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1. Who was/were the first to propose that cell membranes are phospholipid bilayers?
A) H. Davson and J. Danielli
B) I. Langmuir
C) C. Overton
D) S. Singer and G. Nicolson
E) E. Gorter and F. Grendel
Answer: E
2.Some regions of the plasma membrane, called lipid
rafts, have a higher concentration of cholesterol molecules. As a result, these
lipid rafts
A) are more fluid than the surrounding membrane.
B) are more rigid than the surrounding membrane.
C) are able to flip from inside to outside.
D) detach from the plasma membrane and clog arteries.
E) have higher rates of lateral diffusion of lipids and
proteins into and out of the lipid rafts.
Answer: B
3. Singer and Nicolson's fluid mosaic model of the
membrane proposed that
A) membranes are a phospholipid bilayer.
B) membranes are a phospholipid bilayer between two
layers of hydrophilic proteins.
C) membranes are a single layer of phospholipids and
proteins.
D) membranes consist of protein molecules embedded in a
fluid bilayer of phospholipids.
E) membranes consist of a mosaic of polysaccharides and
proteins.
Answer: D
4. Which of the following types of molecules are the
major structural components of the cell membrane?
A) phospholipids and cellulose
B) nucleic acids and proteins
C) phospholipids and proteins
D) proteins and cellulose
E) glycoproteins and cholesterol
Answer: C
5. When biological membranes are frozen and then
fractured, they tend to break along the middle of the bilayer. The best
explanation for this is that
A) the integral membrane proteins are not strong enough
to hold the bilayer together.
B) water that is present in the middle of the bilayer
freezes and is easily fractured.
C) hydrophilic interactions between the opposite membrane
surfaces are destroyed on freezing.
D) the carbon-carbon bonds of the phospholipid tails are
easily broken.
E) the hydrophobic interactions that hold the membrane
together are weakest at this point.
Answer: E
6. The presence of cholesterol in the plasma membranes of
some animals
A) enables the membrane to stay fluid more easily when
cell temperature drops.
B) enables the animal to remove hydrogen atoms from
saturated phospholipids.
C) enables the animal to add hydrogen atoms to
unsaturated phospholipids.
D) makes the membrane less flexible, allowing it to
sustain greater pressure from within the cell.
E) makes the animal more susceptible to circulatory
disorders.
Answer: A
7. According to the fluid mosaic model of cell membranes,
which of the following is a true statement about membrane phospholipids?
A) They can move laterally along the plane of the membrane.
B) They frequently flip-flop from one side of the
membrane to the other.
C) They occur in an uninterrupted bilayer, with membrane
proteins restricted to the surface of the membrane.
D) They are free to depart from the membrane and dissolve
in the surrounding solution.
E) They have hydrophilic tails in the interior of the
membrane.
Answer: A
8. Which of the following is one of the ways that the
membranes of winter wheat are able to remain fluid when it is extremely cold?
A) by increasing the percentage of unsaturated
phospholipids in the membrane
B) by increasing the percentage of cholesterol molecules
in the membrane
C) by decreasing the number of hydrophobic proteins in
the membrane
D) by cotransport of glucose and hydrogen
E) by using active transport
Answer: A
9. In order for a protein to be an integral membrane
protein it would have to be
A) hydrophilic.
B) hydrophobic.
C) amphipathic, with at least one hydrophobic region.
D) completely covered with phospholipids.
E) exposed on only one surface of the membrane.
Answer: C
10. When a membrane is freeze-fractured, the bilayer
splits down the middle between the two layers of phospholipids. In an electron
micrograph of a freeze-fractured membrane, the bumps seen on the fractured
surface of the membrane are
A) peripheral proteins.
B) phospholipids.
C) carbohydrates.
D) integral proteins.
E) cholesterol molecules.
Answer: D
11. Which of the following is a reasonable explanation
for why unsaturated fatty acids help keep any membrane more fluid at lower
temperatures?
