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Homework 1. The graph below shows the changes in blood pressure and velocity of blood flow as the blood travels from the heart to the leg and returns to the heart: [pic] (i) Compare the blood pressure in the artery with that in the vein. Suggest two reasons for the difference. (3 marks) (ii) Explain the importance of the low velocity of blood flow in the capillary. (2 marks) (iii) In the vein of the leg, the blood pressure is very low while the velocity of blood flow is quite high. Describe how such a high velocity of blood flow in the vein is maintained. 2 marks) (iv) Using the same x-axis given above, sketch a graph to show the change in the oxygen content of the blood as it passes through the blood vessels. (3 marks) 2. The photograph below shows the transverse section of a pig’s heart, which has a structure similar to that of the human heart. [pic] i) Which chamber of the heart, A or B, is responsible for sending out blood to all parts of the body except the lungs? Explain your choice. (3 marks) (ii) (1) Name valve X. (1 mark) (2) In a type of heart disorder, valve X cannot close properly.A man suffering from this disorder may faint easily when he performs vigorous exercise. How would you explain this? (4 marks) (iii) Vessel Y is an artery found in the heart wall. Explain why the risk of heart attack would be higher if fatty substances are deposited on the inner wall of vessel Y. (2 marks) 3. The diagram below shows part of the human circulatory system: [pic] (i) Explain why the lymph in vessel X of a person turns from clear to milky after he has eaten some barbecued pork. 3 marks) (ii) Describe how a continuous flow of lymph in vessel Y of the leg is maintained. (2 marks) (iii) For a patient suffering from a disease called elephantiasis, the lymph vessels in his leg are blocked by a kind of parasitic worm. The leg becomes greatly swollen due to the accumulation of tissue fluid. Explain why the tissue fluid accumulates. (2 marks) (iv) Structure Z may become enlarged when a person has a sore throat. Explain why structure Z is enlarged. (2 marks)