JUNE 2012

Question 1

The length of a section of DNA that codes for the complete toxin is longer than the mRNA used for translation. Explain why (1 mark)

Answer 1

1. DNA contains introns, whereas mRNA contains exons only,

Question 2

Explain how a change in the base sequence of mRNA could lead to a change in the tertiary structure of the toxin (1 mark)

Answer 2

1. A different sequence of Amino Acids will be translated.

Question 3

The black mamba’s toxin kills prey by preventing their breathing. It does this by inhibiting the enzyme acetylcholinesterase at neuromuscular junctions. Explains how this prevents breathing (3 marks)

Answer 3

1. Acteylcholine isn’t broken down
2. Sodium ions continue to enter and depolarise the membrane
3. Intercostal muscles stay contracted and cannot relax

Question 4

Increased intensity of exercise leads to an increased heart rate. Explain how. (3 marks)

Answer 4

1. Carbon dioxide increase detected by chemoreceptors in the carotid arteries
2. Impulses are sent to the Medulla Oblongata
3. Frequency of impulses to the SAN are increased via the sympathetic neurone.

Question 5

The jellyfish gene attached to the human Factor IX gene (Stage 2) codes for a protein that glows green under flourescent light. Explain the purpose of attaching this gene (2 marks)

Answer 5

1. Acts as a marker gene
2. Shows those that have taken up the human gene
3. Only those implant cells will fluoresce

Question 6

The promoter DNA from sheep (Stage 3) causes transcription of genes coding for proteins found in sheep milk.
Suggest the advantage of using this promoter DNA (2 marks)

Answer 6

1. Factor IX present in milk
2. Gene only expressed in mammary glands
3. Do not need to kill sheep to obtain factor IX

Question 7

Suggest one reason why very few live births result from the many embryos that are implanted (2 marks)

Answer 7

1, The embryos may be recognised as foreign

2. Embryo rejected by the immune system

Question 8

It is important that scientist still report the results from failed attempts to produce transgenic animals. Explain why. (2 marks)

Answer 8

1. Save time and effort for others

2. Same work won’t be repeated

Question 9

Adrenaline binds to receptors in the plasma membranes of liver cells. Explain how this causes the blood glucose concentration to increase (2 marks)

Answer 9

1. Activates adenylate cyclase
2. Activates enzymes in cell
3. Involved in glycogenolysis or gluconeogenesis

Question 10

The rats were not fed for at least 6 hours before their blood glucose concentration was measured. Explain why. (1 mark)

Answer 10

1. Allow time for blood glucose levels to return to normal

2. Food would affect blood glucose level

Question 11

The rats used in the investigation had type I diabetes. This form of gene therapy may be less effective in treating rats that have type II diabetes. Explain why (1 mark)

Answer 11

1. Type II is a failure to respond to Insulin

Question 12

Research workers have suggested that treating diabetes in humans by this method of gene therapy would be better than injecting insulin. Evaluate this suggestion. (4 marks)

Answer 12

1. Permanent
2. Less restriction in their diet
3. Unknown what the long term effects of the Insulin are
4. Virus used may be harmful on humans
5. Results for rats are different to humans

Question 13

Huntington’s disease is always fatal. Despite this, the allele is passed on in human populations. Use information in the graph to suggest why. (2 marks)

Answer 13

1. Age of onset is later on in life

2. Already had children and passed on the allele by this time.

Question 14

Only one of these people tested positive for Huntington’s disease. Which person was this? Explain your answer (2 marks)

Answer 14

1. PERSON K

2. Has the highest band that has travelled the shortest distance so has the highest number of CAG repeats

Question 15

Suggest how the change in water intake as environmental temperature increases maintains core body temperature (1 mark)

Answer 15

1. Water intake will increases as sweating occurs meaning more water must be taken in to replace the water that is lost

Question 16

Suggest how the change in food intake as the environmental temperature decreases maintains core body temperature (2 marks)

Answer 16

1. Food needs to be broken down into glucose for respiration
2. Can provide heat when the temp is below the favourable

Question 17

Explain the change in milk production as the environmental temp increases (1 mark)

Answer 17

1. More sweating so less water available to make milk

Question 18

The rectal temperatures of cows are recorded to monitor heat stress. This is a better measurement of core body temperature than measuring the temperature of the skin. Explain why. (2 marks)

Answer 18

1. The skin fluctuates in temperature more than the rectal temperatures
2. As affected more by the environment

Question 19

Selective breeding can be used to produce cows with desirable features. This involves mating cows with bulls. Suggest how a bull is selected to increase the probability of producing cows with a high milk yield (1 mark)

Answer 19

1. Select a bull whose mother had a high milk yield

Question 20

The scientists found that the percentage of people who can tolerate lactose is much higher in populations that drink a lot of milk and eat a lot of dairy products.
Use your knowledge of natural selection t explain this finding (4 marks)

Answer 20

1. Selective advantage for those who can produce lactase.
2. People producing lactase will reproduce
3. Pass on allele to the next generation
4. Allele frequency will increase