A) The double bonds form kinks in the fatty acid tails,
preventing adjacent lipids from packing tightly.
B) Unsaturated fatty acids have a higher cholesterol
content and therefore more cholesterol in membranes.
C) Unsaturated fatty acids are more polar than saturated fatty
acids.
D) The double bonds block interaction among the
hydrophilic head groups of the lipids.
E) The double bonds result in shorter fatty acid tails
and thinner membranes.
Answer: A
12. Which of the following is true of integral membrane
proteins?
A) They lack tertiary structure.
B) They are loosely bound to the surface of the bilayer.
C) They are usually transmembrane proteins.
D) They are not mobile within the bilayer.
E) They serve only a structural role in membranes.
Answer: C
13. The primary function of polysaccharides attached to
the glycoproteins and glycolipids of animal cell membranes is
A) to facilitate diffusion of molecules down their
concentration gradients.
B) to actively transport molecules against their
concentration gradients.
C) to maintain the integrity of a fluid mosaic membrane.
D) to maintain membrane fluidity at low temperatures.
E) to mediate cell-to-cell recognition.
Answer: E
14. An animal cell lacking oligosaccharides on the
external surface of its plasma membrane would likely be impaired in which
function?
A) transporting ions against an electrochemical gradient
B) cell-cell recognition
C) maintaining fluidity of the phospholipid bilayer
D) attaching to the cytoskeleton
E) establishing the diffusion barrier to charged
molecules
Answer: B
15. In the years since the proposal of the fluid mosaic
model of the cell membrane, which of the following observations has been added
to the model?
A) The membrane is only fluid across a very narrow
temperature range.
B) Proteins rarely move, even though they possibly can do
so.
C) Unsaturated lipids are excluded from the membranes.
D) The concentration of protein molecules is now known to
be much higher.
E) The proteins are known to be made of only acidic amino
acids.
Answer: D
16. A protein that spans the phospholipid bilayer one or
more times is
A) a transmembrane protein.
B) an integral protein.
C) a peripheral protein.
D) an integrin.
E) a glycoprotein.
Answer: A
17. Which of these are not embedded in the hydrophobic
portion of the lipid bilayer at all?
A) transmembrane proteins
B) integral proteins
C) peripheral proteins
D) integrins
E) glycoproteins
Answer: C
18. The cell membranes of Antarctic ice fish might have
which of the following adaptations?
A) very long chain fatty acids
B) branched isoprenoid lipids
C) a high percentage of polyunsaturated fatty acids
D) a higher percentage of trans-fatty acids
E) no cholesterol
Answer: C
19. In a paramecium, cell surface integral membrane
proteins are synthesized
A) in the cytoplasm by free ribosomes.
B) by ribosomes in the nucleus.
C) by ribosomes bound to the rough endoplasmic reticulum.
D) by ribosomes in the Golgi vesicles.
E) by ribosomes bound to the inner surface of the plasma
membrane.
Answer: C
20. The formulation of a model for a structure or for a
process serves which of the following purposes?
A) It asks a scientific question.
B) It functions as a testable hypothesis.
C) It records observations.
D) It serves as a data point among results.
E) It can only be arrived at after years of
experimentation.
Answer: B
21. Cell membranes are asymmetrical. Which of the
following is the most likely explanation?
A) The cell membrane forms a border between one cell and
another in tightly packed tissues such as epithelium.
B) Cell membranes communicate signals from one organism
to another.
C) The two sides of a cell membrane face different
environments and carry out different functions.
D) The "innerness" and "outerness" of
membrane surfaces are predetermined by genes.
E) Proteins can only be associated with the cell
membranes on the cytoplasmic side.
Answer: C
22. Which of the following is true of the evolution of
cell membranes?
A) Cell membranes have stopped evolving now that they are
fluid mosaics.
B) Cell membranes cannot evolve if the membrane proteins
do not.
