JAN 2011

Question 1

Explain what is meant by a recessive allele (1 mark)

Answer 1

1. Only expressed in the phenotype when homozygous

Question 2

Explain what is meant by codominant alleles (1 mark)

Answer 2

1. Both alleles are expressed in the phenotype

Question 3

Suggest an explanation for the increase in mass of ammonia released over the first four days in the control experiment. (2 marks)

Answer 3

1. Increase in temperature/ urease
2. More enzyme-substrate complexes formed
3. More bacteria to secrete urease

Question 4

Suggest how the addition of NBPT to urea fertiliser could result in increased growth of crop plants. (3 marks)

Answer 4

1. Less urea lost from the soil
2. Ammonia converted to nitrate
3. Nitrate used to make proteins for growth

Question 5

Suggest an explanation for the effect of an increase in the number of newts on the percentage survival of the tadpoles of spring peeper frogs. (2 marks)

Answer 5

1. Newts eat toads

2. Fewer toads feeding on the frogs

Question 6

i) Name the factors that limited the rate of photosynthesis between X and Y (1 mark)
ii) Use information from the graph to explain your answer (2 marks)

Answer 6

i) Temperature and light
ii) 1. Increase in temperature causes increase in rate of photosynthesis
2. Increase in light increases the rate of photosynthesis

Question 7

Creeping azalea is a plant which grows on mountains. Scientists predict that in the area where this plant grows the mean summer temperature is likely to rise from 20 degrees to 23 degrees. It is also likely to become much more cloudier. Describe and explain how these changes are likely to affect the growth of creeping azalea (3 marks)

Answer 7

1. Growth will decrease at a higher temperature
2. Rate of respiration will increase at a higher temperature
3. Rate of photosynthesis decreased as there is limited light

Question 8

The student closed the tap. After 30 minutes the drop of colour liquid had moved to the left. Explain why the drop of coloured liquid moved to the left. (3 marks)

Answer 8

1. Oxygen used up by woodlouse
2. CO2 absorbed by the potassium hydroxide
3. Decrease in pressure

Question 9

What measurements should the student have taken to calculate the rate of aerobic respiration in mm3 of oxygen g-1 h-1? (3 marks)

Answer 9

1. Distance drop moves and time
2. Mass of woodlouse
3. Cross sectional area

Question 10

DNP inhibits respiration by preventing a proton gradient being maintained across membranes. When DNP was added to isolated mitochondria the following changes were observed.
l less ATP was produced
l more heat was produced
l the uptake of oxygen remained constant
Explain how DNP caused these changes (3 marks)

Answer 10

1. No proton movement so less ATP produced
2. Heat produced from electron transport
3. Oxygen used as the final electron acceptor in the electron transport chain

Question 11

Residual food intake (RFI) is the difference between the amount of food an animal actually eats and its expected food intake based on its size and growth rate. Scientists have selectively bred cattle for low RFI.
Explain the advantage to farmer of having cattle with low RFI (2 marks)

Answer 11

1. Reduced cost

2. More growth rate with the same amount of food

Question 12

When RFI is calculated, low values are negative. Explain why they are negative, (1 mark)

Answer 12

1. They are eating less food than expected

Question 13

Scientists have developed a standard procedure for comparing RFI in cattle. They control two factors. These are the type of food and environmental temperature. Explain why each of these factors needs to be controlled.

Answer 13

Type of food: 1. Vary in proportions of protein
2. May affect absorption
Environmental temperature: 1. Will affect heat loss
2. Need to maintain body temp
3. More food/energy can be used for growth

Question 14

Research findings are not always of direct use to farmers. What else would rice farmers need to know before acting on the results of this investigation? (2 marks)

Answer 14

1. May affect yield
2. The treatment may affect other organisms
3. Cost of substance
4. Amount of substance required

Question 15

Methane is produced by anaerobic microorganisms in the soil. The scientists found that rice fields that are not flooded do not produce large amounts of methane. Suggest why (2 marks)

Answer 15

1. With flooding the conditions become anaerobic

2. Less active anaerobic microorganisms

Question 16

Succession occurs in natural ecosystems. Describe and explain how succession occurs (6 marks)

Answer 16

1. Colonisation by pioneer species
2. Changes the environment
3. Enables other species to colonise
4. Changes in diversity
5. Stability increases
6. Climax community

Question 17

Managed ecosystems such as wheat fields are prone to pest infections. Describe the advantages and disadvantages of using biological agents to control pests. (5 marks)

Answer 17

Advantages:
1. Specific (to one pest) 
2. Only needs application 
3. Maintains low population 
4. Pests do not develop resistance 
5. Do not leave chemical in environment 
6. Can be used in organic farming 
Disadvantages: 
1. Does not get rid of pests completely 
2. May become a pest itself 
3. Takes time to reduce the pest population

Question 18

Changes in ecosystems can lead to speciation. In southern California, 10,000 years ago a number of interconnecting lakes contained a single species of pupfish. Increasing temperatures caused evaporation and the formation of separate, smaller lakes and streams. This led to the formation of a numver of different species of pupfish. Explain how these different species evolved. (5 marks)

Answer 18

1. Geographical isolation
2. Seperate gene pools
3. Variation occurs due to mutations
4. As there are different abiotic conditions
5. Selection for advantageous feature
6. Differential reproductive success
7. Leads to change in allele frequency
8. Occurs over a long period of time