QUESTION 21 (5 marks)
a) Glucose is an example of which type of carbohydrate?
[1 mark]
b) Starch and cellulose are both polymers of glucose. Compare the structure of starch and cellulose in terms of their glycosidic links.
[4 marks]
QCAA guide · typeset solution
QCAA sample response and mark allocation
21 | a) | Monosaccharide | • provides monosaccharide [1 mark] | Accept aldose. |
b) | Both starch and cellulose form 1-4 glycosidic links. However, starch is a polymer of α–glucose and cellulose is a polymer of β–glucose. Starch forms a linear polymer due to 1-4 α–glycosidic links (amylose) and a branched polymer due to 1-4 and 1-6 α–glycosidic links (amylopectin). Cellulose only exists as a linear polymer with 1-4, β–glycosidic links. | • identifies that both contain 1-4 links [1 mark] • identifies that starch is a polymer of α–glucose and cellolose is a polymer of β–glucose [1 mark] • indicates that starch can be linear due to 1-4 α–glycosidic links (amylose) and branched due to 1-4 and 1-6 α–glycosidic links [1 mark] • indicates that cellulose only exists as a linear polymer with 1-4, β–glycosidic links [1 mark] |
QCAA sample response and marking criteria reproduced from the official guide.
Compare your working with the guide above.