10.2.4 Nutrient cycles

• The carbon cycle


  1. Photosynthesis

  2. Feeding

  3. Death and decomposition

  4. Respiration

  5. Combustion and pollution

  6. Sedimentation

  
• Photosynthesis


  Removes carbon dioxide from the atmosphere
• Feeding


  Carbon can be passed onto animals and decomposers
• Respiration


  Releases carbon into the atmosphere
• Decomposers


  Break down dead plants and animals in a process called decomposition, releasing carbon dioxide into the atmosphere
• Combustion (burning)


  Releases carbon into the atmosphere

  
• Fossil fuels are formed from the remains of dead animals and plants over millions of years
• Animals and plants contain lots of carbon
• Increasing human populations


  Put demand on resources, leading to deforestation (removing carbon sinks) and more fossil fuel use (more CO2 in atmosphere)
• Nitrogen fixation


  1. Lightning can fix nitrogen gas, splitting the bond between the two atoms and turning them into nitrogen containing compounds in the soil

  2. Nitrogen fixing bacteria found in soil and root nodules of leguminous plants take N2 gas and change it into ammonium ions/ammonia in the soil

  
• Deamination


  The breakdown of amino acids, releasing ammonia in animal urine
• Decomposers


  Break down nitrogen containing compounds in dead plant and animal matter into ammonium compounds in the soil

  
• Nitrates


  Absorbed by plants through active transport

  
• Nitrogen containing compounds


  Used by plants to make proteins and DNA/RNA

  
• Denitrification


  The process where nitrates are converted back into nitrogen gas, removing usable nitrogen compounds from the soil

  
• Denitrification occurs in anaerobic conditions, when denitrifying bacteria respire anaerobically

  
• Waterlogged soils are bad for plants due to denitrification
• Nitrogen cycle summary


  1. Nitrogen gas in air cannot be absorbed by plants

  2. Nitrogen fixing converts N2 into nitrogen compounds

  3. Deamination releases ammonia from animal urine

  4. Decomposition releases ammonium ions

  5. Nitrification converts ammonium to nitrites then nitrates

  6. Plants absorb nitrates

  7. Nitrogen used to make proteins and DNA/RNA

  8. Denitrification converts nitrates back to nitrogen gas

  
• Bacteria involved in nitrogen cycle:

  • Nitrogen fixing bacteria
  • Decomposers
  • Nitrifying bacteria
  • Denitrifying bacteria
• Nitrogen fixing bacteria:

  • Convert nitrogen in the air into nitrogen chemicals
  • Some live in root nodules
• Decomposers:

  Converting nitrogen chemicals (dead cells, urine & faeces) into ammonia (NH3)
• Nitrifying bacteria:

  converts ammonia into:

  1. Nitrite (NO2-)
  2. Nitrate (NO3-)
• Denitrifying bacteria:

  Convert nitrate into nitrogen gas