energy and ecosystems exam questions

Question 1

use your knowledge or NPP to explain why freshwater marshes have a high CUE and the advantage of this
Do not refer to abiotic factors in your answer.
(2 marks)

Answer 1

M1: low respiration
M2: more growth

Question 2

Freshwater marsh soils are normally waterlogged. This creates anaerobic conditions.
Use your knowledge of the nitrogen cycle to suggest why these soils contain relatively high concentrations of ammonium compounds and low concentrations of nitrite ions and nitrate ions (2 marks)

Answer 2

M1: less nitrification
M2: less conversion of ammonium ions to nitrite and nitrate ions

Question 3

The student used the equation above; however she substituted height for biomass. This was because she did not want to destroy the plants to measure their biomass.
State the assumption the student has made and suggest why this assumption might not be valid. (2 marks)

Answer 3

M1: assumed that height is directly proportional to biomass
M2: height does not include the roots

Question 4

Using all the information, evaluate the effect on plant growth of adding the different fertilisers to the soil (5 marks)

Answer 4

M1: potassium nitrate most effective and chicken manure least effective
M2: all fertilisers are more effective than the control
M3: no increase in growth with potassium nitrate above 30g
M4: ammonium sulfate shows small increase after 30g
M5: chicken manure effectiveness decreases after 45g

Question 5

The scientists determined the dry mass of the spinach plants. First, he heated each sample at 80°C for 2 hours.
Suggest what the scientist should do to ensure that he has removed all the water from the sample. (2 marks)

Answer 5

M1: weigh and heat
M2: until mass is constant

Question 6

Arbuscular mycorrhiza fungi are fungi which grow on, and into, the roots of plants. AMF can increase the uptake of inorganic ions such as phosphate. (1 mark)

Answer 6

Used to produce ATP

Question 7

Suggest one way in which AMF may benefit from their association with plants (1 mark)

Answer 7

carbohydrates

Question 8

Explain why an increase in shoot biomass can be taken as measurement of net primary productivity (2 marks)

Answer 8

M1: represents dry mass of carbon
M2: represents gross production minus respiratory loss

Question 9

Using data from the graph, evaluate the effect on plant productivity of adding AMF species and adding phosphate to the soil (4 marks)

Answer 9

M1: no statistical test to determine significant
M2: only 29 weeks of growth
M3: root growth not known
M4: for the control an increase in phosphate increases plant growth

Question 10

The ecologists dried the samples in an oven at 103°C for 24 hours. Describe how the ecologists could have determined whether or not this drying removed all the water from a sample of wood. (2 marks)

Answer 10

M1: after 24 hours record mass and reheat
M2: until constant mass is reached

Question 11

What does the graph show about the relationship between the diameter of the trunk of the trees and their biomass (2 marks)

Answer 11

M1: positive correlation
M2: not linear

Question 12

Using only the information provided suggest how the mass of carbon in the wood of a plantation of trees of a particular species could be estimated.
Start with measuring the diameter of a large number of trees.
Assume that the dry biomass of a tree consists of biological molecules that contain carbon. (4 marks)

Answer 12

M1: calculate a mean diameter
M2: use this to estimate the mean fresh biomass of trees
M3: use the percentage water content to find the dry biomass
M4: use the dried density to calculate the mass of tree

Question 13

Suggest appropriate units for gross productivity.

Answer 13

mass, per area

Question 14

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

Answer 14

M1: less light
M2: reduced photosynthesis

Question 15

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

Answer 15

M1: pioneer species
M2: change in abiotic conditions
M3: increase in diversity

Question 16

use the information in the graph and your knowledge of net productivity to explain why biomass shows little increase after 100 years (2 marks)

Answer 16

M1: net productivity = gross productivity - respiratory loss
M2: decrease in gross productivity and increase in respiration

Question 17

Suggest one reason for conserving woodlands

Answer 17

M1: protecting habitats

Question 18

Explain why the scientists measured the rate of production of oxygen in this investigation (2 marks)

Answer 18

M1: oxygen produced in light dependent reaction
M2: the faster oxygen is produced, the faster the light dependent reaction

Question 19

The scientists suggested that mutant plants producing more chlorophyll b would grow faster than normal plants in all light intensities.
Explain how these data support this suggestion. (4 marks)

Answer 19

At all light intensities, chloroplasts from mutant plants:
M1: have faster production of ATP and reduced NADP
M2: so have faster light dependent reaction
M3: so produce more sugars that can be used in respiration
M4: so have more energy for growth

Question 20

Explain why the scientists sterilised the surfaces of the seeds and grew them in soil that had been heated to 85°C for 2 days
(2 marks)

Answer 20

M1: to kill any bacteria on surface of seeds
M2: so only the added fungus has any effect

Question 21

Explain why it was importantly that the soil contained no mineral ions useful to the plants

Answer 21

So that only nitrate affects growth

Question 22

Explain how groups A and C act as controls (2 marks)

Answer 22

M1: so that effects of nitrate or ammonium alone could be seen
M2: so that effects of fungus can be seen

Question 23

Suggest what the scientists should have done during the drying process to be sure that all of the water had been removed from the plant samples (2 marks)

Answer 23

M1: weigh samples at intervals during drying
M2: to see if weighing became constant

Question 24

What conclusions can be drawn from the data in the table about the following?
The effects of the fungus on growth of pea plants
The effects of nitrate fertiliser and ammonium fertiliser on growth of the pea plants (4 marks)

Answer 24

With fungus
M1: fungus increases growth of roots and shoots in both
M2: produces greater growth with nitrate
With heat-treated fungus
M3: similar dry masses for roots and shoots
M4: no significant difference because SDs overlap

Question 25

Explain why determination of dry masses was an appropriate method the use in this investigation (2 marks)

Answer 25

M1: dry masses measures increase in organic material
M2: water content varies

Question 26

Which treatment gave the best result in commercial terms? Justify your answer (2 marks)

Answer 26

M1: fungus with nitrate containing fertiliser gave largest shoot: root ratio
M2: and largest dry masses measures increase of shoot

Question 27

Give a biological molecule that contains
nitrogen
phosphorus ( 2 marks)

Answer 27

amino acid
DNA

Question 28

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

Answer 28

M1: saprobiotic microorganisms break down remains into ammonium
M2: ammonium ions ion to nitrate and then into nitrate
M3: by nitrifying bacteria

Question 29

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

Answer 29

M1: nitrate absorbed by plants
M2: more producers so more fish