LipidsEdexcel A-Level Biology B: Subtopic test

1. 1
   A food technologist is comparing two cooking fats. Butter is solid at room temperature and contains mostly saturated fatty acids, whereas olive oil is liquid at room temperature and contains mostly unsaturated fatty acids.

   (a)

   Which type of bond joins a fatty acid to glycerol in a triglyceride?

   [1 mark]

   • AGlycosidic bond
   • BPeptide bond
   • CEster bond
   • DHydrogen bond

   (b)

   Which statement describes an unsaturated fatty acid?

   [1 mark]

   • AIts hydrocarbon tail contains at least one C=C double bond
   • BIts hydrocarbon tail contains only single bonds between carbon atoms
   • CIt has a phosphate group in place of the carboxyl group
   • DIt is joined to glycerol by a glycosidic bond

   (c)

   Explain why olive oil is liquid at room temperature but butter is solid.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A camel stores fat in its hump, which it can use as an energy reserve in the desert. A seal living in cold Arctic water has a thick layer of fat, called blubber, under its skin.

   (a)

   Why do triglycerides release more energy per gram than carbohydrates when they are respired?

   [1 mark]

   • AThey are soluble in water so they are respired faster
   • BThey contain more oxygen atoms per molecule
   • CThey are polymers made of many identical units
   • DThey contain a higher proportion of C–H bonds

   (b)

   Which property of triglycerides makes them effective as a waterproofing layer?

   [1 mark]

   • ATheir hydrophilic phosphate heads attract water
   • BTheir hydrocarbon chains are hydrophobic and repel water
   • CThey form hydrogen bonds with water molecules
   • DThey are made of polar fatty acids

   (c)

   Explain how the blubber helps the seal to survive in cold water.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student uses a model kit to build a triglyceride. The model contains one glycerol molecule and three fatty acid molecules. Two of the fatty acids each contain one C=C double bond in the hydrocarbon chain and the third has no C=C double bonds.

   (a)

   Describe how the glycerol and fatty acids in the model are joined to form a triglyceride.

   [3 marks]

   (b)

   State the number of water molecules released and the number of ester bonds formed when the model triglyceride is made, and explain whether the triglyceride is saturated or unsaturated.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Phospholipids are the main component of cell surface membranes. A scientist adds phospholipid molecules to water and observes that they spontaneously form small spheres with a double layer of phospholipids enclosing a droplet of water. These spheres, called liposomes, can be used to carry drugs into cells.

   (a)

   Describe the structure of a phospholipid and explain why phospholipids form a double layer in water.

   [6 marks]

   (b)

   Explain how the structure and properties of phospholipids make them suited to forming cell membranes, and evaluate why liposomes can deliver drugs into cells.

   [6 marks]

   Total for question 4: 12 marks

End of questions