Water

• Dipolar:

  • the oxygen has a slight negative charge and the hydrogen has a slight positive charge
  • the molecule has positive and negative poles and therefore is dipolar
• Specific heat capacity:

  • water molecules stick together so need more energy to separate them
  • so the boiling point of water is high due to its hydrogen bonds
  • so it takes more energy to heat a given mass of water, so it has a high specific heat capacity
  • water can act as a buffer for sudden temperature changes
• Water in metabolism:

  • breaks down complex molecules via hydrolysis
  • chemical reactions occur in an aqueous medium
  • major raw material in photosynthesis
• Water as a solvent:

  • water readily dissolves other substances such as
  • gases
  • waste
  • inorganic ions
  • enzymes
• Hydrogen bonding:

  • the positive poles of one molecule will be attracted to the negative poles of another molecule
  • the attractive forces between these molecules are called hydrogen bonds
• Latent heat of vaporisation:

  • hydrogen bonds mean a lot of energy is neede to evaporate 1 gram of water
  • evaporation of water such as sweat is therefore effective as body heat is used to evaporate the water
• Cohesion and surface tension:

  • the tendency of molecules to stick together is known as cohesion
  • the hydrogen bonds mean it has large cohesive forces, these allow it to be pulled up through a tube (eg xylem)
  • When water molecules meet air they tend to be pulled back into the body of water instead of escaping it. This is called surface tension
  • it allows water to support small animals
• Not easily compressed, therefore provides support
• Transparent:

  • allows aquatic plants to photosynthesise
• Evaporation:

  • allows organisms to control their temperature