# Explain how the structure of a skeletal muscle cell (muscle fibre) is adapted for its function in contraction.

> IB DP Biology Standard Level (2023 syllabus) — B2.3 Cell specialisation · Explain · 4 marks

## Mark scheme (4 marks)

1. Skeletal muscle cells contain many mitochondria, which supply the large amounts of ATP required for repeated contraction.
2. Muscle fibres contain multiple nuclei (are multinucleate), allowing the large cell volume to be controlled and sufficient quantities of contractile proteins to be produced.
3. 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.
4. The cells are elongated/cylindrical in shape, so that shortening along their length translates into movement of the attached bone or tissue.

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