(PMT) Mark Scheme Answers

Question 1

Describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers.
Give two named examples of polymers and their associated monomers to illustrate your answer. (5m)

Answer 1

1) a condensation reaction joins monomers together and forms a chemical bond and release water

2) hydrolysis reaction breaks a chemical bond between monomers using water

3) A suitable example of polymers and the monomers from which they are made

4) second suitable example of polymers and the monomers from which they are made

5) Reference to a correct bond within a named polymer

Question 2

What is a monomer ?

Answer 2

a monomer is a smaller / repeating) unit / molecule from which larger molecules / polymers are made;

Question 3

A biochemical test for reducing sugar produces a negative result with raffinose solution.
Describe a biochemical test to show that raffinose solution contains a non-reducing sugar. (3)

Answer 3

1. Heat with acid and neutralise;
2. Heat with Benedict’s (solution);
3. Red precipitate/colo

Question 4

A student carried out the Benedict’s test. Suggest a method, other than using a colorimeter, that this student could use to measure the quantity of reducing sugar in a solution.

Answer 4

1. Filter and dry (the precipitate)
2. Find mass/weight

Question 5

Lactulose is a disaccharide formed from one molecule of galactose and one molecule of fructose.
Other than both being disaccharides, give one similarity and one difference between the structures of lactulose and lactose.

Answer 5

Similarity - both contain galactose / a glycosidic bond;

Differences - Lactulose contains fructose, whereas lactose contains glucose;

Question 6

Gycogen and cellulose are both carbohydrates.
Describe two differences between the structure of a cellulose molecule and a glycogen molecule.

Answer 6

1. Cellulose is made up of β-glucose (monomers) and glycogen is made up of α-glucose (monomers);
2. Cellulose molecule has straight chain and glycogen is branched;
3. Cellulose has a straight chain and glycogen is coiled.
4. Glycogen has both 1- 4 and 1-6 glycosidic bond whereas cellulose has only 1-4 glycosidic bond

Question 7

Starch is a carbohydrate often stored in plant cells.
Describe and explain two features of starch that make it a good storage molecule

Answer 7

1. Insoluble (in water), so doesn’t affect water potential;
2. Branched / coiled / (α-)helix, so makes molecule compact;

Question 8

(a) Describe the structure of glycogen.

Answer 8

1. Polysaccharide of α-glucose; OR
2. Joined by glycosidic bonds or branched structures.

Question 9

Suggest how glycogen acts as a source of energy.
Do not include transport across membranes in your answer

Answer 9

1. Hydrolysed (to glucose);
2. Glucose used in respiration;

Question 10

Name the monomers from which a maltose molecule is made.

Answer 10

2 x Glucose

Question 11

(d) Explain how you would use the graph to determine the maltose concentration with a light absorbance of 0.45 arbitrary units. (2)

Answer 11

Line of best fit drawn; Read off value at 0.45.

Question 12

Explain the difference in the structure of the starch molecule and the cellulose molecule shown in the diagram above.

Answer 12

1. Starch formed from alpha glucose but cellulose is formed from beta glucose
2. Position of hydrogen and hydroxyl groups on carbon atom 1 inverted

Question 13

Starch molecules and cellulose molecules have different functions in plant cells. Each molecule is adapted for its function.

Explain one way in which starch molecules are adapted for their function in plant cells. ( 2 marks)

Answer 13

1. Insoluble
2. Doesn’t affect water potential
3. Helical
4. Compact

Question 14

Explain how cellulose molecules are adapted for their function in plant cells. (3m)

Answer 14

1. Long and straight chains
2. Become linked together by many hydrogen
3. Provide strength to cell wall.

Question 15

The general structure of a fatty acid is RCOOH.
Name the group represented by COOH (1m)

Answer 15

Carboxyl

Question 16

Name the type of R group shown in Figure 1.
Explain your answer. (2m)

Answer 16

Type R group - unsaturated
Double bond between carbons

Question 17

(c) Describe how you would test for the presence of a lipid in a liquid sample of food.

Answer 17

1. Add ethanol, then add water and shake
2. Test becomes milky white (emulsion)

Question 18

(c) Describe how you would test for the presence of a lipid in a liquid sample of food.

Answer 18

1. One glycerol and three fatty acids;
2. Condensation (reactions) and removal of three molecules of water;
3. Ester bond(s) (formed);

Question 19

Describe how an ester bond is formed in a phospholipid molecule (2)

Answer 19

1. Condensation reaction or loss of water
2. Between glycerol and fatty acid

Question 20

Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst (3m)

Answer 20

1. Substrate binds to active site
2. Active site changes shape (slightly) so it is complementary to substrate
3. Reduces activation energy

Question 21

(a) Messenger RNA (mRNA) is used during translation to form polypeptides.

Describe how mRNA is produced in the nucleus of a cell.

Answer 21

1. Helicase;
2. Breaks hydrogen bonds;
3. Only one DNA strand acts as template;
4. RNA nucleotides attracted to exposed bases;
5. (Attraction) according to base pairing rule;
6. RNA polymerase joins (RNA) nucleotides together;
7. Pre-mRNA spliced to remove introns.