Explain how the structure of a skeletal muscle cell (muscle fibre) is adapted for its function in contraction.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Skeletal muscle cells are long, cylindrical fibres that can generate large forces.
1. They contain many mitochondria, which supply the large amounts of ATP required for repeated contraction.
2. They are multinucleate, so the large cell volume can be controlled and enough contractile proteins can be produced.
3. Their cytoplasm is packed with myofibrils made of actin and myosin; the sliding of these proteins shortens the sarcomere and generates force.
4. The elongated shape means that shortening along the cell’s length translates directly into movement of the attached bone or tissue.
1. They contain many mitochondria, which supply the large amounts of ATP required for repeated contraction.
2. They are multinucleate, so the large cell volume can be controlled and enough contractile proteins can be produced.
3. Their cytoplasm is packed with myofibrils made of actin and myosin; the sliding of these proteins shortens the sarcomere and generates force.
4. The elongated shape means that shortening along the cell’s length translates directly into movement of the attached bone or tissue.
Examiner tips
- Use the word ‘elongated’ to link shape with function; mention mitochondria, multinucleate, myofibrils, actin–myosin sliding; keep each point concise and directly tied to the marks.
- Show the chain: structure → function → movement; avoid extra detail that takes marks away from the required points.
Common mistakes
- Writing that muscle cells are ‘single‑nucleated’; they are multinucleate.
- Forgetting to mention the mitochondria or the sliding filament mechanism.
- Using vague terms like ‘many’ without specifying the key components (actin, myosin, sarcomere).
Mark scheme (4 marks)
- Skeletal muscle cells contain many mitochondria, which supply the large amounts of ATP required for repeated contraction.
- Muscle fibres contain multiple nuclei (are multinucleate), allowing the large cell volume to be controlled and sufficient quantities of contractile proteins to be produced.
- The cells contain myofibrils made up of the contractile proteins actin and myosin, which slide past each other to shorten the sarcomere and generate force.
- The cells are elongated/cylindrical in shape, so that shortening along their length translates into movement of the attached bone or tissue.
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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