BY1 Biological Molecules

Water molecules are polar and they have many uses:
- solvent            - metabolite            - support            - transportation        - thermo-regulation 

Hydrogen atoms are covalently bonded to the oxygen atoms - 2 atoms sharing electrons 

Oxygen pulls shared electrons towards themselves -- through covalent bonds -- as it has more protons. Water molecules becomes polar 

This difference in charge results in each water molecule having a net dipole moment. The net dipole on each water molecule produces an attraction. This attraction is called a hydrogen bond.

Hydrogen Bonds = They occur as a result of an attraction between water molecules due to their net dipole moments.

• They are relatively strong when in large numbers 
• Able to pull water molecules closer together so makes it harder to separate -- high boiling point
• They are responsible for the characteristic crystal lattice structure of ice
• 

Water as a Solvent

> Polar substances like sugar and salt are hydrophilic and are soluble 
> Non-polar such as oil are hydrophobic and insoluble 

Water as a Metabolite

Water is used in many metabolic reactions like in photosynthesis, released in respiration and water helps move reactants around cells. 

Thermal Properties

High heat capacity
A large amount of energy is needed to break the hydrogen bonds so molecules can move faster

             ------> This means that ocean temperatures remain stable so endotherms
                         can maintain a constant body temperature

Thermal Properties - Large latent heat of vaporisation

  ---> Large amount of heat must be absorbed to turn into water vapour. Heat needed to break the hydrogen bonds in order for evaportion - this produces a large cooling effect due to evaporation

  ---> Cooling effect contributes to the stability of lake and pond temperatures - prevents overheating in plants as they transpire and animals as they sweat. 

Ice Floats

At 0c water must lose a large amount of energy before it forms ice crystals
    - Crystalline lattice forms as water reaches 0c  
    - Each hydrogen molecule bonded to maximum of 4 others
    - Bonds far enough apart makes ice 10% less dense than water
    - Ice insulates liquid below preventing whole lakes/ponds etc from freezing over (maintain life)