When a muscle fibre is stimulated, the calcium ions needed for contraction are released from the

  • A. mitochondria
  • B. Golgi apparatus
  • C. nucleus
  • D. sarcoplasmic reticulum

Explanation

The sarcoplasmic reticulum stores calcium and floods the fibre with it when an impulse arrives along the T tubules. Mitochondria supply the ATP for contraction but not the calcium that triggers it.

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