Water

• Water is a polar molecule: oxygen atom has a partial negative charge, while hydrogen atoms have partial positive charges. Hydrogen bonds form between water molecules due to these charges.
• High specific heat capacity:

  • many hydrogen bonds mean lots of energy is needed to break them, so water acts as a buffer against rapid temperature changes
  • provides good habitat for aquatic organisms, as temperature under water is stable
  • ensures stable temperature inside organisms, which helps maintain constant internal body temperature
• High latent heat of vaporisation:

  • many hydrogen bonds mean lots of energy is needed to break them, so lots of heat energy is needed to evaporate water
  • organisms can use water loss through evaporation to cool down without losing too much water
  • eg sweating is an effective cooling mechanism
• Good solvent:

  • due to its polarity, many ions and covalently bonded polar substances can dissolve in water
  • this allows chemical reactions to occur within cells
  • this allows metabolites to be transported efficiently
• Strong cohesion:

  • hydrogen bonds allow strong cohesion between water molecules
  • allows transport of substances eg columns of water to travel up the xylem in plants
  • allows high surface tension where water meets air to support small organisms (eg pond skaters can skate over water)
• Metabolite

  • water is involved in many metabolic reactions
  • eg. condensation reactions: a water molecule is released as a new bond is formed
  • eg. hydrolysis reactions: a water molecule is added to break a bond
• Functions of water:

  1. High specific heat capacity
  2. High latent heat of vaporisation
  3. Good solvent
  4. Strong cohesion
  5. Metabolite
• Extra functions of water

  • Ice floating: maintain aquatic habitat beneath
  • transparent: allows light to penetrate for photosynthesis