5) Some regions of the plasma membrane, called lipid rafts, have a higher concentration of cholesterol molecules. At higher temperatures, these regions _____.
A) are more fluid than the surrounding membrane
B) are less fluid than the surrounding membrane

C) detach from the plasma membrane and clog arteries
D) have higher rates of lateral diffusion of lipids and proteins into and out of these regions

Answer: B

6) Singer and Nicolson's fluid mosaic model of the membrane proposed that membranes_____. A) are a phospholipid bilayer between two layers of hydrophilic proteins
B) are a single layer of phospholipids and proteins
C) consist of protein molecules embedded in a fluid bilayer of phospholipids

D) consist of a mosaic of polysaccharides and proteins

Answer: C

7) 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) attaching the plasma membrane to the cytoskeleton

D) establishing a diffusion barrier to charged molecules

Answer: B

8) 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) All of these are embedded in the hydrophobic portion of the lipid bilayer.

Answer: C

9) 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.

Answer: D

15) Cell membranes are asymmetrical. Which of the following statements is the most likely explanation for the membrane's asymmetrical nature?
A) Since the cell membrane forms a border between one cell and another in tightly packed tissues such as epithelium, the membrane must be asymmetrical

B) Since cell membranes communicate signals from one organism to another, the cell membranes must be asymmetrical.
C) The two sides of a cell membrane face different environments and carry out different functions.

D) Proteins only function on the cytoplasmic side of the cell membrane, which results in the membrane's asymmetrical nature.

Answer: C

16) 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) Some membranes have hydrophobic surfaces exposed to the cytoplasm, while others have hydrophilic surfaces facing the cytoplasm.

Answer: B

17) Which of the following is a reasonable explanation for why unsaturated fatty acids help keep a 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

Answer: A

18) What kinds of molecules pass through a cell membrane most easily?

A) large and hydrophobic
B) small and hydrophobic
C) large polar

D) ionic

Answer: B

19) Which of the following most accurately describes selective permeability?
A) An input of energy is required for transport.
B) Lipid-soluble molecules pass through a membrane.
C) There must be a concentration gradient for molecules to pass through a membrane.

D) Only certain molecules can cross a cell membrane.

Answer: D

20) Which of the following is a characteristic feature of a carrier protein in a plasma membrane?

A) It exhibits a specificity for a particular type of molecule.
B) It requires the expenditure of cellular energy to function.
C) It works against diffusion.

D) It has no hydrophobic regions.

Answer: A

21) 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+

Answer: A

22) Which of the following allows water to move much faster across cell membranes?

A) the sodium-potassium pump
B) ATP
C) peripheral proteins

D) aquaporins

Answer: D

23) You are working on a team that is designing a new drug. 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) hydrophobicity of the drug molecule

B) lack of charge on the drug molecule
C) similarity of the drug molecule to other molecules transported by the target cells

D) lipid composition of the target cells' plasma membrane

Answer: C

24) Diffusion _____.
A) is very rapid over long distances
B) requires an expenditure of energy by the cell
C) is a passive process in which molecules move from a region of higher concentration to a region of lower concentration
D) requires integral proteins in the cell membrane

Answer: C

25) Which of the following processes includes all others?

A) osmosis
B) facilitated diffusion
C) passive transport

D) transport of an ion down its electrochemical gradient

Answer: C

26) When a cell is in equilibrium with its environment, which of the following occurs for substances that can diffuse through the cell?
A) There is random movement of substances into and out of the cell.
B) There is directed movement of substances into and out of the cell.

C) There is no movement of substances into and out of the cell.

D) All movement of molecules is directed by active transport.

Answer: A

27) Which of the following is true of osmosis?
A) Osmosis only takes place in red blood cells.
B) Osmosis is an energy-demanding or "active" process.
C) In osmosis, water moves across a membrane from areas of lower solute concentration to areas of higher solute concentration.
D) In osmosis, solutes move across a membrane from areas of lower water concentration to areas of higher water concentration.

