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Life: The Science of Biology, Eleventh Edition Sadava • Hillis • Heller • Hacker

Chapter 6: Cell Membranes

TEST BANK QUESTIONS Multiple Choice 1. The membrane components that enable a biological membrane to have fluidity are a. integral membrane proteins. b. carbohydrates. c. oligosaccharides. d. peripheral membrane proteins. e. lipids.

Answer: e Learning Outcome: 6.1.1.a Describe the general structure of a biological membrane according to the fluid mosaic model.

Bloom’s Level: 1. Remembering 2. The compounds in a biological membrane that form a barrier to the movement of hydrophilic materials across the membrane are a. integral membrane proteins. b. carbohydrates. c. lipids. d. nucleic acids. e. peripheral membrane proteins.

Answer: c Learning Outcome: 6.1.1.a Describe the general structure of a biological membrane according to the fluid mosaic model.

Bloom’s Level: 2. Understanding 3. In a biological membrane, the phospholipids are arranged in a _______, with the _______. a. bilayer; fatty acid tails pointing toward each other b. bilayer; fatty acid tails facing outward c. single layer; fatty acid tails facing the interior of the cell d. single layer; phosphorus-containing region facing the interior of the cell e. bilayer; phosphorus groups in the interior of the membrane Answer: a Learning Outcome: 6.1.2.a Explain how the hydrophobic and hydrophilic regions of

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phospholipids are involved in membrane formation.

Bloom’s Level: 2. Understanding 4. Refer to the figure below.

Which statement about the lipid bilayer shown in the figure is false? a. The area labeled A contains hydrophilic portions of fatty acids. b. The area labeled A contains polar groups that can interact with water. c. The area labeled B contains hydrophobic regions of fatty acids. d. The area labeled B allows for the movement of charged particles. e. The area labeled B allows for the diffusion of lipid-soluble particles.

Answer: d Learning Outcome: 6.1.2.a Explain how the hydrophobic and hydrophilic regions of phospholipids are involved in membrane formation.

Bloom’s Level: 2. Understanding 5. Which observation can be used as evidence that the cell membrane has a fluid nature? a. In the laboratory, two cells from different species can be fused together to make one large cell. b. Images obtained using freeze-fracture electron microscopy reveal that the membrane contains embedded proteins. c. Chemical analysis reveals that cell membranes contain phospholipids, proteins, and cholesterol as major components. d. Analysis of the amino acids present in protein regions embedded in cell membranes show that they mainly have hydrophobic side chains. e. The cholesterol content in cell membranes varies depending on cell type, and it is

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generally higher than in organelle membranes.

Answer: a Learning Outcome: 6.1.3.a Describe a property of a cell membrane that results from its fluid nature.

Bloom’s Level: 5. Evaluating 6. One student mentioned to another that the fluidity of a cell membrane can be changed by changing the membrane’s lipid composition. The second student expressed doubt about this claim. What evidence could the first student find in a research journal to support his claim? a. A comparison of lipid compositions of membranes in different cells within the same organism b. An analysis of the change in fatty acid compositions of liver cell membranes in juvenile fish as they mature into adults c. Results from cell fusion experiments between the same two cells that measure diffusion rates of different membrane proteins d. Measurement of diffusion rates of the same protein in cell membranes containing different percentages of saturated and unsaturated fatty acids e. An analysis of the saturated and unsaturated fatty acid content in membranes of skin cells from a single population of cane toads Answer: d Learning Outcome: 6.1.4.a Cite experimental evidence to support the claim that composition and temperature affect a membrane’s fluidity.

Bloom’s Level: 5. Evaluating 7. Experimental results from five different studies on cell membranes are given. Which results could be used as evidence to support the claim that temperature affects a membrane’s fluidity? a. Results from freeze-fracture imaging of cell membranes isolated from blood cells of Arctic and desert rabbits b. A comparison of diffusion rates of different membrane proteins at 37°C in the cell membranes of liver cells from mice c. A chemical analysis of the saturated and unsaturated fatty acid content in membranes of intestinal cells from a single population of tropical frogs d. A comparison of lipid compositions of membranes in different cells within the same organism e. An analysis of the change in fatty acid compositions of liver cell membranes in a fish species before and after they migrate from warm to cold waters Answer: e Learning Outcome: 6.1.4.a Cite experimental evidence to support the claim that composition and temperature affect a membrane’s fluidity.

Bloom’s Level: 5. Evaluating 8. The plasma membrane of the bacterium Pseudomonas syringae is able to remain fluid when it is extremely cold. The bacterium most likely accomplishes this by a. increasing the number of cholesterol molecules present.

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b. closing protein channels. c. decreasing the number of hydrophobic proteins present. d. replacing saturated fatty acids with unsaturated fatty acids. e. using fatty acids with longer tails.

Answer: d Learning Outcome: 6.1.4.b Predict how changes in composition or temperature will affect properties of a membrane.

Bloom’s Level: 3. Applying 9. How do the cell membranes of a hibernating animal change in colder temperatures? a. Cholesterol content is increased. b. Saturated fatty acids are more tightly packed. c. Integral membrane proteins increase in number. d. Unsaturated fatty acids make up more of the lipid composition. e. Fatty acids with longer tails increase in number.

Answer: d Learning Outcome: 6.1.4.b Predict how changes in composition or temperature will affect properties of a membrane.

Bloom’s Level: 3. Applying 10. Refer to the table below.

According to the data presented in the table, biological membranes differ in composition because of differences in a. gene expression. b. anatomical location. c. lipid arrangement. d. biological origin. e. biological function.

Answer: e Learning Outcome: 6.1.4.c Analyze experimental results to compare membrane compositions and fluidity across species.

Bloom’s Level: 4. Analyzing

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11. Which membrane protein type would likely be removed most easily from a cell membrane in a laboratory experiment? a. Integral proteins b. Channel proteins c. Peripheral proteins d. Transmembrane proteins e. Gated channels Answer: c Learning Outcome: 6.1.5.a Differentiate between integral proteins and peripheral proteins.

Bloom’s Level: 5. Evaluating 12. If the hydrophilic side chains of a transmembrane protein were removed, the protein would most likely a. remain within the phospholipid bilayer. b. extend farther into the cytoplasm. c. protrude into the extracellular space. d. remain anchored to the cytoskeleton. e. become a peripheral protein.

Answer: a Learning Outcome: 6.1.5.a Differentiate between integral proteins and peripheral proteins.

Bloom’s Level: 3. Applying 13. Membrane proteins are asymmetrically distributed according to the function of the membrane and its lipid composition. Which statement about peripheral membrane proteins is true? a. They do not contain any hydrophilic regions. b. They are embedded in the phospholipid bilayer. c. They are able to move freely within the plasma membrane. d. Their charged regions interact with other proteins or with phospholipids. e. Their hydrophobic side chains interact with the lipid bilayer.

Answer: d Learning Outcome: 6.1.5.a Differentiate between integral proteins and peripheral proteins.

Bloom’s Level: 2. Understanding 14. The hydrophilic regions of a membrane protein would most likely be found a. only in cell membranes. b. associated with the fatty acid region of the lipids. c. in the interior of the membrane. d. exposed on the surface of the membrane. e. either on the surface or inserted into the interior of the membrane.

Answer: d Learning Outcome: 6.1.5.b Describe the various ways that proteins are distributed and can move within membranes.

