1. 1
   A researcher measures sarcomeres in a frog leg muscle fibre using electron micrographs. In the relaxed fibre, each sarcomere is 2.6 µm long, the A-band is 1.6 µm and the H-zone is 0.6 µm. After the fibre is stimulated to contract, each sarcomere is 2.0 µm long, the A-band is still 1.6 µm and the H-zone can no longer be seen. When the relaxed fibre is gently pulled until the sarcomeres reach 3.2 µm and then released, it springs back to 2.6 µm without any ATP being used.

   (a)

   Which band of the sarcomere stays the same length during contraction?

   [1 mark]

   • AA-band
   • BI-band
   • CH-zone
   • DThe whole sarcomere

   (b)

   Which protein is responsible for the fibre springing back after being stretched to 3.2 µm?

   [1 mark]

   • AActin
   • BMyosin
   • CTitin
   • DTropomyosin

   (c)

   Deduce, using the measurements, how the filaments move during contraction.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   In humans, each motor neuron that leaves the spinal cord or brain branches to supply a group of skeletal muscle fibres. In a muscle that moves the eyeball, one motor neuron supplies on average about 10 muscle fibres. In the gastrocnemius (calf) muscle, one motor neuron supplies on average about 1500 muscle fibres. Both muscles contain many hundreds of these units, and the fibres of one unit are scattered among the fibres of other units.

   (a)

   Which is a motor unit?

   [1 mark]

   • AA sensory neuron and the muscle fibres it detects stretch in
   • BOne muscle fibre and all the sarcomeres it contains
   • CAll the motor neurons that supply one whole muscle
   • DOne motor neuron and all the muscle fibres it stimulates

   (b)

   An impulse passes along one motor neuron in the gastrocnemius. What happens?

   [1 mark]

   • AOnly the muscle fibre nearest the spinal cord contracts
   • BAll about 1500 fibres of that unit contract together
   • CEvery fibre in the whole gastrocnemius contracts
   • DThe fibres contract one after another along the muscle

   (c)

   Explain why the eye muscle can be controlled more precisely than the gastrocnemius.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A physiotherapist uses a goniometer to measure the range of motion of a 64-year-old patient's right hip, which has osteoarthritis (the articular cartilage has worn thin). Reference values for a healthy adult hip are: flexion 120°, extension 30°, abduction (leg moved sideways away from the body) 45° and adduction (leg moved across the body) 30°. The patient's right hip measured: flexion 90°, extension 10°, abduction 20° and adduction 25°. Each value is the mean of three readings taken by the same physiotherapist.

   (a)

   Outline the roles of the articular cartilage, synovial fluid and ligaments in the hip joint.

   [3 marks]

   (b)

   Calculate the percentage reduction in the patient's flexion compared with the reference value, Analyse the pattern across the four directions of movement and evaluate how well the data show the effect of osteoarthritis.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Humpback whales (Megaptera novaeangliae) feed on krill in polar waters in summer and migrate up to 8000 km to tropical waters in winter, where they mate and give birth. They dive for up to 15 minutes, surfacing to breathe through a blowhole on the top of the head. Acorn barnacles (Coronula diadema) live cemented to the skin of humpback whales. An adult barnacle never moves from its position; it opens its shell plates and sweeps feathery legs through the water to catch plankton. Its larvae swim freely before settling on a whale.

   (a)

   Explain how the humpback whale is adapted for swimming and diving.

   [6 marks]

   (b)

   Discuss the reasons for locomotion in animals, comparing the humpback whale with the barnacle.

   [6 marks]

   Total for question 4: 12 marks

End of questions