Which statement about muscle contraction is correct?

An earthworm's body consists of a number of fluid-filled compartments, each with its own set of longitudinal and circular muscles. But in the roundworm, a single fluid-filled cavity occupies the body, and there are only longitudinal muscles that run its entire length. Predict how the movement of a roundworm would differ from the movement of an earthworm.

When a person dies, muscles become rigid and fixed in position—a condition known as rigor. Rigor mortis occurs because muscle cells are no longer supplied with ATP (when breathing stops, ATP synthesis ceases). Calcium also flows freely into dying cells. The rigor eventually disappears because the biological molecules break down. Explain, in terms of the mechanism of contraction described in Modules 30.9 and 30.10, why the presence of calcium and the lack of ATP would cause muscles to become rigid, rather than limp, soon after death.

SCIENTIFIC THINKING Imagine you have a friend who had her child's ACTN3 genotype tested. After reviewing the study described in Module 30.12, what cautions would you offer about interpreting the test results?

What type of muscle is striated with intercalated disks?

What do all muscle tissues have in common?

Why is having a hydrostatic skeleton rather than an internal skeleton advantageous to an earthworm?

Locomotion requires that an animal expend energy to overcome __________.

When comparing the different styles and adaptations of each major type of locomotion, what is the most energy-efficient mode of locomotion?