Question

the role of calcium ions in muscle contraction is to bind: a troponin b actin c myosin d atp e tropomyosin

Explanation:

When a muscle is stimulated to contract, calcium ions ($Ca^{2 + }$) are released from the sarcoplasmic reticulum. These $Ca^{2 + }$ ions bind to troponin. This binding causes a conformational change in troponin. As a result, tropomyosin (which normally blocks the myosin - binding sites on actin) is moved out of the way. Then, myosin heads can bind to actin, and muscle contraction can occur. Actin is the thin filament, myosin is the thick filament, ATP provides energy for muscle contraction (myosin heads break down ATP for energy), and tropomyosin is moved by the action of troponin - calcium complex.

Answer:

A. troponin