1. Nitrogen Cycles

2. All life requires nitrogen compounds to form proteins and nucleic acids. Air is major reservoir of nitrogen (~ 78%). Even though air is a large source of N2, most living things cannot use this form, and it must be converted to other forms There are several modes of N2fixation that convert N2into NH3, NO2, or NO3

3. Forms of Nitrogen Inorganic nitrogen: NH3=Ammonia NH4+=Ammonium NO3-=Nitrate NO2-=Nitrite all nutrients, but toxic at high levels Organic nitrogen Livings organisms and their proteins, nucleic acids, urea, and other nitrogenous molecules.

4. Atmospheric nitrogen is almost chemically inert under normal conditions Lavoisier named it “Azote”; meaning “without life”. The N≡N triple bond, however, is very stable, with a bond energy of 930 kJ/mol

5. Nitrogen Fixation “Nitrogen Fixation” is the process that causes the strong two-atom nitrogen molecules found in the atmosphere to break apart so they can combine with other atoms. Nitrogen gets “fixed” when it is combined with oxygen or hydrogen Nitrogen fixation is the process that converts N2into either: NH3,NO3 -,or NO2 - (usable forms).

6. There are three ways that nitrogen gets “fixed”! (a)Atmospheric Fixation (b) Industrial Fixation (c) Biological Fixation

7. Atmospheric Nitrogen (N 2 ) Ammonia (NH 3 ) Nitrogen combines with Hydrogen to make Ammonia Nitrates (NO 3 ) Nitrogen combines with Oxygen to make Nitrates

8. Atmospheric fixation (Only 5 to 8% of the Fixation Process) The enormous energy of lightning breaks nitrogen molecules apart and enables the nitrogen atoms to combine with oxygen forming nitrogen oxides (N 2 O). Nitrogen oxides dissolve in rain, forming nitrates. Nitrates(NO 3 )are carried to the ground with the rain.

9. Lightening breaks N 2 NO 3 Plants use nitrates to grow

10. Industrial Fixation Under great pressure, at a temperature of 600 degrees Celcius, and with the use of a catalyst, atmospheric nitrogen (N 2 )and hydrogen are combined to form ammonia NH 3 Ammonia can be used as a fertilizer.

11. Industrial Plant combines Nitrogen and Hydrogen to form Ammonia Formed Ammonia is used a fertilizer

12. Biological Fixation Biological fixation accounts for the most fixed nitrogen in the biosphere Only in certain organisms can fix atmospheric nitrogen. These are divided into: 1.Non-symbiotic N-fixation carried out by Free- living Organisms (bacteria, Cyanobacteria, & Blue-green algae) 2. Symbiotic N-fixation carried out by organisms living in symbiosis with certain plants (~70% of biological fixation)

13. Biological N 2 fixation Biological N 2 fixation= Conversion of N 2 gas to ammonium via the following reaction: N 2 +10 H + + 8 e-+ 16 ATP 2 NH 4 + H 2 +16 ADP +16 Pi A very energetically expensive reaction

14. The reaction require: Nitrogenase enzyme (of any suitable organism) Large supply of energy Anoxic site (oxygen binds to and inactivates the nitrogenase enzyme)

15. Symbiotic Relationship Bacteria Bacteria live in the roots of legume family plants and provide the plants with ammonia in exchange for the plant’s carbon and a protected home.