Water

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  • Polar Molecule
    • one end of the molecule is slightly positively charged and the other is slightly negatively charged.
      • In water, the hydrogen atom = slight positive charge and the oxygen atom = slight negative charge.
        • Because - oxygen atom takes more than its share of the electrons
    • Water
      • As a Solvent
        • Good solvent for ionic and other polar compounds
      • Thermal properties
        • High specific heat capacity
          • A lot of HEAT ENERGY is needed to cause a small temperature rise = more energy therefore more kinetic movement.
            • temperature of organisms remains constant
            • Constant enviromental temperature to aquatic organisms.
        • Density of water = 4 (degrees Celsius)
          • = ice is less dense than water = floats on surface.
          • Ice insulates the water beneath = preventing from freezing right through = organisms can survive.
      • provides support and buoyancy
        • Denser than air = supports organisms as large as whales. Supports and disperses reproductive structures e.g. larvae and large fruits.
        • Transparent to light = aquatic plants can photosynthesis
        • Molecules can slide over each other (low viscosity) - can flow easily through narrow capillaries.
  • Hydrogen Bonds
    • Occurs between the slightly positively charged hydrogen atoms in one molecule and the slightly negatively charged oxygen atom in another.
    • Water
      • As a Solvent
        • Good solvent for ionic and other polar compounds
      • Thermal properties
        • High specific heat capacity
          • A lot of HEAT ENERGY is needed to cause a small temperature rise = more energy therefore more kinetic movement.
            • temperature of organisms remains constant
            • Constant enviromental temperature to aquatic organisms.
        • Density of water = 4 (degrees Celsius)
          • = ice is less dense than water = floats on surface.
          • Ice insulates the water beneath = preventing from freezing right through = organisms can survive.
      • provides support and buoyancy
        • Denser than air = supports organisms as large as whales. Supports and disperses reproductive structures e.g. larvae and large fruits.
        • Transparent to light = aquatic plants can photosynthesis
        • Molecules can slide over each other (low viscosity) - can flow easily through narrow capillaries.
    • Due to the bonds, water has unique properties = biologically important.
  • cohesion
    • wherever water meets air = it behaves like an elastic 'skin'.
    • Pond skaters:  walk on the surface of the water
    • Mosquito larva:               hang from the surface in order to breathe
  • Why?
    • chemical reactions take place in solutions
    • Used for transport e.g. oxygen in the blood in animals, sugar through phloem tubes in plants
  • High latent heat of vapouisation
    • More energy is required to separate the bonds = sweating is a good method of cooling mammals + Transpiration helps to cool green plants.
  • As a Metabolite
    • Takes part in chemical reactions that take place in living things. Water takes part in reactions such as photosynthesis and hydrolysis.

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