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Like carbon, nitrogen cycles constantly between the living and non-living parts of the environment. The Nitrogen Cycle Biogeochemical cycling of nitrogen atoms; driven by chemical reactions that are performed by prokaryotes (bacteria). Nitrogen atoms must cycle through an ecosystem because living things need nitrogen to make protein. C HON Forms of Nitrogen Common name Nitrogen gas Chemical Formula N2 Where it’s found Atmosphere/air Bio (living) or Geo (nonliving)? Geo Forms of Nitrogen Common name Nitrogen gas Ammonia Chemical Formula N2 NH3 Where it’s found Atmosphere/air Soil Bio (living) or Geo (nonliving)? Geo Geo Forms of Nitrogen Common name Chemical Formula Where it’s found Bio (living) or Geo (nonliving)? Nitrogen gas Ammonia N2 NH3 Atmosphere/air Soil Geo Geo Protein Varies Living things Bio Where is the most nitrogen found? The atmosphere is about 78% N2 gas, making it a nitrogen “sink.” N2 gas O2 gas Other gases Forms of Nitrogen Common name Chemical Formula Where it’s found Bio (living) or Geo (nonliving)? Nitrogen gas Ammonia N2 NH3 Atmosphere/air Soil Geo Geo Protein Varies Living things Bio The air around us is filled with nitrogen… N2 gas O2 gas Other gases But we can’t use any of it. Plants and animals cannot use N2 gas because it contains a triple bond which is too strong to break. On the other hand, living things can easily break the single bonds in NH3. One of the major hurdles in the nitrogen cycle is converting N2 gas into NH3. Not useable (triple bond) Useable (single bond) This chemical reaction is called nitrogen fixation, and it can only be done by one type of organism: bacteria. Nitrogen-Fixation Chemical reaction performed by soil bacteria; nitrogen is “fixed” (made useable) by transforming N2 gas into NH3. Here’s how nitrogen fixation works: H H N H H N H H Nitrogen-fixing bacteria can split N2 because they make an enzyme that lowers the activation energy of the reaction. H H N H H N H H If it weren’t for these bacteria, nitrogen would remain locked in the atmosphere as un-useable N2 gas. You can thank me later. The Nitrogen Cycle N2 gas N N The “Poop Loop” Nitrogen fixation Protein Protein Eating H N H H Ammonia (NH3) In order for the cycle to be complete, nitrogen must return to the atmosphere in the form of N2 gas. This reaction, called denitrification, is performed by a DIFFERENT type of soil bacteria. Denitrification Chemical reaction performed by a second type of soil bacteria; NH3 is converted back into N2 gas. The Nitrogen Cycle N2 gas N N The “Prokaryote Loop” The “Poop Loop” Denitrification Nitrogen fixation Protein Protein Eating H N H H Ammonia (NH3) The process is called “denitrification” because the soil is losing nitrogen. The Nitrogen Cycle N2 gas N N The “Prokaryote Loop” The “Poop Loop” Denitrification Nitrogen fixation Protein Protein Eating H N H H Ammonia (NH3)
