Nutrient cycles

• Nitrogen cycle


  1. Nitrogen-fixing

  2. Nitrification

  3. Denitrification

  4. Ammonification
• Important nitrogen containing compounds

  • Amino acids/proteins
  • DNA
  • RNA
  • ATP
• Mycorrhizae


  Fungal associations between plant roots and fungi
• Fungi in mycorrhizae


  • Long thick strands called hyphae which connect them to plant roots
• Relationship between fungi and plant roots

  Mutualistic/symbiotic relationship
• Saprobionts


  Type of decomposer which feed on the remains of dead plants and animals as well as their waste products - faeces and urine
• How saprobionts digest their food

  1. By extracellular digestion

  2. They secrete enzymes and digest their food externally
• Saprobiotic nutrition


  When saprobionts digest organic molecules (amino acids or faeces) into inorganic ions (ammonium ions)
• Saprobiotic nutrition results in more ammonium ions
• Nitrogen fixation


  1. When nitrogen gas is turned into nitrogen-containing compounds

  2. Nitrogen gas to ammonium
• Nitrogen fixing bacteria


  Bacteria which carry out nitrogen fixation
• Where nitrogen fixing bacteria are found


  • Free-living in the soil
  • Found in the root nodules of leguminous plants
• Leguminous plants


  Plants which contain nitrogen fixing bacteria in roots
• Leguminous plants


  • Peas
  • Clover
  • Beans
• Nitrification


  When ammonium ions in the soil are converted into nitrite ions then nitrate ions
• Nitrifying bacteria


  Bacteria which carry out nitrification
• Denitrification


  Nitrogen containing compounds in the soil are converted back into nitrogen gas in the atmospheres
• Anaerobic denitrifying bacteria


  Bacteria which carry out denitrification
• Denitrification is not useful for the plant as nitrogen is returned to the atmosphere so can not be absorbed by the plant
• Ammonification


  When nitrogen from dead organisms and waste is turned into ammonia
• Saprobionts


  Bacteria which carry out ammonification through saprobiotic nutrition
• Phosphorus is found in mineral form as a phosphate ion in sedimentary rocks
• Examples of phosphorus containing compounds

  • ATP
  • DNA
  • RNA
  • Phospholipid bilayer
• Phosphate ions


  Dissolved in oceans, rivers and water in surrounding soil
• Plants absorbing phosphate ions

  1. Via active transports

  2. Incorporate into organic molecules like DNA and RNA
• Animals consuming plants


  Incorporate phosphate ions into their organic materials
• Animal excretion


  1. Contains phosphate ions

  2. Can go back into oceans, rivers and water in surrounding soil
• Guano


  White material rich in phosphorus, can be used as fertiliser
• Decomposition and animal remains

  Rich in phosphates
• Guano and animal remains eroding and breaking down


  Releasing phosphate ions back into oceans, rivers and water in surrounding soil
• Guano forming phosphate ions in sedimentary rocks

  Deposition
• Sedimentary rocks with phosphate ions eroding


  Returning phosphate ions back into oceans, rivers and water in surrounding soil
• Fertilisers on land


  May cause run off phosphate ions into surrounding oceans, rivers and land
• Sediments from oceans and rivers

  1. Forming sedimentary rocks containing phosphate ions over many years

  2. Sedimentation