C) The evolution of cell membranes is driven by the
evolution of glycoproteins and glycolipids.
D) All components of membranes evolve in response to
natural selection.
E) An individual organism selects its preferred type of
cell membrane for particular functions.
Answer: D
23. Why are lipids and proteins free to move laterally in
membranes?
A) The interior of the membrane is filled with liquid
water.
B) Lipids and proteins repulse each other in the
membrane.
C) Hydrophilic portions of the lipids are in the interior
of the membrane.
D) There are only weak hydrophobic interactions in the
interior of the membrane.
E) Molecules such as cellulose can pull them in various
directions.
Answer: D
24. What kinds of molecules pass through a cell membrane
most easily?
A) large and hydrophobic
B) small and hydrophobic
C) large polar
D) ionic
E) monosaccharides such as glucose
Answer: B
25. Which of the following is a characteristic feature of
a carrier protein in a plasma membrane?
A) It is a peripheral membrane protein.
B) It exhibits a specificity for a particular type of
molecule.
C) It requires the expenditure of cellular energy to
function.
D) It works against diffusion.
E) It has few, if any, hydrophobic amino acids.
Answer: B
26. Nitrous oxide gas molecules diffusing across a cell's
plasma membrane is an example of
A) diffusion across the lipid bilayer.
B) facilitated diffusion.
C) active transport.
D) osmosis.
E) cotransport.
Answer: A
27. Which of the following would likely move through the
lipid bilayer of a plasma membrane most rapidly?
A) CO₂
B) an amino acid
C) glucose
D) K⁺
E) starch
Answer: A
28. Which of the following statements is correct about
diffusion?
A) It is very rapid over long distances.
B) It requires an expenditure of energy by the cell.
C) It is a passive process in which molecules move from a
region of higher concentration to a region of lower concentration.
D) It is an active process in which molecules move from a
region of lower concentration to one of higher concentration.
E) It requires integral proteins in the cell membrane.
Answer: C
29. Water passes quickly through cell membranes because
A) the bilayer is hydrophilic.
B) it moves through hydrophobic channels.
C) water movement is tied to ATP hydrolysis.
D) it is a small, polar, charged molecule.
E) it moves through aquaporins in the membrane.
Answer: E
30. Celery stalks that are immersed in fresh water for
several hours become stiff and hard. Similar stalks left in a 0.15 M salt
solution become limp and soft. From this we can deduce that the cells of the
celery stalks are
A) hypotonic to both fresh water and the salt solution.
B) hypertonic to both fresh water and the salt solution.
C) hypertonic to fresh water but hypotonic to the salt
solution.
D) hypotonic to fresh water but hypertonic to the salt
solution.
E) isotonic with fresh water but hypotonic to the salt
solution.
Answer: C
31. Mammalian blood contains the equivalent of 0.15 M
NaCl. Seawater contains the equivalent of 0.45 M NaCl. What will happen if red
blood cells are transferred to seawater?
A) Water will leave the cells, causing them to shrivel
and collapse.
B) NaCl will be exported from the red blood cells by
facilitated diffusion.
C) The blood cells will take up water, swell, and
eventually burst.
D) NaCl will passively diffuse into the red blood cells.
E) The blood cells will expend ATP for active transport
of NaCl into the cytoplasm.
Answer: A
32. Which of the following statements correctly describes
the normal tonicity conditions for typical plant and animal cells?
A) The animal cell is in a hypotonic solution, and the
plant cell is in an isotonic solution.
B) The animal cell is in an isotonic solution, and the
plant cell is in a hypertonic solution.
C) The animal cell is in a hypertonic solution, and the
plant cell is in an isotonic solution.
D) The animal cell is in an isotonic solution, and the
plant cell is in a hypotonic solution.
E) The animal cell is in a hypertonic solution, and the
plant cell is in a hypotonic solution.
Answer: D
33. In which of the following would there be the greatest
need for osmoregulation?
