Evidence for climate change and its causesEdexcel International A Level Biology: Subtopic test

1. 1
   A research team is drilling a core of ice from the Antarctic ice sheet. The ice was formed from compacted snowfall laid down year after year, and it contains tiny bubbles of air trapped when each layer of snow was buried. The team wants to reconstruct how the concentration of carbon dioxide in the atmosphere has changed over hundreds of thousands of years.

   (a)

   Which feature of the ice core allows scientists to measure the carbon dioxide concentration of the atmosphere at the time each layer formed?

   [1 mark]

   • AThe thickness of each ice layer
   • BThe gas trapped in air bubbles within each layer
   • CThe dissolved minerals in the ice
   • DThe colour of the ice

   (b)

   Over the last 800 000 years the ice core shows that carbon dioxide concentration and temperature rose and fell together. What can validly be concluded from this alone?

   [1 mark]

   • ACarbon dioxide concentration causes every temperature change
   • BTemperature change causes every change in carbon dioxide concentration
   • CThe two variables are correlated, but this alone does not prove which causes the other
   • DThe two variables are unrelated

   (c)

   Describe how the team can use the ice core to find the carbon dioxide concentration of the atmosphere at different times in the past.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Ecologists in northern England have taken a vertical core from a peat bog. The peat is waterlogged and acidic, and it has built up slowly over about 10 000 years. Microscopy of samples from different depths shows many pollen grains from plants that grew in the area when each layer formed. The deepest layers contain mainly pollen of dwarf birch and other plants that tolerate cold, while the shallowest layers contain mainly pollen of oak, hazel and elm.

   (a)

   Pollen grains are often very well preserved in peat. What is the main reason?

   [1 mark]

   • APeat is warm, so pollen dries out and hardens
   • BThe waterlogged, acidic, anaerobic conditions prevent decay by microorganisms
   • CPeat is rich in oxygen, which stabilises the pollen wall
   • DPollen is dissolved by peat and re-formed as fossils

   (b)

   How do scientists identify the plant species that produced a pollen grain found in a peat sample?

   [1 mark]

   • ABy the mass of the grain
   • BBy the colour of the peat around it
   • CBy testing the grain for chlorophyll
   • DBy the shape and surface pattern of the resistant outer wall, using a microscope

   (c)

   Deduce what the pollen record suggests about the change in climate in the area, and suggest one reason why this conclusion may not be fully reliable.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Dendrochronologists are studying oak trees. They have measured the width of each annual ring in a living oak that is 220 years old. They have also measured rings in oak beams from medieval buildings and in preserved oak trunks dug from river sediment. Some of these samples are older than any living tree. They want to build a record of growing conditions covering the last 1000 years.

   (a)

   Explain how dendrochronology can be used to build a record of past growing conditions covering 1000 years from trees that are much younger than this.

   [3 marks]

   (b)

   The mean ring width of the living oak was 2.4 mm for 1700–1750 and 3.1 mm for 1950–2000. A student concludes that the mean temperature rose between these periods. Calculate the percentage increase in mean ring width and evaluate the student's conclusion.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A national scientific panel is reviewing the evidence for climate change. Direct measurements show that the concentration of carbon dioxide in the atmosphere has risen from about 280 ppm before the Industrial Revolution to more than 420 ppm today, and the mean global surface temperature has risen by about 1.1 °C over the same period. A member of the public argues that this shows only a correlation, and that humans have not been shown to be the cause.

   (a)

   Explain the greenhouse effect and explain how human activities have enhanced it.

   [6 marks]

   (b)

   Evaluate the argument that the data show only a correlation, and use your knowledge of the carbon cycle to suggest two ways of reducing the concentration of carbon dioxide in the atmosphere.

   [6 marks]

   Total for question 4: 12 marks

End of questions