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Bloom’s Level: 2. Understanding 15. The LDL receptor is an integral membrane protein that extends both outside and into the interior of the cell. The amino acid side chains (R groups) in the region of the protein that crosses the membrane are most likely a. polar. b. hydrophilic. c. hydrophobic. d. carbohydrates. e. lipids.

Answer: c Learning Outcome: 6.1.5.b Describe the various ways that proteins are distributed and can move within membranes.

Bloom’s Level: 3. Applying 16. If a cell membrane lacking integral proteins is prepared by the freeze-fracture technique and examined under the electron microscope, the exposed interior of the membrane bilayer will a. reveal a bumpy surface. b. show hydrophobic side chains. c. show an asymmetric distribution of proteins. d. show cytoskeletal anchors. e. look smooth.

Answer: e Learning Outcome: 6.1.5.b Describe the various ways that proteins are distributed and can move within membranes.

Bloom’s Level: 3. Applying 17. Ion channels are formed by a particular kind of membrane protein that allows the passage of a specific ion under certain conditions. This type of protein is most likely a(n) a. peripheral protein with additional hydrophobic domains. b. integral protein with a transmembrane domain. c. phospholipid with hydrophilic domains. d. enzyme with an asymmetrical arrangement on either side of the plasma membrane. e. membrane protein that is able to move freely within the phospholipid bilayer.

Answer: b Learning Outcome: 6.1.5.b Describe the various ways that proteins are distributed and can move within membranes.

Bloom’s Level: 3. Applying 18. Protein movement within a membrane may be restricted by a. glycolipids and glycoproteins. b. cell fusion. c. the cytoskeleton. d. cell adhesion. e. peripheral membrane proteins.

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Answer: c Learning Outcome: 6.1.5.b Describe the various ways that proteins are distributed and can move within membranes.

Bloom’s Level: 2. Understanding 19. A biologist wants to compare the fluidity of membranes from different human cells.

Which data will provide information that can be used for this analysis? a. Integral membrane protein and peripheral membrane protein content b. Cholesterol content and phospholipid fatty acid composition and content c. Mass percentage of membrane proteins and mass percentage of lipids d. Integral membrane protein densities in different locations of a membrane e. Glycolipid and glycoprotein content and distribution in a membrane Answer: b Learning Outcome: 6.1.5.c Design an experiment to compare the properties of membranes in different types of cells.

Bloom’s Level: 3. Applying 20. Refer to the figure below showing results from an analysis of the fluidity of neutrophil membranes as a function of their cholesterol content. Neutrophils are a type of white blood cell in humans.

Which statement is consistent with these data? a. Cholesterol has a negligible influence on cell membrane fluidity. b. The greater the cholesterol content in a membrane, the more fluid the membrane is. c. A membrane with less cholesterol is more fluid than a membrane with more cholesterol. d. Membrane fluidity increases with increasing cholesterol concentration. e. There is an inverse relationship between membrane fluidity and cholesterol content.

Answer: c

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Learning Outcome: 6.1.6.a Analyze data collected in investigations of the dynamic nature of membranes.

Bloom’s Level: 4. Analyzing 21. A biologist hypothesizes that a particular membrane protein is distributed throughout the cell and anchored to the cytoskeleton. Which experimental technique could provide evidence to test the biologist’s hypothesis, and why? a. Freeze-fracturing techniques, because they can be used to identify cell locations of membrane proteins b. Freeze-fracturing techniques, because they can distinguish between integral and peripheral proteins c. Cell fusion techniques, because they can be used to analyze the diffusion rate of a membrane protein d. Cell fusion techniques, because they can be used to determine the fluidity of a membrane e. Cell fusion techniques, because they can distinguish between membrane proteins of different sizes by their diffusion rates Answer: c Learning Outcome: 6.1.6.b Compare and contrast information provided by freezefracturing techniques and cell fusion experiments.

Bloom’s Level: 3. Applying 22. Which type of molecule can function as a recognition signal for interactions between cells? a. RNA b. Phospholipids c. Cholesterol d. Fatty acids e. Glycolipids Answer: e Learning Outcome: 6.1.7.a Explain the molecular basis for the high specificity of cell surface recognition sites.

Bloom’s Level: 2. Understanding 23. Two membrane components that serve as cell recognition sites are a. peripheral and integral membrane proteins. b. hydrophilic and hydrophobic domains. c. carbohydrates and proteins. d. glycolipids and glycoproteins. e. amino acids and lipids.

Answer: d Learning Outcome: 6.1.7.a Explain the molecular basis for the high specificity of cell surface recognition sites.

Bloom’s Level: 2. Understanding 24. Cell adhesion occurs through the interactions of

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a. glycoproteins and glycolipids. b. cholesterol and fatty acids. c. phospholipids and glycerol. d. oligosaccharides and oligonucleotides. e. integral proteins and cholesterol.

Answer: a Learning Outcome: 6.2.1.a Explain the molecular basis for the observed specificity of cell adhesion and cell recognition.

Bloom’s Level: 1. Remembering 25. A student claims that cell recognition and cell adhesion refer to the same function.

Which statement best evaluates this claim? a. This statement is accurate, because cell recognition and cell adhesion rely on the ability of molecules from different cells to have complementary surfaces. b. This statement is accurate, because cell recognition and cell adhesion are both abolished if molecules on different cells are prevented from interacting. c. This statement is not accurate, because cell recognition is the basis for cell adhesion, as well as for many other functions. d. This statement is not accurate, because cell adhesion is the basis for cell recognition as well as for many other functions. e. This statement is not accurate, because cell recognition and cell adhesion have no overlap in function.

Answer: c Learning Outcome: 6.2.1.c Compare cell recognition and cell adhesion and the roles of membrane proteins in each.

Bloom’s Level: 5. Evaluating 26. You are working in a lab that is studying cell recognition and cell attachment in a red sponge. You need to culture individual cells in a medium that promotes cell recognition and attachment of isolated cells. Which of the following would you add to the culture medium? a. Cellulose beads b. Glycolipids c. Glycoproteins from a different species of sponge d. A species-specific polysaccharide e. Complementary binding surfaces Answer: d Learning Outcome: 6.2.1.d Design investigations to analyze the function of proteins and carbohydrates in cell adhesion and cell recognition.

Bloom’s Level: 3. Applying 27. Sponges are multicellular organisms whose bodies allow water to circulate freely. If isolated cells from one species were added to a solution of isolated cells from another species, what would you expect in terms of binding among the cells? a. Cells from both species would bind to one another. b. Cells from one species would bind only to others of the same species.

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c. Cell binding would occur according to which type of cell was present in greater numbers. d. The cells would bind according to size, with no difference in species. e. The cells would remain isolated without binding between any groups.

Answer: b Learning Outcome: 6.2.1.d Design investigations to analyze the function of proteins and carbohydrates in cell adhesion and cell recognition.

Bloom’s Level: 3. Applying 28. Which is the name of a specialized cell junction that allows rapid spread of electric current via the flow of ions between animal cells? a. Gap junction b. Tight junction c. Desmosome d. Connexin e. Integrin Answer: a Learning Outcome: 6.2.2.a Compare and contrast the three types of cell junctions found in animals.

Bloom’s Level: 1. Remembering 29. In animal cell junctions, _______ seal intercellular spaces, _______ reinforce attachments, and _______ allow for communication between cells. a. keratins; desmosomes; connexins b. tight junctions; desmosomes; gap junctions c. cell recognition molecules; adhesion molecules; tight junctions d. junction proteins; adhesion molecules; connexins e. desmosomes; gap junctions; tight junctions Answer: b Learning Outcome: 6.2.2.a Compare and contrast the three types of cell junctions found in animals.

