Water

• What does a molecule of water contain?

  1 atom of oxygen chemically bonded to 2 atoms of hydrogen

  The bonds between the oxygen and hydrogen atoms are covalent bonds

  
• Why is water a polar molecule?

  • In water molecules the oxygen atom has a small negative charge
  • and the hydrogen atoms have a small positive charge
• What do the opposite charges in a water molecule mean?

  • the opposite charges mean water molecules are attracted to each other
  • These forces of attraction are call hydrogen bonds
  • even though hydrogen bonds are quite weak - a small volume of water contains a large number of hydrogen bonds

  A) moving randomly with bonds still present

  
• Properties of water

  • An excellent solvent – many substances can dissolve in water
  • A relatively high specific heat capacity
  • A relatively high latent heat of vaporisation
  • Water is less dense when a solid
  • Water has high surface tension and cohesion
  • It acts as a reagent/metabolite
• How is water a good solvent ?

  1. a lot of important substances in metabolic reactions are ionic (they are made from one positively charged atom and one negatively charged atom)
  2. Because water is POLAR the positive end of the molecule will be attracted to the negative ion - and the negative ion will get attracted to the positive ion
  3. This means the ions will get totally surrounded by water molecules - dissolve

  
• why is it useful water is an important metabolite ?

  1. Many metabolic reactions include a condensation or hydrolysis reaction
  2. Hydrolysis reaction requires a molecule of water to break a bond
  3. Condensation reaction releases a molecule of water as a new bond is formed
  4. examples = amino acids are joined together to make polypeptides (proteins) by condensation reactions - Energy from ATP is released by a hydrolysis reaction
• Why is it good that water has a High Latent Heat of Vaporisation?

  1. It takes a lot of energy (heat) to break the hydrogen bonds between water molecules
  2. Therefore water has a High Latent Heat of Vaporisation - a lot of energy is used up when water evaporates
  3. This is useful for living organisms because it means that they can use water loss through evaporation to cool down (sweat) -without losing too much water
• Why is it good that water has a High Specific Heat Capacity?

  1. the hydrogen bonds between water molecules can absorb a lot of energy
  2. So water has a High Specific Heat Capacity - it takes a lot of energy to heat it up
  3. This means water can buffer (resist) changes in temperature
  4. Useful for living organism - water doesn't experience rapid temperature changes - making it a good habitat as underwater temp is likely to be more stable than on land
  5. The water inside organisms also remains at a fairly stable temperature - helping them to maintain a constant internal body temp
• What is Cohesion and whys it good there's strong cohesion between water molecules?

  • Cohesion = the attraction between molecules of the same type (e.g. 2 water molecules)
  • Water molecules are very cohesive (stick together) because they are POLAR
  • Strong cohesion helps water to flow - making it great for transporting substances (e.g. its how water travels in columns up the xylem in plants)
  • STRONG COHESION = WATER HAS A HIGH SURFACE TENSION - when it comes in contact with air -> reason why sweat forms droplets & reason why pond skaters and other insects can walk on the surface of a pond
• Explain links of water and adhesion...

  Water is also able to hydrogen bond to other molecules, such as cellulose, which is known as adhesion.

  • This also enables water to move up the xylem due to transpiration
• Properties of water and its role in living organisms Table ->

  =