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This Document Contains Chapters 4 to 5 Chapter 4: A Tour of the Cell 4.1 Multiple-Choice Questions 1) When biologists wish to study the internal ultrastructure of cells, they can achieve the finest resolution by using a A) phase-contrast light microscope. B) scanning electron microscope. C) transmission electronic microscope. D) confocal fluorescence microscope. E) super-resolution fluorescence microscope. Answer: C 2) The advantage of light microscopy over electron microscopy is that A) light microscopy provides for higher magnification than electron microscopy. B) light microscopy provides for higher resolving power than electron microscopy. C) light microscopy allows one to view dynamic processes in living cells. D) light microscopy provides higher contrast than electron microscopy. E) specimen preparation for light microcopy does not produce artifacts. Answer: C 3) A primary objective of cell fractionation is to A) view the structure of cell membranes. B) sort cells based on their size and weight. C) determine the size of various organelles. D) separate the major organelles so that their particular functions can be determined. E) separate lipid-soluble from water-soluble molecules. Answer: D 4) In the fractionation of homogenized cells using centrifugation, the primary factor that determines whether a specific cellular component ends up in the supernatant or the pellet is A) the relative solubility of the component. B) the size and weight of the component. C) the percentage of carbohydrates in the component. D) the presence or absence of nucleic acids in the component. E) the presence or absence of lipids in the component. Answer: B 5) Which of the following correctly lists the order in which cellular components will be found in the pellet when homogenized cells are treated with increasingly rapid spins in a centrifuge? A) ribosomes, nucleus, mitochondria B) chloroplasts, ribosomes, vacuoles C) nucleus, ribosomes, chloroplasts D) vacuoles, ribosomes, nucleus E) nucleus, mitochondria, ribosomes Answer: E 6) What is the reason that a modern electron microscope (TEM) can resolve biological images to the subnanometer level, as opposed to the tens of nanometers achievable for the best super-resolution light microscope? A) The focal length of the electron microscope is significantly longer. B) Contrast is enhanced by staining with atoms of heavy metal. C) Electron beams have much shorter wavelengths than visible light. D) The electron microscope has a much greater ratio of image size to real size. E) The electron microscope cannot image whole cells at one time. Answer: C 7) What technique would be most appropriate to use to observe the movements of condensed chromosomes during cell division? A) standard light microscopy B) scanning electron microscopy C) transmission electron microscopy D) confocal fluorescence microscopy E) super-resolution fluorescence microscopy Answer: A 8) The smallest cell structure that would most likely be visible with a standard (not super-resolution) research-grade light microscope is A) a mitochondrion. B) a microtubule. C) a ribosome. D) a microfilament. E) a nuclear pore. Answer: A 9) All of the following are part of a prokaryotic cell except A) DNA. B) a cell wall. C) a plasma membrane. D) ribosomes. E) an endoplasmic reticulum. Answer: E 10) Which of the following is a major cause of the size limits for certain types of cells? A) limitation on the strength and integrity of the plasma membrane as cell size increases B) the difference in plasma membranes between prokaryotes and eukaryotes C) evolutionary progression in cell size; more primitive cells have smaller sizes D) the need for sufficient surface area to support the cell's metabolic needs E) rigid cell walls that limit cell size expansion Answer: D 11) Which of the following statements concerning cells of bacteria and archaea is correct? A) Archaea contain small membrane-enclosed organelles; bacteria do not. B) Archaea contain a membrane-bound nucleus; bacteria do not. C) DNA is present in both archaea and bacteria. D) DNA is present in the mitochondria of both bacteria and archaea. Answer: C 12) Prokaryotes are classified as belonging to two different domains. What are the domains? A) Bacteria and Eukarya B) Bacteria and Archaea C) Archaea and Protista D) Bacteria and Protista E) Bacteria and Fungi Answer: B 13) Large numbers of ribosomes are present in cells that specialize in producing which of the following molecules? A) lipids B) glycogen C) proteins D) cellulose E) nucleic acids Answer: C 14) The nuclear lamina is an array of filaments on the inner side of the nuclear membrane. If a method were found that could cause the lamina to