Ecosystems: The Nitrogen Cycle | A-level Biology | OCR, AQA, Edexcel

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The key points covered in this video include:

1. Nitrification
2. Denitrification
3. Overall Process of the Nitrogen Cycle

Nitrification

Nitrification is the process in which ammonium compounds are converted into nitrites and then into nitrates. This is carried out by nitrifying bacteria which are chemotrophic bacteria that obtain energy from oxidising ammonium ions. Some nitrifying bacteria oxidise ammonium ions to nitrites and other nitrifying bacteria then oxidise nitrites to nitrates. Nitrifying bacteria require oxygen in order to oxidise ammonium ions to nitrates and therefore require well-aerated soil. The nitrates are absorbed by plants and the nitrogen is incorporated into organic compounds.

Denitrification

Denitrification is the process in which nitrates are converted back into atmospheric nitrogen gas. Denitrification is carried out by anaerobic denitrifying bacteria which use nitrates in respiration to produce nitrogen gas. Denitrification only occurs in environments with no oxygen and therefore takes place in waterlogged soils.

Overall Process of the Nitrogen Cycle

The overall process of the nitrogen cycle can be shown diagrammatically.

Summary

Nitrogen is needed by plants to manufacture organic compounds such as proteins and nucleic acids
Plants can take up nitrates which are then used to form organic nitrogen compounds which pass up the food chain
The process by which nitrogen is cycled between its inorganic and organic phase is called nitrogen cycle
This includes four main phases: nitrogen fixation, ammonification, nitrification and denitrification
Nitrogen fixation is carried out by free-living or mutualistic bacteria which convert nitrogen gas to ammonia, which is then used to make organic compounds
Ammonification is carried out by saprobiontic microorganisms which convert organic nitrogen in waste or dead matter into ammonia
Nitrification is carried out by nitrifying bacteria which convert ammonia first to nitrites and then to nitrates under aerobic conditions
Denitrification is carried out by anaerobic denitrifying bacteria which convert nitrates to nitrogen gas