PolysaccharidesAQA A-Level Biology: Subtopic test

1. 1
   A student compares three polysaccharides: glycogen from liver tissue, starch from a potato and cellulose from plant cell walls.

   (a)

   Which statement about the monomers of these polysaccharides is correct?

   [1 mark]

   • AGlycogen and starch are made from α-glucose, and cellulose from β-glucose
   • BAll three are made from α-glucose
   • CGlycogen is made from β-glucose, and starch and cellulose from α-glucose
   • DCellulose is made from α-glucose, and starch from β-glucose

   (b)

   What is the result of adding iodine in potassium iodide solution to a sample of potato starch?

   [1 mark]

   • AThe orange-brown solution turns brick-red
   • BThe orange-brown solution turns green
   • CThe orange-brown solution turns blue-black
   • DThe solution turns from colourless to white

   (c)

   Explain how the structure of glycogen makes it suitable as an energy store in liver cells.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   The muscle cells of a sprinter must release glucose for respiration very rapidly during a 100 m race. The cells of a potato tuber, by contrast, store starch for use over several weeks.

   (a)

   Which feature of glycogen allows glucose to be released rapidly?

   [1 mark]

   • AIts helical shape
   • BIts many branches with many ends where enzymes can act
   • CIts β-1,4 glycosidic bonds only
   • DIts solubility in water

   (b)

   Which statement about starch is correct?

   [1 mark]

   • AIt is made from β-glucose
   • BIt contains only unbranched chains
   • CIt is the main storage polysaccharide in animal cells
   • DIt contains unbranched, helical amylose and branched amylopectin

   (c)

   Explain why glycogen is better than unbranched amylose as a store of glucose for rapid release.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Plant cell walls contain cellulose. A plant cell placed in pure water takes in water by osmosis, but it does not burst.

   (a)

   Explain how cellulose molecules are arranged to give the cell wall strength.

   [3 marks]

   (b)

   Explain why the plant cell does not burst, whereas an animal cell placed in pure water would.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student is asked to compare the structure and function of the polysaccharides starch, glycogen and cellulose, and to test a sample of potato for starch.

   (a)

   Describe how she should test for starch, and explain how the structure of starch makes it suited to energy storage in a potato tuber.

   [6 marks]

   (b)

   Compare the structure and function of glycogen and cellulose.

   [6 marks]

   Total for question 4: 12 marks

End of questions