Eukaryotic Cells Chapter 12

1.Which of the following membrane transport proteins forms tiny hydrophilic pores in the membrane through which solutes can pass by diffusion?
A. A transporter
B. A channel
C. A pump

B. A channel

2.Lipid bilayers are highly impermeable to:
A. carbon dioxide. B. water.
C. Na+ and Cl-. D. ethanol.

C. Na+ and Cl-

3.Which of the following inhibits ions from passing through a lipid bilayer?
A. The watery environment on either side of the lipid bilayer
B. The hydrophilic exterior of the lipid bilayer
C. The hydrophobic interior of the lipid bilayer

C. The hydrophobic interior of the lipid bilayer

4.In general, which of the following will diffuse across a lipid bilayer most rapidly?
A. A small hydrophilic molecule
B. A small hydrophobic molecule
C. A large hydrophilic molecule
D. A large hydrophobic molecule

B. A small hydrophobic molecule

5.Sodium ions, oxygen (O2), and glucose pass directly through lipid bilayers at dramatically different rates. Which of the following choices presents the correct order, from fastest to slowest?
A. Glucose, oxygen, sodium ions
B. Glucose, sodium ions, oxyg

C. Oxygen, glucose, sodium ions

6.Which of the following statements is true?
A. Na+ is the most plentiful positively charged ion outside the cell, while K+ is the most plentiful inside.
B. K+ is the most plentiful positively charged ion outside the cell, while Na+ is the most plentiful

A. Na+ is the most plentiful positively charged ion outside the cell, while K+ is the most plentiful inside.

7.Which of the following statements is true?
A. Inside the cell the quantity of positively charged ions is greater than the quantity of negatively charged ions.
B. Inside the cell the quantity of positively charged ions is less than the quantity of negati

C. Inside the cell the quantity of positively charged ions is almost exactly equal to the quantity of negatively charged ions.

8.The voltage difference across a membrane of a cell is called the:
A. electrical potential. B. electrical current.
C. membrane potential. D. potential energy.

C. membrane potential

9.What is the difference between transporters and channels?
A. Transporters discriminate between solutes mainly on the basis of size and electric charge; channels bind their solutes with great specificity in the same way an enzyme binds its substrate.
B.

B. Channels discriminate between solutes mainly on the basis of size and electric charge; transporters bind their solutes with great specificity in the same way an enzyme binds its substrate.

10.Which type of membrane transport protein can perform either passive or active transport?
A. Transporters
B. Channels

A. Transporters

11.The movement of an ion down its electrochemical gradient is called:
A. active transport. B. passive transport. C. osmosis.
D. pumping.

B. passive transport.

12.Which of the following scenarios requires an input of energy to occur?
A. The movement of a solution from a region of higher concentration on one side of a membrane to a region of lower concentration on the other side.
B. The movement of a solution fro

B. The movement of a solution from a region of lower concentration on one side of a membrane to a region of higher concentration on the other side.

13.When glucose moves across a phospholipid bilayer by passive transport, which factor determines the direction of its transport?
A. (A) The concentrations of glucose on either side of the membrane
B. (B) The charge difference across the membrane
C. (C) T

A. (A) The concentrations of glucose on either side of the membrane

14.The inside of a cell:
A. is more positive than the outside of a cell.
B. is more negative than the outside of a cell.
C. has the same charge as the outside of the cell.

B. is more negative than the outside of a cell.

15.All other factors (e.g., concentration, solute size) being equal, which type of solute does a cell tend to pull inside?
A. Positively charged solutes
B. Negatively charged solutes
C. Uncharged solutes

A. Positively charged solutes

16.In passive transport, a charged solute moves spontaneously in which way?
A. Down its concentration gradient B. Down its electrochemical gradient C. Down its osmotic gradient

B. Down its electrochemical gradient

17.An electrochemical gradient has a chemical component and voltage component. Which of the following will have the largest electrochemical gradient? A. A positively charged ion present in high concentrations inside the cell
B. A positively charged ion pr

B. A positively charged ion present in high concentrations outside the cell

18.Which of the following has a larger electrochemical gradient across a cell's plasma membrane?
A. K+
B. Na+

B. Na+

19.Osmosis can be described as:
A. the movement of water from an area of high solute concentration to an area of low solute concentration.
B. the movement of water from an area of low water concentration to an area of high water concentration.
C. the move

C. the movement of water from an area of low solute concentration to an area of high solute concentration.

20.Which of the following mechanisms prevents osmotic swelling in plant cells?
A. The collection of water in contractile vacuoles
B. Tough cell walls
C. The activity of Na+-K+ pumps

B. Tough cell walls

21.The direction that glucose is transported across the membrane is determined by:
A. the electrochemical gradient.
B. the membrane potential.
C. the concentration gradient.
D. the molecule's charge.

C. the concentration gradient.

22.Which of the following statements is NOT true regarding active transport?
A. Some solutes are moved against their concentration gradients, from one side of a membrane to the other, using energy from ATP hydrolysis.
B. Light-driven pumps couple the move

C. A coupled transporter brings two different types of solutes across the membrane, both moving from higher concentration to lower concentration.

