Properties of Water

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  • Created by: SYusuf
  • Created on: 26-10-15 16:19
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  • Water
    • Latent Heat of Vaporisation
      • The energy required to transform a given quantity of water from a liquid to a gas.
        • Because the molecules are held together by hydrogen bonds a lot of energy is needed to of water molecules to evaporate
          • Therefore water is useful to cool down living organisms to maintain homoeostasis
            • Plants are cooled when water evaporates from mesophyll cells in transpiration
            • Humans sweat to cool down their body temperature
    • Liquid
      • Hydrogen bonds are constantly broken and remade when water molecules move in liquid.
        • These bonds make it difficult for the molecules to escape as gas. Other molecules of similar size (such as H2S) are gas at room temperature.
          • Because water is liquid at room temperature it is able to:
            • Provide a medium for chemical reactions
            • Form a major component of living tissues
            • Provide a medium for transport e.g in blood plasma
            • Provide a habitat, e.g. in rivers, lakes and seas.
    • Density
      • The density of water is perfect for aquatic organisms to be able to float.
      • Unlike most liquids which become more dense when they cool, water becomes less dense between 4-0 degrees. This allows ice to float on top of water.
        • Aquatic animals have a stable environment to live in the winter (under and atop the layer of ice)
        • Bodies of water are insulated against extreme cold by a layer of ice which reduces the rate of heat loss.
    • Solvent
      • Water is a good solvent for ionic molecules and covalent molecules.
        • Because water is polar it is attracted to the  slightly charged parts of the solutes. They cluster around these charged parts and will separate them and keep them apart.
          • This helps molecules and ions move around and react together in water e.g in the cytoplasm
          • This also helps molecules and ions to be transported around the body while dissolved in water/
    • Cohesion & Surface Tension
      • Hydrogen bonding pulls water molecules together
        • This causes them to stick together (cohere) instead of spreading out
        • This also means that water contracts as molecules on the surface are pulled inwards by hydrogen bonds to molecules beneath.
          • This means water is able to resist force applied to it, this property is known as surface tension.
            • This allows:
              • Columns of water in plant vascular tissue to be pulled up the xylem together from the roots.
              • Insects like pond skaters to walk on water.
    • Specific Heat Capacity
      • The amount of energy needed to raise the temperature of 1 kg of water by 1 degree celcius.
        • Due to hydrogen bonds water has a high SHC of 4.2 kJ. This means it does not heat up or cool down easily
          • Because the main component of living organisms is water this makes it easier to maintain a constant temperature needed for enzyme controlled reactions.
    • Reactant
      • Water is important for the digestion of large biological molecules (such as starch, proteins and lipids) through hydrolysis.
      • Water is a reactant in photosynthesis which is important for the synthesis of glucose
  • A lot of water's properties are due to its polar nature, which allows for the formation of hydrogen bonds




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