Download Nitrogen Cycle

This is the nitrogen cycle, Nitrogen is the
most abundant element in the
atmosphere and is essential to all life.
Earth's atmosphere is approximately 7071% nitrogen!!!
Nitrogen Cycle
 The absorption of nitrogen by plants from the
soil, then consumption of plants by animals and
when the animals and bacteria decompose them,
returning back of nitrogen to the soil, the whole
cycle is called as nitrogen cycle.
 In this cycle, nitrogen converts into its various
chemical forms. Both biological and non biological
methods are involved in this cycle.
 Nitrogen is the most important component of the air.
Among all the gases present in the air, nitrogen is most
abundantly present.
 It is an odorless and colorless gas.
 It is the most important gas for all organisms on
earth.
 Nitrogen is present in DNA, RNA and other proteins
which are the building blocks of human body as well as
all other organisms.
Nitrogen present in the air is not in the usable
form.
 There are certain bacteria which convert the
atmospheric nitrogen into nitrogen compounds
so that it can be used by all living beings.
 There is a process for this purpose called as
nitrogen cycle.
Steps involved in Nitrogen Cycle:To convert the atmospheric nitrogen into
usable nitrogen, five steps are involved.
 Nitrogen fixation
 Nitrification
 Assimilation
 Ammonification
 Denitrification
Nitrogen fixation
o Nitrogen present in the air is in the static form
N2 that is it cannot be used by any organism until it
is fixed by a process called nitrogen cycle.
o Through precipitation, nitrogen enters the soil
and surface waters.
oWhen it settles down in the soil or water, it
converts into two separate atoms by undergoing
some changes which combine nitrogen with
Hydrogen.
oThe resulting compound is called as ammonium.
o Microorganisms present in the soil are responsible
for carrying out this conversion.
o They are placed into three groups such as bacteria
live in symbiotic relationship with legume plants, free
aerobic bacteria and algae.
o All the microorganisms are beneficial for the soil.
o There are certain bonds between atmospheric
nitrogen which make it inert.
o Bacteria and other microbes break these bonds with
the help of an enzyme nitrogenase.
o When the bond breaks, nitrogen converts into two
forms each combing with hydrogen and other
chemicals.
o Sometimes light also plays an important role in
breaking down the bond in atmospheric nitrogen and
converts it into ammonia and nitrates.
o When there is no oxygen, only then the enzyme
nitrogenase acts. Therefore, the microbes involved in
nitrogen cycle live at places where there is no oxygen
like root nodules. Eg. Rhizobium
Nitrification
 It is a process of conversion of ammonia into
nitrites and then nitrates.
 Special kinds of bacteria are involved in this
process which occurs naturally in the environment.
 Bacteria like Nitrosomonas and Nitrococcus
convert the ammonia into nitrite and then
Nitrobacter convert the nitrites into nitrates by
oxidizing NO2 to NO3.
Assimilation
 In this step, all the nitrites and nitrates produced in
the whole nitrogen cycle are consumed by plants and
animals and use it in their cellular processes.
 For example, NO3 and NH4 both are consumed by
plants which take them through their roots into
various plant parts to make proteins and other
nucleic acids.
 When animals eat these plants, the nitrates and
nitrites automatically transfer into their body
Ammonification
• When an animal or plant dies or release wastes
from their bodies, nitrogen is released in the organic
form.
• This organic nitrogen is converted into ammonium
by fungi and bacteria through the process
Ammonification.
•The ammonia produced can be used in other
biological processes of plants.
Denitrification
 When the ammonia is converted back into inert
nitrogen, the process is called as denitrification.
 Bacteria are involved in this process which takes
place in anaerobic conditions.
 Places like deep soils and deep water are the places
without oxygen.
 Pseudomonas and Clostridium are responsible for
the step of denitrification.
These bacteria can also live in the places where there
is availability of oxygen.
Nitrogen Balance
Nitrogen Balance
An individual’s nitrogen balance is dependent
on a combination of:
Nitrogen intake nitrogen excretion
Dietary amino acids,
nucleotides etc.
Urine, faeces, hair and
skin loss, perspiration
Nitrogen balance status can be:
1) In balance
2) Positive
3) Negative
NITROGEN BALANCE
Nitrogen balance = nitrogen ingested - nitrogen excreted
(primarily as protein) (primarily as urea)
Nitrogen balance = 0 (nitrogen equilibrium)
protein ingested = protein excretion
Positive nitrogen balance
Observed in adults
protein ingested > protein excretion
during pregnancy, infancy, childhood , body building and recovery from
severe illness or surgery
Negative nitrogen balance
protein ingested < protein excretion
starvation, following severe trauma, surgery or infections.
Prolonged periods of negative balance are dangerous and fatal if the loss of
body protein reaches about one-third of the total body protein
Excess or insufficient dietary amino acid intake leads
to the catabolism of amino acids
o Excess amino acids can be used for energy
o Insufficient dietary amino acids lead to the
catabolism of proteins
o Insufficient dietary energy leads to the
catabolism of proteins
o For amino acids to be utilised for energy, they
must have their a-amino groups removed