LipidsAQA A-Level Biology: Subtopic test

1. 1
   Fatty acids have the general formula R–COOH, where R is a hydrocarbon chain. Palmitic acid is CH₃(CH₂)₁₄COOH. Oleic acid is CH₃(CH₂)₇CH=CH(CH₂)₇COOH.

   (a)

   Which statement about these fatty acids is correct?

   [1 mark]

   • ABoth are saturated
   • BPalmitic acid is unsaturated and oleic acid is saturated
   • CBoth are unsaturated
   • DPalmitic acid is saturated and oleic acid is unsaturated

   (b)

   What is the name of the bond formed between glycerol and a fatty acid?

   [1 mark]

   • AGlycosidic bond
   • BEster bond
   • CPeptide bond
   • DPhosphodiester bond

   (c)

   Explain why oleic acid is described as an unsaturated fatty acid.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A triglyceride is made from one molecule of glycerol and three molecules of palmitic acid. To the nearest whole number the relative formula masses are: glycerol 92, palmitic acid 256 and water 18.

   (a)

   How many molecules of water are released when one of these triglyceride molecules is formed?

   [1 mark]

   • AOne
   • BTwo
   • CThree
   • DFour

   (b)

   What is the relative formula mass of the triglyceride?

   [1 mark]

   • A806
   • B860
   • C842
   • D914

   (c)

   Describe how the emulsion test could be used to show that a sample contains a triglyceride.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Phospholipids and triglycerides both contain fatty acids joined to glycerol. In a phospholipid one fatty acid is replaced by a phosphate-containing group. Phospholipids form the cell surface membrane, whereas triglycerides are stored in fat cells.

   (a)

   Describe how the structure of a phospholipid differs from the structure of a triglyceride.

   [3 marks]

   (b)

   Explain how the structure of phospholipids causes them to form a bilayer in the cell surface membrane.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A bear survives for several months of hibernation on triglyceride stored in its fat cells. Throughout this time the phospholipids in its cell membranes keep the contents of each cell separate from the surrounding fluid.

   (a)

   Explain how the structure of triglycerides makes them a suitable energy store for the bear.

   [6 marks]

   (b)

   Compare the properties of triglycerides and phospholipids, relating them to their structures, and describe how an emulsion test would show that a sample of bear fat contains lipid.

   [6 marks]

   Total for question 4: 12 marks

End of questions