2.4 Water and it's Functions

2.4 Water and it's Functions

1. The Dipolar water molecule

   • A water molecule is made up of one Oxygen atom, and two hydrogen atoms
     • oxygen has slightly negative charge, hydrogen has a slightly positive charge
       • This means a water molecule has both negative and positive poles = dipolar

2. Hydrogen Bonding

   • Different poles attract
   • Positive pole of one H2O Molecule is attracted to negative pole of another water molecule
     • This is a hydrogen bond
   • Although each H bond is fairly weak, together they form important forces that cause the water molecules to stick together
   • These bonds give water its unusual properties

3. Specific Heat Capacity of Water

   • Hydrogen bonds between water molecules can absorb a lot of energy
     • Water has a high specific heat capacity
       • this means it takes a lot of energy to heat it up
         • So water doesnt experience rapid temperature changes
           • This means it is a good habitat, as the temperature underwater would be more stable
           • It also means the water inside organisms is a fairly stable temperature - helping them to maintain a constant internal body temperature

4. Latent Heat of Vaporisation of Water

   • Water has high latent heat of vaporisation
     • takes a lot of energy to break the H bonds between H2O molecules
       • a lot of energy is used up to evaporate water
         • Effective means of cooling when sweating as body heat is used to evaporate the water

5. Cohesion and Surface tension

   • Cohesion - the attraction between molecules of the same type
     • H2O molecules are very cohesive (tend to stick together) because they're polar
   • Strong cohesion helps water flow = great for transporting substances
     • E.g/ Its how water travels in columns up the xylem in plants
   • Strong cohesion = water has high surface tension when it comes into contact with air
     • This is the reason why sweat --> droplets
     • Reason why pond skaters and some other insects can 'walk' on the surface of a pond

6. Water is an important METABOLITE

   • Produced in condensation reactions
     • forming a new bond
   • Used in hydrolysis reactions
     • breaking a bond

7. Water as a solvent

   • dissolves gases e.g/ O2 and CO2
   • dissolves wastes e.g NH3
   • disolves inorganic ions and small hydrophilic molecules e.g/ Amino acids, monosaccharides and ATP
   • dissolves enzymes, whose reactions take place in solution