fall into disarray, what would you expect to be the most likely immediate consequence? A) the loss of all nuclear function B) the inability of the nucleus to divide during cell division C) a change in the shape of the nucleus D) failure of chromosomes to carry genetic information E) inability of the nucleus to keep out destructive chemicals Answer: C 15) A cell with a predominance of free ribosomes is most likely A) producing primarily proteins for secretion. B) producing primarily cytoplasmic proteins. C) constructing an extensive cell wall or extracellular matrix. D) digesting large food particles. E) enlarging its vacuole. Answer: B 16) Which structure is the site of the synthesis of proteins that may be exported from the cell? A) rough ER B) lysosomes C) plasmodesmata D) Golgi vesicles E) free cytoplasmic ribosomes Answer: A 17) ECM proteins are made by ribosomes in which part of a eukaryotic cell? A) mitochondria B) cytoplasm C) nuclear envelope D) Golgi apparatus E) rough ER Answer: E 18) The volume enclosed by the plasma membrane of plant cells is often much larger than the corresponding volume in animal cells. The most reasonable explanation for this observation is that A) plant cells are capable of having a much higher surface-to-volume ratio than animal cells. B) plant cells have a much more highly convoluted (folded) plasma membrane than animal cells. C) plant cells contain a large vacuole that reduces the volume of the cytoplasm. D) animal cells are more spherical, whereas plant cells are elongated. E) plant cells can have lower surface-to-volume ratios than animal cells because plant cells synthesize their own nutrients. Answer: C 19) The liver is involved in detoxification of many poisons and drugs. Which of the following structures is primarily involved in this process and therefore abundant in liver cells? A) rough ER B) smooth ER C) Golgi apparatus D) nuclear envelope E) transport vesicles Answer: B 20) Which of the following statements correctly describes some aspect of protein secretion from prokaryotic cells? A) Prokaryotes are unlikely to be able to secrete proteins because they lack an endomembrane system. B) The mechanism of protein secretion in prokaryotes is probably the same as that in eukaryotes. C) Proteins that are secreted by prokaryotes are synthesized on ribosomes that are bound to the cytoplasmic surface of the plasma membrane. D) In prokaryotes, the ribosomes that are used for the synthesis of secreted proteins are located outside of the cell. E) Prokaryotes contain large pores in their plasma membrane that permit the movement of proteins out of the cell. Answer: C 21) Which type of organelle or structure is primarily involved in the synthesis of oils, phospholipids, and steroids? A) ribosome B) lysosome C) smooth endoplasmic reticulum D) mitochondrion E) contractile vacuole Answer: C 22) The Golgi apparatus has a polarity or sidedness to its structure and function. Which of the following statements correctly describes this polarity? A) Transport vesicles fuse with one side of the Golgi and leave from the opposite side. B) Proteins in the membrane of the Golgi may be sorted and modified as they move from one side of the Golgi to the other. C) Lipids in the membrane of the Golgi may be sorted and modified as they move from one side of the Golgi to the other. D) Soluble proteins in the cisternae (interior) of the Golgi may be sorted and modified as they move from one side of the Golgi to the other. E) All of the above correctly describe polar characteristics of the Golgi function. Answer: E 23) The difference in lipid and protein composition between the membranes of the endomembrane system is largely determined by A) the physical separation of most membranes from each other. B) the transportation of membrane lipids among the endomembrane system by small membrane vesicles. C) the function of the Golgi apparatus in sorting and directing membrane components. D) the modification of the membrane components once they reach their final destination. E) the synthesis of different lipids and proteins in each of the organelles of the endomembrane system. Answer: C 24) Hydrolytic enzymes must be segregated and packaged to prevent general destruction of cellular components. In animal cells, which of the following organelles contains these hydrolytic enzymes? A) chloroplast B) lysosome C) central vacuole D) peroxisome E) glyoxysome Answer: B 25) Tay-Sachs disease is a human genetic abnormality that results in cells accumulating and becoming clogged with very large, complex, undigested lipids. Which cellular organelle must be involved in this condition? A) the endoplasmic reticulum B) the Golgi apparatus C) the lysosome D) mitochondrion E) membrane-bound