A) an animal connective tissue cell bathed in isotonic
body fluid
B) cells of a tidepool animal such as an anemone
C) a red blood cell surrounded by plasma
D) a lymphocyte before it has been taken back into lymph
fluid
E) a plant being grown hydroponically (in a watery
mixture of designated nutrients)
Answer: B
34. When a plant cell, such as one from a peony stem, is
submerged in a very hypotonic solution, what is likely to occur?
A) The cell will burst.
B) The cell membrane will lyse.
C) Plasmolysis will shrink the interior.
D) The cell will become flaccid.
E) The cell will become turgid.
Answer: E
35. Which of the following membrane activities require
energy from ATP hydrolysis?
A) facilitated diffusion of chloride ions across the
membrane through a chloride channel
B) movement of water into a cell
C) Na⁺ ions moving out of a mammalian cell bathed in
physiological saline
D) movement of glucose molecules into a bacterial cell
from a medium containing a higher concentration of glucose than inside the cell
E) movement of carbon dioxide out of a paramecium
Answer: C
36. The phosphate transport system in bacteria imports
phosphate into the cell even when the concentration of phosphate outside the
cell is much lower than the cytoplasmic phosphate concentration. Phosphate
import depends on a pH gradient across the membrane–more acidic outside the
cell than inside the cell. Phosphate transport is an example of
A) passive diffusion.
B) facilitated diffusion.
C) active transport.
D) osmosis.
E) cotransport.
Answer: E
37. Glucose diffuses slowly through artificial
phospholipid bilayers. The cells lining the small intestine, however, rapidly
move large quantities of glucose from the glucose-rich food into their
glucose-poor cytoplasm. Using this information, which transport mechanism is
most probably functioning in the intestinal cells?
A) simple diffusion
B) phagocytosis
C) active transport pumps
D) exocytosis
E) facilitated diffusion
Answer: E
38. What is the voltage across a membrane called?
A) water potential
B) chemical gradient
C) membrane potential
D) osmotic potential
E) electrochemical gradient
Answer: C
39. In most cells, there are electrochemical gradients of
many ions across the plasma membrane even though there are usually only one or
two electrogenic pumps present in the membrane. The gradients of the other ions
are most likely accounted for by
A) cotransport proteins.
B) ion channels.
C) carrier proteins.
D) passive diffusion across the plasma membrane.
E) cellular metabolic reactions that create or destroy
ions.
Answer: A
40. The sodium-potassium pump is called an electrogenic
pump because it
A) pumps equal quantities of Na⁺ and K⁺ across the
membrane.
B) pumps hydrogen ions out of the cell.
C) contributes to the membrane potential.
D) ionizes sodium and potassium atoms.
E) is used to drive the transport of other molecules
against a concentration gradient.
Answer: C
41. Which of the following is most likely true of a
protein that cotransports glucose and sodium ions into the intestinal cells of
an animal?
A) The sodium ions are moving down their electrochemical
gradient while glucose is moving up.
B) Glucose entering the cell along its concentration
gradient provides energy for uptake of sodium ions against the electrochemical
gradient.
C) Sodium ions can move down their electrochemical
gradient through the cotransporter whether or not glucose is present outside
the cell.
D) The cotransporter can also transport potassium ions.
E) A substance that blocks sodium ions from binding to
the cotransport protein will also block the transport of glucose.
Answer: E
42. The movement of potassium into an animal cell
requires
A) low cellular concentrations of sodium.
B) high cellular concentrations of potassium.
C) an energy source such as ATP.
D) a cotransport protein.
E) a potassium channel protein.
Answer: C
43. Ions diffuse across membranes through specific ion
channels
A) down their chemical gradients.
B) down their concentration gradients.
C) down the electrical gradients.
D) down their electrochemical gradients.
E) down the osmotic potential gradients.
Answer: D
44. Which of the following would increase the
electrochemical potential across a membrane?
