Cell Bio Chapter 12 Quiz

We can test the relative permeability of a phospholipid bilayer by using a synthetic membrane that does not contain any protein components. Some uncharged, polar molecules are found to diffuse freely across these membranes, to varying degrees. Which of the following has the lowest rate of diffusion across an artificial membrane? a. Glucose b. Water c. Glycerol d. Ethanol

a. Glucose

Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell. Which of the following ions is the most abundant outside a typical mammalian cell? a. Na+ b. K+ c. Ca2+ d. Cl-

a. Na+

Voltage-gated channels contain charged protein domains, which are sensitive to changes in membrane potential. By responding to a threshold in the membrane potential, these voltage sensors trigger the opening of the channels. Which of the following best describes the behavior of a population of channels exposed to such a threshold? a. Some channels remain closed and some open completely. b. All channels open completely. c. All channels open partly, to the same degree. d. All channels open partly, each to a different degree.

a. Some channels remain closed and some open completely.

Pumps are transporters that are able to harness energy provided by other components in the cells to drive the movement of solutes across membranes, against their concentration gradient. This type of transport is called _____________. a. active transport. b. free diffusion. c. facilitated diffusion d. passive transport.

a. active transport.

Transporters, in contrast to channels, work by ________________. a. specific binding to solutes. b. a gating mechanism. c. filtering solutes by charge. d. filtering solutes by size

a. specific binding to solutes.

If Na+ channels are opened in a cell that was previously at rest, how will the resting membrane potential be affected? a. The membrane potential is not affected by Na+. b. It becomes more negative. c. It becomes more positive. d. It is permanently reset.

c. It becomes more positive.

When the net charge on either side of the plasma membrane is zero, what else is true? a. There is an equal number of K+ ions on each side of the plasma membrane. b. The K+ leak channels are open. c. The electrochemical potential across the membrane is zero. d. The resting membrane potential is between -20 mV and -200 mV.

c. The electrochemical potential across the membrane is zero.

Some cells have aquaporins—channels that facilitate the flow of water molecules through the plasma membrane. For these cells, what regulates the rate and direction of water diffusion across the membrane? a. aquaporin conformation b. resting membrane potential c. solute concentrations on either side of the membrane d. availability of ATP

c. solute concentrations on either side of the membrane

The Na+-K+ ATPase is also known as the Na+-K+ pump. It is responsible for maintaining the high extracellular sodium ion concentration and the high intracellular potassium ion concentration. What happens immediately after the pump hydrolyzes ATP? a. Na+ is bound b. ADP is bound c. the pump is phosphorylated d. the pump changes conformation

c. the pump is phosphorylated

You have generated antibodies that recognize the extracellular domain of the Ca2+-pump. Adding these antibodies to animal cells blocks the active transport of Ca2+ from the cytosol into the extracellular environment. What do you expect to observe with respect to intracellular Ca2+? a. Ca2+-pumps in vesicle membranes keep cytosolic calcium levels low. b. Ca2+-pumps in the endoplasmic reticulum membrane keep cytosolic calcium levels low. c. Ca2+-pumps in the Golgi apparatus keep cytosolic calcium levels low. d. Ca2+ concentrations in the cytosol increase at a steady rate.

b. Ca2+-pumps in the endoplasmic reticulum membrane keep cytosolic calcium levels low.

Ion channels are classified as membrane transport proteins. Channels discriminate by size and charge. In addition to Na+, which one of the following ions would you expect to be able to freely diffuse through a Na+ channel? a. Mg2+ b. H+ c. K+ d. Cl-

b. H+

Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell. Which of the following ions is the most abundant inside a typical mammalian cell? a. Na+ b. K+ c. Ca2+ d. Cl-

b. K+

Active transport requires the input of energy into a system so as to move solutes against their electrochemical and concentration gradients. Which of the following is not one of the common ways to perform active transport? a. Na+-coupled b. K+-coupled c. ATP-driven d. light-driven

b. K+-coupled

Which of the following occur without coupling transport of the solute to the movement of a second solute? a. import of glucose into gut epithelial cells b. export of Ca2+ from the cytosol c. export of H+ from animal cells for pH regulation d. the export of Na+ from cells to maintain resting membrane potential

b. export of Ca2+ from the cytosol

Ca2+-pumps in the plasma membrane and endoplasmic reticulum are important for ________________. a. maintaining osmotic balance. b. preventing Ca2+ from altering the activity of molecules in the cytosol. c. providing enzymes in the ER with Ca2+ ions that are necessary for their catalytic activity. d. maintaining a negative membrane potential.

b. preventing Ca2+ from altering the activity of molecules in the cytosol.

In a method called patch-clamping, a glass capillary can be converted into a microelectrode that measures the electrical currents across biological membranes. Which of the following is not true about the patch-clamp method? a. The glass capillary adheres to a "patch" of membrane through the application of suction. b. The aperture in the glass capillary used to make a microelectrode is about 1 μm in diameter. c. If the experimental conditions are held constant, fluctuations in electrical currents across the patch of membrane are still observed. d. Single-channel patch-clamp recordings have demonstrated that gated membrane channels will only open and close in response to specific stimuli.

d. Single-channel patch-clamp recordings have demonstrated that gated membrane channels will only open and close in response to specific stimuli.

Which of the following statements does not accurately describe the events involved in the propagation of an action potential? a. An initial influx of Na+ through a small cluster of channels causes local depolarization of the membrane. b. Local depolarization causes nearby Na+ channels to open. c. Channels in depolarized regions of the membrane are inactivated until the resting membrane potential is reestablished d. The opening of transmitter-gated K+ channels helps to repolarize the membrane.

d. The opening of transmitter-gated K+ channels helps to repolarize the membrane.

K+ leak channels are found in the plasma membrane. These channels open and close in an unregulated, random fashion. What do they accomplish in a resting cell? a. They set the K+ concentration gradient to zero. b. They set the membrane potential to zero. c. They disrupt the resting membrane potential. d. They keep the electrochemical gradient for K+ at zero.

d. They keep the electrochemical gradient for K+ at zero.

The stimulation of auditory nerves depends on the opening and closing of channels in the auditory hair cells. Which type of gating mechanism do these cells use? a. voltage-gated b. extracellular ligand-gated c. intracellular ligand-gated d. stress-gated

d. stress-gated

Which of the following is required for the secretion of neurotransmitters in response to an action potential? a. neurotransmitter receptors b. Na+-K+ pumps c. voltage-gated K+ channels d. voltage-gated Ca2+ channels

d. voltage-gated Ca2+ channels