Which of these events is necessary for the contraction of a muscle cell? A. the shortening of myosin molecules. B. the hydrolysis of ATP to ADP & HPO 4 2− in the myosin cross-bridge. C. Ca 2+ binding to tropomyosin causing it to change shape. D. the movement of Ca 2+ from the sarcoplasm into the sarcoplasmic reticulum.
Option B . The hydrolysis of ATP to ADP and HPO4 2- in the myosine cross bridge is the necessary event for muscle contraction.