ribosomes Answer: C 26) Which of the following produces and modifies polysaccharides that will be secreted? A) lysosome B) vacuole C) mitochondrion D) Golgi apparatus E) peroxisome Answer: D 27) One of the key innovations in the evolution of eukaryotes from a prokaryotic ancestor is the endomembrane system. What eukaryotic organelles or features might have evolved as a part of, or as an elaboration of, the endomembrane system? A) plasma membrane B) chloroplasts C) mitochondria D) nuclear envelope E) none of these Answer: D 28) Which of the following contains hydrolytic enzymes? A) lysosome B) vacuole C) mitochondrion D) Golgi apparatus E) peroxisome Answer: A 29) Which organelle often takes up much of the volume of a plant cell? A) lysosome B) vacuole C) mitochondrion D) Golgi apparatus E) peroxisome Answer: B 30) A cell has the following molecules and structures: enzymes, DNA, ribosomes, plasma membrane, and mitochondria. It could be a cell from A) a bacterium. B) an animal, but not a plant. C) nearly any eukaryotic organism. D) any multicellular organism, such as a plant or an animal. E) any kind of organism. Answer: C 31) Which type of organelle is found in plant cells but not in animal cells? A) ribosomes B) mitochondria C) nuclei D) plastids E) none of these Answer: D 32) Why isn't the mitochondrion classified as part of the endomembrane system? A) It is a static structure. B) Its structure is not derived from the ER or Golgi. C) It has too many vesicles. D) It is not involved in protein synthesis. E) It is not attached to the outer nuclear envelope. Answer: B 33) What types of proteins are not synthesized in the rough ER? A) endoplasmic reticulum proteins B) extracellular matrix proteins C) secreted proteins D) mitochondrial proteins E) plasma membrane proteins Answer: D 34) Which organelle is the primary site of ATP synthesis in eukaryotic cells? A) lysosome B) vacuole C) mitochondrion D) Golgi apparatus E) peroxisome Answer: C 35) Which plant cell organelle contains its own DNA and ribosomes? A) glyoxysome B) vacuole C) mitochondrion D) Golgi apparatus E) peroxisome Answer: C 36) Which animal cell organelle contains enzymes that transfer hydrogen from various substrates to oxygen? A) lysosome B) vacuole C) mitochondrion D) Golgi apparatus E) peroxisome Answer: E 37) Thylakoids, DNA, and ribosomes are all components found in A) vacuoles. B) chloroplasts. C) mitochondria. D) lysosomes. E) nuclei. Answer: B 38) In a plant cell, DNA may be found A) only in the nucleus. B) only in the nucleus and mitochondria. C) only in the nucleus and chloroplasts. D) in the nucleus, mitochondria, and chloroplasts. E) in the nucleus, mitochondria, chloroplasts, and peroxisomes. Answer: D 39) The chemical reactions involved in respiration are virtually identical between prokaryotic and eukaryotic cells. In eukaryotic cells, ATP is synthesized primarily on the inner membrane of the mitochondria. In light of the endosymbiont theory for the evolutionary origin of mitochondria, where is most ATP synthesis likely to occur in prokaryotic cells? A) in the cytoplasm B) on the inner mitochondrial membrane C) on the endoplasmic reticulum D) on the plasma membrane E) on the inner nuclear envelope Answer: D 40) The evolution of eukaryotic cells most likely involved A) endosymbiosis of an aerobic bacterium in a larger host cell–the endosymbiont evolved into mitochondria. B) anaerobic archaea taking up residence inside a larger bacterial host cell to escape toxic oxygen–the anaerobic bacterium evolved into chloroplasts. C) an endosymbiotic fungal cell that evolved into the nucleus. D) acquisition of an endomembrane system, and subsequent evolution of mitochondria from a portion of the Golgi. Answer: A 41) In a liver cell detoxifying alcohol and some other poisons, the enzymes of the peroxisome remove hydrogen from these molecules and A) combine the hydrogen with water molecules to generate hydrogen peroxide. B) use the hydrogen to break down hydrogen peroxide. C) transfer the hydrogen to the mitochondria. D) transfer the hydrogen to oxygen molecules to generate hydrogen peroxide. Answer: D 42) How does the cell multiply its peroxisomes? A) They bud off from the Golgi. B) They are brought into the cell from the environment. C) They are built de novo from cytosol materials. D) They split in two after they become sufficiently large. E) The cell synthesizes hydrogen peroxide and encloses it in a membrane. Answer: D 43) Which organelle or structure is absent in plant cells? A) mitochondria B) Golgi vesicles C) microtubules D) centrosomes E) peroxisomes Answer: D 44) Motor proteins provide for molecular motion in cells by interacting with what types of cellular structures? A) sites of energy production in