18 7 Haemoglobin transports oxygen within the blood. The graph shows the relationship between the partial pressure of oxygen and the saturation of haemoglobin with oxygen at three partial pressures of carbon dioxide. 2 4 6 8 10 Partial pressure of oxygen / kPa PCO2 low PCO2 high PCO2 medium Saturation (%) 100 80 60 40 20 0 0 (a) (i) The curve moves to the right when more carbon dioxide is present. This move to the right is due to the (1) A Bohr effect B chloride shift C dissociation curve D oxygen debt Turn over 19 (ii) Explain why the curves are S-shaped. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (iii) Calculate the difference between the percentage change in saturation of haemoglobin with oxygen as the partial pressure of oxygen changes from 8 kPa to 2 kPa for low carbon dioxide compared with high carbon dioxide. (2) Difference .............................................................. % (iv) Analyse the data to explain the advantage to the mammal of the curve moving to the right. (3) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 20 (b) Mammals that live at high altitudes are in an environment with a lower partial pressure of oxygen. Explain the position of the haemoglobin dissociation curve for mammals that live at high altitude. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (Total for Question 7 = 10 marks) Turn over 21 BLANK PAGE