The Nitrogen Cycle

Nitrogen is required by living things to:

1. make proteins, become enzymes and make up the structures of living things
2. make nucleic acids that become DNA, the hereditary material of living things

– 80% of the air around us is nitrogen gas (N₂) but N₂ cannot be used by most living things
– N₂ must be converted into nitrate ions (NO₃^–) for living things to be able to use nitrogen

Nitrogen Cycle

– begins with nitrogen fixation; nitrogen gas is converted into nitrates

Lightning

– can fix nitrogen; N₂ reacts with O₂ -> NO₃^–
– accounts for only a very small amount of total nitrogen fixation in the ecosystem
Bacteria (some) – located in soil and in nodules on the roots of legume plants
– accounts for the vast majority of nitrogen fixation in an ecosystem

Decomposers (bacteria)

– break down animal waste nitrogen (NH₃) and nitrogen trapped in the dead bodies of living things
– these bacteria require oxygen to live
– this is why farmers add manure or dead matter to their crops/plants

Denitrification

– lose of nitrates in the form of nitrogen gas
– done by bacteria that do not require oxygen
– ensures a balance within the nitrogen cycle; nitrate levels in soil that are too high may be bad for the plants in an ecosystem
– sped up by very acid or water-logged soils