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    • Bacteria and fungi involved in decomposition feed saprotrophically
      • They secrete enzymes onto dead and waste material
        • The enzymes digest the material into small molecules which are then absorbed into the organisms body
          • Once absorbed, the molecules are stored or respired to release energy
      • When lightening  strikes or during the haber process nitrogen is fixed
      • Nitrogen fixing bacteria eg Rhizobium live in root nodules
        • They have a mutualistic relationship,  the bacteria provide fixed nitrogen and they recieve carbon compounds in return
          • Proteins in the nodules also absorb oxygen, leaving favourable anaerobic conditions, where the bacteria use nitrogenase to reduce nitrogen gas into ammonium ions
      • Chemoauto - trophic bacteria in the soil absorb ammonium ions
        • Ammonium ions are released by bacteria involved in putrefaction of proteins found in dead or waste organic matter
          • Chemoauto - trophic bacteria obtain energy by oxidising ammonium ions to nitrate ions, or by oxidising nitrite ions to nitrate ions
            • Oxidising ammonium ions to nitrate ions Nitrosomonas bacteria
            • Oxidising nitrite ions to nitrate ions Nitrobacter bacteria
            • Oxidation requires oxygen so these reactions only happen in well aerated soils
              • Nitrate ions can be absorbed from the soil by plants and used to make nucleotide bases
      • Some bacteria convert nitrate ions back to nitrogen gas
        • When these bacteria are under anaerobic conditions eg waterlogged soil, they use nitrate ions as a source of oxygen for respiration and produce nitrogen gas and nitrous oxide


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