nutrient cycles

• Why do farmers apply fertilisers?

  to replace nutrients removed from the soil when livestock are removed and crops harvested
• explain eutrophication

  mineral ions from excess fertiliser leach into bodies of water causing algal bloom

  algal bloom blocks sunlight therefore plants below the surface of water cannot photosynthesise

  algae runs out of nutrients and begins to die

  saprobionts feed on dead organic matter and increase in number

  saprobionts respire aerobically so use up dissolved oxygen in water

  dissolved oxygen decreases causing aquatic organisms to die
• what does phosphorus mainly exists as ?

  mainly exists as phosphate ions in sedimentary rock deposits
• how do phosphate ions become available for absorption ?


  weathering and erosion of these rocks help phosphate ions become dissolved
• summarise phosphorus cycle

  1. Rocks contain phosphate. Harsh weather conditions break down rocks, releasing phosphate into the soil.
  2. Some phosphate is absorbed by plants to make phosphate-containing compounds like ATP.
  3. Plants are eaten by animals, which can then make their own phosphate-containing compounds.
  4. Both plants and animals die, and animals also excrete.
  5. The waste of animals and plants is broken down by saprobionts, releasing phosphate back into the soil.
  6. Some phosphate moves throughout the soil to bodies of water, like the sea.
  7. Over thousands of years, phosphate is used to form new rocks.
• how do animals obtain phosphorus ?

  feeding on plants
• Saprobionts release phosphates into the soil. What happens to these phosphates?

  They move throughout the soil to bodies of water, like the sea .

  They are reabsorbed by plants to make phosphate-containing compounds .
• Describe the stages of the phosphorus cycle.

  phosphate ions in rocks are dissolved into the soil by weathering and erosion phosphate ions are absorbed by plants - to form ATP and other phosphorus containing matter animals feed on plants and create own phosphate containing compound  

  animals excrete and die

  animal waste dissolved into the soil broken down by saprobionts and released back into the soil

  Some phosphate moves throughout the soil to bodies of water, like the seaOver thousands of years phosphate is used to form new rocks - after which the phosphorus cycle repeats
• A natural event occurs that causes weathering to local mountains and produces rockfalls. Some time later, nearby crops start to grow better than identical crops further away.Suggest why, using your knowledge of the phosphate cycle

  1. Rock contains phosphate.
  2. The area near rock weathering and rockfalls is likely to receive additional phosphate into the soil.
  3. As a result, nearby crops are able to absorb more phosphate (compared to crops further away).
  4. If all other conditions are the same, crops that absorb more phosphate will be able to produce more ATP to grow. In contrast, identical crops further away will receive less phosphate and grow at a slower rate
• Describe how dead organisms are utilised in the phosphorus cycle

  Dead organisms within the soil attract saprobionts.These saprobionts break down phosphorus-containing compounds to phosphate.The phosphate is either moved into bodies of water to form rocks, or directly absorbed by plants through the soil.
• what is the process of converting nitrogen gas into ammonia ?

  nitrogen fixation
• Mutualistic bacteria provide ammonia directly to the plant. Where do mutualistic bacteria live?

  roots of the plant
• Describe how nitrogen gas is converted into ammonium ions during the nitrogen cycle

  Free-living nitrogen-fixing bacteria exist in the soil and convert nitrogen gas to ammonia

  This ammonia is then converted to ammonium ions in the soil
• Describe how ammonium ions are converted into a nitrogen-containing compound which plants can absorb

  Plants absorb nitrogen through nitrates in the soil

  First, ammonium ions are converted to nitrite, which is then converted to nitrate

  The process of converting ammonium ions to nitrate is known as nitrification

  The bacteria that carry out nitrification are called nitrifying bacteria

  In order to carry out nitrification, nitrifying bacteria need oxygen.
• what is Free-living nitrogen-fixing bacteria called ?

  Azotobacter
• what is Mutualistic nitrogen-fixing bacteria called ?

  Rhizobium
• what is the nitrifying bacteria called that converts ammonium ions to nitrite ?

  Nitrosomonas
• what is the nitrifying bacteria called that converts nitrite to nitrate ?

  Nitrobacter
• describe the role of saprobionts in the nitrogen cycle

  1. saprobionts contain nitrogen-containing compounds such as amino acids and DNA
  2. producing ammonium ions
• Describe how nitrogen is returned to the soil via death and excretion

  Nitrogen-containing compounds in waste/excreted products/dead plants or animals, are broken down by saprobionts.

  This forms ammonia which is released into the soil, forming ammonium ions.

  This process is known as ammonification.
• In the nitrogen cycle, describe how nitrate is converted to nitrogen gas

  by a process called denitrification , nitrate is converted into nitrogen gas by denitrifying bacteria which under go anaerobic respiration
• summarise the nitrogen cycle

  1. Free-living nitrogen-fixing bacteria and mutualistic nitrogen-fixing bacteria convert nitrogen gas into ammonia. When released into water in the soil, ammonia forms ammonium ions.
  2. Nitrifying bacteria convert ammonium ions into nitrate. This process requires oxygen.
  3. Saprobionts break down nitrogen-containing compounds, such as DNA, in waste material to ammonia. When released into water in the soil, ammonia forms ammonium ions.
  4. Denitrifying bacteria convert nitrate to nitrogen gas when they carry out anaerobic respiration.
• Describe the nitrogen cycle

  Free-living nitrogen-fixing bacteria and mutualistic nitrogen-fixing bacteria convert nitrogen gas from the atmosphere into ammonia. This is known as nitrogen fixation.

  When released into water in the soil, ammonia forms ammonium ions.

  Nitrifying bacteria convert ammonium ions into nitrite which is then converted into nitrate.

  This process is called nitrification, which requires oxygen.

  Saprobionts break down nitrogen-containing compounds in waste material (such as DNA) into ammonia.

  When released into water in the soil, ammonia forms ammonium ions.

  This process is called ammonification.

  Finally, denitrifying bacteria convert nitrate to nitrogen gas when they carry out anaerobic respiration.

  This process is called denitrification.
• Which two processes produce ammonium ions in the nitrogen cycle?

  ammonification and nitrogen fixation
• In areas where the soil is less aerated, plants have stunted growth. Suggest why.


  Denitrifying bacteria respire anaerobically, so less aerated soil would mean more denitrification

  Additionally, there would be less nitrification as nitrifying bacteria respire aerobically

  Overall, this leads to less nitrate available in the soil for the plants to absorb for growth
• Mycorrhizae are fungi associated with the roots of plants. They are especially important in areas that have poor water and ion supply. Suggest why

  Mycorrhizae provide a large surface area in roots to increase water and ion uptake
• describe the nature and role of mycorrhizae in nutrient cycling

  • mycorrhizae are fungi which are connected to plant roots
  • mycorrhizal relationship is symbiotic because plants benefit from improved water and inorganic ion uptake whilst fungi receive sugars and amino acids