The Nitrogen CycleThe Nitrogen Cycle

Cycling of Nitrogen in a Cycling of Nitrogen in a Closed SystemClosed System

The Nitrogen CycleThe Nitrogen Cycle

The The atmosphereatmosphere is composed of 78% is composed of 78% nitrogen (Nnitrogen (N22) gas) gas

•FertilizersFertilizers often often contain ammonia (NHcontain ammonia (NH33), ), ammonium nitrate ammonium nitrate (NH(NH44NONO33), ), or urea ((NHor urea ((NH22)2CO))2CO)

The Nitrogen CycleThe Nitrogen Cycle

ProteinsProteins are composed of amino are composed of amino acids, and all amino acids contain an acids, and all amino acids contain an amine (nitrogen) groupamine (nitrogen) group

The Nitrogen CycleThe Nitrogen Cycle

DNADNA (Deoxyribonucleic acid) is a nucleic (Deoxyribonucleic acid) is a nucleic acid, which contains nucleotides. The four acid, which contains nucleotides. The four bases (adenine, thymine, guanine, and bases (adenine, thymine, guanine, and cytosine) contain many nitrogen atoms.cytosine) contain many nitrogen atoms.

Adenine Thymine Guanine Cytosine

More on NitrogenMore on Nitrogen

Although nitrogen is abundant in our Although nitrogen is abundant in our atmosphere, most organisms cannot atmosphere, most organisms cannot absorb nitrogen directly from the air.absorb nitrogen directly from the air.

In order to make nitrogen available In order to make nitrogen available to all organisms, different forms of to all organisms, different forms of nitrogen move slowly between living nitrogen move slowly between living things, dead things, the air, soil and things, dead things, the air, soil and water through the water through the Nitrogen CycleNitrogen Cycle..

Nitrogen FixationNitrogen Fixation

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:

1) Atmospheric fixation by lightning2) Industrial fixation3) 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)

Biological Nitrogen FixationBiological Nitrogen Fixation

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“)

Biological Nitrogen FixationBiological 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.

Nitrification and DenitrificationNitrification and Denitrification

Nitrification:Nitrification: the process by which ammonia (NH3) is converted back into nitrates (NO3

-) by nitrifying bacteria.

Denitrification:Denitrification: the process by which nitrates (NO3

-) in the soil are converted back into the nitrogen gas (N2) by denitrifying bacteria.

Sources of NitrogenSources of Nitrogen

ProducersProducers 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.

Sources of NitrogenSources of Nitrogen

ConsumersConsumers 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.

Making Sense of It…Making Sense of It…

ProcessProcess Who Does Who Does It?It?

Starting Starting FormForm

End End ProductProduct

Who Who Takes It Takes It Up?Up?

NitrificationNitrification

Nitrogen FixationNitrogen Fixation

DenitrificationDenitrification

AmmonificationAmmonification

AssimilationAssimilation

EutrophicationEutrophication

EutrophicationEutrophication

EutrophicationEutrophication

Algal BloomAlgal Bloom

Homework Homework (Due Tuesday, March 24(Due Tuesday, March 24thth))

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