24 8 Hypoxia is an inadequate supply of oxygen to tissues and cells that restricts their function. (a) The normal partial pressures of oxygen vary from tissue to tissue. The table shows the normal partial pressure of oxygen in two tissues. Tissue Partial pressure of oxygen / kPa Pulmonary arterial blood 5.3 Other arterial blood 13.3 (i) Calculate the ratio of the partial pressures of oxygen in these two tissues. Give your answer to one decimal place. (1) Answer .............................................................. (ii) Explain why the partial pressures of oxygen in these two tissues are different. 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Turn over 25 (b) The body responds to hypoxia by releasing hypoxia‑inducible transcription factors (HIF). Investigations have shown that one effect of HIF is an increase in the rate of glycolysis in the affected cells. (i) Explain how HIF could result in an increase in the rate of glycolysis. 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(ii) Explain why cells need to respond to hypoxia with an increase in the rate of glycolysis. (4) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... 26 (iii) The graph shows the changes in levels of two HIFs, HIF‑1 and HIF‑2, before and during hypoxia. Time Before hypoxia During hypoxia HIF‑1 HIF‑2 Level of HIF Compare and contrast the changes in the levels of HIF‑1 and HIF‑2 during hypoxia. 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(iv) Explain the changes in levels of HIF‑1 and HIF‑2 during hypoxia. 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(Total for Question 8 = 13 marks)