The Nitrogen Cycle

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The Nitrogen Cycle
2014-04-30 15:02:50
Biology cycles camturnbull

AQA BIOL4 Nitrogen Cycle
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  1. How is nitrogen stored within organisms
    Within amino acids
  2. What is deamination?
    Ammonia found in excess proteins is released in the liver and converted to urea through the ornithine cycle, finally being excreted
  3. What is saprobiotic digestion?
    Proteins found in dead matter are broken sown into amino acids by decomposing bacteria and fungi
  4. What is ammonification?
    The conversion of amino acids to ammonium ions
  5. Give the three stages of nitrification
    Ammonium ions > Nitrate ions > Nitrate ions
  6. How are ammonium ions converted into nitrates
    Through nitrification carried out by nitrifying bacteria
  7. How is the energy released from nitrification used?
    Bacteria use the energy released from the oxidisation reactions for their own metabolism
  8. What are the nitrates taken up into?
    Root hair cells
  9. Through which process are nitrates absorbed?
    Active transport
  10. How are nitrates converted into amino acids?
    They are reacted with glucose
  11. Give one use for amino acids
    Protein synthesis
  12. Where does denitrification of soil occur?
    Within waterlogged soil in which there is no oxygen to support aerobic nitrifying bacteria
  13. What are nitrates converted into during denitrification and by what are they converted?
    • Nitrogen gas
    • Denitrifying bacteria
  14. What happens to nitrogen gas produced during denitrification?
    It escapes into the atmosphere and is lost
  15. How is nitrogen gas converted into ammonia?
    Through a reduction reaction known as nitrogen fixation
  16. Where do nitrogen fixing bacteria live?
    Within root nodules of leguminous plants such as clover and pea
  17. How is the relationship between nitrogen fixing bacteria and leguminous plants an example of mutualism?
    • Both organisms benefit:
    • The plant obtains ammonia that can be used to synthesise amino acids
    • The bacteria obtain sugars that can be used as an energy source
  18. Why must fertiliser be added to crops?
    In nitrate levels fall productivity is limited
  19. What effects does rain have on nitrates?
    Soluble nitrates are leeched into fresh water sources
  20. Why are artificial fertilisers less likely to be leeched?
    They are less water soluble
  21. State two actions that increase the rate of leeching
    • Removal of hedgerows 
    • Loss of organic matter and humus of soil
  22. Describe the process of eutrophication
    • Nitrates are leeched into fresh water
    • This causes excessive growth of algae
    • This mass of algae blocks light to organisms at greater depths
    • Water plants and algae lower in the water can no longer photosynthesise 
    • Algae and water plants eventually die and sink to the bottom of the water 
    • Aerobic saprobiotic bacteria decay the algae and reproduce rapidly 
    • Increased numbers of bacteria absorb the oxygen in the water for use in respiration eventually depleting it as no photosynthesis is occurring 
    • Aquatic animals cannot respire aerobically and die
  23. What effects does the presence of sewage in a water source have?
    • Bacteria will feed directly from the organic matter contained within
    • This decreases oxygen levels