Skeletal muscle structureAQA A-Level Biology: Mind map

Exam questions on Skeletal muscle structure

1. A physiotherapist is explaining arm movement to a patient who is recovering from an elbow injury. She uses the biceps muscle on the front of the upper arm and the triceps muscle on the back of the upper arm, both of which are attached by tendons to bones of the forearm and shoulder.
   The biceps and triceps are described as an antagonistic pair. Explain how they work together to bend and then straighten the elbow.2 marks
2. In a relaxed sarcomere from a mammalian skeletal muscle, the distance from one Z line to the next is 2.4 µm. The dark A band is 1.6 µm long. In the centre of the A band is a lighter region, the H zone, which is 0.4 µm long.
   Explain why the A band appears darker than the I band in an electron micrograph.2 marks
3. A physiologist takes muscle biopsies from the thigh of a marathon runner and of a sprinter. About 80% of the fibres in the runner's sample are slow fibres, compared with about 25% in the sprinter's sample. The sprinter's fast fibres have thicker myosin filaments, a large store of phosphocreatine, high concentrations of glycolytic enzymes and few mitochondria.
   Explain why a high proportion of slow fibres is an advantage in the leg muscles of a marathon runner.3 marks