The Nitrogen Cycle

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The Nitrogen Cycle

• A2 OCR Biology

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Asking questions is a sign of INTELLIGENCE ?

• Unfortunately all questions must wait until the
  end of the lecture.

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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. 
• (k) describe the role of decomposers in the
  decomposition of organic material
• (l) describe how microorganisms recycle nitrogen
  within ecosystems. (Only Nitrosomonas,
  Nitrobacter and Rhizobium need to be identified
  by name).

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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

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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.

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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.

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Forms of Nitrogen

• Urea ? CO(NH2)2
• Ammonia ? NH3 (gaseous)
• Ammonium ? NH4
• Nitrate ? NO3
• Nitrite ? NO2
• Atmospheric Dinitrogen ?N2
• Organic N
• CHEMISTS WE NOW NEED TO CORRECT SOME OF THESE
  IONS!!

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Nitrates are recycled via microbes
Animal protein
Soil organic nitrogen
Ammonification
Ammonium NH4
Nitrification
Nitrite NO2-
Nitrification
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Importance of bacteria in the nitrogen cycle

• Nitrogen fixing bacteria
• Nitrifying bacteria
• Denitrifying bacteria

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Nitrogen fixing bacteria (Mr M discuss
nitrogenase here!!)

• Function.
• converts nitrogen into nitrogen containing
  compounds
• E.g. .
• Rhizobium
• Found in .
• .. Roots nodules of leguminous plants and soil

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Mutualism
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Nitrifying bacteria

• Function.
• .. Convert ammonia in nitrite ions and then into
  nitrate ions.
• E.g. ..
• ..Nitrosomonas and Nitrobacter.
• Found in.
• .well aerated soils.

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Denitrifying bacteria

• Function.
• . Convert nitrates into nitrogen gas
• Found in.
• . Sewage works, compost and wet soils

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Nitrogen in the air
animal protein
nitrogen fixing plant eg pea, clover
plant made protein
dead plants animals urine faeces
denitrifying bacteria
root nodules (containing nitrogen fixing
bacteria)
decomposition by bacteria fungi
nitrates absorbed
ammonia
nitrates
nitrites
bacteria
bacteria
(nitrifying bacteria)
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Other ways in which nitrogen can be fixed

• Lightning
• Haber process

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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.

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Haber process
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Basic summary of the nitrogen cycle
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Eutrophication
Yet another example of pollution, eutrophication
is when lakes become stagnant due to careless use
of fertiliser. There are six steps
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Eutrophication
Cantbreathe
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Eutrophication
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