water

• water -

  • medium for metabolic reactions and an important constituent of cells
  • dipole - positively charged end (hydrogen) and a negatively charged end (oxygen)
  • hydrogen bonds form between them - weak on their own but large number of them makes the molecules difficult to separate and gives water a wide range of properties
• water as a solvent -

  • attract charged particles such as ions and other polar molecules such as glucose which dissolve into it
  • acts as a transport medium - in animals plasma transports dissolved substances, in plants water transports minerals in the xylem and sucrose and amino acids in the phloem.
  • non polar molecules such as lipids do not dissolve in water
• • hydrolysis - water splits a molecule - maltose + water = glucose + glucose
  • condensation reaction - water is a product - glucose + fructose = sucrose + water
• water has a high specific heat capacity -

  • large amount of heat energy needed to raise its temperature because hydrogen bonds restrict the movement of the molecules which resists an increase in kinetic energy
  • this prevent large fluctuations in temperature which is important in keeping aquatic habitats stable and allows enzymes in cells to work efficiently
• water has a high latent heat of vaporisation -

  • lot of heat energy needed to change it from a liquid to a vapor
  • this is important in temperature control - evaporating sweat from the skin
• cohesion of water -

  • when there are many hydrogen bonds the molecules stick together in a lattice - it's what allows columns of water to be drawn up the xylem
• high surface tension of water -

  • highest of any liquid except mercury, cohesion at the surface allows insects such as pond skater to be supported
• high density of water -

  • denser than air, provides support and buoyancy for aquatic animals - ice is less dense and a good insulator so stops large bodies of water from completely freezing
• transparency of water -

  • allows light through for aquatic plants to photosynthesise.