Nitrogen Cycle

• Organic Compounds which contain Nitrogen

  • Amino Acids & Proteins
  • Nucleotides & Nucleic Acids
  • ATP
  • NAD & NADP
• There are 4 stages to the nitrogen cycle:

  • Nitrogen Fixation
  • Ammonification
  • Nitrification
  • Denitrification
• Nitrogen Fixation - the fixation of nitrogen gas into nitrogen containing compounds
• Ways of Nitrogen Fixation 1

  Free living nitrogen fixing bacteria in soil - reduce N2 to NH3 which they use to make organic compounds. They release these nitrogen rich compounds into soil when they die.
• Ways to Nitrogen Fixation 2

  Mutualistic nitrogen fixing bacteria (e.g. Rhizobium) in the root nodules of leguminous plants - receive carbohydrates from the plant which receives ammonia from the bacteria in return.
• Ways to Nitrogen Fixation 3 & 4

  Lightning

  Harber Process
• Ammonification

  The production of ammonia from nitrogen containing compounds such as urea, proteins and nucleic acids in the dead remains of organisms and in faeces and urine.

  Saprobiotic microorganisms, mainly fungi and bacteria feed on these materials releasing extracellular enzymes. As a result ammonia is released into the soil which dissolves to form ammonium ions.

  Nitrogen has entered the non-living component of the ecosystem.
• Nitrification

  The conversion of ammonium ions to nitrate ions
• Nitrification Stage 1

  bacteria oxidises NH4+ ions and converts them to NO2-
• Nitrification Stage 2

  Bacteria oxidise NO2- ions into NO3- ions.
• Denitrification

  The conversion of soil nitrates into gaseous nitrogen by anaerobic denitrifying bacteria in waterlogged soils or wherever conditions are anaerobic.