Nutrient Cycles

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  • Production of ammonia from ammonium-containing compounds 
  • Include urea, proteins, nucleic acid and vitamins
  • Saprobiotic micro-organisms feed on these and release ammonia
  • Forms ammonium ions in soil
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  • Conversion of ammonium ions into nitrate ions
  • Happens in two stages 
    • Oxidation of ammonium ions to nitrite ions
    • Oxidation of nitrite ions to nitrate ions
  • Nitrifying bacteria need oxygen to do these conversions
  • Need soil that has many air spaces 
  • Raise productivity by ploughing
  • Drainage of soil also prevents waterlogged soil
  • Prevents air being forced out of the soil
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Nitrogen Fixation

  • Nitrogen gas converted into nitrogen-containing compounds
  • Most important form is carried out by micro-organisms
    • Free-living nitrogen-fixing bacteria- reduce gaseous nitrogen to ammonia- use to manufacture amino acids. Nitrogen-rich compounds released when they die and decay
    • Mutualistic nitrogen-fixing bacteria- live in nodules of roots of plants (e.g. beans and peas). Obtain CHO from plants and plant gains amino acids from bacteria
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  • Soil becomes waterlogged and short of oxygen
  • Type of micro-organism changes
  • Fewer aerobic nitrifying and nitrogen-fixing bacteria found
  • Increase in anaerobic dentrifying bacteria
  • Convert nitrates into gaseous nitrogen
  • Reduces availablity of nitrogen-containing compounds
  • Less uptake by plants
  • Cannot grow as much- productivity reduced
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The carbon cycle

  • Carbon dioxide is dissolved in the air and oceans
  • Carbon dioxide in the air diffuses into leaves of plants through stomata and is used in photosynthesis
  • These plants then either die or are eaten by consumers
    • If they die, saprobiotic micro-organisms secrete enzymes onto its surface and hydrolyse the carbon-containing compounds into soluble, small molecules. Absorbed by micro-organism and released to atmopshere through respiration and decay
    • If eaten, the carbon-containing compounds are passed to the consumers, who undergo the above process when they die
  • If decay is prevented, fossil fuels are formed and then burned for energy for human activity
  • Combustion of fossil fuels releases carbon dioxide back into the atmosphere
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