Energy transfer and nutrient cycles in ecosystemsAQA A-Level Biology: Topic test

20 questions, 54 marks

AQA A-Level Biology

Energy transfer and nutrient cycles in ecosystems topic test

Total 54 marks

Name

Class

Date

1
In a kelp forest, the gross primary production (GPP) of the kelp is 6 800 kJ m⁻² year⁻¹ and the kelp lose 2 900 kJ m⁻² year⁻¹ in respiration. Sea urchins feed on the kelp, and the net production of the sea urchins is 390 kJ m⁻² year⁻¹.
(a)
What is the net primary production (NPP) of the kelp, in kJ m⁻² year⁻¹?
[1 mark]
A9 700
B3 900
C2 900
D6 800
(b)
What percentage of the kelp's net primary production is converted into sea urchin biomass?
[1 mark]
A5.7%
B13.4%
C10%
D1.0%
(c)
Productivity is measured in kJ m⁻² year⁻¹. Explain why both an area and a time are included in the units.
[2 marks]
Total for question 1: 4 marks
2
A gardener adds ammonium sulfate fertiliser to her vegetable bed. Over the following three weeks the concentration of ammonium ions in the soil falls, and the concentration of nitrate ions rises.
(a)
Which process is mainly responsible for the rise in nitrate ion concentration?
[1 mark]
ANitrification
BDenitrification
CAmmonification
DNitrogen fixation
(b)
Heavy rain falls on the bed a week later. What is the most likely effect on the nitrate ions?
[1 mark]
AThey are converted to nitrogen gas in the air.
BThey are held tightly by soil particles.
CThey are absorbed by saprobionts.
DThey are washed out of the soil because they are very soluble (leaching).
(c)
Name the process by which ammonium ions are released from the proteins in dead plant material, and describe the role of the organisms responsible.
[2 marks]
Total for question 2: 4 marks
3
A salmon farmer measures the energy budget of one salmon over one growing period. The fish ingest food containing 12 000 kJ of chemical energy. They lose 3 000 kJ in faeces and urine and 7 200 kJ in respiration.
(a)
Calculate the net production of the fish and the percentage of the ingested energy that is converted into fish biomass. Show your working.
[3 marks]
(b)
Describe and explain two ways in which the farmer could increase the percentage of ingested energy converted into fish biomass.
[4 marks]
Total for question 3: 7 marks
4
A farmer has land that can be used either to grow soya beans for people to eat directly, or to grow soya beans to feed to pigs that are reared for pork. The pigs produce a liquid waste, slurry, which the farmer spreads on his fields.
(a)
Explain why more people can be fed from each hectare if the soya beans are eaten directly than if they are fed to pigs.
[6 marks]
(b)
Explain how spreading the slurry on the fields could benefit the crop, and how it could harm a nearby river.
[6 marks]
Total for question 4: 12 marks
5
A compost heap of grass cuttings and dead leaves is kept moist and is turned regularly. After several weeks the material has become dark and crumbly, and it contains ammonium ions, nitrate ions and phosphate ions.
(a)
How do saprobionts feed on the dead plant material in the heap?
[1 mark]
AThey ingest whole pieces of leaf and digest them inside their cells.
BThey make organic compounds from carbon dioxide using light.
CThey fix nitrogen gas into ammonium ions in their cells.
DThey secrete enzymes onto the material and absorb the soluble products.
(b)
Which statement about the phosphorus cycle is correct?
[1 mark]
ABacteria fix phosphorus gas from the air.
BSaprobionts release phosphate ions from dead organic matter, which plants can absorb.
CNitrifying bacteria convert phosphate ions into nitrate ions.
DPhosphate ions are returned to the air as a gas by denitrifying bacteria.
(c)
Explain why turning the heap regularly increases the rate at which nutrients are released from the plant material.
[2 marks]
Total for question 5: 4 marks
6
A river downstream of a sewage works receives effluent rich in phosphate ions. Biologists record dense growth of algae at the surface in summer, and a later fall in the number of fish.
(a)
What is the first likely effect of the extra phosphate ions on the river?
[1 mark]
ARapid growth of algae at the surface
BAn increase in the dissolved oxygen concentration
CMore light reaching plants on the river bed
DA fall in the population of saprobionts
(b)
What is the main reason for the later fall in the number of fish?
[1 mark]
AThe algae release toxic oxygen.
BThe phosphate ions are poisonous to fish.
CSaprobionts decomposing dead algae and plants use up the dissolved oxygen.
DThe fish cannot find enough food because plants die.
(c)
Explain why submerged plants in the river die as a result of the algal growth.
[2 marks]
Total for question 6: 4 marks
7
A farmer tests different rates of nitrogen fertiliser on a barley crop. At 0, 50, 100, 150 and 200 kg of nitrogen per hectare, the yields are 4.0, 5.5, 6.6, 7.0 and 7.1 tonnes per hectare. The fertiliser costs £1.20 per kg of nitrogen and the barley sells at £150 per tonne.
(a)
Calculate the extra income from the extra yield and the extra cost of fertiliser when the application rate is raised from 100 to 150 kg of nitrogen per hectare. State the effect on profit.
[3 marks]
(b)
Evaluate the data to recommend a rate of nitrogen application, and explain one environmental reason that supports your recommendation.
[4 marks]
Total for question 7: 7 marks
8
In a tropical rainforest, most of the nitrogen and phosphorus is held in the living plants. After a patch of forest is cleared, the land is planted with a crop that is harvested and removed each year, and the soil soon becomes much less fertile.
(a)
Explain why the soil of the cleared land becomes less fertile.
[6 marks]
(b)
Evaluate the use of natural and artificial fertilisers to restore the fertility of the cleared land.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).