A) a chloride channel
B) a sucrose-proton cotransporter
C) a proton pump
D) a potassium channel
E) both a proton pump and a potassium channel
Answer: C
45. The sodium-potassium pump in animal cells requires
cytoplasmic ATP to pump ions across the plasma membrane. When the proteins of
the pump are first synthesized in the rough ER, what side of the ER membrane
will the ATP binding site be on?
A) It will be on the cytoplasmic side of the ER.
B) It will be on the side facing the interior of the ER.
C) It could be facing in either direction because
proteins are properly reoriented in the Golgi apparatus.
D) It doesn't matter, because the pump is not active in
the ER.
Answer: A
46. Proton pumps are used in various ways by members of
every domain of organisms: Bacteria, Archaea, and Eukarya. What does this most
probably mean?
A) Proton pumps must have evolved before any living
organisms were present on Earth.
B) Proton gradients across a membrane were used by cells
that were the common ancestor of all three domains of life.
C) The high concentration of protons in the ancient
atmosphere must have necessitated a pump mechanism.
D) Cells of each domain evolved proton pumps
independently when oceans became more acidic.
E) Proton pumps are necessary to all cell membranes.
Answer: B
47. Several epidemic microbial diseases of earlier
centuries incurred high death rates because they resulted in severe dehydration
due to vomiting and diarrhea. Today they are usually not fatal because we have
developed which of the following?
A) antiviral medications that are efficient and work well
with all viruses
B) antibiotics against the viruses in question
C) intravenous feeding techniques
D) medication to prevent blood loss
E) hydrating drinks that include high concentrations of
salts and glucose
Answer: E
48. An organism with a cell wall would most likely be
unable to take in materials through
A) diffusion.
B) osmosis.
C) active transport.
D) phagocytosis.
E) facilitated diffusion.
Answer: D
49. White blood cells engulf bacteria through what
process?
A) exocytosis
B) phagocytosis
C) pinocytosis
D) osmosis
E) receptor-mediated exocytosis
Answer: B
50. Familial hypercholesterolemia is characterized by
which of the following?
A) defective LDL receptors on the cell membranes
B) poor attachment of the cholesterol to the
extracellular matrix of cells
C) a poorly formed lipid bilayer that cannot incorporate
cholesterol into cell membranes
D) inhibition of the cholesterol active transport system
in red blood cells
E) a general lack of glycolipids in the blood cell
membranes
Answer: A
51. The difference between pinocytosis and
receptor-mediated endocytosis is that
A) pinocytosis brings only water molecules into the cell,
but receptor-mediated endocytosis brings in other molecules as well.
B) pinocytosis increases the surface area of the plasma
membrane whereas receptor-mediated endocytosis decreases the plasma membrane
surface area.
C) pinocytosis is nonselective in the molecules it brings
into the cell, whereas receptor-mediated endocytosis offers more selectivity.
D) pinocytosis requires cellular energy, but
receptor-mediated endocytosis does not.
E) pinocytosis can concentrate substances from the
extracellular fluid, but receptor-mediated endocytosis cannot.
Answer: C
52. In receptor-mediated endocytosis, receptor molecules
initially project to the outside of the cell. Where do they end up after
endocytosis?
A) on the outside of vesicles
B) on the inside surface of the cell membrane
C) on the inside surface of the vesicle
D) on the outer surface of the nucleus
E) on the ER
Answer: C
53. A bacterium engulfed by a white blood cell through
phagocytosis will be digested by enzymes contained in
A) peroxisomes.
B) lysosomes.
C) Golgi vesicles.
D) vacuoles.
E) secretory vesicles.
Answer: B
54. card image
Which component is the peripheral protein?
A) A
B) B
C) C
D) D
E) E
Answer: D
55. card image
Which component is cholesterol?
A) A
B) B
C) C
D) D
E) E
Answer: E
56. card image
Which component is the fiber of the extracellular matrix?
A) A
B) B
C) C
D) D
E) E
Answer: A
57. card image
Which component is a microfilament of the cytoskeleton?
