The Nitrogen Cycle (Leaving Cert Biology): Revision Notes
📚 Revision Notes
The Nitrogen Cycle
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Nutrient recycling: The way in which elements or minerals are absorbed by organisms, released into the atmosphere when organisms decompose and are absorbed by other organisms. Carbon and nitrogen can be continuously recycled and reused.
The Nitrogen Cycle
Nitrogen Cycle in Plants and Animals
- Plants need nitrogen to make proteins.
- They can't use nitrogen gas from the air directly; it must be converted into usable forms.
- Nitrogen-fixing bacteria are found in nodules on the roots of legumes (e.g. peas, beans, clover).
- These bacteria convert nitrogen gas into nitrates.
- Plants use nitrates to make proteins.
- Nitrogen-fixing bacteria and plants have a mutualistic relationship, meaning both benefit.
- Mutualism is a form of symbiosis.
- Animals obtain nitrogen by eating plants and assimilating plant proteins.
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Symbiosis: Two organisms from different species that live in close association, where at least one of them benefits. Mutualism: Form of symbiosis where both organisms benefit.
Parasitic: One organism benefits, one organism suffers.
- When plants and animals die, they are decomposed by bacteria and fungi.
- This decomposition releases ammonia (a nitrogen compound) into the soil.
- Nitrifying bacteria in the soil convert ammonia into nitrites, and then into nitrates.
- These nitrates can be absorbed by plants and used to make proteins.
- Denitrifying bacteria convert nitrates back into nitrogen gas, completing the cycle.
Bacteria Involved
- Nitrogen fixing bacteria
- Decomposing bacteria
- Nitrifying bacteria
- Denitrifying bacteria
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Quick Recap:
- Nitrogen-fixing bacteria take nitrogen gas (N2) from the air and turn it into nitrates.
- Plants use those nitrates to create proteins.
- Animals get nitrogen by eating plants or other animals.
- When plants and animals die, decomposers release ammonia into the soil.
- Nitrifying bacteria convert ammonia into nitrites, then into nitrates for plants.
- Denitrifying bacteria turn nitrates back into nitrogen gas, completing the cycle.