cellular respiration B) membrane proteins C) ribosomes D) cytoskeletal structures E) cellulose fibers in the cell wall Answer: D 45) Movement of vesicles within the cell depends on what cellular structures? A) microtubules and motor proteins B) actin filaments and microtubules C) actin filaments and ribosomes D) centrioles and motor proteins E) actin filaments and motor proteins Answer: A 46) Which of the following contain the 9 + 2 arrangement of microtubules, consisting of nine doublets of microtubules surrounding a pair of single microtubules? A) both motile cilia and primary (nonmotile) cilia B) centrioles only C) both flagella and motile cilia D) both basal bodies and primary (nonmotile) cilia E) both centrioles and basal bodies Answer: C 47) Vinblastine, a drug that inhibits microtubule polymerization, is used to treat some forms of cancer. Cancer cells given vinblastine would be unable to A) form cleavage furrows during cell division. B) migrate by amoeboid movement. C) separate chromosomes during cell division. D) extend pseudopods. E) maintain the shape of the nucleus. Answer: C 48) Centrioles, cilia, flagella, and basal bodies have remarkably similar structural elements and arrangements. Which of the following hypotheses is most plausible in light of such structural similarities? A) Cilia and flagella arise from the centrioles. B) Loss of basal bodies should lead to loss of all cilia, flagella, and centrioles. C) Motor proteins such as dynein must have evolved before any of these four kinds of structures. D) Cilia and flagella coevolved in the same ancestral eukaryotic organism. E) Natural selection for cell motility repeatedly selected for microtubular arrays in circular patterns in the evolution of each of these structures. Answer: A 49) Cytochalasin D is a drug that prevents actin polymerization. A cell treated with cytochalasin D will still be able to A) perform amoeboid movement. B) form cleavage furrows. C) contract muscle fibers. D) extend pseudopodia. E) move vesicles around the cell. Answer: E 50) Which of the following statements about the cytoskeleton is true? A) The dynamic aspect of cytoskeletal function is made possible by the assembly and disassembly of a large variety of proteins into complex aggregates. B) Microfilaments are structurally rigid and resist compression, whereas microtubules resist tension (stretching). C) Movement of cilia and flagella is the result of motor proteins causing microtubules to move relative to each other. D) Chemicals that block the assembly of the cytoskeleton would cause little effect on the cell's response to external signals and stimuli. E) Transport vesicles among the membranes of the endomembrane system produce the cytoskeleton. Answer: C 51) Cells require which of the following to form cilia or flagella? A) tubulin B) laminin C) actin D) intermediate filaments E) secretory vesicles Answer: A 52) A mutation that disrupts the ability of an animal cell to add polysaccharide modifications to proteins would most likely cause defects in its A) nuclear lamina and nuclear matrix. B) nuclear matrix and extracellular matrix. C) mitochondria and Golgi apparatus. D) Golgi apparatus and extracellular matrix. E) nuclear pores and secretory vesicles. Answer: D 53) All of the following serve an important role in determining or maintaining the structure of plant cells. Which of the following are distinct from the others in their composition? A) microtubules B) microfilaments C) plant cell walls D) intermediate filaments E) nuclear lamina Answer: C 54) What do the cell walls of plants and the extracellular matrix of animal cells have in common? A) They are largely composed of phospholipids and glycoproteins. B) Their proteins are made by free cytoplasmic ribosomes. C) They form rigid structures that provide structural support for cells but limit their expansion. D) They limit the passage of small molecules. E) They have functional connections with the cytoskeleton inside the cell. Answer: E 55) The cell walls of bacteria, fungi, and plant cells and the extracellular matrix of animal cells are all external to the plasma membrane. Which of the following is a characteristic common to all of these extracellular structures? A) They must block water and small molecules in order to regulate the exchange of matter and energy with their environment. B) They must permit information transfer between the cell's cytoplasm and the nucleus. C) They must provide a rigid structure that maintains an appropriate ratio of cell surface area to volume. D) They are constructed of polymers that are synthesized in the cytoplasm and then transported out of the cell. E) They are composed of a mixture of lipids and carbohydrates. Answer: D 56) When a potassium