The Nitrogen Cycle

HideShow resource information
  • Created by: Max123
  • Created on: 30-03-13 21:29
Preview of The Nitrogen Cycle

First 197 words of the document:

The Nitrogen Cycle
All living organisms depend upon the availability of
nitrogen compounds for their growth and development
Large amounts of nitrogen are required for the formation of
proteins, nucleic acids and other cellular components
Four processes participate in the cycling of nitrogen
through the biosphere:
Nitrogen Fixation
There is an abundant supply of nitrogen in the earth's atmosphere
Nitrogen gas makes up nearly 79% of the earth's atmosphere
Most living organisms cannot use nitrogen in this form as the gas is
generally unreactive due to the triple bonds forming its molecules (NN)
Plants obtain their nitrogen supply in `fixed' form ­ that is incorporated
into nitrogen compounds such as nitrate and ammonium ions
Nitrogen fixation within the biosphere involves three main processes:
· Atmospheric fixation ­ the effect of lightning
· Industrial fixation ­ the Haber process for ammonia manufacture
· Biological fixation ­ the ability of certain bacteria to `fix' nitrogen gas
into nitrogen compounds
Biological fixation accounts for the majority of
`fixed' nitrogen found in soil and water

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

A relatively small amount of
nitrogen fixation occurs
during lightning
The enormous amounts of
energy released by lightning
break nitrogen molecules
apart, allowing their atoms to
combine with oxygen and
form nitrogen oxides
These oxides dissolve in rain
and form nitrates that are
carried to the earth's surface
Nitrates formed during thunderstorms account for around
5-8% of total nitrogen fixation
Biological Nitrogen Fixation
The ability to fix nitrogen is
found only in a few species
of prokaryotic bacteria and
blue-green bacteria
Some nitrogen-fixing bacteria
live…read more

Page 3

Preview of page 3

Here's a taster:

Biological Nitrogen Fixation
Nitrogen-fixing bacteria possess
the enzyme nitrogenase that
enables them to reduce nitrogen
gas into ammonia
Nitrogen + hydrogen
N2 + 3H2 2NH3
The Nitrogen Cycle
Most plants absorb nitrogen through their
roots in the form of nitrate (NO3-) or
ammonium ions (NH4+)
Nitrate ions form the major pool of nitrogen available
to plants, with fewer species utilising ammonium ions
directly because of their toxic nature at
high concentrations
Inorganic nitrogen compounds taken up by plants are
incorporated into organic…read more

Page 4

Preview of page 4

Here's a taster:

Nitrogen-containing organic compounds, such as
proteins, pass along food chains
Nitrogen-containing organic compounds are made available
to the decomposers when animals excrete nitrogenous waste
products, and when animals and plants die
Saprophytic fungi and bacteria are the principal decomposers
responsible for converting organic nitrogen compounds into
AMMONIA (NH3) ­ this process is called AMMONIFICATION
4…read more

Page 5

Preview of page 5

Here's a taster:

Chemosynthetic bacteria play an essential role in
the nitrogen cycle
These bacteria are autotrophs and obtain their
energy by oxidising simple inorganic compounds
In both terrestrial and aquatic environments, the
ammonia (NH3) released by the decomposers dissolves
in water to form ammonium ions (NH4+)
NITRIFIYING BACTERIA oxidise ammonium ions (NH4+) to
nitrite ions (NO2-) and nitrite ions to nitrate ions (NO3-)
The oxidation of ammonium ions and nitrite ions to nitrates
is known as…read more

Page 6

Preview of page 6

Here's a taster:

The nitrogen cycle is closed when
a group of bacteria known as the
denitrifying bacteria reduce
nitrates to nitrogen gas
Denitrifying bacteria live deep in
the soil and in aquatic sediments
where oxygen levels are low
These bacteria reverse the
nitrifying process and convert
nitrates to nitrites, and nitrites to
nitrogen gas
Denitrifying bacteria use nitrates as an alternative to
oxygen during respiration and their activities result in
losses of nitrogen into the atmosphere
Certain Images © 2003
Copyright ©2003 SSER Ltd.…read more


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all resources »