Bloom’s Level: 1. Remembering 30. Heart muscle cells beat in unison because of the rapid spread of electrical current through a. tight junctions. b. desmosomes. c. gap junctions. d. integral membrane proteins. e. neurons.

Answer: c Learning Outcome: 6.2.2.a Compare and contrast the three types of cell junctions found in animals.

Bloom’s Level: 2. Understanding 31. If tight junctions were replaced by desmosomes in cells lining the bladder,

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a. dissolved substances would move freely through the extracellular matrix. b. membrane protein migration would be restricted. c. intercellular spaces would be sealed off. d. the number of gap junctions would increase. e. pressure on the desmosomes would increase.

Answer: a Learning Outcome: 6.2.2.a Compare and contrast the three types of cell junctions found in animals.

Bloom’s Level: 3. Applying 32. Refer to the figure below.

The type of cell junction shown is most efficient in a. animal cells that must exchange a lot of material with adjacent cells. b. animal cells that conduct electrical activity, as in the heart. c. muscles, where rapid reflexes are required. d. epithelial cells that line animal body cavities. e. skin cells that receive stress.

Answer: d Learning Outcome: 6.2.2.a Compare and contrast the three types of cell junctions found in animals.

Bloom’s Level: 3. Applying 33. Refer to the figure below.

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The type of cell junction shown is most efficient in a. animal cells that require a tight structure. b. animal cells that conduct electrical activity, as in the heart. c. muscles, where rapid reflexes are required. d. epithelial cells that line animal body cavities. e. skin cells that receive stress.

Answer: b Learning Outcome: 6.2.2.a Compare and contrast the three types of cell junctions found in animals.

Bloom’s Level: 3. Applying 34. You are studying the effects of different substances on frog heart muscle cells. You treat the cells with a substance that blocks gap junctions. What do you expect will occur? a. The cells will not be able to maintain their structure. b. The gap junctions will not be able to provide stability. c. The electric current will not spread evenly to adjacent heart cells. d. Nutrients will not pass between the cells. e. Nerve impulses will not be transmitted to the cells.

Answer: c Learning Outcome: 6.2.2.b Explain the biological advantages of cell junctions to a multicellular animal.

Bloom’s Level: 3. Applying 35. A group of transmembrane proteins involved in maintaining animal cell structure via their interactions with the cytoskeleton are known as a. integrins. b. desmosomes. c. seal tissues. d. connexins. e. keratins.

Answer: a Learning Outcome: 6.2.3.a Describe molecular interactions between a cell and the extracellular matrix that are important in maintaining the integrity of a tissue Bloom’s Level: 1. Remembering 36. Scientists have been able to engineer young laboratory mice to have a defective gene for a particular integrin protein only in epidermal skin cells. These mice develop into adults with severe hair loss and skin blistering. Which statement explains the connection between the mutation and the observed physical problems of the mice? a. A membrane protein receptor is absent, causing loss of cell signaling. b. The mice cannot produce any extracellular matrix proteins. c. Cell–cell communication is lost because of a lost cell junction. d. Epidermal cells cannot express their genes properly. e. Epidermal cells cannot connect to the extracellular matrix.

Answer: e

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Learning Outcome: 6.2.3.a Describe molecular interactions between a cell and the extracellular matrix that are important in maintaining the integrity of a tissue.

Bloom’s Level: 3. Applying 37. Integrin on the cell surface of a white blood cell binds reversibly with the extracellular matrix of blood vessel walls. This reversibility allows for a. communication between cells. b. homotypic binding. c. heterotypic movement. d. cell movement. e. passage of dissolved materials.

Answer: d Learning Outcome: 6.2.3.b Explain the role of integrin in an animal’s body.

Bloom’s Level: 2. Understanding 38. Osmosis is a specific form of a. diffusion. b. facilitated transport. c. active transport. d. secondary active transport. e. movement of water by carrier proteins.

Answer: a Learning Outcome: 6.3.1.a Define diffusion and give an example of diffusion across a biological membrane.

Bloom’s Level: 1. Remembering 39. Which factor does not affect the rate of diffusion of a substance? a. Temperature of the solution b. Concentration gradient c. Density of the solution d. Presence of other solutes in the solution e. Molecular diameter of the diffusing material Answer: d Learning Outcome: 6.3.2.a Predict rates of diffusion of substances under different conditions.

Bloom’s Level: 2. Understanding 40. You are monitoring the diffusion of a molecule across a membrane. Of the options listed below, the fastest rate of diffusion would result from an internal concentration of _______ M and an external concentration of _______ M. a. 5; 60 b. 35; 40 c. 50; 40 d. 50; 50 e. 100; 120 Answer: a

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Learning Outcome: 6.3.2.a Predict rates of diffusion of substances under different conditions.

Bloom’s Level: 3. Applying 41. A molecule is present at two different concentrations on either side of a membrane.

The molecule will have the greatest diffusion rate if the concentration is _______ M on one side and _______ M on the other. a. 10; 20 b. 20; 30 c. 50; 60 d. 30; 30 e. 15; 50 Answer: e Learning Outcome: 6.3.2.a Predict rates of diffusion of substances under different conditions.

Bloom’s Level: 3. Applying 42. Which statement about the process of diffusion is true? a. The concentration gradient of a solute depends on the size of the molecule. b. Equilibrium in a solution is the end point of diffusion. c. The net movement of particles depends on the temperature of the solution. d. Diffusion is most efficient over long distances. e. Diffusion can reduce selective permeability of a membrane.

Answer: b Learning Outcome: 6.3.3.a Describe what happens during diffusion across a biological membrane and after equilibrium is reached.

Bloom’s Level: 2. Understanding 43. If equal volumes of differently colored solutions are poured into opposite sides of a shallow pool of water, what will be the result at equilibrium? a. Each solution will be uniformly distributed in the side of the pool into which it was poured. b. The solutions will be uniformly distributed throughout the pool. c. Each solution will have moved against its concentration gradient. d. The concentration of each solution will be higher in one side of the pool than in the other. e. The solutions will have sunk to the bottom of the pool and remained separate.

Answer: b Learning Outcome: 6.3.3.a Describe what happens during diffusion across a biological membrane and after equilibrium is reached.

Bloom’s Level: 3. Applying 44. Suppose that a new drug shows promise in treating cancer because it can enter cells by simple diffusion. Which statement about the drug is false? a. It depends on a specific carrier protein to enter the cells.

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b. Diffusion of the drug continues until its concentrations across membranes are in equilibrium. c. The drug molecules move from areas of higher concentration to areas of lower concentration. d. Diffusion of the drug molecules is a random process. e. The rate of its diffusion is affected by temperature.

Answer: a Learning Outcome: 6.3.3.a Describe what happens during diffusion across a biological membrane and after equilibrium is reached.

Bloom’s Level: 3. Applying 45. Refer to the table below.

Which list contains every substance in the table that can be predicted to pass via simple diffusion across a biological membrane? a. 6, 7 b. 1, 6, 7 c. 2, 3, 5 d. 1, 2, 3, 6 e. 1, 3, 6, 7 Answer: e Learning Outcome: 6.3.4.a Identify and explain the types of molecules that can pass via simple diffusion through a biological membrane.

