Muscle contractionAQA A-Level Biology: Mind map

Exam questions on Muscle contraction

1. A biochemist is investigating how protein filaments interact within the sarcomeres of skeletal muscle. She works with isolated myofibrils from a mammal, to which she can add ATP and calcium ions as she chooses.
   Explain how the movement of myosin heads causes the sarcomere to shorten.2 marks
2. Within a few hours of death, the skeletal muscles of an animal become stiff and cannot be stretched (rigor mortis). During life, a resting muscle is soft and its myofibrils are easily stretched. After death, ATP is no longer made in the muscle and calcium ions leak out of the sarcoplasmic reticulum.
   When stimulation of a living muscle stops, the muscle relaxes. Explain how.2 marks
3. In a 100 m sprint, a muscle uses ATP at a rate of 4 mmol kg⁻¹ s⁻¹. At the start of the race the muscle contains an ATP store of 5 mmol kg⁻¹ and a phosphocreatine store of 25 mmol kg⁻¹. One molecule of phosphocreatine can regenerate one molecule of ATP.
   Calculate for how long the ATP and phosphocreatine stores together could supply the sprint. State what the muscle must rely on after this time.3 marks