In a water molecule, the oxygen atom has a slightly negative charge, whilst the hydrogen atoms have a slightly positive charge.

Water is directly involved in metabolic reactions.

Water is either used up in hydrolysis reactions or produced during condensation reactions. 

Because it dissolves more substances than any other liquid.

Because most biological reactions take place in solution. 

Dissolved substances can be transported around the body.

A lot of energy is required to raise the temperature of water.   

Because there are many hydrogen bonds between water molecules. 

These bonds absorb a lot of energy before being broken.

High specific heat capacity allows organisms to maintain a fairly stable body temperature as their bodies are made up mostly of water.

1. Water has a relatively high specific heat capacity

Ignore numbers relating to heat capacity

2. Can gain / lose a lot of heat / energy without changing temperature

OR Takes a lot of heat / energy to change temperature

Accept due to H bonding between water molecules

A lot of energy is needed to break the hydrogen bonds to change water from liquid to gas.

Provides a cooling effect via evaporation, without losing too much water. 

The tendency of water molecules to stick together.

The tendency of water molecules to stick to other materials. 

Water cohesion supports columns of water in the tube-like transport cells of plants and produces surface tension where water meets air.

Property: Polar molecule

Importance: Acts as a universal solvent

Property: Universal solvent

Importance: Metabolic reactions occur faster in solution

Property: Reactive

Importance: Takes part in hydrolysis / condensation / named reaction

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

Property: High specific heat capacity

Explanation: Buffers changes in temperature

Accept ideas such as a lot of energy needed/gained to change temperature

Buffers changes in temperature

Accept descriptions of buffering changes in temperature, e.g. resists temperature changes

Water has ahigh specific heat capacity and a high latent heat of vaporisation. 

This means that water does not change temperature or evaporate easily.

Floating ice forms an insulating layer that prevents the underneath water from freezing, allowing aquatic organisms to survive and move.