Bloom’s Level: 3. Applying 46. The difference between osmosis and diffusion is that a. diffusion is passive transport, whereas osmosis is active transport. b. only in diffusion do molecules move from areas of high concentration to areas of low concentration. c. only diffusion refers to the movement of materials across a semipermeable membrane. d. osmosis refers specifically to the movement of water, whereas diffusion is the movement of any molecule. e. the process of osmosis varies according to the kinds of particles present.

Answer: d

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Learning Outcome: 6.3.5.a Using examples from animal and plant cells, define osmosis.

Bloom’s Level: 2. Understanding 47. Which statement about osmosis is false? a. Osmosis refers to the movement of water along a concentration gradient. b. In osmosis, water moves in a direction from low solute concentrations to high solute concentrations. c. The movement of water across a membrane can affect the turgor pressure of some cells. d. If osmosis occurs across a membrane, then diffusion is not occurring. e. Water may move through membrane channels during the process of osmosis.

Answer: d Learning Outcome: 6.3.5.a Using examples from animal and plant cells, define osmosis.

Bloom’s Level: 5. Evaluating 48. The process of osmosis allows water molecules to pass through specialized channels in membranes. Which statement about osmosis is true? a. The direction of osmosis depends on temperature. b. Water will move across a membrane to a region with less solute. c. Water will move across a membrane to a region with more solute. d. If the membrane does not allow solutes to pass, water will be equal on both sides. e. A higher solute concentration on one side of a membrane indicates a higher water concentration on that side.

Answer: c Learning Outcome: 6.3.5.b Differentiate between hypotonic, isotonic, and hypertonic solutions and explain how they determine the direction of water movement across a membrane.

Bloom’s Level: 2. Understanding 49. Refer to the figure below.

Which statement regarding the red blood cells in the figure is true? a. Cell C has been immersed in a hypertonic solution. b. The concentration of solutes inside cell C is higher than in the solution surrounding the cell. c. Cell A has been immersed in a hypotonic solution. d. Osmosis occurs when a cell goes from condition B to C but not from condition B to A. e. Diffusion of solutes out of the cell is causing the events shown in the transition from condition B to A.

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Answer: b Learning Outcome: 6.3.5.b Differentiate between hypotonic, isotonic, and hypertonic solutions and explain how they determine the direction of water movement across a membrane.

Bloom’s Level: 4. Analyzing 50. Refer to the figure below.

Which statement regarding the sequence of events shown in the figure is true? a. The cells in condition B have less turgor pressure than the cells in condition A. b. The cells in condition A have been placed in a hypotonic solution. c. The cells in condition C have been placed in a hypertonic solution. d. The cells in condition C have been placed in an isotonic solution. e. The cells in condition C have greater turgor pressure than the cells in condition B. Answer: e Learning Outcome: 6.3.5.b Differentiate between hypotonic, isotonic, and hypertonic solutions and explain how they determine the direction of water movement across a membrane.

Bloom’s Level: 4. Analyzing 51. If a red blood cell with an internal salt concentration of about 0.85 percent is placed in a solution that is 4 percent salt, a. the cell will lose water and shrivel. b. the cell will gain water and burst. c. the turgor pressure in the cell will increase greatly. d. the turgor pressure in the cell will decrease greatly. e. the cell will remain unchanged.

Answer: a Learning Outcome: 6.3.5.c Predict the effect of different environmental conditions on the movement of water into and out of living cells.

Bloom’s Level: 3. Applying 52. If a hospital patient is mistakenly administered pure water instead of a saline solution that is isotonic to blood during intravenous (IV) therapy, the patient’s red blood cells will a. shrink and collapse. b. release water to the plasma along its concentration gradient. c. absorb water from the plasma and eventually burst. d. allow water to move through protein channels in the cell membrane in both directions.

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e. lose their function, and the water level in the plasma will be maintained by white blood cells instead.

Answer: c Learning Outcome: 6.3.5.c Predict the effect of different environmental conditions on the movement of water into and out of living cells.

Bloom’s Level: 3. Applying 53. When placed in water, wilted plants regain their leaf turgor because of the a. active transport of salts from the water into the plant cells. b. active transport of salts from the plant cells into the water. c. osmosis of water into the plant cells. d. osmosis of water out of the plant cells. e. diffusion of water out of the plant cells.

Answer: c Learning Outcome: 6.3.5.c Predict the effect of different environmental conditions on the movement of water into and out of living cells.

Bloom’s Level: 3. Applying 54. Which strategy is paired with an appropriate consequence that would enable a cell to maintain homeostasis when placed in a vessel of pure water? a. Reduce the number of aquaporins in the cell membrane to stop water from moving out of the cytoplasm and into the external environment. b. Decrease the movement of salts out of the cytoplasm to stop water from moving into the cytoplasm. c. Expend energy to pump water out of the cytoplasm and into the external environment as the internal fluid levels become too high. d. Expend energy to pump salts into the cytoplasm from the external environment as the cytoplasm swells from water moving in by osmosis. e. Allow water to diffuse across the cell membrane until equilibrium is reached.

Answer: c Learning Outcome: 6.3.5.d Explain how an organism could maintain homeostasis when the external environment is either hypertonic or hypotonic to its cells.

Bloom’s Level: 3. Applying 55. In facilitated diffusion, the diffusion rate of a specific molecule across a membrane does not continue to increase as the molecule’s concentration difference across the membrane increases beyond a certain point. The reason is that a. facilitated diffusion requires the use of ATP. b. as the concentration difference increases, molecules interfere with one another. c. the carrier proteins become saturated. d. the transport protein is a channel protein. e. the diffusion constant depends on the concentration difference.

Answer: c Learning Outcome: 6.3.6.a Explain the role of channel proteins in facilitating diffusion across membranes.

Bloom’s Level: 2. Understanding

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56. Refer to the figure below.

Which statement regarding channel proteins shown in the figure is false? a. Channel proteins can assist polar molecules to cross the plasma membrane by facilitated diffusion. b. The gated ion channel can allow ions to pass when stimulated to open. c. The surface of a channel protein in contact with the bilayer would likely have hydrophilic amino acids. d. Water plays a role in determining which ions are allowed to pass through an ion channel. e. Aquaporins are channel proteins that facilitate the diffusion of water across membranes.

Answer: c Learning Outcome: 6.3.6.a Explain the role of channel proteins in facilitating diffusion across membranes.

Bloom’s Level: 2. Understanding 57. Channel proteins allow ions that would not normally pass through the cell membrane to pass through via the channel. The property of the channel protein that makes this possible is its pore, which is composed of a. polar amino acid groups. b. hydrophobic amino acid groups. c. Ca2+. d. carbohydrates. e. nonpolar R groups.

Answer: a Learning Outcome: 6.3.6.a Explain the role of channel proteins in facilitating diffusion across membranes.

Bloom’s Level: 2. Understanding

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58. The directions of ions as they move into and out of the cell are determined by the a. ability of the ions to let go of their water. b. ion concentration gradient. c. number of channel proteins present. d. size and charge of the ions. e. presence of specific stimuli to open gated channel proteins.

Answer: b Learning Outcome: 6.3.6.a Explain the role of channel proteins in facilitating diffusion across membranes.

Bloom’s Level: 2. Understanding 59. If cells that normally contain aquaporins undergo a mutation that destroys aquaporin function, which outcome can be expected? a. The cells will experience uncontrollable water loss. b. The cells will experience uncontrollable sodium and potassium ion uptake. c. The cells will lose the ability to take up or release sodium and potassium ions. d. The cells’ membranes will become impermeable to water. e. The cells will have no means for any polar compounds to diffuse across their membranes.