A) A
B) B
C) C
D) D
E) E
Answer: C
58. card image
Which component is a glycolipid?
A) A
B) B
C) C
D) D
E) E
Answer: B
59. card image
The solutions in the two arms of this U-tube are
separated by a membrane that is permeable to water and glucose but not to
sucrose. Side A is half-filled with a solution of 2 M sucrose and 1 M glucose.
Side B is half-filled with 1 M sucrose and 2 M glucose. Initially, the liquid
levels on both sides are equal.
Initially, in terms of tonicity, the solution in side A
with respect to that in side B is
A) hypotonic.
B) plasmolyzed.
C) isotonic.
D) saturated.
E) hypertonic.
Answer: C
60. card image
After the system reaches equilibrium, what changes are
observed?
A) The molarity of sucrose and glucose are equal on both
sides.
B) The molarity of glucose is higher in side A than in
side B.
C) The water level is higher in side A than in side B.
D) The water level is unchanged.
E) The water level is higher in side B than in side A.
Answer: C
61. card image
The solutions in the arms of a U-tube are separated at
the bottom of the tube by a selectively permeable membrane. The membrane is
permeable to sodium chloride but not to glucose. Side A is filled with a
solution of 0.4 M glucose and 0.5 M sodium chloride (NaCl), and side B is
filled with a solution containing 0.8 M glucose and 0.4 M sodium chloride.
Initially, the volume in both arms is the same.
At the beginning of the experiment,
A) side A is hypertonic to side B.
B) side A is hypotonic to side B.
C) side A is isotonic to side B.
D) side A is hypertonic to side B with respect to
glucose.
E) side A is hypotonic to side B with respect to sodium
chloride.
Answer: B
62. card image
If you examine side A after three days, you should find
A) a decrease in the concentration of NaCl and glucose
and an increase in the water level.
B) a decrease in the concentration of NaCl, an increase
in water level, and no change in the concentration of glucose.
C) no net change in the system.
D) a decrease in the concentration of NaCl and a decrease
in the water level.
E) no change in the concentration of NaCl and glucose and
an increase in the water level.
Answer: D
63. card image
Five dialysis bags, constructed from a semipermeable
membrane that is impermeable to sucrose, were filled with various
concentrations of sucrose and then placed in separate beakers containing an
initial concentration of 0.6 M sucrose solution. At 10-minute intervals, the
bags were massed (weighed) and the percent change in mass of each bag was
graphed.
Which line in the graph represents the bag that contained
a solution isotonic to the 0.6 M solution at the beginning of the experiment?
A) A
B) B
C) C
D) D
E) E
Answer: C
64. card image
Which line in the graph represents the bag with the
highest initial concentration of sucrose?
A) A
B) B
C) C
D) D
E) E
Answer: A
65. card image
Which line or lines in the graph represent(s) bags that
contain a solution that is hypertonic at 50 minutes?
A) A and B
B) B
C) C
D) D
E) D and E
Answer: B
66. card image
Human immunodeficiency virus (HIV) infects cells that
have both CD4 and CCR5 cell surface molecules. The viral nucleic acid molecules
are enclosed in a protein capsid, and the protein capsid is itself contained
inside an envelope consisting of a lipid bilayer membrane and viral
glycoproteins. One hypothesis for viral entry into cells is that binding of HIV
membrane glycoproteins to CD4 and CCR5 initiates fusion of the HIV membrane
with the plasma membrane, releasing the viral capsid into the cytoplasm. An alternative
hypothesis is that HIV gains entry into the cell via receptor-mediated
endocytosis, and membrane fusion occurs in the endocytotic vesicle. To test
these alternative hypotheses for HIV entry, researchers labeled the lipids on
the HIV membrane with a red fluorescent dye.
What would be observed by live-cell fluorescence
microscopy if the red fluorescent lipid dye-labeled HIV membrane fuses with the
target cell plasma membrane?