ion (K+) moves from the soil into the vacuole of a cell on the surface of a root, it must pass through several cellular structures. Which of the following correctly describes the order in which these structures will be encountered by the ion? A) plasma membrane → primary cell wall → cytoplasm → vacuole B) secondary cell wall → plasma membrane → primary cell wall → cytoplasm → vacuole C) primary cell wall → plasma membrane → cytoplasm → vacuole D) primary cell wall → plasma membrane → lysosome → cytoplasm → vacuole E) primary cell wall → plasma membrane → cytoplasm → secondary cell wall → vacuole Answer: C 57) The extracellular matrix is thought to participate in the regulation of animal cell behavior by communicating information from the outside to the inside of the cell via which of the following? A) gap junctions B) the nucleus C) DNA and RNA D) integrins E) plasmodesmata Answer: D 58) Plasmodesmata in plant cells are most similar in function to which of the following structures in animal cells? A) peroxisomes B) desmosomes C) gap junctions D) extracellular matrix E) tight junctions Answer: C 59) Ions can travel directly from the cytoplasm of one animal cell to the cytoplasm of an adjacent cell through A) plasmodesmata. B) intermediate filaments. C) tight junctions. D) desmosomes. E) gap junctions. Answer: E 60) Which of the following makes it necessary for animal cells, although they have no cell walls, to have intercellular junctions? A) Cell membranes do not distinguish the types of ions and molecules passing through them. B) Large molecules, such as proteins and RNA molecules, do not readily get through one, much less two, adjacent cell membranes. C) Cell-to-cell communication requires physical attachment of one cell to another. D) Maintenance of tissue integrity and barriers to fluid leakage requires cells to adhere tightly to one another. E) The relative shapelessness of animal cells requires a mechanism for keeping the cells aligned. Answer: D 61) Signals from the ECM to the cytoskeleton may be transmitted by A) fibronectin. B) proteoglycans. C) integrins. D) collagen. E) middle lamella. Answer: C 4.2 Art Question Table 4.1 1) The differences among the three categories of cytoskeletal elements outlined in the table above would suggest that each of the following has specialized roles. Which of the following is a correct match? (All three elements are involved in the maintenance of cell shape.) A) microfilaments and the nuclear lamina B) microtubules and cleavage furrow formation C) microfilaments and ciliary motion D) intermediate filaments and cytoplasmic streaming E) microtubules and chromosome movement Answer: E 4.3 Scenario Questions 1) A biologist wants specifically to examine the surfaces of different types of cells in kidney tubules of small mammals. The cells in question can be distinguished by external shape, size, and 3-D characteristics. Which of the following would be the optimum method for her study? A) transmission electron microscopy B) cell fractionation C) light microscopy using stains specific to kidney function D) light microscopy of living unstained material E) scanning electron microscopy Answer: E 2) A newspaper ad for a local toy store indicates that a very inexpensive microscope available for a small child is able to magnify specimens nearly as much as the much more costly microscope available in your college lab. What is the primary reason for the price difference? A) The ad agency is misrepresenting the ability of the toy microscope to magnify. B) The toy microscope does not have the same fine control for focus of the specimen. C) The toy microscope magnifies a good deal, but has low resolution and therefore poor-quality images. D) The college microscope produces greater contrast in the specimens. E) The toy microscope usually uses a different wavelength of light source. Answer: C 3) A biologist ground up some plant leaf cells and then centrifuged the mixture to fractionate the organelles. Organelles in one of the heavier fractions could produce ATP in the light, whereas organelles in the lighter fraction could produce ATP in the dark. The heavier and lighter fractions are most likely to contain, respectively, A) mitochondria and chloroplasts. B) chloroplasts and peroxisomes. C) peroxisomes and chloroplasts. D) chloroplasts and mitochondria. E) mitochondria and peroxisomes. Answer: D 4.4 End-of-Chapter Questions 1) Which structure is not part of the endomembrane system? A) nuclear envelope B) chloroplast C) Golgi apparatus D) plasma membrane E) ER Answer: B 2) Which structure is common to plant and animal cells? A) chloroplast B) wall made of cellulose C) central vacuole D) mitochondrion E) centriole Answer: D 3) Which of the following is