Answer: d Learning Outcome: 6.3.6.a Explain the role of channel proteins in facilitating diffusion across membranes.

Bloom’s Level: 3. Applying 60. Which helps ensure the diffusion of glucose into a cell that has a high energy need? a. A glucose pump b. Ion channels found in large muscle cells c. A high number of carrier proteins specific for glucose d. An extracellular environment high in glucose e. Additional pores through which water can flow, carrying dissolved glucose Answer: c Learning Outcome: 6.3.6.a Explain the role of channel proteins in facilitating diffusion across membranes.

Bloom’s Level: 3. Applying 61. Refer to the figure below.

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According to the graph, as the number of glucose molecules increases, the rate of diffusion across a membrane a. increases indefinitely. b. decreases. c. increases until a plateau is reached. d. can either increase or decrease. e. remains unchanged.

Answer: c Learning Outcome: 6.3.7.a Compare and contrast the different types of facilitated diffusion.

Bloom’s Level: 3. Applying 62. Which is an example of passive transport? a. Facilitated diffusion b. The sodium–potassium pump c. Turgor pressure d. ATP-driven transport e. Endocytosis Answer: a Learning Outcome: 6.4.1.a Compare and contrast diffusion and active transport.

Bloom’s Level: 2. Understanding 63. In passive transport, molecules move a. against their concentration gradient. b. more slowly than in active transport. c. toward a region of higher concentration. d. so as to reduce differences in concentration across a membrane. e. until a state of equilibrium is reached and movement stops.

Answer: d Learning Outcome: 6.4.1.a Compare and contrast diffusion and active transport.

Bloom’s Level: 2. Understanding 64. Facilitated diffusion and active transport both a. require ATP.

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b. require the use of proteins as carriers or channels. c. carry ions and not small molecules. d. increase without limit as the concentration gradient increases. e. depend on the solubility of the solute in lipids.

Answer: b Learning Outcome: 6.4.1.a Compare and contrast diffusion and active transport.

Bloom’s Level: 2. Understanding 65. Refer to the figure below showing concentrations of three ions inside and outside a cell, as well as the direction of transport of each ion facilitated by a membrane protein.

Which ions are moved by active transport and why? a. K+ and Na+, because they are present in millimolar concentrations in the cell b. Ca2+, because it is present in concentrations below the micromolar level in the cell c. K+, because it is being moved into the cell and not out of the cell d. K+, Na+, and Ca2+, because they are charged particles e. K+, Na+, and Ca2+, because they are moving from lower to higher concentration Answer: e Learning Outcome: 6.4.1.b Explain why active transport requires energy.

Bloom’s Level: 3. Applying 66. In the intestine, Na+ and an amino acid bind to the same transport protein that moves the two substances in the same direction. This type of active transport involves a. a symporter. b. an antiporter. c. secondary active transport. d. facilitated transport. e. a diffusion mechanism.

Answer: a Learning Outcome: 6.4.2.a Describe and give examples of the different types of proteins that carry out active transport.

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Bloom’s Level: 1. Remembering 67. Secondary active transport occurs in the small intestine, where the uptake of glucose is coupled to the transport of sodium ions into the cells lining this organ. This type of transport system is called a. a uniporter. b. a symporter. c. an exchange channel. d. diffusion. e. an antiporter.

Answer: b Learning Outcome: 6.4.2.a Describe and give examples of the different types of proteins that carry out active transport.

Bloom’s Level: 3. Applying 68. For each molecule of ATP consumed during active transport of sodium and potassium, there is an import of _______ ion(s) and an export of _______ ion(s). a. two Na+; three K+ b. two Na+; one K+ c. one K+; three Na+ d. two K+; three Na+ e. three K+; two Na+ Answer: d Learning Outcome: 6.4.2.a Describe and give examples of the different types of proteins that carry out active transport.

Bloom’s Level: 1. Remembering 69. The sodium‒potassium pump found in animal cells is a(n) a. uniporter. b. carrier protein. c. symporter. d. peripheral membrane protein. e. antiporter.

Answer: e Learning Outcome: 6.4.2.a Describe and give examples of the different types of proteins that carry out active transport.

Bloom’s Level: 1. Remembering 70. The sodium‒potassium pump changes shape in response to a. the binding of ions. b. the hydrolysis of ATP and phosphorylation. c. the release of Na+ ions outside the cell. d. the influx of K+ ions. e. secondary active transport.

Answer: b Learning Outcome: 6.4.2.a Describe and give examples of the different types of proteins

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that carry out active transport.

Bloom’s Level: 2. Understanding 71. If a cell were bathed in an extracellular solution high in Na+, what type of ion movement would maintain the proper balance of Na+ ions between the inside and the outside of the cell? a. Active transport of Na+ against its concentration gradient b. Facilitated diffusion of Na+ through ion channels c. Secondary active transport of K+ d. Simple diffusion of Na+ e. Simple diffusion of K+ Answer: a Learning Outcome: 6.4.2.a Describe and give examples of the different types of proteins that carry out active transport.

Bloom’s Level: 3. Applying 72. Transporters that move two substances at once are known as a. uniporters. b. facilitated transporters. c. secondary active transporters. d. coupled transporters. e. directional transporters.

Answer: d Learning Outcome: 6.4.2.b Explain why symporters and antiporters are known as coupled transporters.

Bloom’s Level: 1. Remembering 73. Which is not involved in secondary active transport? a. Energy b. A coupled transporter c. A concentration gradient d. The bilayer membrane e. A uniporter Answer: e Learning Outcome: 6.4.3.a Differentiate between primary and secondary active transport.

Bloom’s Level: 2. Understanding 74. Both primary and secondary active transport a. generate ATP. b. are based on passive movement of Na+ ions. c. include the passive movement of glucose molecules. d. use ATP directly. e. can move solutes against their concentration gradients.

Answer: e Learning Outcome: 6.4.3.a Differentiate between primary and secondary active transport.

Bloom’s Level: 2. Understanding

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75. Refer to the figure below, which is being created to illustrate secondary active transport.

The small red circles represent the molecules being transported, and the H+ symbols represent hydrogen ions. The natural concentration gradient of the red molecules is shown. The hydrogen ion gradient was established by a membrane protein that is not shown. Given this information, which symbol should appear in the oval to indicate the direction of movement of hydrogen ions and red molecules? a.

b.

c.

d.

e.

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Answer: d Learning Outcome: 6.4.3.b Create a sketch to show how coupled transport proteins could be used for secondary active transport.

Bloom’s Level: 3. Applying 76. Refer to the figure below, which is being created to illustrate secondary active transport.

What is missing from the figure? a. A concentration gradient b. Arrows showing movement of sodium ions c. A coupled transporter acting to create a concentration gradient d. Arrows showing movement of glucose molecules e. A source of energy for sodium ion transport Answer: b Learning Outcome: 6.4.3.b Create a sketch to show how coupled transport proteins could be used for secondary active transport.

Bloom’s Level: 4. Analyzing 77. Regardless of the specific type of molecule or particle being transported, endocytosis always involves a. phagocytosis. b. pinocytosis. c. receptor proteins. d. membrane invagination. e. phagosomes.

Answer: d Learning Outcome: 6.5.1.a Diagram and explain the steps in endocytosis.

