The nitrogen cycle (OCR A level biology)

What are the seven stores of nitrogen?

1. Atmospheric nitrogen.
2. Nitrogen compounds in plants.
3. Nitrogen compounds in animals.
4. Ammonia.
5. Ammonium ions.
6. Nitrites.
7. Nitrates.

What are the four processes in the nitrogen cycle?

1. Nitrogen fixation.
2. Ammonification.
3. Nitrification.
4. Denitrification.

What is the process of nitrogen fixation?

When nitrogen gas in the atmosphere is converted to ammonia. The ammonia can then be used in plants.

What bacteria are involved in nitrogen fixation?

Azotobacter: found in soil (they do not form mutualistic relationships with plants.)
Rhizobium: found inside root nodules of leguminous plants (they form a mutualistic relationship with plants, they provide the plants with nitrogen and the plant provides them with carbohydrates)

What is the process of ammonification?

nitrogen compounds from dead organisms are turned into ammonia by decomposers, which goes on to form ammonium ions.

What is the process of nitrification?

Ammonium ions in the soil are changed into nitrogen compounds that can be used by plants.

What are the bacteria involved in nitrification?

Nitrifying bacteria.
Nitrosomonas change ammonium ions into nitrites.
Nitrobacter change nitrites into nitrates.

What is the equation for nitrosomas bacteria?

NH4+ -> NO2-

What is the equation for nitrobacter?

NO2- -> NO3-

What is the process of denitrification?

When nitrates in the soil are converted to nitrogen gas and released back into the atmosphere. It happens under anaerobic conditions e.g., in waterlogged soils.

What is the bacteria involved in denitrification?

Pseudomonas

What are two other ways that nitrogen enters the nitrogen cycle?

1. Lightening strikes.
2. Artificial fertilisers produced by the Haber process.