Topic 1---B: More biological molecules- 4. Water

Question 1

What is the importance of water?

Answer 1

• Water is a metabolite in loads of important metabolic reactions (including hydrolysis and condensation reactions).
• Water is a solvent which means some substances dissolve in it and most metabolic reactions take place in a solution
• Water helps with temperature control because of a high latent heat of vaporisation and a high specific heat capacity.
• Water molecules are very cohesive which helps transport in plants

Question 2

What does a molecule of water consist of?

Answer 2

1 atom of oxygen joined to 2 atoms of hydrogen by shared electrons

Question 3

What makes water a polar molecule?

Answer 3

• Because the shared negative hydrogen electrons are pulled towards the oxygen atom, the other side of each hydrogen atom is left with a slight positive charge.
• The unshared negative electrons on the oxygen atom give it a slight negative charge.

Question 4

Hydrogen bonding in water

Answer 4

• Hydrogen bonds are weak bonds between a slightly positively charged hydrogen atom in one molecule and a slightly negatively charged atom in another molecule.
• Hydrogen bonds form between water molecules because the slightly negatively charged oxygen atoms of water attract the slightly positively charged hydrogen atoms.

Question 5

Properties of water

Answer 5

• Important Metabolite
• Good solvent
• High latent heat of vapourisation
• High specific heat capapcity
• Very cohesive

Question 6

Important metabolite

Answer 6

Many metabolic reactions involve a condensation or hydrolsis reactiom which involves a molecule of water.

Question 7

Good solvent

Answer 7

So can transfer substances

Question 8

High latent heat of vaporisation

Answer 8

• It takes a lot of energy to break the hydrogen bonds between water molecules so a lot of energy is used up when water evaporates.
• Provides a cooling effect without losing too much water.

Question 9

High specific heat capacity

Answer 9

• The energy needed to raise 1g of a substance by 1 degree.
• When water is heated up a lot of energy is used to break the hydrogen bonds between the water molecules so this means there is less heat energy available to actually increase the temperature of the water.
• Can buffer changes in temperature

Question 10

Very cohesive

Answer 10

• Cohesion is the attraction between molecules of the same type
• Strong cohesion helps water to flow making it great for transporting substances.