Nitrogen cycle (paper 2)

• Why is nitrogen needed by living organisms

  Nitrogen is required by living organisms to make proteins
• absorbing N2


  Neither plants nor animals can absorb nitrogen gas (N2) from the air. N2 needs to be fixed to produce nitrates before nitrogen can be absorbed by plants and passed on to animals.
• How is nitrogen gas converted into a usable form during the nitrogen cycle

  Nitrogen gas can be converted into a usable form as follows:

  • Nitrogen-fixing bacteria convert N2 gas into ammonium compounds, which can then be converted to usable nitrates
  • Lightning can split the bond between the two N atoms, turning them into nitrous oxides that dissolve in rainwater and leach into the soil
• What is the role of nitrogen-fixing bacteria in the nitrogen cycle

  Nitrogen-fixing bacteria are bacteria that convert nitrogen gas into ammonium compounds, which can then be converted to usable nitrates; this is known as nitrogen fixation.
• In what form do plants absorb nitrogen from the soil

  Plants absorb nitrogen from the soil in the form of nitrates
• How do animals obtain the nitrogen they need


  Animals get the nitrogen they need from plant proteins or from the tissues of other animals when they eat
• example of a group of organisms that can act as decomposers

  • Bacteria
  • Fungi

  There are other organisms that consume dead material, e.g. earthworms and woodlice, but these organisms do not release nutrients into the environment in the same way as decomposers
• what do decomposers do 


  Decomposers break down proteins in the dead and waste material, allowing nitrogen to return to the soil
• What is the role of nitrifying bacteria in the nitrogen cycle


  Nitrifying bacteria convert ammonium compounds to nitrites and then to nitrates, which can then be absorbed by plants
• what do Denitrifying bacteria do 


  Denitrifying bacteria take nitrates out of the soil and convert them back into nitrogen gas, reducing soil fertility and plant growth