3.5 Summary Questions & Exam Style Questions

Question 1

Using your knowledge of the structure of fatty acids, describe why oils are liquids and fats are solid at room temperature. [4]

Answer 1

Oils are (usually) unsaturated (1); unsaturated fatty acids contain double bond(s) (1); molecules
cannot pack closely (1); fats are usually saturated so fatty acids have no double bonds (1).

Question 2

Describe the formation and the hydrolysis of an ester bond. [4]

Answer 2

Hydroxyl group from glycerol (1); hydroxyl group from fatty acid (1); condensation reaction (forms
ester bond) (1); idea that hydrolysis is reverse of the process described (1).

Question 3

Suggest why phospholipids in the membranes of extremophiles can withstand extremes of temperatures and pH. [2]

Answer 3

Cross links (1); stabilise membrane (1)

Question 4

Read the following statements.
Lipids are not soluble in water.
Lipids and ethanol are soluble in water.
Water is more soluble than lipids in ethanol.

Use the information to explain how the emulsion test for lipids works. [4]

Answer 4

procedure for emulsion test statement 2, sample / lipid, dissolved in ethanol (1); water is mixed with
ethanol (and lipid) solution (1); statement 3, idea that water displaces lipid from ethanol forming
suspension (1); statement 1, (suspension forms because) lipids not soluble in water (1)