2.3 Biogeochemical cyclesIB Environmental Systems and Societies SL: Subtopic test

1. 1
   The Flow Country in northern Scotland is one of the largest areas of blanket bog in Europe. Waterlogged conditions slow the decomposition of dead plant material, which has built up as peat over thousands of years. In some areas the bog was drained and planted with conifers for timber.

   (a)

   Which process transfers carbon from the atmosphere into the plants of the bog?

   [1 mark]

   • ACellular respiration
   • BPhotosynthesis
   • CDecomposition
   • DCombustion

   (b)

   Which statement about the peat in the bog is correct?

   [1 mark]

   • AIt is an inorganic store of carbon with a short residence time
   • BIt is an inorganic store of carbon in the soil
   • CIt is a source of carbon while it remains waterlogged
   • DIt is an organic store of carbon with a long residence time

   (c)

   Explain why draining the bog could turn it from a carbon store into a carbon source.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Since the Industrial Revolution the average pH of the surface ocean has fallen from about 8.2 to about 8.1. Shellfish hatcheries on the Pacific coast of the United States have reported that young oysters have difficulty forming their shells when the incoming seawater has a low pH.

   (a)

   By which process does carbon dioxide from the atmosphere enter the ocean?

   [1 mark]

   • ADissolving at the surface
   • BPhotosynthesis by fish
   • CCellular respiration by plankton
   • DDecomposition in the atmosphere

   (b)

   Which change in the ocean is the direct result of more carbon dioxide dissolving in seawater?

   [1 mark]

   • AA rise in the pH of the water
   • BA fall in the concentration of hydrogen ions
   • CAn increase in the acidity of the water
   • DA rise in the amount of calcium carbonate in solution

   (c)

   Outline how ocean acidification harms marine animals such as oysters.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A mature oak woodland covers 40 hectares. Each year photosynthesis removes 6.0 tonnes of carbon per hectare from the atmosphere, while respiration and decomposition return 5.2 tonnes of carbon per hectare. An arable farm of 40 hectares next to the wood is ploughed every year and the soil organic matter is falling by 0.8 tonnes of carbon per hectare each year.

   (a)

   Calculate the net change in carbon in the woodland each year, giving the unit, and state whether the woodland is acting as a source or a sink.

   [3 marks]

   (b)

   Suggest two ways the farmer could change the farming technique so that the farm acts as a carbon store or sink instead of a source, explaining each.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   The Sleipner gas field lies in the North Sea off Norway. Since 1996 the carbon dioxide removed from the natural gas has been injected into a deep layer of porous rock under the seabed instead of being released into the air, at about one million tonnes a year. Norway introduced a tax on carbon dioxide emissions from offshore oil and gas production in 1991. Elsewhere, governments have also relied on planting forests and on reducing the use of fossil fuels.

   (a)

   Explain how the burning of fossil fuels has altered the carbon cycle.

   [6 marks]

   (b)

   Evaluate the measures that could be used to alleviate the effects of human activities on the carbon cycle, referring to the examples above.

   [6 marks]

   Total for question 4: 12 marks

End of questions