Chapter 7 MB
What happens when two solutions separated by a selectively permeable membrane reach osmotic equilibrium? a. Water molecules move between the two solutions, but there is no net movement of water across the membrane. b. Water molecules continue to move from the hypotonic solution to the hypertonic solution. c. Water molecules no longer move between the solutions.
a
Which factors affect the rate of osmotic movement of water? a. The rate of osmosis increases with increasing differences in solute concentrations between two solutions separated by a selectively permeable membrane. b. No factors have an effect; the rate of osmosis is constant. c.Hydrostatic pressure applied to a hypertonic solution separated from a hypotonic solution by a selectively permeable membrane increases osmotic movement across the membrane.
a
Which of the following best describes the structure of a biological membrane? a. two layers of phospholipids with proteins either crossing the layers or on the surface of the layers b. two layers of phospholipids with proteins embedded between the two layers c. a fluid structure in which phospholipids and proteins move freely between sides of the membrane d. two layers of phospholipids (with opposite orientations of the phospholipids in each layer) with each layer covered on the outside with proteins e. a mixture of covalently linked phospholipids and proteins that determines which solutes can cross the membrane and which cannot
a
Which of the following factors would tend to increase membrane fluidity? a. a greater proportion of unsaturated phospholipids b. a greater proportion of relatively large glycolipids compared with lipids having smaller molecular masses c. a relatively high protein content in the membrane d. a greater proportion of saturated phospholipids e. a lower temperature
a
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 are more polar than saturated fatty acids. c. Unsaturated fatty acids have a higher cholesterol content and, therefore, more cholesterol in membranes. d. The double bonds block interaction among the hydrophilic head groups of the lipid
a
Which of the following statements about a typical plasma membrane is correct? a. The two sides of the plasma membrane have different lipid and protein composition. b. Phospholipids are the primary component that determines which solutes can cross the plasma membrane. c. The plasma membrane is a covalently linked network of phospholipids and proteins that controls the movement of solutes into and out of a cell. d. Carbohydrates on the membrane surface are important in determining the overall bilayer structure. e. The hydrophilic interior of the membrane is composed primarily of the fatty acid tails of the phospholipids.
a
Which of the following would increase the electrochemical gradient across a membrane? a. a proton pump b. a sucrose-proton cotransporter c. a potassium channel d. both a proton pump and a potassium channel
a
Active and passive transport of solutes across a membrane typically differ in which of the following ways? a. Active transport is usually down the concentration gradient of the solute, whereas passive transport is always against the concentration gradient of the solute. b. Active transport always involves the utilization of cellular energy, whereas passive transport does not require cellular energy. c. Active transport is always faster than passive transport. d. Active transport uses protein carriers, whereas passive transport uses carbohydrate carriers. e. Active transport is used for ions, passive transport is used for uncharged solutes
b
Based on Figure 7.18 in your textbook, 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. adding a substance that makes the membrane more permeable to hydrogen ions d. decreasing cytoplasmic pH e. adding an inhibitor that blocks the regeneration of ATP
b
In what way do membranes vary among eukaryotic cells? a. Only certain membranes are constructed from amphipathic molecules. b. Certain proteins are unique to each membrane. c. Some membranes have hydrophobic surfaces exposed to the cytoplasm, while others have hydrophilic surfaces facing the cytoplasm. d. Phospholipids are found only in certain membranes. e. Only certain membranes of the cell are selectively permeable.
b
Select the correct statement about osmosis. a. If a dead cell is placed in a solution hypotonic to the cell contents, osmosis will not occur. b. Osmosis is the diffusion of water molecules across a selectively permeable membrane. c. Osmotic equilibrium cannot be reached unless solute concentrations equalize across the membrane.
