Water - functions and properties.

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  • Water
    • A dipole
      • A polar molecule with a positive and negative charge, separated by a very small distance.
      • No overall charge
    • Hydrogen Bonds
      • The weak attractive force between a  ?+ hydrogen atom of one molecule and a  ?- oxygen atom on another.
    • Essential properties for life as we know it.
      • A solvent
        • Chemical reactions take place in solution. Transport medium eg. animal plasma and xylem and poem in plants.
      • As a metabolite
        • Reactant in many biochemical reactions e.g. with carbon dioxide to produce glucose.
        • Hydrolysis e.g. - maltose + water = glucose + glucose.
        • Condensation.e.g. glucose + fructose = sucrose + water
      • High specific heat capacity
        • A large amount of heat energy is needed to raise the temperature. Prevents large fluctuations in water temperature, important in stability of aquatic environments.
      • High latent heat of vaporisation
        • A lot of energy required to change state from liquid to a vapour. Important in temperature control.
      • Cohesion
        • Water can be drawn up in columns via xylem vessels due to H-bonds.
      • High surface tension
        • At ordinary temperatures water has the highest liquid tension (apart from mercury). Supports insect bodies e.g. pond skater.
      • High density
        • Denser than air, provides support for aquatic organisms. Maximum density 4C.
        • Ice less dense than water so floats, proving  a good insulator. Organisms beneath can survive.
      • Transparent
        • Allows light to pass through and for photo synthesis


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