Answer: C

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.

28) Refer t o the figure. Initially, in terms of tonicity, the solution in side A with respect to the solution in side B is _____.

A) hypotonic
B) isotonic

C) saturated
D) hypertonic

Answer: B

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.

29) Refer to the figure. After the system reaches equilibrium, what changes are observed?

A) The molarity of sucrose is higher than that of glucose on side A.
B) The water level is higher in side A than in side B.
C) The water level is unchanged.

D) The water level is higher in side B than in side A.

Answer: B

30) A patient was involved a serious accident and lost a large quantity of blood. In an attempt to replenish body fluids, distilled water—equal to the volume of blood lost—is added to the blood directly via one of his veins. What will be the most probable result of this transfusion?
A) The patient's red blood cells will shrivel up because the blood has become hypotonic compared to the cells.

B) The patient's red blood cells will swell and possibly burst because the blood has become hypotonic compared to the cells.
C) The patient's red blood cells will shrivel up because the blood has become hypertonic compared to the cells.

D) The patient's red blood cells will burst because the blood has become hypertonic compared to the cells.

Answer: B

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..

31) Refer to the figure. 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 hypertonic to side B with respect to glucose.

D) side A is hypotonic to side B with respect to NaCl.

Answer: B

32) Refer to the figure. 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) a decrease in the concentration of NaCl and a decrease in the water level
D) no change in the concentration of NaCl and glucose and an increase in the water level

Answer: C

36) Celery stalks that are immersed in fresh water for several hours become stiff. Similar stalks left in a 0.15 M salt solution become limp. From this we can deduce that the fresh water_____.

A) and the salt solution are both hypertonic to the cells of the celery stalks
B) is hypotonic and the salt solution is hypertonic to the cells of the celery stalks

C) is hypertonic and the salt solution is hypotonic to the cells of the celery stalks

D) is isotonic and the salt solution is hypertonic to the cells of the celery stalks

Answer: B

37) What will happen to a red blood cell (RBC), which has an internal ion concentration of about 0.9 percent, if it is placed into a beaker of pure water?
A) The cell would shrink because the water in the beaker is hypotonic relative to the cytoplasm of the RBC.

B) The cell would shrink because the water in the beaker is hypertonic relative to the cytoplasm of the RBC.
C) The cell would swell because the water in the beaker is hypotonic relative to the cytoplasm of the RBC.

D) The cell will remain the same size because the solution outside the cell is isotonic.

Answer: C

38) Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells? The animal cell is in _____.
A) a hypotonic solution, and the plant cell is in an isotonic solution
B) an isotonic solution, and the plant cell is in a hypertonic solution

C) a hypertonic solution, and the plant cell is in an isotonic solution

D) an isotonic solution, and the plant cell is in a hypotonic solution

Answer: D

39) 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) a salmon moving from a river into an ocean
C) a red blood cell surrounded by plasma

D) a plant being grown hydroponically in a watery mixture of designated nutrients

Answer: B

40) When a plant cell, such as one from a rose stem, is submerged in a very hypotonic solution, what is likely to occur?
A) The cell will burst.
B) Plasmolysis will shrink the interior.

C) The cell will become flaccid.
D) The cell will become turgid.

Answer: D

41) A sodium-potassium pump _____.
A) moves three potassium ions out of a cell and two sodium ions into a cell while producing an ATP for each cycle
B) move three sodium ions out of a cell and two potassium ions into a cell while consuming an ATP for each cycle
C) moves three potassium ions out of a cell and two sodium ions into a cell while consuming 2 ATP in each cycle
D) move three sodium ions out of a cell and two potassium ions into a cell and generates an ATP in each cycle

Answer: B

42) The sodium-potassium pump is called an electrogenic pump because it _____.

