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The Nitrogen Cycle

The Nitrogen Cycle. N 2. Free nitrogen occurs in the atmosphere as the inert N 2 molecule, making up about 80% of the earth’s atmosphere. This nitrogen must be “fixed”, or converted to an organic form that can be used by organisms. N 2.

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The Nitrogen Cycle

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  1. The Nitrogen Cycle N2 Free nitrogen occurs in the atmosphere as the inert N2 molecule, making up about 80% of the earth’s atmosphere. This nitrogen must be “fixed”, or converted to an organic form that can be used by organisms. N2 Usable forms include nitrate (NO3-) and ammonium (NH4+) N2 Nitrogen is not very reactive, so there are not many processes which convert it to a usable compound. N2

  2. The Nitrogen Cycle N2 Ammonium Ion NH4+ Nitrogen Fixation Biological Fixation: By certain symbiotic bacteria (Rhizobium ) and free-living bacteria (Azotobacter and cyanobacteria, or blue-green algae) which convert gaseous nitrogen to ammonium Chemical Reaction: N2 + 6 e- + 8H+ ---> 2 NH4+ (ammonium ion) Part of a clover root system bearing naturally occurring nodules of Rhizobium, bacteria that can fix atmospheric nitrogen. Each nodule is about 2-3 mm long.

  3. The Nitrogen Cycle Nitrate NO3- N2 Nitrogen Fixation Nitrite NO2- Atmospheric Fixation: by lightening N2 + O2 --------------> 2 NO (nitric oxide) Nitrous oxide combines with oxygen to form nitrogen dioxide: 2 NO + O2 ---------------> 2NO2 Nitrogen dioxide readily dissolves in water to product nitric and nitrous acids: 2 NO2 + H2O -------> HNO3 + HNO2 These acids form nitrate and nitrite ions by releasing the hydrogen. HNO3 --------> H+ + NO3- (nitrate ions) HNO2 --------> H+ + NO2- (nitrite ions) lightning

  4. The Nitrogen Cycle N2 Nitrogen Oxides NOx Nitrogen Fixation By combustion of fossil fuels N2 Ammonia NH3 Nitrogen Fixation Industrial Fixation: process of creating fertilizers Also known as the Haber–Bosch process, this accounts for almost half of the nitrogen fixation today.

  5. Ammonia (NH3) Nitrification: Ammonia  Nitrites  Nitrates Nitrite (NO2-) Nitrogen Fixation Nitrate (NO3-) Nitrosonomas Convert NH3 into N02- NH3 + 1.5 O2 + Nitrosomonas → NO2- + H2O + H+ Nitrobacter Convert N02- to N03- NO2- + 0.5 O2 + Nitrobacter → NO3-

  6. Nitrogen compounds are taken up by plants and animals and used to form proteins (amino acids, proteins, DNA, RNA) Ammonia (NH3) Nitrite (NO2-) Nitrogen Assimilation In this way Nitrogen is passed further and further up the food chain. Nitrate (NO3-)

  7. Ammonificationor Mineralization Plants and animals die or animals excrete waste, which is then broken down by bacteria into Ammonium.

  8. Ammonium Ion NH4+ Nitrification: Ammonia  Nitrites  Nitrates Nitrosonomas Convert NH3 into N02- NH3 + 1.5 O2 + Nitrosomonas → NO2- + H2O + H+ Nitrobacter Convert N02- to N03- NO2- + 0.5 O2 + Nitrobacter → NO3-

  9. Nitrite (NO2-) N2 N2 N2 Denitrofication N2 Nitrate (NO3-) Denitrofication occurs under anaerobic conditions where bacteria such as Pseudomonas and Clostridium essentially breathe nitrate, use the oxygen, and exhale nitrogen back into the atmosphere. NO3- N2+ N2O NO3- NO2-NO N2O +N2. Note: Nitric Oxide (NO) contributes to smog and N20 is a greenhouse gas, contributing to climate change

  10. Denitrofication Nitrogen Fixation Nitrification Assimilation Nitrification Amonification

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