IGCSEScienceEdexcelScience (Double Award) (Modular)Biology Unit 2Exam Questions5. Ecology & the EnvironmentCycles within Ecosystems

Cycles within Ecosystems (Edexcel IGCSE Science (Double Award) (Modular): Biology Unit 2): Exam Questions

Exam code: 4XSD1

34 mins4 questions
Easy
Medium
Hard
1a
1 mark

Which of A - D is the carbon cycle process by which carbon enters the tissues of living organisms from the atmosphere?

  • Decomposition

  • Photosynthesis

  • Aerobic respiration

  • Evaporation

Choose your answer

1b
2 marks

Part of the carbon cycle is shown in the diagram below.

Flow diagram of part of the carbon cycle. Carbon dioxide in the air is at the top, with plants and animals below it, dead organisms below them, and fossil fuels at the bottom. An arrow runs from carbon dioxide in the air down to plants, and a second arrow runs from plants back up to carbon dioxide in the air. An arrow runs from plants across to animals, and an arrow runs from animals up to carbon dioxide in the air. Arrows run from plants and from animals down to dead organisms, and an arrow runs from dead organisms down to fossil fuels. A long curved arrow labelled X runs up the left-hand side from fossil fuels to carbon dioxide in the air. A second long curved arrow labelled Y runs up the right-hand side from dead organisms to carbon dioxide in the air.

Name processes X and Y in the diagram.

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1c
2 marks

Describe how carbon is released during process Y in part (b).

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1d
2 marks

Carbon is an element that is present in biological molecules such as proteins.

Name two other elements that are present in all protein molecules.

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1a
1 mark

The diagram shows a cycle found in ecosystems.

Diagram of the carbon cycle. Sunlight shines down onto a group of trees on the left. The words carbon dioxide sit at the top of the diagram. A curved arrow labelled Y runs from carbon dioxide down to the trees on the left. A vertical arrow labelled X runs up from the ground to carbon dioxide, and a second curved arrow labelled X runs from a tree on the right up to carbon dioxide. A curved arrow labelled W runs from the smoke above a factory, labelled factory burning fuel, up to carbon dioxide. An arrow labelled Z curves down from the trees on the left towards the ground, and a second arrow curves down from the trees to a dead animal labelled decaying organisms. A short arrow runs from the decaying organism to a black deposit underground labelled fossil fuel, and another arrow runs from that deposit up to the factory. Two further arrows point to two sheep grazing on the ground, one from the tree on the right and one from grass at the river bank.

Give the name of the cycle.

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1b
1 mark

In the image in part (a), which process is represented by the letter W?

  • Combustion

  • Decomposition

  • Feeding

  • Respiration

Choose your answer

1c
1 mark

Name a group of organisms that is responsible for decomposition.

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1d
6 marks

Carbon dioxide is released into the atmosphere by the decomposition of organic material.

The rate of this decomposition depends on a number of factors.

Design an investigation to find out if changing the pH of organic material affects the rate of decomposition.

Include experimental details in your answer and write in full sentences.

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1e
1 mark

In the image in part (a), which process is represented by the letter X?

  • Combustion

  • Decomposition

  • Feeding

  • Respiration

Choose your answer

2a
2 marks

The following table shows changes in atmospheric carbon dioxide levels over time.

Year

Carbon dioxide concentration / ppm

1960

316

1970

325

1980

338

1990

354

2000

369

2010

387

Calculate the percentage increase in carbon dioxide concentration between 1960 and 2010. Give your answer to one decimal place.

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2b
4 marks

Use the data provided in part (a) to plot a graph that shows the change in atmospheric carbon dioxide levels over time.

Use a ruler to join the points with straight lines.

Blank graph paper in portrait orientation, ruled with a fine grid of small squares and heavier lines every ten squares. There are no axes, scales, labels or plotted points.

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1a
5 marks

'Carbon flux' is a term used to describe the transfer of carbon from one store to another in the carbon cycle.

The following data show fluxes in carbon between different storage reserves in an ecosystem, measured in gigatonnes per year (GT yr-1). A gigatonne equals 1 billion tonnes.

Process of carbon transfer

Flux / GT yr-1

Release from the oceans

101

Dissolving in the ocean

104

Release from soil

62

Fossil fuel formation during incomplete decomposition

52

Respiration of terrestrial organisms

53

Photosynthesis

117

Deforestation and burning of plant matter

2.0

Combustion of fossil fuels

4.9

(i) Calculate the difference between the amount of carbon entering the atmosphere and the amount of carbon leaving the atmosphere over the course of a year in this ecosystem.

[3]

(ii) The figure calculated in part (i) is known as the 'net flux' of carbon in the ecosystem; this refers to the overall direction of carbon transfer.

Explain why the net flux of carbon is important at a global level.

[2]

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1b
2 marks

Explain why the combustion of fossil fuels can have a large impact on the carbon balance in the atmosphere.

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1c
4 marks

Estimating global carbon fluxes is of great interest to scientists, even though it may be challenging to make accurate measurements.

(i) Suggest why it is difficult to make accurate measurements when studying the transfer of carbon.

[2]

(ii) Suggest why estimating carbon fluxes is of such interest to scientists.

[2]

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