The nitrogen cycle describes the natural process by which nitrogen is converted between its various chemical forms and circulated between living organisms and the atmosphere. Nitrogen is essential for building proteins and other organic molecules in living things. It enters ecosystems through nitrogen fixation by bacteria or lightning. Nitrifying bacteria then convert nitrogen into nitrites and nitrates that can be absorbed by plants. Plants and animals incorporate nitrogen into their tissues through consumption or root uptake, and nitrogen returns to the atmosphere through decomposition, denitrification, and other processes. The nitrogen cycle is crucial for supporting life but anthropogenic nitrogen pollution from sources like fossil fuel combustion and fertilizer runoff can disrupt ecosystems.

1. Done by
Saquib ahmed

2.  Nitrogen cycle is a natural cyclic process in
which it becomes a part of the living
organisms, before it is sent back to the
atmosphere.
 The nitrogen cycle represents one of the
most important nutrient cycles found in
terrestrial ecosystems. Nitrogen is used by
living organisms to produce a number of
complex organic molecules like amino
acids, proteins, and nucleic acids.

4.  Ammonification or Mineralization is
performed by bacteria to convert the
ammonia to ammonium. Nitrification can
then occur to convert the ammonium to
nitrite and nitrate
 This process liberates a lot of energy
which can be used by the saprotrophic
microbes

5.  Nitrification is the process by which ammonia is
converted to nitrites and then nitrates. This
process naturally occurs in the environment,
where it is carried out by specialized bacteria.
 This energy is the only source of energy for
these prokaryotes
 They are chemoautotrophs
 Chemoautotroph is an organism, typically a
bacterium, which derives energy from the
oxidation of inorganic compounds.
 Prokaryote is a microscopic single-celled
organism which has neither a distinct nucleus
with a membrane nor other specialized organs.

6. Out
gassing
Atmospheric
fixation
Root uptake
Nitrate NO3
-
Plant
protein
Soil organic
nitrogen
Atmospheric Nitrogen
Biological
fixation

7. Electrical storms
Lightning provides sufficient energy
to split the nitrogen atoms of
nitrogen gas,
Forming oxides of nitrogen NO and
NO2

8.  This also happens inside the internal
combustion engines of cars
 The exhaust emissions of cars contribute a
lot to atmospheric pollution in the form of
NOx
 These compounds form photochemical smog
 They are green house gases
 They dissolve in rain to contribute to acid
rain in the form of nitric acid
 The rain falling on soil and running into rivers
 They contribute to the eutrophication of
water bodies
 Nox are oxides of nitrogen, especially as
atmospheric pollutants

9.  Adding nitrate fertiliser clearly helps the growth
of plants
 The presence of microbes permits the peas to
grow much better.
 The peas grow better in the presence of the
microbes than they do with nitrate fertiliser
added
 The difference is due to the present of
mutualistic nitrogen fixing bacteria which live in
the pea roots.
 Mutualism is the way two organisms of different
species exist in a relationship in which each
individual benefits. Similar interactions within a
species are known as co-operation.

10.  Cyan bacteria are nitrogen fixers that also
fix carbon (these are photosynthetic).
 Rhizobium bacteria are mutualistic with
certain plant species e.g. Legumes.
 They grow in root nodules.
 Azotobacter are bacteria associated with
the rooting zone (the rhizosphere) of plants
in grasslands.

11. Alafalfa (Medicago sativa)

12. Nitrate NO3
-
Atmospheric
fixation
Out
gassin
g
Plant
protein
Atmospheric Nitrogen
Ammonium
NH4
+
Soil organic
nitrogen
Biological
fixation

13.  The need for synthetic fertilisers can be
reduced by cultural practices
 Avoiding the use of soluble fertilisers in soil
prevents leaching
 Rotating crops permits the soil to recover
from nitrogen hungry crops (e.g. wheat)
 Adding a nitrogen fixing crop into the
rotation cycle
 Ploughing aerates the soil and reduces
denitrification
 Draining water logged soil also helps reduce
denitrification

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