1. Cycling of Nitrogen in a Closed System
The Nitrogen Cycle
Cycling of Nitrogen in a Closed System

2. The Nitrogen Cycle The atmosphere is composed of 78% nitrogen (N2) gas
Fertilizers often
contain ammonia (NH3),
ammonium nitrate (NH4NO3),
or urea ((NH2)2CO)

3. The Nitrogen Cycle
Proteins are composed of amino acids, and all amino acids contain an amine (nitrogen) group

4. The Nitrogen Cycle
DNA (Deoxyribonucleic acid) is a nucleic acid, which contains nucleotides. The four bases (adenine, thymine, guanine, and cytosine) contain many nitrogen atoms.
Adenine
Thymine
Guanine
Cytosine

5. More on Nitrogen
Although nitrogen is abundant in our atmosphere, most organisms cannot absorb nitrogen directly from the air.
In order to make nitrogen available to all organisms, different forms of nitrogen move slowly between living things, dead things, the air, soil and water through the Nitrogen Cycle.

6. Nitrogen Fixation
Nitrogen Fixation: the process by which nitrogen is taken from its relatively inert molecular form (N2) in the atmosphere and converted into ammonia (NH3) or nitrate (NO3-)
Three processes are responsible for most of the nitrogen fixation in the biosphere:
Atmospheric fixation by lightning
Industrial fixation
Biological fixation by certain microbes - alone or in a symbiotic relationship with some plants and animals (this is the important on for the Nitrogen Cycle)

7. Biological Nitrogen Fixation
The ability to fix nitrogen is found only in certain bacteria and archaea (nitrogen-fixing bacteria), and requires a complex set of enzymes and a huge expenditure of ATP.
Some bacteria (Rhizobia) live in a
symbiotic relationship with plants
of the legume family
(e.g., soybeans, alfalfa)
Some establish symbiotic
relationships with animals
(e.g., termites and "shipworms“)

8. Biological Nitrogen Fixation
Some nitrogen-fixing bacteria live free in the soil.
Nitrogen-fixing cyanobacteria are essential to maintaining the fertility of semi-aquatic environments like rice paddies.

9. Nitrification and Denitrification
Nitrification: the process by which ammonia (NH3) is converted back into nitrates (NO3-) by nitrifying bacteria.
Denitrification: the process by which nitrates (NO3-) in the soil are converted back into the nitrogen gas (N2) by denitrifying bacteria.

10. Sources of Nitrogen Producers
About 80 percent of Earth’s atmosphere is nitrogen gas (N2).
Nitrifying bacteria can fix nitrogen and convert it into ammonia (NH3) or nitrates (NO3). These bacteria are found in the soil and in the roots of some plants.
Plants cannot use N2 gas directly. They can absorb it, however, in a converted form.

11. Sources of Nitrogen Consumers Decomposers
Consumers can obtain usable nitrogen by eating.
Decomposers
When decomposers break down decaying plant and animal materials, they return nitrogen to the soil.
Some denitrifying bacteria can release nitrogen into the atmosphere.

14. Making Sense of It… Process Who Does It? Starting Form End Product
Who Takes It Up?
Nitrification
Nitrogen Fixation
Denitrification
Ammonification
Assimilation

15. Eutrophication

16. Eutrophication

17. Eutrophication

18. Algal Bloom

19. Homework (Due Tuesday, March 24th)
Instructions:
Draw your interpretation of the natural nitrogen cycle.
Next, incorporate a human activity into the nitrogen cycle and demonstrate how this human activity effects the cycle.
Along with your drawing you must include a one page written summary that addresses the effects on the soil, atmosphere, fresh-water ecosystems, and marine ecosystems.
Be sure to include the following terms in your diagram order to obtain full marks: nitrogen fixation, nitrate, nitrogen-fixing bacteria, ammonia, nitrification, nitrogen (N2), nitrifying bacteria, decomposers, denitrification, producers, denitrifying bacteria, and consumers