1.7 Water

• what is the structure of a water molecule?

  • H2O Hydrogen atoms are covalently bonded to one oxygen atom
  • polar molecule - oxygen is slightly negative, and hydrogen is slightly positive
  • hydrogen bonds form between water molecules.
• why is water a polar molecule?

  • oxygen has a higher electronegativity than hydrogen so it pulls electrons closer
  • this makes oxygen slightly negative and hydrogen slightly positive
  • opposite charges allow hydrogen bonds to form between molecules.
• What are the key properties of water?

  • high specific heat capacity - maintains stable temperature in organisms and environments, stable body temp for enzyme function.
  • high latent heat of vaporisation - provides cooling effect eg sweating and transpiration
  • cohesion and surface tension - enables water transport in the xylem and organisms to walk on water
  • good solvent - dissolves ions, aiding transport in blood/ plasma. enables metabolic reactions in the cytoplasm.
  • less dense than ice - ice floats, insulating aquatic life/prevents from freezing
• water in metabolic reactions

  used in hydrolysis, condensation, photosynthesis and universal medium for enzyme-controlled reactions.