June 2019

Question 1

1.2. Explain why the structure of a membrane is described as ‘fluid-mosaic’. (2)

Answer 1

(1) Idea of phospholipid molecules moving = fluid

(2) Idea of proteins (embedded) in membrane in separate locations = mosaic

Question 2

1.3. Suggest the function of cholesterol in the plasma membrane. (1)

Answer 2

Restricts the movement of other molecules making up the membrane

Question 3

2.4. The gene extracted from the mitochondrial DNA codes for a protein. Suggest one possible function of this protein. (1)

Answer 3

Suitable suggestion e.g. enzyme involved in (aerobic) respiration/ transport protein (in mitochondrial membrane)

Question 4

2.5. Comparing the base sequence of a gene provides more information than comparing the amino acid sequence of the protein for which the gene codes.
Explain why. (2)

Answer 4

(1) Reference to base triplet / triplet code / more bases than amino acids / longer base sequence than amino acid sequence
(2) Idea that the genetic code is degenerate

Question 5

2.6. Suggest 2 reasons why scientists are concerned about the release of individual salamanders from the captive breeding farms. (2)

Answer 5

(1) May release individuals with a disease / cause release of pathogen OR Species B may increase (interspecific) competition / outcompete other species for resources e.g. food / disrupt food chains OR Cross-breeding / may form hybrids

(2) (Leads to) reduced biodiversity / loss of other species

Question 6

4.1. Describe how the students should’ve put the solution containing a mixture of amino acids onto the chromatography paper before the paper is put in the jar. (3)

Answer 6

3 max:
(1) (Draw) start line / origin in pencil
(2) Use pipette / glass rod / capillary tube / pin (to transfer solution) onto start line / origin
(3) Apply several drops on the same spot
(4) Allow to dry between each application

Question 7

4.2. Suggest 2 practical precautions that the students should take when doing this investigation. (2)

Answer 7

Any two from:
1. The solvent should start below the pencil line
2. Stop before the solvent reaches the top of the paper/draw (pencil) line for solvent front before the solvent dries
3. Don’t allow the paper to touch the sides of the jar / don’t move the jar during the investigation
4. Use a fume cupboard
5. Don’t touch the paper with bare hands/wear gloves when touching the paper
6. No flames near the solvent

Question 8

4.5. There are 2 spots on the chromatography that are very close to each other, it’s hard to distinguish between them. Describe 2 ways that the students could use chromatography to separate the 2 spots more clearly. (2)

Answer 8

Any two from:
1. Turn the chromatogram 90° / run at right angle;
2. Using a different solvent;
3. Run chromatography for longer time;

Question 9

5.8. Suggest why the time taken for hydrolysis is much longer if there are fewer 1-6 glycosidic bonds in the glycogen molecule. (2)

Answer 9

(1) Enzymes only break down the glycogen from the end glucose molecules
(2) Fewer branches mean fewer ends available (for the enzymes to hydrolyse)

Question 10

8.3. Name the enzyme that synthesises a new strand of DNA by forming bonds between the DNA nucleotides (1)

Answer 10

DNA Polymerase