2.1.2 Biological Molecules – Lipids

Question 1

Give three functions of lipids

Answer 1

• Store/source of energy
• Energy store
• Phospholipids in membranes
• Cholesterol in membranes
• Thermal insulation
• Protection of organs
• Hormones e.g. steroids
• Buoyancy
• Waterproofing
• Source of water (from respiration)

Question 2

Why are lipids examples of macromolecules?

Answer 2

They are large organic molecules.

Question 3

What monomers is a triglyceride made up of?

Answer 3

3 fatty acids and 1 glycerol

Question 4

Draw the structure of glycerol

Question 5

If a fatty acid is saturated, what does this mean?

Answer 5

There are only single bonds in the hydrocarbon chain.

Question 6

If a fatty acid is unsaturated, what does this mean?

Answer 6

There is at least one double bond in the hydrocarbon chain (between the carbons).

Question 7

Apart from their bonds, give three differences between saturated and unsaturated fatty acids.

Answer 7

• Saturated fatty acid are more commonly found in animal fats whereas unsaturated are found in plants.
• Saturated fatty acids are solid at room temperature (e.g. form fats) whereas unsaturated fatty acids are liquid at room temperature (e.g. form oils).
• Saturated fatty acids contain more hydrogen atoms than unsaturated fatty acids.

Question 8

What monomers is a phospholipid made up of?

Answer 8

2 fatty acids, 1 glycerol and 1 phosphate group

Question 9

How is the structure of a phospholipid arranged?

Answer 9

The glycerol and phosphate group from a hydrophilic head at one end and the fatty acids form hydrophobic tails at the opposite end.

Question 10

What type of bond forms between the fatty acids and the glycerol in lipids?

Answer 10

An ester bond

Question 11

What is the scientific name for the formation of an ester bond?

Answer 11

Esterification

Question 12

What type of reaction joins the fatty acids and glycerol together to form a triglyceride?

Answer 12

A condensation reaction

Question 13

What type of reaction breaks a triglyceride into fatty acids and glycerol?

Answer 13

A hydrolysis reaction

Question 14

Which biological test is used for lipids?

Answer 14

The emulsion test

Question 15

What is the positive result for the emulsion test?

Answer 15

A white, milky layer at the top of the sample

Question 16

What is the method for the emulsion test?

Answer 16

1. Add the oil to a test tube.
2. Add ethanol and shake well to mix.
3. Fill a second test tube half full of water.
4. Pour the oil and ethanol on top of the water.