Bloom’s Level: 2. Understanding 78. Phagocytosis, pinocytosis, and receptor-mediated endocytosis all involve

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a. the intake of large particles. b. invagination of the plasma membrane. c. the export of macromolecules. d. the presence of receptor proteins. e. the intake of fluids by the cell.

Answer: b Learning Outcome: 6.5.1.a Diagram and explain the steps in endocytosis.

Bloom’s Level: 2. Understanding 79. What term is used to describe the nonspecific uptake of fluids and dissolved solutes by a cell? a. Osmosis b. Diffusion c. Receptor-mediated endocytosis d. Phagocytosis e. Pinocytosis Answer: e Learning Outcome: 6.5.2.a Compare and contrast the three types of endocytosis.

Bloom’s Level: 1. Remembering 80. Both phagocytosis and receptor-mediated endocytosis a. are methods used by a cell to expel materials into the environment. b. involve vesicle formation as materials are taken up from the environment. c. are nonspecific in terms of the materials they transport. d. use membrane receptors as recognition sites for the molecules they target. e. involve a process in which vesicles in the cytoplasm fuse with the cell membrane on the interior of a cell.

Answer: b Learning Outcome: 6.5.2.a Compare and contrast the three types of endocytosis.

Bloom’s Level: 2. Understanding 81. A receptor in receptor-mediated endocytosis is a(n) a. ligand. b. clathrin molecule. c. glycolipid present in the lipid bilayer. d. cholesterol molecule embedded in the membrane. e. integral membrane protein.

Answer: e Learning Outcome: 6.5.3.a Describe the process of receptor-mediated endocytosis.

Bloom’s Level: 2. Understanding 82. Refer to the figure below showing the process of receptor-mediated endocytosis.

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Which statement regarding this process is false? a. Receptor-mediated endocytosis involves receptor proteins located on the cell’s surface. b. Coated pits are lined on their cytoplasmic surface by clathrin. c. Receptor-mediated endocytosis is important in cellular uptake of cholesterol. d. Coated vesicles eventually become part of the endoplasmic reticulum. e. Coated vesicles contain materials that were previously extracellular.

Answer: d Learning Outcome: 6.5.3.a Describe the process of receptor-mediated endocytosis.

Bloom’s Level: 3. Applying 83. Refer to the table below.

A hormone called epidermal growth factor is taken up by certain cells in mammals through receptor mediated endocytosis. Once inside cells, this hormone stimulates cell growth and differentiation. Female mice known to carry a mutation in the epidermal growth factor receptor were observed to have the characteristics summarized in the table. This mutation likely affects mammals in general. Of the types listed, which mammalian cells are likely affected by this mutation? a. Mammary glands b. Ovaries c. Heart d. Kidneys e. Lungs Answer: a

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Learning Outcome: 6.5.3.b Explain how a genetic mutation can disrupt receptor-mediated endocytosis and cause disease in humans.

Bloom’s Level: 4. Analyzing 84. Very high cholesterol levels in those with familial hypercholesterolemia are cause by a. hyperactive aquaporins. b. the inability to hydrolyze ATP. c. deficient LDL receptor proteins. d. malformed gap junctions. e. defective ion channels.

Answer: c Learning Outcome: 6.5.3.b Explain how a genetic mutation can disrupt receptor-mediated endocytosis and cause disease in humans.

Bloom’s Level: 1. Remembering 85. Refer to the figure below showing a series of events in a cell.

Which statement describes what is happening during the phase labeled 2 in the diagram? a. Chemical bond energy is expended as a vesicle membrane inserts itself into and fuses with the cell membrane. b. An enzyme associated with a vesicle opens a hole in the cell membrane, allowing the vesicle to fuse with it. c. New phospholipids are synthesized at the interface between a vesicle and the cell membrane to allow the two lipid bilayers to fuse. d. As a vesicle membrane contacts the cell membrane, the lipid bilayers of the two membranes merge to form one interconnected membrane. e. Enzymes within a vesicle digest part of the vesicle membrane to allow the remaining portion to fuse with the cell membrane.

Answer: d Learning Outcome: 6.5.4.a Diagram and explain the steps in exocytosis.

Bloom’s Level: 3. Applying 86. Receptor-mediated endocytosis is the mechanism for the import of a. clathrin. b. all macromolecules. c. large ions.

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d. cholesterol. e. integral membrane proteins.

Answer: d Learning Outcome: 6.5.4.b Provide examples of processes that involve endocytosis and/or exocytosis.

Bloom’s Level: 1. Remembering 87. Bacteria and other foreign particles that enter the body can be made harmless by a. phagocytosis by white blood cells. b. pinocytosis, which dissolves the foreign material. c. active transport of the foreign particles by a membrane pump. d. exocytosis through vesicles that fuse with the cell membrane. e. specific receptors that mediate their entry into a cell.

Answer: a Learning Outcome: 6.5.4.b Provide examples of processes that involve endocytosis and/or exocytosis.

Bloom’s Level: 1. Remembering 88. Which experimental observation would suggest that a cellular organism is protecting itself against a bacterium that is present in its environment? a. An increase in the number of membrane transporter proteins for the bacterium b. An increase in the rate of endocytosis of macromolecules c. An increase in the rate of phagocytosis of the bacterium d. Changes in the plasma membrane composition to prevent diffusion of the bacterium e. An increase in the number of vesicles releasing the bacterium into the extracellular fluid Answer: c Learning Outcome: 6.5.4.b Provide examples of processes that involve endocytosis and/or exocytosis.

Bloom’s Level: 3. Applying 89. If a cell needs to acquire cholesterol, it is usually transported into the cell by a. endocytosis. b. receptor-mediated endocytosis. c. pinocytosis. d. active transport. e. phagocytosis.

Answer: b Learning Outcome: 6.5.4.b Provide examples of processes that involve endocytosis and/or exocytosis.

Bloom’s Level: 1. Remembering 90. Cells can move substances from their cytoplasms into the external environment via a. exocytosis. b. pinocytosis. c. phagocytosis.

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d. receptor-mediated endocytosis. e. endocytosis.

Answer: a Learning Outcome: 6.5.4.b Provide examples of processes that involve endocytosis and/or exocytosis.

Bloom’s Level: 1. Remembering

Fill in the Blank 91. Biological membranes are composed of a continuous lipid bilayer in which proteins are embedded. This general design is known as the _______ model.

Answer: fluid mosaic Learning Outcome: 6.1.1.a Describe the general structure of a biological membrane according to the fluid mosaic model.

Bloom’s Level: 1. Remembering 92. Because some of the lipids composing biological membranes contain a phosphate group in their hydrophilic heads, they are called _______.

Answer: phospholipids Learning Outcome: 6.1.2.a Explain how the hydrophobic and hydrophilic regions of phospholipids are involved in membrane formation.

Bloom’s Level: 1. Remembering 93. Refer to the table below showing data collected from analyses of the phospholipid compositions of cell membranes isolated from four different species.

Use the data to rank the four species according to the temperature conditions characteristic of their native environments. The predicted ranking from coldest to warmest is _______.

Answer: B, D, C, A Learning Outcome: 6.1.4.c Analyze experimental results to compare membrane compositions and fluidity across species.

Bloom’s Level: 4. Analyzing

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94. Refer to the image below.

In order to study the distribution of proteins within membranes from different types of cells, a researcher could use the _______ technique to generate images by electron microscopy, such as the one shown above.