A) A spot of red fluorescence will remain on the infected
cell's plasma membrane, marking the site of membrane fusion and HIV entry.
B) The red fluorescent dye-labeled lipids will diffuse in
the infected cell's plasma membrane and become difficult to detect.
C) A spot of red fluorescence will move into the infected
cell's cytoplasm.
D) A spot of red fluorescence will remain outside the
cell after delivering the viral capsid.
E) Fluorescence microscopy does not have enough
resolution to visualize fluorescently labeled HIV virus particles.
Answer: B
67. card image
What would be observed by live-cell fluorescence
microscopy if HIV is endocytosed first, and then fuses with the endocytotic
vesicle membrane?
A) A spot of red fluorescence will remain on the infected
cell's plasma membrane, marking the site of membrane fusion and HIV entry.
B) The red fluorescent dye-labeled lipids will diffuse in
the endocytotic vesicle membrane and become difficult to detect.
C) A spot of red fluorescence will move into the infected
cell's interior.
D) A spot of red fluorescence will remain outside the
cell after delivering the viral capsid.
E) Fluorescence microscopy does not have enough
resolution to visualize fluorescently labeled HIV virus particles.
Answer: C
68. card image
Using live-cell fluorescence microscopy, researchers
observed that a red fluorescent spot moved from the plasma membrane into the
interior of target cells when red fluorescent dye-labeled HIV was added to the
cells. What is the best conclusion from these observations?
A) The hypothesis that HIV enters the cell via fusion
with the target cell plasma membrane is proved.
B) The hypothesis that HIV enters the cell via fusion
with the target cell plasma membrane is not supported.
C) The hypothesis that HIV enters the cell via
endocytosis is proved.
D) The hypothesis that HIV enters the cell via
endocytosis is not supported.
E) Neither hypothesis is supported by these results.
Answer: B
69. card image
If HIV first enters the cell in an endocytotic vesicle,
instead of directly fusing with the plasma membrane, then
A) HIV infection should be hindered by microtubule
polymerization inhibitors such as nocodazole.
B) HIV infection should be more efficient at lower
temperatures.
C) intact cortical actin microfilaments should interfere
with HIV infection.
D) cells lacking integrins should be resistant to HIV
infection.
E) addition of ligands for other cell-surface receptors
to stimulate their endocytosis should increase the efficiency of HIV infection.
Answer: A
70. card image
In an HIV-infected cell producing HIV virus particles,
the viral glycoprotein is expressed on the plasma membrane. How do the viral
glycoproteins get to the plasma membrane?
A) They are synthesized on ribosomes on the plasma
membrane.
B) They are synthesized by ribosomes in the rough ER, and
arrive at the plasma membrane in the membrane of secretory vesicles.
C) They are synthesized on free cytoplasmic ribosomes,
and then inserted into the plasma membrane.
D) They are synthesized by ribosomes in the rough ER,
secreted from the cell, and inserted into the plasma membrane from the outside.
E) They are synthesized by ribosomes on the HIV viral
membrane, which fuses with the plasma membrane from inside the cell.
Answer: B
71. Cystic fibrosis is a genetic disease in humans in
which the CFTR protein, which functions as a chloride ion channel, is missing
or nonfunctional in cell membranes.
71) The CFTR protein belongs to what category of membrane
proteins?
A) gap junctions
B) aquaporins
C) electrogenic ion pumps
D) cotransporters
E) hydrophilic channels
Answer: C
72. If the sodium ion concentration outside the cell
increases, and the CFTR channel is open, in what direction will chloride ions
and water move across the cell membrane?
A) Chloride ions will move out of the cell, and water
will move into the cell.
B) Both chloride ions and water will move out of the
cell.
C) Chloride ions will move into the cell, and water will
move out of the cell.
D) Both chloride ions and water will move into the cell.
E) The movement of chloride ions and water molecules will
not be affected by changes in sodium ion concentration outside the cell.
