The Nitrogen Cycle

Nitrogen is important for making proteins in all living things. It is also a component of the nitrogenous bases used in nucleic acids.

Nitrogen Gas makes up 80% of the atmosphere, but only a few types of bacteria can use the nitrogen in that form and convert it to other molecules.
Plants take in useable nitrogen from the soil to make their proteins, then those proteins are dismantled and rebuilt as they work their way through the food chain.
A different type of bacteria can release nitrogen gas back into the atmosphere.
Humans can overuse fertilizer and damage the ecosystem by introducing too much nitrogen.

The Movement of Nitrogen

Nitrogen is necessary for protein and is very abundant, yet hard to find.

Nitrogen gas makes up 80% of the molecules in the air.
- No plants or animals have the ability to directly take it from the air and make proteins.
Nitrogen Fixing Bacteria can convert Nitrogen Gas into Ammonia (NH3).
- Nitrifying bacteria convert ammonia to Nitrates - a plant fertilizer
Plants absorb nitrates from the soil and use the nitrogen to make proteins
- Legumes (beans, peas, clover etc.) are a family of plants that can house Nitrogen Fixing Bacteria in their roots (beans and peas are a better source of protein than most vegetables)
Heterotrophs eat protein, and are then broken down by decomposers.
Denitrifying bacteria can convert decomposed molecules back into nitrogen gas.

Disturbances to the Nitrogen Cycle

Nitrogen is usually a limiting factor in ecosystems. Plants can only grow so much with the limited nitrogen in the soil. Humans can stimulate more plant growth by adding fertilizers with high levels of nitrogen.

Adding too much nitrogen can cause Eutrophication
- Nitrogen runs off into bodies of water and fertilize algae at the surface.
- Increased surface algae blocks sunlight from other underwater plants, but releases oxygen to the air, not the water.
- Dead underwater plants do not give off oxygen, and when they decompose, bacteria actually use whatever oxygen is left in the water.
- The lack of oxygen causes "dead zones" than cannot support fish or other aquatic animals.