26 8 The photograph shows a glacier that is melting. As the glacier gradually melts, it leaves behind bare rock. melting glacier (Source: © CHARLES D. WINTERS/SCIENCE PHOTO LIBRARY) Scientists sampled the soil from areas that had been uncovered for different lengths of time after the glacier ice had melted. The table shows the results from the samples. Length of time since glacier melted / years Soil depth / cm Mass of nitrate in soil / mg m–2 Mass of leaf litter that falls to ground each year / g m–2 yr–1 5 5.2 3.8 1.5 15 6.4 4.1 1.7 40 7.0 5.3 12.8 100 9.2 21.8 277.0 150 10.8 35.4 335.0 200 15.1 53.3 277.0 250 16.2 61.4 261.0 (a) Which of the following should be used to determine if there is an association between length of time since the glacial ice has melted and soil depth? (1) A chi squared B correlation coefficient C standard deviation D t-test Turn over 27 (b) Explain how succession brings about the changes in the soil during this period of time. 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The graph shows the oxygen dissociation curve for leghaemoglobin and the oxygen dissociation for haemoglobin. 0 20 18 16 14 12 10 8 6 4 2 100 80 60 40 20 0 Partial pressure of oxygen / kPa Oxygen saturation (%) haemoglobin leghaemoglobin (i) Leghaemoglobin is a protein that is similar in structure to myoglobin. Both of these proteins have one subunit. Explain how the oxygen dissociation curve shows that the structure of leghaemoglobin is more similar to myoglobin than to haemoglobin. 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Turn over 29 (ii) Explain how leghaemoglobin enables these plants to grow in waterlogged and compact soils. 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(Total for Question 8 = 12 marks) 30 BLANK PAGE