26 8 The graph shows the oxygen dissociation curves of human haemoglobin and human myoglobin. 12 0 10 20 30 40 50 60 70 80 90 100 0 2 4 6 8 10 Percentage saturation of haemoglobin with oxygen (%) Partial pressure of oxygen (pO2) / kPa haemoglobin myoglobin (a) (i) Calculate the volume of oxygen bound to haemoglobin at a partial pressure of oxygen of 6 kPa in 100 cm3 blood. The concentration of haemoglobin is 15 g per dm3 blood. When fully saturated, there is 1.36 cm3 oxygen per g of haemoglobin. (3) Answer .............................................................. 27 Turn over (ii) Explain why the oxygen dissociation curves for haemoglobin and myoglobin are different. (4) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 28 (b) In an investigation, the oxygen dissociation of haemoglobin from Tibetan people and European people was compared. The Tibetan people were living at high altitude. The European people were living at low altitude. The graph shows the results of this investigation. 0 10 20 30 40 50 60 70 80 90 100 0 2 4 6 8 10 12 Percentage saturation of haemoglobin with oxygen (%) Partial pressure of oxygen (pO2) / kPa haemoglobin from Tibetans, at low partial pressure of CO2 haemoglobin from Europeans, at low partial pressure of CO2 haemoglobin from Europeans, at high partial pressure of CO2 haemoglobin from Tibetans, at high partial pressure of CO2 Comment on the oxygen dissociation curves of the Tibetan people. (4) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 29 Turn over (c) Tibetan populations have a recessive allele that helps them to survive at high altitude. In a village in Tibet, 1950 people out of a population of 2500 people carry two copies of this allele. (i) Calculate the number of heterozygous people in the village. Use the Hardy-Weinberg equation p2 + 2pq+q2 = 1 (3) Answer .............................................................. 30 (ii) This allele is currently found only in human populations in Tibet. The allele has also been found in the fossil bones of an extinct form of modern humans called the Denisovans. Fossils of Denisovans have been found in Tibet. Explain why scientists think that the Denisovans belonged to the same species as modern humans. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (Total for Question 8 = 16 marks)