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Multiple Choice
Which structure within a muscle fiber stores calcium ions necessary for muscle contraction?
A
Myofibril
B
Sarcolemma
C
T-tubule
D
Sarcoplasmic reticulum
Verified step by step guidance
1
Understand the role of calcium ions in muscle contraction: Calcium ions are essential for initiating the interaction between actin and myosin filaments, which leads to muscle contraction.
Identify the structure responsible for storing calcium ions: Within a muscle fiber, calcium ions are stored in a specialized organelle called the sarcoplasmic reticulum.
Differentiate the sarcoplasmic reticulum from other structures: The sarcoplasmic reticulum is a network of membranous tubules that surrounds the myofibrils, distinct from the sarcolemma (the muscle cell membrane) and T-tubules (which transmit electrical signals).
Understand the release mechanism: When a muscle fiber is stimulated, the sarcoplasmic reticulum releases calcium ions into the cytoplasm, triggering the contraction process.
Conclude the correct answer: Based on the function and location, the sarcoplasmic reticulum is the structure within a muscle fiber that stores calcium ions necessary for muscle contraction.