3.1.7 Water

Question 1

Briefly describe the structure of a water molecule.

Answer 1

A molecule of water (H₂O) is one atom of oxygen (O) joined to two atoms of hydrogen (H₂) by shared electrons.

Question 2

Why is water’s high specific heat capacity useful for living organisms?

Answer 2

• Water doesn’t experience rapid temperature changes. This makes water a good habitat because the temperature underwater is likely to be more stable than on land.
• The water inside organisms remains at a fairly stable temperature - helping them to maintain a constant internal body temperature.

Question 3

List the useful properties of water.

Answer 3

• acts as an important metabolite
• has a high latent heat of vaporisation
• can resist changes in temperature
• a good solvent
• a strong cohesion between water molecules

Question 4

In hot temperatures, elephants commonly spray themselves with water. With reference to the structure and properties of water, explain:
- why this behaviour acts as a cooling mechanism for the elephant.
[3 marks]

Answer 4

• As the water evaporates from the surface of the elephant’s body, …
• …some of the elephant’s heat energy is used to break the hydrogen bonds which hold the water molecules together.
• This cools the surface of the elephant’s body.

Question 5

In hot temperatures, elephants commonly spray themselves with water. With reference to the structure and properties of water, explain:
- why water forms droplets when the elephant sprays it from its trunk.
[2 marks]

Answer 5

• There is strong cohesion between water molecules.

- This results in water having a high surface tension when in contact with air, causing it to form droplets.