The nitrogen cycle

• Why can't plants and animals obtain nitrogen through the air?

  • N2 contains a strong triple bond that requires a lot of energy to break
• How much of the air is nitrogen?

  • 78%
• what biological molecules contain nitrogen?

  • Protein, ATP, DNA
• What happens in the nitrogen cycle?

  • atmospheric nitrogen is converted into ammonium by nitrogen fixing bacteria in the soil OR in the legumes of plants
  • Ammonium is converted to nitrites by nitrifying bacteria
  • Nitrites are converted into nitrates by nitrifying bacteria
  • If there is no oxygen, anaerobic denitrifying bacteria release the nitrogen back into the air
  • Nitrates are absorbed by plants and eaten by animals
  • saprobionts and decomposers break down nitrogen containing compounds (urea + DNA) into ammonium and the cycle repeats