Cell Bio Ch. 12

12-2 Which of the following channels would not be expected to generate a change in voltage by movement of its substrate across the membrane where it is found?

(a) an aquaporin

(b) a sodium channel

(c) a calcium channel

(d) a proton channel

(a) an aquaporin

12-3 Although the extracellular environment has a high sodium ion concentration and the intracellular environment has a high potassium ion concentration, both must be neutralized by negatively charged molecules. In the extracellular case, what is

the principal anion?

(a) HCO3-

(b) Cl-

(c) PO43-

(d) OH-

(b) Cl-

12-5 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? Why?

(a) glucose

(b) water

(c) glycerol

(d) ethanol

(a) glucose

12-6 Below is a list of molecules with different chemical characteristics. Knowing that all molecules will eventually diffuse across a phospholipid bilayer, select the option below that most accurately predicts the relative rates of diffusion of these molecules (fastest to slowest).

alanine estrogen propanol sodium

(a) alanine > propanol > sodium > estrogen

(b) sodium > propanol > alanine > estrogen

(c) estrogen > propanol > sodium > alanine

(d) estrogen > propanol > alanine > sodium

(d) estrogen > propanol > alanine > sodium

12-8 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+

12-9 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+

12-10 Cells use membranes to help maintain set ranges of ion concentrations inside and outside the cell. Which of the following negatively charged ions is not primarily used to buffer positive charges inside the cell?

(a) PO43-

(b) OH-

(c) Cl-

(d) HCO3-

(c) Cl-

12-11 Negatively charged ions are required to balance the net positive charge from metal ions such as K+, Na+, and Ca2+. Which of the following negatively charged ions is the most abundant outside the cell and which ion does most often neutralize (written in parentheses)?

(a) Cl- (Ca2+)

(b) PO43- (K+)

(c) PO43- (Ca2+)

(d) Cl- (Na+)

(d) Cl- (Na+)

12-12 Which of the following statements about resting membrane potential is not true?

(a) The resting membrane potential for most animal cells is 0 mV, because the

positive and negative ions are in balance.

(b) The resting membrane potential for most animal cells is positive, because

Na+ ions are so plentiful inside cells.

(c) The resting membrane potential for most animal cells is negative, because

the inside of the cell is more negatively charged than the outside of the

cell.

(d) At the resting membrane potential, no ions enter or exit the cell.

(c) The resting membrane potential for most animal cells is negative, because

the inside of the cell is more negatively charged than the outside of the

cell.

12-13 A hungry yeast cell lands in a vat of grape juice and begins to feast on the sugars there, producing carbon dioxide and ethanol in the process:

C6H12O6 + 2ADP + 2Pi + H+!2CO2 + 2CH3CH2OH + 2ATP + 2H2O

Unfortunately, the grape juice is contaminated with proteases that attack some of the transport proteins in the yeast cell membrane, and the yeast cell dies. Which of the following could account for the yeast cell's demise?

(a) toxic buildup of carbon dioxide inside the cell

(b) toxic buildup of ethanol inside the cell

(c) diffusion of ATP out of the cell

(d) inability to import sugar into the cell

(d) inability to import sugar into the cell

12-15 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

12-16 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.

12-17 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.

12-20 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) A TP-driven

(d) light-driven

(b) K+-coupled

12-21 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

12-27 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.

12-28 Cells make use of H+ electrochemical gradients in many ways. Which of the following proton transporters is used to regulate pH in animal cells?

(a) light-driven pump

(b) H+ A TPase

(c) H+ symporter

(d) Na+-H+ exchanger

(d) Na+-H+ exchanger

12-29 Which of the following statements is true?

(a) Amoebae have transporter proteins that actively pump water molecules

from the cytoplasm to the cell exterior.

(b) Bacteria and animal cells rely on the Na+-K+ pump in the plasma

membrane to prevent lysis resulting from osmotic imbalances.

(c) The Na+-K+ pump allows animal cells to thrive under conditions of very

low ionic strength.

(d) The Na+-K+ pump helps to keep both Na+ and Cl- ions out of the cell.

(d) The Na+-K+ pump helps to keep both Na+ and Cl- ions out of the cell.

12-30 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 endoplasmic reticulum 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.

12-35 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

12-36 Which of the following best describes the behavior of a gated channel?

(a) It stays open continuously when stimulated.

(b) It opens more frequently in response to a given stimulus.

(c) It opens more widely as the stimulus becomes stronger.

(d) It remains closed if unstimulated.

(b) It opens more frequently in response to a given stimulus.

12-39 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

12-41 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.

12-42 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.

12-43 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.

12-46 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.

12-48 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.

12-52 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

12-59 The stimulation of a motor neuron ultimately results in the release of a neurotransmitter at the synapse between the neuron and a muscle cell. What type of neurotransmitter is used at these neuromuscular junctions?

(a) acetylcholine

(b) glutamate

(c) GABA

(d) glycine

(a) acetylcholine

12-60 Both excitatory and inhibitory neurons form junctions with muscles. By what mechanism do inhibitory neurotransmitters prevent the postsynaptic cell from firing an action potential?

(a) by closing Na+ channels

(b) by preventing the secretion of excitatory neurotransmitters

(c) by opening K+ channels

(d) by opening Cl- channels

(d) by opening Cl- channels

12-62 Which of the following statements best reflects the nature of synaptic plasticity?

(a) New synapses are created due to the postnatal generation of neurons.

(b) Synaptic response changes in magnitude depending on frequency of

stimulation.

(c) There is a change in the type of neurotransmitter used at the synapse.

(d) Neuronal connections are pruned during normal development.

(b) Synaptic response changes in magnitude depending on frequency of

stimulation.

12-63 Approximately, how many distinct synapses are established on the dendrites and cell body of a motor neuron in the spinal cord?

(a) tens

(b) hundreds

(c) thousands

(d) millions

(c) thousands

12-64 Which of the following statements about GABA receptors is not true?

(a) They are located on postsynaptic membranes.

(b) They are ligand-gated channels.

(c) They inhibit synaptic signaling.

(d) They promote neuronal uptake of Na+.

(d) They promote neuronal uptake of Na+

12-66 Which of the following gated ion channels are involved in inhibitory synaptic signaling?

(a) voltage-gated Na+ channels

(b) voltage-gated Ca2+ channels

(c) glycine-gated Cl- channels

(d) glutamate-gated cation channels

c) glycine-gated Cl- channels