A) pumps equal quantities of Na+ and K+ across the membrane
B) contributes to the membrane potential
C) ionizes sodium and potassium atoms
D) is used to drive the transport of other molecules against a concentration gradient

Answer: B

43) Which of the following membrane activities requires energy from ATP?
A) facilitated diffusion of chloride ions across the membrane through a chloride channel

B) movement of Na+ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid
C) movement of glucose molecules into a bacterial cell from a medium containing a higher concentration of glucose than inside the cell
D) movement of carbon dioxide out of a paramecium

Answer: B

44) The voltage across a membrane is called the _____.

A) chemical gradient
B) membrane potential
C) osmotic potential

D) electrochemical gradient

Answer: B

45) Ions diffuse across membranes through specific ion channels down _____.

A) their chemical gradients
B) their concentration gradients
C) the electrical gradients

D) their electrochemical gradients

Answer: D

46) Which of the following would increase the electrochemical gradient across a membrane? A) a sucrose-proton cotransporter
B) a proton pump
C) a potassium channel

D) both a proton pump and a potassium channel

Answer: B

47) 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) cotransport

Answer: D

48) In some cells, there are many ion electrochemical gradients across the plasma membrane even though there are usually only one or two proton pumps present in the membrane. The gradients of the other ions are most likely accounted for by _____.
A) cotransport proteins

B) ion channels
C) pores in the plasma membrane
D) passive diffusion across the plasma membrane

Answer: A

49) 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) Sodium and glucose compete for the same binding site in the cotransporter.
B) Glucose entering the cell down 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) A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose.

Answer: D

50) 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 gradients across a membrane were used by cells that were the common ancestor of all three domains of life.

B) The high concentration of protons in the ancient atmosphere must have necessitated a pump mechanism.
C) Cells of each domain evolved proton pumps independently when oceans became more acidic.

D) Proton pumps are necessary to all cell membranes.

Answer: A

51) 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 most viruses
B) intravenous feeding techniques
C) medications to slow blood loss
D) hydrating drinks with high concentrations of salts and glucose

Answer: D

52) The force driving simple diffusion is _____, while the energy source for active transport is _____.
A) the concentration gradient; ADP
B) the concentration gradient; ATP

C) transmembrane pumps; electron transport
D) phosphorylated protein carriers; ATP

Answer: B

53) An organism with a cell wall would most likely be unable to take in materials through _____.

A) osmosis
B) active transport
C) phagocytosis

D) facilitated diffusion

Answer: C

54) White blood cells engulf bacteria using _____.

A) phagocytosis
B) pinocytosis
C) osmosis

D) receptor-mediated exocytosis

Answer: A

55) Familial hypercholesterolemia is characterized by _____.
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

Answer: A

56) 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 can concentrate substances from the extracellular fluid, but receptor-mediated endocytosis cannot.

Answer: C

57) 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

Answer: C

58) A bacterium engulfed by a white blood cell through phagocytosis will be digested by enzymes contained in _____.
A) lysosomes
B) Golgi vesicles

C) vacuoles
D) secretory vesicles

Answer: A

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.

59) 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? They are synthesized _____.
A) on ribosomes on the plasma membrane

B) by ribosomes in the rough ER and arrive at the plasma membrane in the membrane of secretory vesicles
C) on free cytoplasmic ribosomes and then inserted into the plasma membrane
D) by ribosomes in the rough ER, secreted from the cell, and inserted into the plasma membrane from the outside

Answer: B

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.

60) What would be observed by live-cell fluorescence microscopy immediately after HIV entry if HIV is endocytosed first, and then later fuses with the endocytotic vesicle membrane?
A) A spot of red fluorescence will be visible on the infected cell's plasma membrane, marking the site of membrane fusion and HIV entry.

B) The red fluorescent dye-labeled lipids will appear in the infected cell's interior.
C) A spot of red fluorescence will diffuse in the infected cell's cytoplasm.
D) A spot of red fluorescence will remain outside the cell after delivering the viral capsid.

Answer: B