JUNE 2015

Question 1

Figure 2 includes one process in which microorganisms add ammonium salts to soil.
Describe another process carried out by microorganisms which adds ammonium ions to soil (2 marks)

Answer 1

1. Proteins broken down into ammonium ions

2. By saprobiontic microorganisms

Question 2

Denitrification requires anaerobic conditions. Ploughing aerates the soil. Explain how ploughing would affect the fertility of the soil. (2 marks)

Answer 2

1. Fertility of the soil is increased as more nitrate is formed 2. Less denitrification occurs as there are less denitryifying bacteria

Question 3

One farming practice used to maintain high crop yield is crop rotation. This involves growing a different crop each year in the same field.
Suggest two ways in which crop rotation may lead to high crop yields. (2 marks)

Answer 3

1. Grow crops with nitrogen fixing bacteria
2. Different crops use different minerals
3. Different crops have different pests

Question 4

Explain the decrease in gross productivity as the woodland matures (2 marks)

Answer 4

1. Less light as the woodland matures because there is more competition for light
2. Less light will be available for photosynthesis

Question 5

Use your knowledge of succession to explain the increase in biomass during the first 20 years (3 marks)

Answer 5

1. Initially, only a pioneer species existed
2. They changed the abiotic conditions of the environment and made it less hostile so more habitats and niches can exist
3. Increases the species diversity of the plants

Question 6

Using figure 3 and your knowledge of net productivity, explain why biomass shows little increase after 10 years (2 marks)

Answer 6

1. NPP = GPP - R

2. Decrease in GPP/ photosynthesis or increase in respiration

Question 7

Suggest one reason for conserving woodlands (1 mark)

Answer 7

1. Conserves habitats 
Protects endangered species 
Reduces global warming 
Source of medicine/chemicals/wood 
Reduces erosion

Question 8

Explain what is meant by codominant alleles (1 mark)

Answer 8

1. When both alleles are expressed in the phenotype

Question 9

Describe how acetylcoenzyme A is formed in the link reaction (2 marks)

Answer 9

1. Oxidation of pyruvate and carbon dioxide is released

2. Addition of coenzyme A

Question 10

In muscles, pyruvate is converted to lactate during anaerobic respiration.
Explain why converting pyruvate to lactate allows the continued production of ATP during anaerobic respiration (2 marks)

Answer 10

1. Regenerates NAD

2. NAD used in glycolysis

Question 11

In muscles, some of the lactate is converted back to pyruvate when they are well supplied with oxygen. Suggest one advantage of this. (1 mark)

Answer 11

1. Pyruvate is used in anaerobic respiration

Question 12

Suggest how climate change could cause an increase in soil salinity (2 marks)

Answer 12

1. Increase in temperature due to global warming

2. Evaporation of water from the soil

Question 13

Explain why crop plants do not grow when soil salinity is 2% or higher (2 marks)

Answer 13

1. Soil has reduced water potential

2. Water diffuses out of the plant by osmosis

Question 14

Suggest one way in which these bacteria could stimulate an increase in the dry mass of cucumber plants (1 mark)

Answer 14

1. Bacteria may be nitrogen fixing

Question 15

The scientists grew the cucumber plants in pots. They removed any weeds which grew in the pots during the investigation. Explain why they removed the weeds. (2 marks)

Answer 15

1. Would compete for minerals

2. Would reduce the dry mass of the cucumbers

Question 16

On islands in the Caribbean, there are almost 150 species of lizard belonging to the genus Anolis. Scientists believe that these species evolved from two species found on mainland USA. Explain how the Caribbean species could have evolved. (6 marks)

Answer 16

1. The two species would be geographically isolated
2. No interbreeding would occur so there would be separate gene pools between the populations
3. Variation would occur in the population due to mutations that would randomly occur
4. Different selection pressures would exist in each population due to the different environments
5. Those organisms with the favourable characters would survive and reproduce
6. Leads to change in the allele frequency of the two populations

Question 17

Anolis sagrei is a species of lizard that is found on some of the smallest Caribbean islands. Describe how you could use the mark-release-recapture method to estimate the number of Anolis sangrei on one of these islands. (4 marks)

Answer 17

1. Capture and mark the species of lizard then release back into the environment
2. Use a non-toxic paint that does not harm the lizard
3. Leave sufficient time for the lizards to distribute randomly on the island
4. (Population = number in first sample× number in second sample divided by number of marked lizards in
   second sample)

Question 18

Large areas of tropical forest are still found on some Caribbean islands. The
concentration of carbon dioxide in the air of these forests changes over a period of
24 hours and at different heights above ground.
Use your knowledge of photosynthesis and respiration to describe and explain how the
concentration of carbon dioxide in the air changes:
 over a period of 24 hours
 at different heights above ground. (5 marks)

Answer 18

1, Increase in carbon dioxide concentration at night when only respiration occurs

2. No photosynthesis in the dark as it only occurs in the light
3. In the light, the rate of photosynthesis is greater than the rate of respiration
4. Decrease in carbon dioxide concentration as height increases
5. At ground level, less photosynthesis will occur.