How did data on sarcomere structure inspire the sliding-filament model of muscle contraction?
Explain why the observation that muscle cells contain many mitochondria and extensive smooth endoplasmic reticulum turned out to be logical once the molecular mechanism of muscular contraction was understood.

Arm muscles and leg muscles are arranged in antagonistic pairs. How does this affect their functioning?

a. It provides a backup if one of the muscles is injured.

b. One muscle of the pair pushes while the other pulls.

c. A single motor neuron can control both of them.

d. It allows the muscles to produce opposing movements.

Which of the following is critical to the function of most exoskeletons, endoskeletons, and hydrostatic skeletons?

a. Muscles interact with the skeleton in antagonistic groups.

b. Muscles attach to each of these types of skeletons via tendons.

c. Muscles extend joints by pushing skeletal elements.

d. Segments of the body or limbs are extended when paired muscles relax in unison.

Gravity would have the least effect on the movement of which of the following? (Explain your answer.)

a. A salmon

b. A snake

c. A sparrow

d. A grasshopper

Which of the following bones in the human arm corresponds to the femur in the leg?

a. Radius

b. Tibia

c. Humerus

d. Metacarpal

Which of the following animals is correctly matched with its type of skeleton?

a. Fly—endoskeleton

b. Earthworm—exoskeleton

c. Lobster—exoskeleton

d. Bee—hydrostatic skeleton

Rigor mortis is the stiffening of a body after death that occurs when myosin binds to actin but cannot unbind. What prevents myosin from unbinding?

When a dog is running fast, its body position is stabilized by

a. Side-to-side undulation

b. Energy stored in tendons

c. Foot contact with the ground

d. Its momentum

What is the role of calcium in muscle contraction?

a. Its binding to a regulatory protein causes the protein to move, exposing actin binding sites to the myosin heads.

b. It provides energy for contraction.

c. It blocks contraction when the muscle relaxes.

d. It forms the heads of the myosin molecules in the thick filaments inside a muscle fiber.