A-Level Biology AQA Notes

3.1.7 Water

Water
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Water
  • Water molecules consist of 2 hydrogen molecules covalently to an oxygen molecule.
  • The molecules are slightly polar because the oxygen nucleus pulls the shared electrons away from the hydrogen nuclei. Giving the oxygen nuclei a δ- charge, and the hydrogen nuclei a δ+ charge.
  • The polarity of water causes attraction between water molecules. This force of attraction is called a hydrogen bond.
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Property of Water
Why is it useful
Liquid medium​
​Provides habitats for aquatic organisms, medium for chemical reactions & used for transport
Important metabolite​
Used in hydrolysis & condensation reactions
High specific heat capacity​
​Keeps aquatic & cellular environments stable
High latent heat of vaporisation​
Evaporation has a cooling effect on organism
Cohesion of molecules​
​Water is drawn up the xylem
Surface tension​
​Allows pond-skaters to walk on the surface
Good solvent and transport medium​
​Dissolves ionic and polar molecules, allowing them to easily be transported
Good reaction medium
​The cytoplasm in cells is an aqueous solution where many chemical reactions happen
Incompressible
​Can prevent plants from wilting & act as a hydrostatic skeleton for invertebrates

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Water
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