Leaving certificate biology Nutrient recycling The nitrogen cycle

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Lesson 2, Topic 3

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The nitrogen cycle

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What is the nitrogen cycle ?

The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmosphere, terrestrial, and marine ecosystems. The conversion of nitrogen can be carried out through both biological and physical processes

Why is the nitrogen cycle important ?

Plants need nitrogen to make protein.
Plants can not use the nitrogen gas in the air to do this
The nitrogen cycle allows plants via bacteria to get nitrogen in a form they can use to make proteins

The role of nitrogen fixing bacteria in the nitrogen cycle

They are found in swellings called nodules on the roots of legumes (peas , beans).
These bacteria convert nitrogen gas into nitrate
Plants can then use these nitrates to make protein
This is an example of mutualism as both organisms benefit

The role of decomposers in the nitrogen cycle

When animals eat plants they assimilate the nitrogen in the plants into their own proteins
When plants and animals die they are decomposed by bacteria and fungi in the soil
As they decay nitrogen compounds such as ammonium salts are released into the soil

The role of nitrifying bacteria in the nitrogen cycle

Nitrifying bacteria in the soil convert ammonium salts into nitrites and then onto nitrates
These nitrates ate absorbed by plants to make protein

The role of denitrifying bacteria in the nitrogen cycle

They convert nitrates into nitrogen gas

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