Biology B6

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Microscopic life in Water

Advantages and disadvantages of living in water:

  • No risk of water shortage/dehydration
  • Water temp varies less than air temp
  • Water helps provide support
  • Waste products easily disposed of into water
  • Water content of body can vary - needs to be controlled
  • Water = denser than air - resists movement
  • Freshwater - organisms take up too much water by osmosis
  • Salt water - water lost to surroundings by osmosis
  • Ameoba = contractile vacuole - stores excess water
  • Vacuole - fuses with cell membrane, empty water to outside

Variations in number of Organisms

  • Numbers of phytoplankton and zooplankton vary at different depths in different seasons
  • Phytoplankton:
  • Less light in winter, deeper in water
  • Temp lower in winter, deeper in water
  • Minerals used up near end of summer
  • Food webs rely on different food sources:
  • Most rely on green plants
  • Those deeper in ocean feed on marine snow
  • Some rely on bacteria

Water Pollution

  • Sewage and fertiliser run-off = eutrophication = rapid growth of algae, which die and decay
  • Uses up oxygen causing animal deaths (unable to respire)
  • Some species are more sensitive to pollution - used as biological indicators
  • Chemicals ( PBCs/DDT) kill animals:
  • They are toxic
  • Don't break down quickly, accumulate, become concentrated at higher end of food chain


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