Question

rigor mortis occurs because _______.

no atp is available to release attached actin and myosin molecules

sodium ions leak into the muscle causing continued contractions

proteins are beginning to break down, thus preventing a flow of calcium ions

the cells are dead

Explanation:

Rigor mortis occurs when there is no ATP available. ATP is needed to release the attached actin and myosin molecules. When a person dies, ATP production stops. Without ATP, the cross - bridges (formed by actin and myosin interaction) cannot be broken, leading to muscle stiffness. Sodium ions do not cause continued contractions in rigor mortis as the ion balance is disrupted in a different way. Proteins breaking down is not the immediate cause related to the actin - myosin interaction. Just the cells being dead is too general; it is the lack of ATP (a key molecule for muscle relaxation) that is the specific cause related to the actin - myosin complex.

Answer:

A. no ATP is available to release attached actin and myosin molecules