industrial Fixation
(c) Biological Fixation
Atmospheric Nitrogen (N2)
Ammonia (NH3)
Nitrates (NO3)
combines with
Hydrogen to
make Ammonia
combines with
Oxygen to make
Atmospheric fixation
• (Only 5 to 8% of the Fixation Process)
• The enormous energy of lightning breaks
nitrogen molecules apart and enables the
nitrogen atoms to combine with oxygen
forming nitrogen oxides (N2O).
• Nitrogen oxides dissolve in rain, forming
• Nitrates(NO 3)are carried to the ground with
the rain.
Lightening breaks N2
Plants use nitrates to grow
Industrial Fixation
• Under great pressure, at a temperature of
600 degrees Celcius, and with the use of a
catalyst, atmospheric nitrogen (N2)and
hydrogen are combined to form ammonia
• Ammonia can be used as a fertilizer.
Industrial Plant combines Nitrogen
and Hydrogen to form Ammonia
Formed Ammonia is used a fertilizer
Biological Fixation
• Biological fixation accounts for the most fixed
nitrogen in the biosphere
• Only in certain organisms can fix atmospheric
nitrogen. These are divided into:
1. Non-symbiotic N-fixation carried out by Freeliving Organisms (bacteria, Cyanobacteria, &
Blue-green algae)
2. Symbiotic N-fixation carried out by organisms
living in symbiosis with certain plants (~70% of
biological fixation)
Biological N2 fixation
• Biological N2 fixation= Conversion of N2 gas to
ammonium via the following reaction:
• N2 +10 H++ 8 e-+ 16 ATP
2 NH4 + H2 +16
ADP +16 Pi
• A very energetically expensive reaction
The reaction require:
• Nitrogenase enzyme (of any suitable
• Large supply of energy
• Anoxic site
(oxygen binds to and inactivates the
nitrogenase enzyme)
Symbiotic Relationship Bacteria
Bacteria live in the roots of legume family plants
and provide the plants with ammonia in exchange
for the plant’s carbon and a protected home.