Answer: freeze-fracturing Learning Outcome: 6.1.5.c Design an experiment to compare the properties of membranes in different types of cells.

Bloom’s Level: 3. Applying 95. Refer to the figure below, which shows the results of an experiment in which cells from two different species were fused to form a single large cell. Membrane proteins labeled with different-colored dyes were observed and found to undergo mixing and become uniformly distributed after 40 minutes.

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The experiment was repeated at a lower temperature, and the same uniform distribution was observed, but it required a much longer time to achieve. These results indicate that temperature affects the _______ of a biological membrane.

Answer: fluidity Learning Outcome: 6.1.6.a Analyze data collected in investigations of the dynamic nature of membranes.

Bloom’s Level: 4. Analyzing 96. Vertebrate animals have integral membrane proteins known as cadherins that all have similar structures and function in cell adhesion. Certain mutations in these proteins found in mice cause cells in mouse embryos to fall apart, leading to deaths of the embryos. Some of these mutations could affect the hydrophilic part of the protein molecule, disrupting its ability to recognize and _______to a region of another cadherin molecule.

Answer: bind Learning Outcome: 6.1.7.b Describe how cells physically attach to other cells.

Bloom’s Level: 3. Applying 97. Binding between two identical molecules on two cells in cell adhesion is called _______ binding.

Answer: homotypic Learning Outcome: 6.2.1.b Differentiate between homotypic and heterotypic binding.

Bloom’s Level: 1. Remembering 98. Binding that occurs between different molecules on different cells that have an affinity for each other, such as a mammalian egg and sperm cell, is referred to as _______ binding.

Answer: heterotypic Learning Outcome: 6.2.1.b Differentiate between homotypic and heterotypic binding.

Bloom’s Level: 1. Remembering 99. When cells arrange themselves into groups through cell recognition and specific types of binding, the connections between the cells are further strengthened by _______.

Answer: cell adhesion Learning Outcome: 6.2.1.c Compare cell recognition and cell adhesion and the roles of membrane proteins in each.

Bloom’s Level: 1. Remembering 100. The cells of the intestinal epithelium are linked together in order to prevent substances from passing between them. The type of cell junction linking these cells is called a(n) _______.

Answer: tight junction Learning Outcome: 6.2.2.a Compare and contrast the three types of cell junctions found in animals.

Bloom’s Level: 1. Remembering

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101. Channels that run between pores of adjacent heart cells are called _______.

Answer: gap junctions Learning Outcome: 6.2.2.a Compare and contrast the three types of cell junctions found in animals.

Bloom’s Level: 1. Remembering 102. Heart defects can cause severe problems in newborn infants. One type of defect occurs when an infant inherits a mutation in the gene encoding connexin, the protein that is the structural component of gap junctions between heart cells. Connexin mutants can cause arrhythmia, which is an abnormal heartbeat. In these cases, cardiac cells are unable to beat in unison because of the lack of a rapid spread of ________ among cells.

Answer: electric current Learning Outcome: 6.2.2.b Explain the biological advantages of cell junctions to a multicellular animal.

Bloom’s Level: 3. Applying 103. The process of random movement of molecules toward a state of equilibrium is called _______.

Answer: diffusion Learning Outcome: 6.3.1.a Define diffusion and give an example of diffusion across a biological membrane.

Bloom’s Level: 1. Remembering 104. Diffusion is the net movement of particles toward regions of (higher/lower) _______ concentration.

Answer: lower Learning Outcome: 6.3.1.a Define diffusion and give an example of diffusion across a biological membrane.

Bloom’s Level: 1. Remembering 105. Refer to the figure below showing the molecular structure of dimethylmercury.

Exposure of human skin to a single drop of dimethylmercury can lead to death, as it passes easily through cell membranes because it is _______.

Answer: nonpolar Learning Outcome: 6.3.4.a Identify and explain the types of molecules that can pass via simple diffusion through a biological membrane.

Bloom’s Level: 3. Applying

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106. When plant cells are placed in a hypotonic solution, water enters the cells and exerts pressure against the cell wall. This force is called _______.

Answer: turgor pressure Learning Outcome: 6.3.5.a Using examples from animal and plant cells, define osmosis.

Bloom’s Level: 1. Remembering 107. Solution X is hypotonic relative to solution Y if X has a solute concentration that is _______ the solute concentration of Y. Answer: lower than Learning Outcome: 6.3.5.b Differentiate between hypotonic, isotonic, and hypertonic solutions and explain how they determine the direction of water movement across a membrane.

Bloom’s Level: 1. Remembering 108. If a cell placed within a solution shrinks in volume, the solution is _______ relative to the cell.

Answer: hypertonic Learning Outcome: 6.3.5.b Differentiate between hypotonic, isotonic, and hypertonic solutions and explain how they determine the direction of water movement across a membrane.

Bloom’s Level: 3. Applying 109. To survive in a hypertonic saltwater environment, a unicellular organism would have to expend energy to pump water (into/out of) _______ its cytoplasm.

Answer: into Learning Outcome: 6.3.5.d Explain how an organism could maintain homeostasis when the external environment is either hypertonic or hypotonic to its cells.

Bloom’s Level: 3. Applying 110. Root hair cells in plant roots use active transport to take up nitrate ions from the soil. Active transport is used because it requires energy to move nitrate ions from a _______ concentration in the soil into the plant cells.

Answer: low Learning Outcome: 6.4.1.b Explain why active transport requires energy.

Bloom’s Level: 3. Applying 111. The membrane protein that transports glucose and sodium ions into intestinal epithelial cells simultaneously is an example of a(n) _______.

Answer: symporter Learning Outcome: 6.4.2.b Explain why symporters and antiporters are known as coupled transporters.

Bloom’s Level: 3. Applying 112. The sodium–potassium pump of cell membranes is an example of a membrane protein called a(n) _______ that moves two substances in opposite directions across a membrane.

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Answer: antiporter Learning Outcome: 6.4.2.b Explain why symporters and antiporters are known as coupled transporters.

Bloom’s Level: 1. Remembering 113. Primary active transport requires energy released from the hydrolysis of _______.

Answer: ATP Learning Outcome: 6.4.3.a Differentiate between primary and secondary active transport.

Bloom’s Level: 2. Understanding 114. The process by which the cell membrane engulfs large particles or even whole cells is called _______.

Answer: phagocytosis Learning Outcome: 6.5.2.a Compare and contrast the three types of endocytosis.

Bloom’s Level: 1. Remembering 115. The process of _______ involves coated pits, clathrin, and coated vesicles.

Answer: receptor-mediated endocytosis Learning Outcome: 6.5.3.a Describe the process of receptor-mediated endocytosis.

Bloom’s Level: 1. Remembering

Short Answer/Essay 116. Refer to the diagram below showing the fluid mosaic model.

Which of the labeled components is a transmembrane protein?

Answer: B Learning Outcome: 6.1.1.b Sketch and label a model for the molecular structure of the cell membrane.

Bloom’s Level: 3. Applying 117. Refer to the diagram below showing the fluid mosaic model.

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Which of the labeled components affects the fluidity of the animal cell membrane according to the numbers of this component that are present, as well as other characteristics?

Answer: D Learning Outcome: 6.1.1.a Describe the general structure of a biological membrane according to the fluid mosaic model.

Bloom’s Level: 3. Applying 118. Diagram a cell membrane and label the phospholipid bilayer, integral proteins, peripheral proteins, and carbohydrates. Describe the fluid mosaic model with reference to your diagram.

