Download The Nitrogen Cycle

The Nitrogen
Cycle
A2 OCR Biology
By the end of this session I will:
• be able to describe the importance of
nitrogen in living systems.
• outline the role of micro-organisms in the
cycling of nitrogen
• Describe the nitrogen cycle using the
appropriate AS/A2 scientific language.
Nitrogen the basics – needed for
• Nitrogen (N) is an
element like carbon. All
creatures need nitrogen
to survive.
• Nitrogen is needed for the
synthesis of proteins e.g.
enzymes.
• Nitrogen is also an
important component of
nucleic acids
Nitrogen the basics – chemistry of
• There are huge amounts of nitrogen gas in
the atmosphere, but most animals and
plants have no way of using it as it is very
unreactive due to the triple covalent bond.
• It needs to be fixed (put into a biologically
useful compound). After it is fixed, it can
then start to move through the cycles and
organisms in an ecosystem.
Nitrogen the basics – sources of
• Let's start with the main sources of nitrogen.
Nitrogen gas is the most abundant element in
our atmosphere.
• The other main source of nitrogen is in the
nitrates of soil. The nitrogen in the atmosphere
cannot be used while the nitrates in the soil can
be used by plants. Nitrogen can be converted
into useful nitrate compounds by bacteria,
algae, and even lightning. Once in the soil, the
nitrogen becomes biologically accessible.
Importance of bacteria in the
nitrogen cycle
• Nitrogen fixing
bacteria
• Nitrifying bacteria
• Denitrifying bacteria
Nitrogen fixing bacteria
Function…….
…… converts nitrogen into
nitrogen containing
compounds
E.g. ….
…… Rhizobium
Found in ….
….. Roots nodules of
leguminous plants and
soil
Mutualism
Nitrifying bacteria
Function….
….. Convert
ammonia in
nitrite ions and
then into nitrite
ions.
E.g. …..
…..Nitrosomonas
and
Nitrobacter.
Found in….
….well aerated
soils.
Denitrifying bacteria
Function….
…. Convert
nitrate into
nitrogen gas
Found in….
…. Sewage
works,
compost and
wet soils
Other ways in which nitrogen can
be fixed
Lightning
Haber process
Lightning
• The electrical energy of lightning causes
nitrogen gas (N2) to react with oxygen
(O2) in the atmosphere to produce nitrate
ions (NO3-) which reach the soil dissolved
in precipitation.
• Recent research suggests the amount of
nitrates produced by lightning may be as
high as 50%.
Haber process
Basic summary of the nitrogen cycle