nitrogen cycle

• All life requires nitrogen compounds - proteins and nucleic acids 
• Air is 78% nitrogen is the largest store of nitrogen. 
• Most organisms cannot use nitrogen in its gas form as its inert. 
• Plants secure nitrogen in a fixed form - nitrate ions (NO-3). 
• processes:

  1. Nitrogen fixation 
  2. Decomposition 
  3. Nitrification 
  4. Denitrification 
• 1. Nitrogen fixation 

  Free living bacteria and symbiotic bacteria in root modules of legumes.

  Rhizobium contains an enzyme called nitrogenase to convert nitrogen and hydrogen to ammonia. 

  The ammonia is used to make amino acids which the legume can use to make proteins in return for supplying the bacteria with carbohydrates. 

   
• 1. Decomposition/ammonification

  Proteins made by plants pass through food webs, at each trophic level nitrogen is excreted. Saprobionts use these molecules to make ammonia. 

  Molecules that are decomposed include:

  • DNA/RNA 
  • Proteins 
  • ATP
  • Urea

   
• 1. Nitrification

  Most ammonia produced by Saprobionts is converted to nitrates by nitrifying bacteria. 

  Step 1 - bacteria oxidise ammonia to nitrites 

  Step 2 - Different bacteria oxidise the nitrites to nitrates. 

   
• 1. Denitrification

  Reduction of nitrates to nitrogen gas by bacteria to return to the atmosphere. 

  Bacteria use nitrates as an alternative to oxygen for the final electron acceptor in respiration.