During a weightlifting competition, an athlete repeatedly lifts heavy barbells overhead. Each lift requires muscles to contract powerfully. Explain the role of ATP, actin, myosin and calcium ions in bringing about a single muscle contraction.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
During a weightlifting competition, an athlete repeatedly lifts heavy barbells overhead. Each lift requires the muscles to contract powerfully and rapidly.
Model answer (5 marks)
ATP provides the energy needed for muscle contraction.
Calcium ions are released from the sarcoplasmic reticulum when a nerve impulse arrives, triggering contraction.
Myosin heads bind to binding sites on actin filaments, forming cross‑bridges.
The myosin heads pivot/pull the actin filaments toward the centre of the sarcomere (power stroke), causing the filaments to slide.
ATP allows the myosin head to detach from actin and reset, so the cycle can repeat.
Calcium ions are released from the sarcoplasmic reticulum when a nerve impulse arrives, triggering contraction.
Myosin heads bind to binding sites on actin filaments, forming cross‑bridges.
The myosin heads pivot/pull the actin filaments toward the centre of the sarcomere (power stroke), causing the filaments to slide.
ATP allows the myosin head to detach from actin and reset, so the cycle can repeat.
Examiner tips
- Use the exact terminology (ATP, actin, myosin, calcium, sarcoplasmic reticulum, cross‑bridge, power stroke).
- Show the sequence: calcium release → cross‑bridge formation → power stroke → ATP‑driven detachment and reset.
- Keep the answer concise – 5 points, one sentence per point.
Common mistakes
- Confusing calcium with potassium or sodium; only calcium triggers contraction.
- Forgetting to mention ATP’s role in detaching the myosin head.
- Using vague terms like ‘energy’ without specifying ATP.
Mark scheme (5 marks)
- ATP provides the energy needed for muscle contraction
- Calcium ions are released (from the sarcoplasmic reticulum) when a nerve impulse arrives, triggering contraction
- Myosin heads bind to binding sites on actin filaments, forming cross-bridges
- Myosin heads pivot / pull the actin filaments towards the centre of the sarcomere (power stroke), causing the filaments to slide
- ATP allows the myosin head to detach from actin and reset, so the cycle can repeat
Key terms in this question
ATP · actin · myosin · calcium ions
Related
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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