Biological Molecules; Physical Properties of Water

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  • Physical Properties of Water
    • Polar molecule forming hydrogen bonds. Non-linear molecule.  H-bonds are weak but together make water very stable. Oxygen more negative due to more electrons; hence unequal negative charge. H-bonds formed due to electrostatic attraction
      • Hydrogen bonds in a water molecule.
        • Weak hydrogen bonds allow water to exist as a liquid
    • A good solvent
      • An excellent solvent for other polar molecules and ions. e.g Nitrates/Mg2+/  O2/CO2
        • Allows metabolic reactions to take place. Allows ions to be mobile. Used as a transport system e.g blood, lymph, xylem, phloem.
    • High specific heat capacity.
      • A large amount  of energy is required to raise the temperature of  water by 1oC; slow to warm up and slow to cool down
        • Allows for minimum fluctuations of temperature within cells and large bodies of water called thermal stability buffer. [enzymes = temperature sensitive]
    • High latent heart of vapourisation
      • H-Bonds attract water molecules so difficult to escape as vapour. Hence high boiling point.
        • Allows organisms to evaporate water in the cooling process e.g sweating (thermoregulation)
    • High latent heat of fusion
      • Energy required in changing a liquid into a solid.
        • Reduces chances of ice crystals forming in cells.
    • Water molecules are attached to each other; know as COHESION
      • Due to H-bonding.
        • Surface tension exists on the surface of water e.g pondskaters and transpiration stream.
    • Water molecules attached to other surfaces; known as ADHESION
      • Due to H-bonding
        • A driving force for the upward movement of water in xylem vessels.
    • Capillarity properties- particularly in very narrow vessels.
      • Due to adhesive forces causing  high tensile strength. Very difficult to break column of water.
        • Allows upward movement of unbroken columns of water in very fine vessels e.g xylem vessels.
    • The density of water decreases as the temperature falls below 4oC . Water expands as it freezes; maximum density is at 4oC
      • Ice therefore floats on the top of a pond. Water molecules in ice fit better together than in water; but spread out into a crystal structure
        • Ice can insulate the pond below. Water below doesn't freeze. Allows nutrient to circulate.
    • Cannot be easily compressed.
      • Due to cohesive forces
        • Used as a support structure in hydrostatic skeletons e.g jellyfish and earthworms. Bouyancy
    • Acts as a lubricant.
      • Due to cohesive and adhesive forces.
        • Synovial fluid. Mucus. Pericardial fluid. Amniotic fluid.
    • Transparency
      • Allows for photosynthesis in aquatic plants and visibility of aquatic organisms.
        • Different wavelengths penetrate the sea at different depths.
    • Takes part /chemical reagent in chemical reactions
      • Photosynthesis
        • 6H2O + 6CO2 ---> C6H12O6  + 6O2
    • Involved in the breaking of chemical bonds.
      • Hydrolysis; addition of water.
        • Catabolic reactions
    • Involved in the formation of bonds.
      • Condensation; removal of water
        • Anabolic reactions
    • Low viscosity
      • Due to freedom of movement of water molecules. H-bonds break and reform
        • Allows free movement of organisms (to swim)
    • Structure and support in plant cells.
      • Makes plant cells turgid.


Faith Thompson


Brilliant mindmap!!

Bethany Cunningham


This will definitely help in my revision, I am glad you have related what this means in terms of the effects on organisms.



A very useful Mind map on the physical and chemical properties of water which have been usefully linked to the possible biological consequences. Colour has been used effectively to separate the key ideas. Adding little images to the downloaded map would make it even more memorable. "Water and living organisms"  is a title often set as a synoptic essay at A2 so this would be a useful  resource to use as a basis for a practice essay.

martin phiri


this is a way to now

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