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?

Gravity would have the least effect on the movement of which of the following? (Explain your answer.)a. a salmona. a snakea. a sparrowa. a grasshopper

Which of the following bones in the human arm corresponds to the femur in the leg?a. radiusb. tibiac. humerusd. metacarpal

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.

Which of the following animals is correctly matched with its type of skeleton?a. fly—endoskeletonb. earthworm—exoskeletonc. lobster—exoskeletond. bee—hydrostatic skeleton

When a dog is running fast, its body position is stabilized bya. 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.

Muscle A and muscle B have the same number of fibers, but muscle A is capable of more precise control than muscle B. Which of the following is likely to be true of muscle A? (Explain your answer.)a. It is controlled by more neurons than muscle B.b. It contains fewer motor units than muscle B.c. It is controlled by fewer neurons than muscle B.d. It has larger sarcomeres than muscle B.

Which of the following statements about skeletons is true?a. Chitin is a major component of vertebrate skeletons.b. Loss of forelimbs in snakes involved little change in the axial skeleton.c. Most cnidarians must shed their skeleton periodically to grow.d. Vertebrate bones contain living cells.