Turn over 19 7 Moving a limb involves the interaction of muscles, tendons and ligaments. (a) Muscles can contain fast twitch and slow twitch muscle fibres. (i) Describe two structural differences between fast twitch muscle fibres and slow twitch muscle fibres. 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(ii) Muscles can be extensors or flexors. Which of the following correctly describes the state of the muscles described? (1) When the arm is bent at the elbow, the flexor muscle is When the lower leg is straightened at the knee, the flexor muscle is A contracted contracted B contracted relaxed C relaxed contracted D relaxed relaxed 20 (b) Tendons and ligaments are important structures in elbow and knee joints. (i) Which of the following identifies the structures that join bones to bones in an elbow joint? (1) A ligaments only B ligaments and tendons C tendons only D neither ligaments nor tendons (ii) One type of joint injury is a torn ligament. This may be treated by adding a piece of tendon to the ligament. This is because after a period of time, the tendon tissue changes and responds in the same way as a ligament. Which of the rows in the table correctly describe the changes in this piece of tendon? (1) Row Piece of tendon shows a change in its The change is 1 genotype an anatomical adaptation 2 genotype a physiological adaptation 3 phenotype an anatomical adaptation 4 phenotype a physiological adaptation A row 1 only B row 3 only C rows 1 and 2 D rows 3 and 4 Turn over 21 *(iii) The photograph shows athletes competing in the modern triathlon. © Gonzalo Arroyo Moreno / Stringer The modern triathlon involves three sports: swimming, cycling and running. An investigation was carried out to compare the level of demand on the body of these three sports during a triathlon. The investigation involved 12 athletes who were all males of the same age. Each athlete carried out the triathlon as shown in the flow diagram. There was no rest period between each sport. 1.5 km swim 40 km cycle 10 km run The heart rate for each athlete was measured as they completed each sport. The mean heart rate for each sport was then calculated and is shown in the table. Sport Mean heart rate / bpm Swimming 163 Cycling 165 Running 159 22 The blood lactate level for each athlete was also measured as they completed each sport. Means for lactate level after each sport were calculated. The results are shown in the graph. Swimming Cycling Running 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 Blood lactate concentration / mmol dm−3 It was concluded that cycling was the most demanding of the three triathlon sports. This was followed by swimming and then running. Evaluate the validity of this conclusion. 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(Total for Question 7 = 11 marks)