june 2014

Question 1

Describe the role of microorganisms in producing nitrates from the remains of dead organisms (3 marks)

Answer 1

1. Saprobiontic microorganisms break down remains
2. Into ammonium then nitrate then nitrite
3. By nitrifying bacteria

Question 2

Upwelling often results in high primar productivity in coastal waters.
Explain why some of the most productive fishing areas are found in coastal waters. (2 marks)

Answer 2

1. Nitrate used by plants

2. More producers so fish can survive and reproduce more.

Question 3

Explain why CO2 uptake is a measure of net productivity (1 mark)

Answer 3

1. More carbon dioxide used in photsynthesis than respiration

Question 4

Yeast can also respire aerobically. The student repeated the investigation with a fresh sample of yeast in glucose solution, but without the oil. All other conditions remained the same.
Explain what would happen to the volume of gas in the syringe if the yeast were only respiring aerobically (2 marks)

Answer 4

1. Stays at the same level (remains constant)

2. Same volume of oxygen uptake and carbon dioxide release.

Question 5

Respiration produces more ATP per molecule of glucose in the presence of oxygen that it does when oxygen is absent. Explain why (2 marks)

Answer 5

1. Oxygen is the final electron acceptor
2. Oxidative phosphorylation occurs where the electron transport chain provides ATP
3. Only glycolysis occurs without oxygen

Question 6

The scientists obtained the biomass of each sample by heating it to 75c for 2hrs. They then weighed the sample, reheated it for 15 minutes, and weighed it again. They continued this cycle of reheating and reweighing until they found the sample had a constant mass.
Explain how this method helped to provide a reliable measurement of the biomass (2 marks)

Answer 6

1. Removes water in the plant

2. Water content in the plant can vary

Question 7

The scientists isolated the fungus from the tissue of the Hydrilla growing in its country of origin. Suggest two possible advantages of using this fungus as the biological control agent. (2 marks)

Answer 7

1. Survives in Hydrilla
2. Only one application required as they can reproduce
3. Does NOT become a pest

Question 8

During the light - independant reaction of photosynthesis, carbon dioxide is converted into organic substances. Describe how. ( 6 marks)

Answer 8

1. CO2 combines with RUBP
2. Produces two molecules of GP
3. GP reduced to TP
4. Using reduced NADP
5. Using ENERGY from ATP
6. Triose phosphate converted into glucose and other useful organic substances

Question 9

The bluebell is a flowering plant found in woodlands. Global warming has been associated with a change in the population of bluebells. Describe how you could estimate the number of bluebells in a small woodland (5 marks)

Answer 9

1. Use a grid
2. Obtain random co-ordinates using a random number generator
3. Count frequency of plants in a quadrat
4. Calculate the mean per quadrat
5. Mean number of plants in quadrat x number of quadrats to calculate the total number of bluebells