23.The Na+-K+ pump in the plasma membrane of animal cells uses the energy from ATP hydrolysis to pump sodium and potassium ions against their electrochemical gradients. In which direction are the ions pumped across the membrane?
A. Na+ out and K+ in B. K+

A. Na+ out and K+

24.Which of the following statements is true about the concentration of calcium ions in cells?
A. Calcium levels are kept high in the cytosol compared to outside the cell.
B. Calcium levels are kept low in the cytosol compared to outside the cell.
C. Calc

B. Calcium levels are kept low in the cytosol compared to outside the cell.

25.Which organelle is important for controlling the concentration of calcium ions in the cytosol?
A. The Golgi apparatus
B. The nucleus
C. Lysosomes
D. The endoplasmic reticulum

D. The endoplasmic reticulum

26.Which term describes a coupled transporter that moves both solutes in the same direction across a membrane?
A. Antiport
B. Symport
C. Uniport

B. Symport

27.The glucose-Na+ symport in epithelial cells uses the electrochemical gradient of Na+ to draw glucose into the cell.
A. True
B. False

A. True

28.In fungi, plants, and bacteria, which pump helps to drive the import of solutes?
A. ATP pumps
B. H+ pumps
C. Ca2+ pumps
D. K+ pumps

B. H+ pumps

29.What is typically true of ion channels?
A. They are open all the time.
B. They are gated.
C. They operate by active transport.

B. They are gated.

30.An ion channel undergoes conformational changes with each ion it passes.
A. True B. False

B. False

31.Which of the following statements describes a resting membrane potential of a neuron?
A. A state in which the flow of positive and negative ions across the plasma
membrane is precisely balanced
B. A measure of 0 millivolts (mV) across the membrane
C. A

A. A state in which the flow of positive and negative ions across the plasma is precisely balanced

32.In most animal cells, which ion can move through "leak" channels in the plasma membrane and, in so doing, establishes the resting membrane potential?
A. Cl-
B. K+
C. Na+
D. Ca2+

B. K+

33.When Na+ channels are opened in an animal cell, what happens to the membrane potential?
A. It stays the same.
B. It becomes less negative.
C. It becomes more negative.

B. It becomes less negative

34.When an individual ion channel is stimulated to open (for example, by the binding of a neurotransmitter), what is the typical activity of the ion channel?
A. It opens and stays open until the neurotransmitter detaches.
B. It opens and then very quickly

C. It flickers between open and closed states, but spends more time open while the neurotransmitter is bound.

35.Auditory hair cells in the ear depend on what type of ion channel to detect sound vibrations?
A. Voltage-gated
B. Ligand-gated
C. Stress-gated

C. Stress-gated

36.Which type of ion channel plays the major role in propagating electrical signals in nerve cells?
A. Voltage-gated
B. Ligand-gated
C. Stress-gated

A. Voltage-gated

37.For voltage-gated channels, a change in the membrane potential has what effect on the channel?
A. It changes the width of the channel opening.
B. It alters the probability that the channel will be found in its open conformation.
C. It either opens the

B. It alters the probability that the channel will be found in its open conformation.

38.When a neuron is stimulated by a signal, the response is at first spread locally along the membrane by what means?
A. Passive spread
B. Active transport
C. Action potential

C. Action potential

39.What is incorrect about a nerve impulse?
A. It is another term for an action potential.
B. It is electrical activity of the plasma membrane that is propagated rapidly along the membrane and sustained by automatic renewal along the way.
C. It depends on

C. It depends on the action of ligand-gated ion channels.

40.When a neuron opens voltage-gated Na+ channels, what happens to the membrane?
A. It polarizes
B. It depolarizes
C. No change in the membrane potential occurs

B. It depolarizes

41.During an action potential, which of the following actions does not help return the membrane to its resting potential?
A. The opening of voltage-gated Na+ channels
B. The opening of voltage-gated K+ channels
C. The inactivation of voltage-gated Na+ cha

B. The opening of voltage-gated K+ channels

42.Which of the following activities restores the ion gradients across the plasma membrane of an axon after an action potential has occurred?
A. The opening of voltage-gated Na+ channels
B. The opening of voltage-gated K+ channels
C. The activity of K+ le

D. Pumping by the Na+/K+ ATPase

43.What is the name of the specialized junction between a neuron and a target cell?
A. Synapse
B. Dendrite
C. Nerver terminal

A. Synapse

44.An electrical signal crosses the synaptic cleft between the presynaptic and postsynaptic cells.
A. True
B. False

B. False

45.When an action potential reaches a nerve terminal, what type of voltage-gated channels are opened and result in the fusion of synaptic vesicles with the cell membrane?
A. Na+
B. Ca2+ C. K+ D. Cl-

B. Ca2+

46.The communication between neurons involves the conversion between electrical and chemical signals.
A. True
B. False

A. True

47.When transmitter-gated ion channels in the membrane of a post-synaptic cell open in response to neurotransmitter binding, they:
A. alter the ion permeability of the postsynaptic membrane, which in turn may depolarize the postsynaptic membrane.
B. trigg

A. alter the ion permeability of the postsynaptic membrane, which in turn may depolarize the postsynaptic membrane.

48.Inhibitory neurotransmitters such as glycine and GABA make a postsynaptic cell harder to depolarize by:
A. allowing an influx of Na+.
B. allowing Na+ to escape.
C. allowing an influx of Cl-. D. allowing an influx of K+.