Answer: B
73. In the small airways of the lung, a thin layer of
liquid is needed between the epithelial cells and the mucus layer in order for
cilia to beat and move the mucus and trapped particles out of the lung. One
hypothesis is that the volume of this airway surface liquid is regulated
osmotically by transport of sodium and chloride ions across the epithelial cell
membrane. How would the lack of a functional chloride channel in cystic
fibrosis patients affect sodium ion transport and the volume of the airway
surface liquid?
A) Sodium ion transport will increase; higher osmotic
potential will increase airway surface liquid volume.
B) Sodium ion transport will increase; higher osmotic
potential will decrease airway surface liquid volume.
C) Sodium ion transport will decrease; lower osmotic
potential will decrease airway surface liquid volume.
D) Sodium ion transport will decrease; lower osmotic
potential will increase the airway surface liquid volume.
E) Sodium ion transport will be unaffected; lack of
chloride transport still reduces osmotic potential and decreases the airway
surface liquid volume.
Answer: C
74. A patient has had a serious accident and lost a lot
of blood. In an attempt to replenish body fluids, distilled water–equal to the
volume of blood lost–is transferred directly into one of his veins. What will
be the most probable result of this transfusion?
A) It will have no unfavorable effect as long as the
water is free of viruses and bacteria.
B) The patient's red blood cells will shrivel up because
the blood fluid has become hypotonic compared to the cells.
C) The patient's red blood cells will swell because the
blood fluid has become hypotonic compared to the cells.
D) The patient's red blood cells will shrivel up because
the blood fluid has become hypertonic compared to the cells.
E) The patient's red blood cells will burst because the blood
fluid has become hypertonic compared to the cells.
Answer: C
75. You are working on a team that is designing a new
drug. In order for this drug to work, it must enter the cytoplasm of specific
target cells. Which of the following would be a factor that determines whether
the molecule selectively enters the target cells?
A) blood or tissue type of the patient
B) hydrophobicity of the drug molecule
C) lack of charge on the drug molecule
D) similarity of the drug molecule to other molecules
transported by the target cells
E) lipid composition of the target cells' plasma membrane
Answer: D
76. In what way do the membranes of a eukaryotic cell
vary?
A) Phospholipids are found only in certain membranes.
B) Certain proteins are unique to each membrane.
C) Only certain membranes of the cell are selectively
permeable.
D) Only certain membranes are constructed from
amphipathic molecules.
E) Some membranes have hydrophobic surfaces exposed to
the cytoplasm, while others have hydrophilic surfaces facing the cytoplasm.
Answer: B
77. According to the fluid mosaic model of membrane
structure, proteins of the membrane are mostly
A) spread in a continuous layer over the inner and outer
surfaces of the membrane.
B) confined to the hydrophobic interior of the membrane.
C) embedded in a lipid bilayer.
D) randomly oriented in the membrane, with no fixed
inside-outside polarity.
E) free to depart from the fluid membrane and dissolve in
the surrounding solution.
Answer: C
78. Which of the following factors would tend to increase
membrane fluidity?
A) a greater proportion of unsaturated phospholipids
B) a greater proportion of saturated phospholipids
C) a lower temperature
D) a relatively high protein content in the membrane
E) a greater proportion of relatively large glycolipids
compared with lipids having smaller molecular masses
Answer: A
79. Which of the following processes includes all others?
A) osmosis
B) diffusion of a solute across a membrane
C) facilitated diffusion
D) passive transport
E) transport of an ion down its electrochemical gradient
Answer: D
80. card image
Based on the figure above, which of these experimental
treatments would increase the rate of sucrose transport into the cell?
A) decreasing extracellular sucrose concentration
B) decreasing extracellular pH
C) decreasing cytoplasmic pH
D) adding an inhibitor that blocks the regeneration of
ATP
E) adding a substance that makes the membrane more
permeable to hydrogen ions
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