1.6 Water

Question 1

Why is water important?

Answer 1

• As a reactant in cells (e.g. photosynthesis, hydrolysis).
• Provides structural support in cells.
• Keeps organisms cool to maintain an optimum body temperature.

Question 2

What are the 5 special properties of water?

Answer 2

5 special properties of water are:
- Metabolic importance.
- High heat capacity.
- Heat of vaporization.
- Cohesive properties.
- Useful as a solvent.

Question 3

What molecules is water made of?

Answer 3

One oxygen atom.
Two hydrogen atoms.

Question 4

How is water a polar molecule?

Answer 4

The oxygen atoms in water are slightly negatively charged.
The hydrogen atoms in water are slightly positively charged.

Question 5

What causes hydrogen bonding between water molecules?

Answer 5

The polarity of water molecules means that a hydrogen atom on one water molecule is attracted to the oxygen atom on another water molecule.
This attraction is called hydrogen bonding.

Question 6

How is water a good metabolite?

Answer 6

Water is used or formed in many metabolic reactions, such as condensation and hydrolysis reactions.

Question 7

Why is water’s high heat of vaporisation important?

Answer 7

The specific latent heat of vaporisation is the amount of energy needed to change 1 kg of a liquid substance to a gas.
As liquid water heats up, hydrogen bonding makes it difficult to separate the water molecules from each other. This means that a lot of energy is needed for water to evaporate.
When water evaporates, energy is used up - this cools the environment where the evaporation is taking place.
This is why sweating helps with body temperature regulation.

Question 8

Why is water’s high specific heat capacity important?

Answer 8

Specific heat capacity is the amount of heat one gram of a substance must absorb or lose to change its temperature by 1oC.
Water has a high heat capacity so takes a long time to heat and cool.

Question 9

How is water a good solvent?

Answer 9

Water is a good solvent because ions and polar molecules can easily dissolve in it.

Question 10

Why are water’s cohesive properties important?

Answer 10

The strong attraction between water molecules due to hydrogen bonds is called cohesion.
Plants use this when transporting water from roots to leaves.