Answer:

The fluid mosaic model states that the phospholipid bilayer allows the embedded proteins to float freely through the bilayer.

Learning Outcome: 6.1.1.b Sketch and label a model for the molecular structure of the cell membrane.

Bloom’s Level: 6. Creating 119. Refer to the table below summarizing information about two membrane proteins.

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Diffusion coefficients indicate the rates at which proteins diffuse laterally through the cell membrane. What property of cell membranes is illustrated by a comparison of the information shown about these two proteins, and how does this property fit in with the current model used to describe the cell membrane?

Answer: Cell membranes are fluid in nature, and this is illustrated by a comparison of the information provided in the table. Unless a membrane protein is anchored to the cytoskeleton, as fibronectin is, it moves freely throughout the membrane. The diffusion coefficients of fibronectin and rhodopsin make this clear since fibronectin, which is anchored, has a much lower diffusion coefficient than rhodopsin, which is not anchored and can move freely. This fluid nature fits in with the current model of the cell membrane, the fluid mosaic model, which describes the cell membrane as a fluid lipid bilayer in which proteins are embedded. Both lipids and membrane proteins that are not tethered either to the cytoskeleton or to the extracellular matrix can move freely.

Learning Outcome: 6.1.3.a Describe a property of a cell membrane that results from its fluid nature.

Bloom’s Level: 4. Analyzing 120. Refer to the figure below.

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The experimental technique shown in the figure is used to analyze cell membranes. How does this technique differ from freeze-fracturing techniques in terms of the information about cell membranes it can provide?

Answer: The figure shows a cell fusion experiment, which can provide information about the fluidity of a cell membrane and how rapidly membrane proteins can diffuse when two cells are fused together. In contrast, freeze-fracturing techniques allow the lipid bilayer of a cell membrane to be split apart so that the pattern of embedded proteins can be viewed.

This does not provide information about dynamic changes in protein movement over time within a membrane, as a cell fusion experiment can provide. Instead, freeze-fracturing experiments provide information about the density and distribution of proteins within a membrane at a single point in time.

Learning Outcome: 6.1.6.b Compare and contrast information provided by freezefracturing techniques and cell fusion experiments.

Bloom’s Level: 3. Applying 121. Studies of isolated animal cells mixed together randomly and then placed in culture dishes have shown that they sort themselves out according to the types of membrane proteins they express. The figure below shows an example of this sorting-out process.

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Explain the molecular basis for how cells sort themselves out and form attachments to one another in producing the end product shown.

Answer: Extracellular parts of the membrane protein X stick out from one cell surface and bind to similar parts of membrane protein X sticking out from another cell surface.

The same thing happens between membrane protein Y on one cell and membrane protein Y on another cell. Each of these peptide chains has unique three-dimensional features with chemical properties that allow binding to another like it but not to a different peptide chain. These binding features may involve amino acid side chains and/or oligosaccharides covalently attached to amino acids in the proteins.

Learning Outcome: 6.1.7.b Describe how cells physically attach to other cells.

Bloom’s Level: 3. Applying 122. You are examining the membrane of a cell and notice many carbohydrates in the cell membrane. What role do these carbohydrates most likely play?

Answer: Carbohydrates located on the surface of the cell membrane are important in recognizing specific molecules.

Learning Outcome: 6.2.1.a Explain the molecular basis for the observed specificity of cell adhesion and cell recognition.

Bloom’s Level: 2. Understanding 123. Refer to the figure below, in which the interaction of two substances controls cell movement.

What are these substances?

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Answer: Integrin and the extracellular matrix Learning Outcome: 6.2.3.b Explain the role of integrin in an animal’s body.

Bloom’s Level: 2. Understanding 124. A marathon runner has just arrived in the emergency room with severe dehydration, and the physician must decide which type of solution to pump into his veins: pure water, 0.9 percent saline, or 1.5 percent saline. Blood cells are approximately 0.9 percent saline.

Describe what is likely to happen to the blood cells when they are exposed to each solution.

Answer: In pure water, the blood cells will take on water through osmosis, swell, and eventually rupture. In 0.9 percent saline, the cells should neither gain nor lose a significant amount of water. In a 1.5 percent saline solution, the cells should lose water and shrivel. In order to rehydrate the runner, a solution isotonic to the patient’s blood cells, 0.9 percent, should be infused into his bloodstream.

Learning Outcome: 6.3.5.c Predict the effect of different environmental conditions on the movement of water into and out of living cells.

Bloom’s Level: 3. Applying 125. Refer to the diagram below illustrating one type of membrane protein involved in facilitated diffusion of a substance across a biological membrane.

Identify the type of transporter shown, and explain how it differs from the other major type of transporter involved in facilitated diffusion.

Answer: The diagram shows a channel protein that provides a pore through which substances that are otherwise repelled by biological membranes can pass. The other type of transporter that carries out facilitated diffusion is a carrier protein, which differs from a channel protein in that it only moves one molecule or ion at a time, while a channel protein can move many molecules or ions through a membrane at once. In addition, a carrier protein changes conformation in response to binding of the molecule or ion it transports. A channel protein can change conformation in response to a ligand, but the ligand is not the substance being transported, and its role is to open and close the channel to the substance being transported.

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Learning Outcome: 6.3.7.a Compare and contrast the different types of facilitated diffusion.

Bloom’s Level: 3. Applying 126. Refer to the graph below showing the relationship between glucose concentration outside a cell and the rate of facilitated diffusion of glucose across a cell membrane via carrier proteins.

Which label on the graph represents saturation of the carrier proteins?

Answer: D Learning Outcome: 6.3.7.a Compare and contrast the different types of facilitated diffusion.

Bloom’s Level: 3. Applying 127. You are examining a membrane that contains a number of proteins that appear to be involved in transport of an ion across that membrane. Design an experiment that will allow you to determine whether these transporters are passive transporters or active transporters.

Answer: The main difference between active and passive transport is that active transport goes against a concentration gradient and requires energy, whereas passive transport works passively by diffusion and does not require energy. To determine the type of transport occurring, you would measure the movement of the ions across a membrane.

One side of the membrane should have a high concentration of the ion, and the other, a low concentration. If ions move only from areas of high concentration to low concentration, then the transporter is a passive transporter. If the addition of ATP is needed for movement to occur, it is an active transporter.

Learning Outcome: 6.4.1.a Compare and contrast diffusion and active transport.

Bloom’s Level: 6. Creating 128. Refer to the figure below.

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Name the three types of proteins involved in transport, represented by A, B, and C. Answer: A = uniporter, B = symporter, C = antiporter Learning Outcome: 6.4.2.a Describe and give examples of the different types of proteins that carry out active transport.

Bloom’s Level: 3. Applying 129. Refer to the figure below showing the beginning sketch of a secondary transport system that moves lactose into a cell.

The system is known to have a lactose transporter and a proton pump. Complete the sketch to show how this system could transport lactose into the cell.

Answer:

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Learning Outcome: 6.4.3.b Create a sketch to show how coupled transport proteins could be used for secondary active transport.

Bloom’s Level: 6. Creating 130. Refer to the figures below:

What is the correct sequence of these figures in the process of exocytosis?

Answer: 3, 2, 4, 1 Learning Outcome: 6.5.4.a Diagram and explain the steps in exocytosis.

Bloom’s Level: 3. Applying

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