C. allowing an influx of Cl-.

49.Prozac, among many other drugs, functions by altering neurotransmitter levels in the brain. How does Prozac work?
A. By making serotonin-gated channel easier to open
B. By increasing the amount of serotonin released from the presynaptic neuron, increas

C. By blocking the reuptake of serotonin after it has been released, increasing
the amount available in the synapses that use it

50.Synaptic plasticity is largely dependent on the increase of which ion in the postsynaptic cell?
A. H+
B. Na+
C. K+ D. Ca2+

D. Ca2+

51. 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 princ

(b) Cl-

Circle the molecule in bilayer.
each pair that is more likely to diffuse through the lipid
A. amino acids or benzene
B. Cl- or ethanol
C. glycerol or RNA
D.H2O or O2
E. adenosine or ATP

Benzene
Ethanol
Glycerol
O2
Adenosine

A molecule moves down its concentration gradient by __________________ transport, but requires __________________ transport to move up its concentration gradient. Transporter proteins and ion channels function in membrane transport by providing a ________

Passive
Active
Hydrophilic
Transporters
Channels

54. 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

55. 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 transp

(a) active transport

It is thought that the glucose transporter switches between two conformational states in a completely random fashion. How is it possible for such a system to move glucose across the membrane efficiently in a single direction?

Although the opening of the glucose transporter on one side of the membrane or the
other is random, the binding of glucose into the binding site of the transporter is not a random event. The affinity between the glucose molecule and the transporter govern

58. 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+ ATPase
(c) H+ symporter
(d) Na+-H+ exchanger

(d) Na+-H+ exchanger

59. 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

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

60. 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 and
from reacting with organic anions to form preci

(b) preventing Ca2+ from altering the activity of molecules in the cytosol and
from reacting with organic anions to form precipitate

For an uncharged molecule, the direction of passive transport across a membrane is determined solely by its __________________ gradient. On the other hand, for a charged molecule, the __________________ must also be considered. The net driving force for a

Concentration
Membrane potential
Electrochemical gradient
Coupled
Symport
Antiport

62. 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
d) it remains closed if unstimulated

b) it opens more frequently in response to a given stimulus

63. Which of the following is true
a)Gap junctions are large pores that connect the cytosol to the extracellular space.
b)Aquaporin channels are found in the plasma membrane, allowing the rapid passage of water molecules and small ions in and out of cells

(d)= Most ion channels are gated, which allow them to open and close in response to a specific stimulus rather than allowing the constant, unregulated flow of ions.

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-gat

(d) stress-gated

A. The acetylcholine receptor in skeletal muscle cells is a(n)
__________________ ion channel.
B. __________________ ion channels are found in the hair cells of the
mammalian cochlea.
C. __________________ ion channels in the mimosa plant propagate the
le

A.The acetylcholine receptor in skeletal muscle cells is a(n) ligand-gated ion
B. Stress-gated ion channels are found in the hair cells of the mammalian cochlea.
C. Voltage-gated ion channels in the mimosa plant propagate the leaf-closing
response.
D. Vol

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 de

(a) Some channels remain closed and some open completely.

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.

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

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 res

(c) It becomes more positive.

Which of the following statements is TRUE?
a) Neurotransmitters are small molecules released into the synaptic cleft after the fusion of synaptic vesicles with the postsynaptic membrane.
b)Action potentials are usually mediated by voltage-gated Ca2+ chann

c) Voltage-gated Na+ channels become automatically inactivated shortly after opening, which ensures that the action potential cannot move backward along the axon.

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

The action potential is a wave of __________________ that spreads rapidly along the neuronal plasma membrane. This wave is triggered by a local change in the membrane potential to a value that is __________________ negative than the resting membrane poten

The action potential is a wave of depolarization that spreads rapidly along the neuronal
plasma membrane. This wave is triggered by a local change in the membrane potential to a value that is less negative than the resting membrane potential. The action p

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

(a) acetylcholine

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

(d) by opening Cl- channels

Neurons communicate with each other through specialized sites called __________________. Many neurotransmitter receptors are ligand-gated ion channels that open transiently in the __________________ cell membrane in response to neurotransmitters released

Neurons communicate with each other through specialized sites called synapses. Many
neurotransmitter receptors are ligand-gated ion channels that open transiently in the postsynaptic cell membrane in response to neurotransmitters released by the presynapt