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.. Refer to the figure. If you examine side A after three days, you should find _____. a. no change in the concentration of NaCl and glucose and an increase in the water level b. a decrease in the concentration of NaCl and a decrease in the water level c. a decrease in the concentration of NaCl, an increase in water level, and no change in the concentration of glucose d. a decrease in the concentration of NaCl and glucose and an increase in the water level
b
Three lab groups carried out an experiment to identify the correct molarities for five solutions. Each unknown contained one of the following sucrose concentrations: 0.0 M, 0.2 M, 0.4 M, 0.6 M, 0.8 M, and 1.0 M. Each data entry represents the average of 3 sample replications of 1 cm3 sweet potato cubes expressed as percent change in mass after an overnight (24 hr) soak in the unknown solutions. From the data given, which statement most accurately describes what is occurring in response to a particular unknown solution. Unknown Percent change in mass Group 1 Group 2 Group 3 A 6.6 7.8 7.5 B 3.1 3.7 2.9 C -2.7 -3.5 -2.5 D 0.7 0.5 1.1 E -11.6 -12.3 -12.6 F -5.2 -6.2 -4.9 a. Unknown solution C represents a sucrose molarity slightly lower than the molarity of sweet potato cells, thus water is transported out of the cells. b. Osmosis of water molecules from unknown solution A likely caused the increase in mass observed. c. Unknown solution E contains the highest concentration of sucrose and the change in mass is due to the active transport of sucrose into the cell in exchange for water molecules. d. Passive transport of sucrose out of the potato cells explains the change in mass observed for unknown solution F.
b
Which of the following processes includes all others? a. transport of an ion down its electrochemical gradient b. passive transport c. osmosis d. diffusion of a solute across a membrane e. facilitated diffusion
b
Which statement is correct? a. A solution of distilled water is hypotonic. b. The contents of a red blood cell are hyperosmotic to distilled water. c. A solution of seawater is hypertonic.
b
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 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. D d. D and E
b
The permeability of a biological membrane to a specific polar solute may depend on which of the following? a. the amount of cholesterol in the membrane b. the types of transport proteins in the membrane c. the phospholipid composition of the membrane d. the presence of unsaturated fatty acids in the membrane e. the types of polysaccharides present in the membrane
b.
According to the fluid mosaic model of cell membranes, phospholipids _____. a. frequently flip-flop from one side of the membrane to the other b. occur in an uninterrupted bilayer, with membrane proteins restricted to the surface of the membrane c. can move laterally along the plane of the membrane d. have hydrophilic tails in the interior of the membrane
c
According to the fluid mosaic model of membrane structure, proteins of the membrane are mostly a. free to depart from the fluid membrane and dissolve in the surrounding solution. b. randomly oriented in the membrane, with no fixed inside-outside polarity. c. embedded in a lipid bilayer. d. spread in a continuous layer over the inner and outer surfaces of the membrane. e. confined to the hydrophobic interior of the membrane.
c
For the following question, match the labeled component of the cell membrane in the figure with its description. Which component is a microfilament (actin filament) of the cytoskeleton? a. A b. B c. C d. D
c
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 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 remain outside the cell after delivering the viral capsid. b. A spot of red fluorescence will be visible on the infected cell's plasma membrane, marking the site of membrane fusion and HIV entry. c. The red fluorescent dye-labeled lipids will appear in the infected cell's interior. d. A spot of red fluorescence will diffuse in the infected cell's cytoplasm.
c
If the concentration of phosphate in the cytosol is 2.0 mM and the concentration of phosphate in the surrounding fluid is 0.1 mM, how could the cell increase the concentration of phosphate in the cytosol? a. passive transport b. diffusion c. active transport d. osmosis e. facilitated diffusion
c
The movement of glucose into a cell against a concentration gradient is most likely to be accomplished by which of the following? a. receptor-mediated endocytosis b. passive diffusion of the glucose through the lipid bilayer c. cotransport of the glucose with a proton or sodium ion that was pumped across the membrane using the energy of ATP hydrolysis d. movement of glucose into the cell through a glucose channel e. facilitated diffusion of the glucose using a carrier protein
c
What kinds of molecules pass through a cell membrane most easily? a. large and hydrophobic b. ionic c. small and hydrophobic d. large polar
c
When a cell is in equilibrium with its environment, which of the following occurs for substances that can diffuse through the cell? a.. All movement of molecules is directed by active transport. b. There is directed movement of substances into and out of the cell. c. There is random movement of substances into and out of the cell. d. There is no movement of substances into and out of the cell.
