Nitrogen cycle

Nitrogen is transferred between living organisms and their environment.

Nitrogen cycle decomposition

Decomposition

Bacteria carry out the following processes in the nitrogen cycle:

Nitrogen fixation

  • Nitrogen gas is converted into nitrates.
  • This is carried out by nitrogen fixing bacteria.
  • Nitrogen fixing bacteria need oxygen as they are aerobic.
  • This process is quickened by the presence of oxygen and higher temperatures.
  • These bacteria can be found ‘free’ in the soil or in roots nodules found on the roots of plants such as peas, beans, and clover.
  • Within the root nodules the bacteria gain carbohydrates from the plant and the plant gains a source of nitrates in return

Decomposition

  • Bacteria/fungi break down protein found in dead plants and animals, urine and faeces into ammonia.

Nitrification

  • Ammonia is converted into nitrates.
  • This is carried out by nitrifying bacteria.
  • Nitrifying bacteria needs oxygen as they are aerobic.
  • This process is quickened by the presence of oxygen and higher temperatures.

Denitrification

  • Nitrates are converted into nitrogen gas.
  • This process is disadvantageous for the soil and plants.
  • This is carried out by denitrifying bacteria.
  • Denitrifying bacteria do not need oxygen as they are anaerobic (therefore they thrive in waterlogged soil).