3.1.7 Water

Question 1

What role does water play in metabolic reactions?

Answer 1

Water is a metabolite involved in condensation reactions where it is removed to form bonds and hydrolysis reactions where it is added to break bonds.

Question 2

Why is water an important solvent in biological systems?

Answer 2

Water is a polar molecule allowing it to dissolve and transport ionic and polar substances essential for metabolic reactions.

Question 3

How does water’s high heat capacity benefit organisms?

Answer 3

Water has a high heat capacity which buffers changes in temperature maintaining a stable internal and external environment.

Question 4

What is the significance of water’s large latent heat of vaporisation?

Answer 4

Water requires a large amount of energy to evaporate providing a cooling effect with minimal water loss via evaporation.

Question 5

How does water’s strong cohesion contribute to transport in plants?

Answer 5

Water molecules exhibit strong cohesion due to hydrogen bonding which supports continuous columns of water in xylem vessels.

Question 6

What is the effect of water cohesion on surface tension?

Answer 6

Strong cohesion between water molecules creates surface tension at air-water interfaces allowing small organisms to move on the surface.

Question 7

Explain five properties that make water important for organisms.

Answer 7

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;