c
Which of the following correctly describes some aspect of exocytosis or endocytosis? a. The inner surface of a transport vesicle that fuses with or buds from the plasma membrane is most closely related to the inner surface of the plasma membrane. b. Endocytosis and exocytosis involve passive transport. c. Exocytosis and endocytosis temporarily change the surface area of the plasma membrane. c. Both processes provide a mechanism for exchanging membrane-impermeable molecules between the organelles and the cytosol. e. These two processes require the participation of mitochondria.
c
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. A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose. d. Sodium ions can move down their electrochemical gradient through the cotransporter whether or not glucose is present outside the cell.
c
Which of the following membrane activities requires energy from ATP? a. movement of glucose molecules into a bacterial cell from a medium containing a higher concentration of glucose than inside the cell b. facilitated diffusion of chloride ions across the membrane through a chloride channel c. movement of Na+ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid d. movement of carbon dioxide out of a paramecium
c
Which of the following molecular movements is due to diffusion or osmosis? a. The sodium-potassium pump pumps three sodium ions out of a neuron for every two potassium ions it pumps in. b. Cells of the pancreas secrete insulin into the bloodstream. c. When a plant cell is placed in concentrated salt water, water moves out of the cell.
c
Which of the following statements about osmosis is correct? a. If a cell is placed in an isotonic solution, more water will enter the cell than leaves the cell. b. If a solution outside the cell is hypertonic compared to the cytoplasm, water will move into the cell by osmosis. c. The presence of aquaporins (proteins that form water channels in the membrane) should speed up the process of osmosis. d. Osmosis is the diffusion of water from a region of lower water concentration to a region of higher water concentration. e. Osmotic movement of water into a cell would likely occur if the cell accumulates water from its environment.
c
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. an isotonic solution, and the plant cell is in a hypotonic solution d. a hypertonic solution, and the plant cell is in an isotonic solution
c
Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly? a. an amino acid b. glucose c. CO2 d. K+
c
An animal cell lacking oligosaccharides on the external surface of its plasma membrane would likely be impaired in which function? a. establishing a diffusion barrier to charged molecules b. attaching the plasma membrane to the cytoskeleton c. transporting ions against an electrochemical gradient d. cell-cell recognition
d
An organism with a cell wall would most likely be unable to take in materials through _____. a. facilitated diffusion b. active transport c. osmosis d. phagocytosis
d
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. detach from the plasma membrane and clog arteries c. have higher rates of lateral diffusion of lipids and proteins into and out of these regions d. are less fluid than the surrounding membrane
d
The difference between pinocytosis and receptor-mediated endocytosis is that _____. a. pinocytosis increases the surface area of the plasma membrane, whereas receptor-mediated endocytosis decreases the plasma membrane surface area. b. pinocytosis brings only water molecules into the cell, but receptor-mediated endocytosis brings in other molecules as well. c. pinocytosis can concentrate substances from the extracellular fluid, but receptor-mediated endocytosis cannot. d. pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis offers more selectivity.
d
The force driving simple diffusion is _____, while the energy source for active transport is _____. a. transmembrane pumps; electron transport b. phosphorylated protein carriers; ATP c. the concentration gradient; ADP d. the concentration gradient; ATP
d
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. 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 B than in side A. c. The water level is unchanged. d. The water level is higher in side A than in side B.
d
Which of the following is least likely to be important in holding the components of a biological membrane together? a. hydrophobic interactions among the fatty acid tails of phospholipids on opposite sides of the membrane b. hydrophobic interactions among the fatty acid tails of phospholipids on the same side of the membrane c. hydrophobic interactions between the phospholipid tails and the surface of integral membrane proteins buried in the membrane d. covalent interactions between the phospholipid and protein components of the membrane e. polar interactions among the phospholipid head groups on the same surface of the membrane
d
In facilitated diffusion, what is the role of the transport protein? a. Transport proteins organize the phospholipids to allow the solute to cross the membrane. b. Transport proteins provide a protein site for ATP hydrolysis, which facilitates the movement of a solute across a membrane. c. Transport proteins provide the energy for diffusion of the solute. d. Transport proteins provide a low-resistance channel for water molecules to cross the membrane. e. Transport proteins provide a hydrophilic route for the solute to cross the membrane.
e
