Nutrient Cycle

• Processes which release carbon back into the air

  1. Respiration

  2. Combustion
• Process which takes carbon out of the air and builds it up into carbohydrate/glucose

  Photosynthesis
• Over time, the parts of plants and animals which are not broken down by microbes undergo fossilisation
• As a result of fossilisation

  Carbon can be put back into the atmosphere through combustion
• How the decay of plants and animals puts CO2 back into the air

  Respiration by decomposers
• Nitrification


  The build-up of nitrogen into amino acids and protein in plants and animals and the eventual breakdown of these compounds into nitrates
• Nitrification


  1. Plants absorb nitrogen as nitrates and use them to make protein

  2. As plants and animals are eaten, they are digested and then built up into other proteins in sequence

  3. Eventually the nitrogen is returned to the ground as urine or through the process of death and decay

  4. Bacteria and fungi breakdown the proteins to release ammonia

  5. Nitrifying bacteria convert ammonia or ammonium compounds into nitrates
• Nitrification


  • Occurs better in warm soil which is well aerated (lots of oxygen present)
• Nitrogen fixation


  A process carried out by nitrogen-fixing bacteria which can convert nitrogen gas into nitrates
• Nitrogen fixation


  1. Nitrogen-fixing bacteria can be found in the soil or frequently in small swellings (root nodules) in the roots of a group of plants called legumes which include peas, beans and clover

  2. The bacteria gain carbohydrates from the legumes and the legumes obtain nitrates from the bacteria

  3. Nitrogen fixation can also be carried out by bacteria which live freely in the soil
• Nitrogen fixation


  • Warm aerated soils will encourage this process
• Denitrification


  Denitrifying bacteria convert nitrates into atmospheric nitrogen
• Denitrification


  A process that is wasteful and undesirable for farmers because it removes nitrates from the soil and reduces the amount available for plants to use
• Denitrifying bacteria


  • They are anaerobic
  • They are most commonly found in waterlogged soils
• Denitrifying bacteria in well-drained and aerated soils


  Their effect is much reduced
• Reducing denitrification


  1. Field drainage

  2. Ploughing
• Root Hair Cells


  Found in plant roots

  adapted for their function of taking up water and minerals e.g nitrates

  large surface area achieved by having long extension to cell
• What important biological molecule do plants produce from absorbed nitrates

  Protein
• Eutrophication


  Sewage/fertiliser runoff - increases nitrate content

  Algae bloom occurs. May cause death of some aquatic plants due to shading

  algae and plants quickly use up nitrates and algae die

  aerobic bacteria decompose dead material, using up dissolved oxygen in water

  oxygen depletion causes aquatic vertebrates and invertebrates to die as they’re unable to respire