Water

Question 1

Explain five properties that make water important for organisms.

Answer 1

1. A metabolite in condensation/hydrolysis/ photosynthesis/respiration;
2. A solvent so (metabolic) reactions can occur
   OR
   A solvent so allowing transport of substances;
3. High (specific) heat capacity so buffers changes in temperature;
   For ‘buffer’ accept ‘resist’.
4. Large latent heat of vaporisation so provides a cooling effect (through
   evaporation);
   Reject latent heat of evaporation
5. Cohesion (between water molecules) so supports columns of water
   (in plants);
   For ‘columns of water’ accept ‘transpiration stream’.
   Do not credit ‘transpiration’ alone but accept
   description of ‘stream’.
   For ‘columns of water’ accept ‘cohesion-tension
   (theory)’.
6. Cohesion (between water molecules) so produces surface tension
   supporting (small) organisms;
   For cohesion accept hydrogen bonding
   Ignore reference to pH. Allow other suitable
   properties but must have a valid explanation.
   For example
   * ice floating so maintaining aquatic habitat beneath
   * water transparent so allowing light penetration for
   photosynthesis