Skeletal muscle and movementEdexcel International A Level Biology: Subtopic test

1. 1
   A physiotherapist is demonstrating how the human arm moves at the elbow joint. The biceps muscle on the front of the upper arm and the triceps muscle on the back of the upper arm both attach, by tendons, to the bones of the lower arm. The bones of the upper and lower arm are held together at the elbow by ligaments.

   (a)

   Which row correctly identifies the muscle that flexes the elbow and the structure that connects a muscle to a bone?

   [1 mark]

   • ATriceps; ligament
   • BBiceps; tendon
   • CBiceps; ligament
   • DTriceps; tendon

   (b)

   The physiotherapist explains that muscles act as antagonistic pairs. What is the main reason muscles must work in antagonistic pairs?

   [1 mark]

   • AA muscle can produce a force only when it contracts, so a second muscle is needed to move the bone back
   • BA muscle can push as well as pull, so two muscles double the force
   • CTendons are elastic and need a second muscle to stretch them
   • DLigaments cannot hold a joint in place without a second muscle

   (c)

   Explain how the biceps and triceps interact with the bones of the arm to extend (straighten) the elbow.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student prepares a thin longitudinal section of mammalian skeletal muscle and examines a single muscle fibre with an electron microscope. The fibre is long and cylindrical, contains many nuclei, and is packed with parallel bundles of protein filaments that show a regular pattern of light and dark bands.

   (a)

   Which organelle in the muscle fibre stores calcium ions and releases them when the fibre is stimulated?

   [1 mark]

   • ASarcoplasmic reticulum
   • BMitochondrion
   • CSarcolemma
   • DMyofibril

   (b)

   What is a sarcomere?

   [1 mark]

   • AThe region of a myofibril between two M lines
   • BThe part of the sarcoplasm containing the nuclei
   • CThe region of a myofibril between two adjacent Z lines
   • DThe region of a myofibril containing only myosin filaments

   (c)

   The muscle fibre contains many mitochondria lying close to the myofibrils. Explain the advantage of this.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A sports scientist takes small muscle samples (biopsies) from the thigh of two athletes, a marathon runner and a 100 m sprinter, and examines the fibres. Sample X: dark red fibres with a very high density of mitochondria, a high concentration of myoglobin and a dense network of capillaries; low stores of glycogen. Sample Y: pale fibres with few mitochondria, little myoglobin, a sparse capillary network, high stores of glycogen and phosphocreatine, thicker myosin filaments and a high ATPase activity.

   (a)

   Deduce which sample came from the sprinter. Explain your answer using the data.

   [3 marks]

   (b)

   Explain why the fibres in Sample Y fatigue more quickly than the fibres in Sample X.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A sports scientist is comparing sprinters and marathon runners. Biopsies from the thigh muscle (vastus lateralis) of elite athletes showed the following mean percentages of fibre types. Sprinters: 76% fast twitch and 24% slow twitch. Marathon runners: 19% fast twitch and 81% slow twitch. Each group contained 12 athletes. At the knee, the quadriceps (extensor) and the hamstrings (flexor) form an antagonistic pair acting on the femur and tibia.

   (a)

   Describe and explain how the skeleton, tendons, ligaments and antagonistic muscles interact to extend the knee when a sprinter drives out of the blocks, and then bend it again to bring the leg forward.

   [6 marks]

   (b)

   Using the data and your knowledge of muscle fibres, evaluate the suggestion that the proportions of fast and slow twitch fibres in the thigh muscle determine whether an athlete succeeds as a sprinter or as a marathon runner.

   [6 marks]

   Total for question 4: 12 marks

End of questions