The Nitrogen Cycle

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.

• 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

1. Nitrogen fixing bacteria
2. Decomposing bacteria
3. Nitrifying bacteria
4. Denitrifying bacteria