Nutrient Cycles

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  1. What are complex organic molecules broken down by?
    Saprobiotic microbes
  2. Give 2 examples of decomposers

  3. How do saprobiotic microbes absorb nutrients from a dead organism?
    Enzymes are secreted

    These enzymes break down complex molecules into more simple ones such as monosaccharides via hydrolysis 

    The molecules are taken in through active transport
  4. How is the carbon returned to the atmosphere?
    The microbes respire, releasing carbon dioxide
  5. Give one reason for short term fluctuations in carbon dioxide concentrations within the atmosphere
    Varying rates of respiration: levels are higher at night as plants cannot photosynthesise without sunlight
  6. Give two reasons for long term change in carbon dioxide concentrations within the atmosphere
    Deforestation: this reduces the amount of carbon dioxide used by trees for photosynthesis 

    Increased combustion of fossil fuels
  7. The increased concentration of which two gases in the atmosphere causes the greenhouse effect?
    Carbon Dioxide

  8. How is methane produced by microbes
    As a product of anaerobic respiration
  9. Give two significant producers of methane?
    The intestines of cattle 

    Waterlogged rice fields
  10. Describe the changes to radiation of UV rays caused by greenhouse gases
    The UV rays from the sun are radiated back into space from the surface of the earth

    The greenhouse gases absorb the heat energy from these rays 

    The energy is then re-radiated back to the Earth's surface
  11. What does the re-radiation of UV rays cause?
    Gradual warming of the Earth's surface (Global Warming)
  12. What benefits will global warming have on crops and why?
    The rates of light independent reactions will increase due to increased enzyme activity caused by an increase in kinetic energy
  13. Why will global warming reduce productivity of crops?
    Rates of respiration will be increased
  14. Give three reasons that global warming may cause plant death
    • Temperatures denaturing enzymes
    • Increased evaporation of water
    • Rising sea levels flooding areas with salty water
  15. How may a rise in temperature benefit crops in some areas
    • A rise in temperature in an area previously too cool to support a high yield of crops due to enzyme inactivity would increase yield
    • All plants benefit from higher carbon dioxide levels
  16. How may temperate rise cause an increase in the number of insect pests?
    • More insects and their larvae will survive winter
    • More will be present in the following year laying more eggs
  17. How may the distribution of Xerophytes change due to rising temperatures?
    Areas that become prone to drought would have increased numbers of these plant species
  18. How may the distribution of halophytes change as a result of rising temperatures?
    Areas flooded with sea water would be colonised by halophytes
  19. How may the ranges of animal species change as a result of rising temperatures
    Animals may migrate northwards in the northern hemisphere to follow the distribution of plant species on which they feed
  20. How is nitrogen stored within organisms
    Within amino acids
  21. What is deamination?
    Ammonia found in excess proteins is released in the liver and converted to urea through the ornithine cycle, finally being excreted
  22. What is saprobiotic digestion?
    Proteins found in dead matter are broken sown into amino acids by decomposing bacteria and fungi
  23. What is ammonification?
    The conversion of amino acids to ammonium ions
  24. Give the three stages of nitrification
    Ammonium ions > Nitrate ions > Nitrate ions
  25. How are ammonium ions converted into nitrates
    Through nitrification carried out by nitrifying bacteria
  26. How is the energy released from nitrification used?
    Bacteria use the energy released from the oxidisation reactions for their own metabolism
  27. What are the nitrates taken up into?
    Root hair cells
  28. Through what process are nitrates absorbed?
    Active transport
  29. How are nitrates converted into amino acids
    They are reacted with glucose
  30. Give one use for amino acids
    Protein synthesis
  31. Where does denitrification of soil occur?
    Within waterlogged soil in which there is no oxygen to support aerobic nitrifying bacteria
  32. What are nitrates converted into during denitrification and by what are they converted?
    • Nitrogen gas
    • Denitrifying bacteria
  33. What happens to nitrogen gas produced during denitrification?
    It escapes into the atmosphere and is lost
  34. How is nitrogen gas converted into ammonia?
    Through a reduction reaction known as nitrogen fixation
  35. Where do nitrogen fixing bacteria live?
    Within root nodules of leguminous plants such as clover and pea
  36. 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 and the bacteria obtain sugars that can be used as an energy source
  37. Why must fertiliser be added to crops?
    If nitrate levels fall, productivity will be limited
  38. What effects does rain have on nitrates?
    Soluble nitrates are leeched into fresh water
  39. Why are artificial fertilisers less likely to be leeched?
    They are less soluble
  40. State two actions that increase the rate of leeching
    • Removal of hedgerows
    • Loss of organic humus in soul
  41. 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
  42. What effects does the presence of sewage in a water source have?
    Bacteria will feed directly from the organic matter contained within decreasing oxygen levels
Card Set
Nutrient Cycles
BIOL4 Populations and environments
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