The diagram shows the internal structure of the human heart and associated blood vessels. [Figure 4.1]

1. (a)Name two blood vessels shown in the diagram that carry oxygenated blood. 1 2[2]
2. (b)(i)Blood flows through a valve when the left ventricle of the heart contracts. Diagram 1 shows this valve in the open and closed positions. [Figure 4.2] Label, using the letter X on the diagram of the heart, the location of this valve.[1]
3. (b)(ii)A small number of people develop a medical condition that causes changes to this valve. Diagram 2 shows the same heart valve in the open and closed positions in a person with this condition. [Figure 4.3] Explain how this medical condition will affect the flow of blood when the left ventricle contracts and relaxes.[4]
4. (b)(iii)Describe and explain the effect of this condition on the ability of the person to exercise.[3]
5. (c)It is possible for the valve to be replaced by surgery. The human valve is removed from the patient and can be replaced with a valve containing tissue from another species. This tissue is treated with a chemical to prevent rejection by the human body. Suggest how the cells of the tissue are modified by the chemical treatment and explain how this will prevent rejection by the human body.[4]

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