8 3 Doctors sometimes prescribe beta-blockers for their patients. Beta-blockers are a type of drug with antihypertensive properties. (a) In one study, the effect of beta-blockers on the heart rate during exercise was investigated. In this study, volunteers were placed randomly into one of four groups shown in the table. Group Dose of beta-blocker A none B very low C low D high The heart rate of each volunteer was recorded during a period of exercise. A mean value was calculated separately for the males and females in each group. The graph shows the results of this study. Mean heart rate during exercise / beats per minute Beta-blocker dose 250 200 150 100 50 0 Very low Low High None Key Males Females (i) Calculate the percentage change in male heart rate caused by increasing the dose of beta-blocker from very low to high. (2) Answer .............................................................. Turn over 9 (ii) Deduce the effect of beta-blockers on the supply of blood to muscle during exercise. 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(b) Explain why beta-blockers are prescribed for some people. 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Adrenaline is produced by the adrenal glands located on top of each kidney. Adrenaline acts on the heart to cause changes in heart rate. Deduce how adrenaline can cause a change in heart rate. 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(Total for Question 3 = 12 marks) Turn over 11 BLANK PAGE