Biology B6

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
• …