Question: 2

A number of different biological molecules are represented in Fig. 3.1.

(a) (i) State the letter of the molecule shown in Fig. 3.1 that represents:

a triglyceride

a monosaccharide

a protein

[3]

(ii) State the letter of the molecule shown in Fig. 3.1 that contains:

phosphate

glycosidic bonds

peptide bonds

disulfide bonds

[4]

(b) Molecule E shown in Fig. 3.1 is part of the carbohydrate molecule glycogen.

Explain why glycogen makes a good storage molecule.

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[3]

(c) (i) When glycogen is hydrolysed, molecule A shown in Fig. 3.1 is produced.

State the precise name of molecule A

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[1]

(ii) State one function of molecule A.

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[1]

(iii) State the letter of a molecule shown in Fig. 3.1, other than molecule E, that is used as a storage molecule.

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(d) Cellulose is a carbohydrate molecule found in plants.

Complete the table below to give three differences in the structures of glycogen and cellulose.

One difference has been done for you.

glycogen
	cellulose
	
no hydrogen bonding
	hydrogen bonding

		

[3]
[Total: 16]

Question: 3

Fig. 2.1 shows part of an amylose molecule. This is an unbranched form of starch.

When iodine solution is added to starch, iodine fits into the helix of the amylose molecule, producing a colour change.

(a) (i) State the colour of iodine solution in the presence of starch.

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[1]

(ii) Hydrogen bonds hold the amylose molecule in its helical shape.

Describe how a hydrogen bond is formed.

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[2]

(iii) Using the information in Fig. 2.1, suggest what would happen to the iodine-amylose complex if the solution was heated to 60°C.

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[2]

(b) Amylase is an enzyme that hydrolyses amylose to maltose. Maltose, like glucose, is a reducing sugar.

A student investigated the action of amylase on amylose. She mixed amylase with amylose and placed the mixture in a water bath.

Describe how she could measure the change in concentration of maltose (reducing sugar) as the reaction proceeds.

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[7]
 [Total: 12]

Question: 4

In the search for new biofuels, research has been done into the digestion of wood waste by fungi.

The cellulase enzymes produced by the fungi break cellulose into sugars. These sugars can then be converted into ethanol, a biofuel. 

Fig. 3.1 shows the stages in this digestion process.

(a) (i) Name bonds A and B shown in Fig. 3.1.

A

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B

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[2]

(ii) State how bond B is broken in the digestion of the disaccharide.

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[1]

(iii) Name the sugar that is the final product of this digestion process.

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[1]

(b) Explain why different enzymes are involved in each stage of the digestion process.

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[3]

(c) Fig. 3.2 shows the effect of changing pH on the rate of activity of enzyme 2.

(i) Explain why the activity of enzyme 2 falls to zero at pH 7.

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[3]

(ii) State two factors that should have been controlled when investigating the effect of pH on the activity of enzyme 2.

1

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2

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[2]

(d) The activity of an enzyme can be measured by testing for the concentration of its product at regular intervals.

Describe how the concentration of a reducing sugar can be measured using a colorimeter.

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[6] [Total: 16]