Biology 2.2.2 Properties of water

  • Created by: AabirA
  • Created on: 03-04-17 15:01


  • As water molecules move around in liquid form they constantly make and break hydrogen bonds
  • Hydrogen bonds make it more difficult for water molecules to escape to become a gas
  • This makes water a liquid at room temperature, with a much higher boiling point than expected
  • Because of this, water can:
    • provide habitats for living things
    • form a major component of tissues
    • provide a reaction medium for chemical reactions
    • provide an effective transport system due to low viscosity
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  • The density of water provides an ideal habitat for living things
  • Water becomes more dense as it gets colder until about 4 C
  • From 4 C to freezing, because of its polar nature, the molecules align themselves in a particular structure
  • This makes ice less dense than water
  • Because of this:
    • aquatic organisms have a stable environment
    • bodies of water are insulated by ice at the top
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  • Water is a good solvent for many substances found in living things
  • These include ionic solutes (salts) or colavent solutes (glucose)
  • Because water is polar its positive and negative parts are attracted to the positive and negative parts of the solutes
  • Because of this, water:
    • forms a major part of tissues (70% of the cytoplasm)
    • provides a reaction medium, including in the cytoplasm of cells
    • provides an effective transport system as minerals and ions can be transported around while dissolved
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Cohesion and surface tension

  • The surface of water contracts because the hydrogen bonds make the surface molecules more attracted to the molecules beneath than the air molecules above, demonstrating cohesion
  • This allows water surface to resist force applied to it, known as surface tension
  • Because of this:
    • water can be but transported, such as up xylem tissue
    • small insects can walk on water, e.g. pond-skaters
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High specific heat capacity

  • The specific heat capacity of a substance is the amount of energy (kJ) needed to raise the temperature of 1kg by 1 C
  • Water's is relatively high, 4.2 kJ
  • This means water doesn't heat up or cool down easily
  • Because of this:
    • living things have a stable internal environment
    • aquatic environments are stable
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High latent heat of vaporisation

  • Large amounts of energy are needed for water to evaporate
  • This is because hydrogen bonds hold the molecules together
  • Because of this, water can:
    • cool living things, e.g. through sweat, keeping temperature stable
    • form a stable environment
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  • Water is an important reactant
  • For example:
    • photosynthesis
    • hydrolysis reactions - digestion
  • Its properties as a reactant don't directly draw on its polarity
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