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

In muscle cells, myosin molecules continue moving along actin molecules as long asa. ATP is present and troponin is not bound to Ca2+.b. ADP is present and tropomyosin is released from intracellular stores.c. ADP is present and the intracellular acetylcholine level is high.d. ATP is present and the intracellular Ca2+ concentration is high

During the contraction of a vertebrate skeletal muscle fiber, calcium ionsa. break cross-bridges as a cofactor in hydrolysis of ATP.b. bind with troponin, changing its shape so that the myosin-binding sites on actin are exposed.c. transmit action potentials from the motor neuron to the muscle fiber.d. spread action potentials through the T tubules.

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 skeleton 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.

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

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?