2. CONTENTS
• What is Nitrogen?
• Why is it important?
• Nitrogen fixation and its types
• Process of Nitrogen fixation
3.
4.
5.
6. Why is Nitrogen fixation important?
• The nitrogen cycle is more complex than other
biogeochemical cycles because most organisms
cannot use the nitrogen found in the
atmosphere - even though almost 80% of the
air is nitrogen!
• In order for plants and humans to get the
nitrogen they need, the nitrogen must be
converted into ammonia - NH3.
7. • The conversion of this atmospheric nitrogen to
the usable form of ammonia is known as
nitrogen fixation. Nitrogen fixation can be
defined as the process of creating ammonia
from atmospheric nitrogen. Without this
process, most plants and animals would not
have the nitrogen needed to live.
8.
9. • It is brought about by ionizing phenomena
such
as cosmic radiations, meteor trails ,lightning,
thunderstorms, volcanic eruptions etc.
• These provides high energy for breaking N≡N
&
also for the formation of free N₂ with oxygen
or
hydrogen (H₂0).
10. Industrial N2 fixation
• Accomplished by Haber -Bosch process.
• Developed in Germany 1914 by Fritz Haber & Karl Bosch.
• Process-
• N2 and H2 react with each other in presence of
1. Industrial catalyst( nickel / iron)
2. High temperature about 500 ͦ c
3. High pressure – 200 atm
To form NH3
11. Biological Nitrogen Fixation
• Biological nitrogen fixation was discovered by the
German agronomist Hermann Hellriegel and Dutch
microbiologist Martinus Beijerinck.
• Biological nitrogen fixation (BNF) occurs when
atmospheric nitrogen is converted to ammonia by an
enzyme called nitrogenase.
• The reaction for BNF is:
N2+16ATP+8H++8 e− → 2NH3+H2+16ADP+16Pi
12. • BNF is mostly accomplished by microorganisms
called diazotrophs or N₂ fixers.
• They include some species of bacteria, fungi,blue
green algae,lichens etc.
• Fixation of atmospheric Nitrogen into nitrogenous
salts with the help of MICRO_ORGANISMS.
Two types of Nitrogen fixation
• Symbiotic
• Non-symbiotic
13. NON-SYMBIOTIC FIXATION
• Fixation is carried out by free living micro-
organism. They inhabit both terrestrial and
aquatic habitat. They can be Aerobic,
Anaerobic or Blue green algae.
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15.
16. SYMBIOTIC FIXATION
• Fixation of free nitrogen by micro-organisms
living in soil symbiotically inside the plants
• ‘Symbiosis’ – coined by DeBary.
Three categories
1. Nodule formation in leguminous plants
2. Nodule formation in non-leguminous plants
3. Non nodulation
17. Nodule formation
• Root nodules formed due to infection of
Rhizobium.
• Free living bacteria growing , near the root of
legumes are unable to fix nitrogen in free
conditions.
• Roots of the legumes secrete some growth factors
that helps in fast multiplication of bacteria.
(E.g.) Pisum sativum secretes homo serine & also
carbohydrate containing protein Lectins over their
surface.
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22. Structure and function of nodule
• Outermost layer of nodule-bacteriod zone-enclosed
by cortical cells.
• Rate of N- fixation of nodule directly proportional to
the volume of the nodule.
• Nodules are small-contain leghaemoglobin.
• Leghaemoglobin
• Effective nodules are larger- pink in colour -due to the presence
of red coloured leghaemoglobin.
• This pigment is similar to haemoglobin of blood.
• Found in nodules between bacteriods & membrane envelops,
enclosing them.
23. • It is heme protein.
• Contain heme moiety attached to a peptide chain represent
globin part.
• The amount of leghaemoglobin in nodules has direct
relationship between amount of atm N fixed by legumes.
MW-16,000-17,000 daltons.
24.
25.
26. Pathway of nitrogen fixation in root nodules
• Glucose-6-phosphate acts as a electron donor.
• Glucose-6-phosphate is converted to
phosphogluconic acid.
• Glucose-6-phosphate + NADP+ + H2O 6phosphogluconic acid
+ NADPH + H+
• NADPH donates electrons to ferrodoxin. Proton is
released and ferrodoxin is reduced.
• Reduced ferrodoxin acts as electron carrier.
Donate electron to Fe-protein to reduce it.
Electrons released from ferrodoxin thus oxidized
27.
28. • Reduced Fe-protein combines with ATP in the
presence of Mg +2.
• Second sub unit is activated and reduced.
• It donates electrons to N2 to NH3
• Enzyme set free after complete reduction of
N2 to NH3.