present in a prokaryotic cell? A) mitochondrion B) ribosome C) nuclear envelope D) chloroplast E) ER Answer: B 4) Which structure-function pair is mismatched? A) nucleolus; production of ribosomal subunits B) lysosome; intracellular digestion C) ribosome; protein synthesis D) Golgi; protein trafficking E) microtubule; muscle contraction Answer: E 5) Cyanide binds to at least one molecule involved in producing ATP. If a cell is exposed to cyanide, most of the cyanide will be found within the A) mitochondria. B) ribosomes. C) peroxisomes. D) lysosomes. E) endoplasmic reticulum. Answer: A 6) What is the most likely pathway taken by a newly synthesized protein that will be secreted by a cell? A) ER → Golgi → nucleus B) Golgi → ER → lysosome C) nucleus → ER → Golgi D) ER → Golgi → vesicles that fuse with plasma membrane E) ER → lysosomes → vesicles that fuse with plasma membrane Answer: D 7) Which cell would be best for studying lysosomes? A) muscle cell B) nerve cell C) phagocytic white blood cell D) leaf cell of a plant E) bacterial cell Answer: C Chapter 5: Membrane Transport and Cell Signaling 5.1 Multiple-Choice Questions 1) Some regions of the plasma membrane, called lipid rafts, have a higher concentration of cholesterol molecules. At high temperatures, these regions A) are more fluid than the surrounding membrane. B) are less fluid than the surrounding membrane. C) are able to flip from inside to outside. D) detach from the plasma membrane and clog arteries. E) have higher rates of lateral diffusion of lipids and proteins into and out of these regions. Answer: B 2) Singer and Nicolson's fluid mosaic model of the membrane proposed that membranes A) are a phospholipid bilayer. B) are a phospholipid bilayer between two layers of hydrophilic proteins. C) are a single layer of phospholipids and proteins. D) consist of protein molecules embedded in a fluid bilayer of phospholipids. E) consist of a mosaic of polysaccharides and proteins. Answer: D 3) Which of the following types of molecules are the major structural components of the cell membrane? A) phospholipids and cellulose B) nucleic acids and proteins C) phospholipids and proteins D) proteins and cellulose E) glycoproteins and cholesterol Answer: C 4) When biological membranes are frozen and then fractured, they tend to break along the middle of the bilayer. The best explanation for this is that A) the integral membrane proteins are not strong enough to hold the bilayer together. B) water that is present in the middle of the bilayer freezes and is easily fractured. C) hydrophilic interactions between the opposite membrane surfaces are destroyed on freezing. D) the carbon-carbon bonds of the phospholipid tails are easily broken. E) the hydrophobic interactions that hold the membrane together are weakest at this point. Answer: E 5) The presence of cholesterol in the plasma membranes of some animals A) enables the membrane to stay fluid more easily when cell temperature drops. B) enables the animal to remove hydrogen atoms from saturated phospholipids. C) enables the animal to add hydrogen atoms to unsaturated phospholipids. D) makes the membrane less flexible, allowing it to sustain greater pressure from within the cell. E) makes the animal more susceptible to circulatory disorders. Answer: A 6) According to the fluid mosaic model of cell membranes, which of the following is a true statement about membrane phospholipids? A) They can move laterally along the plane of the membrane. B) They frequently flip-flop from one side of the membrane to the other. C) They occur in an uninterrupted bilayer, with membrane proteins restricted to the surface of the membrane. D) They are free to depart from the membrane and dissolve in the surrounding solution. E) They have hydrophilic tails in the interior of the membrane. Answer: A 7) Which of the following is one of the ways that the membranes of winter wheat are able to remain fluid when it is extremely cold? A) by increasing the percentage of unsaturated phospholipids in the membrane B) by increasing the percentage of cholesterol molecules in the membrane C) by decreasing the number of hydrophobic proteins in the membrane D) by cotransport of glucose and hydrogen E) by using active transport Answer: A 8) In order for a protein to be an integral membrane protein it would have to be A) hydrophilic. B) hydrophobic. C) amphipathic, with at least one hydrophobic region. D) completely covered with phospholipids. E) exposed on only one surface of the membrane. Answer: C 9) When a membrane is freeze-fractured, the bilayer splits down the middle between the two layers of phospholipids. In an electron micrograph of a freeze-fractured membrane, the bumps seen on the fractured surface of the membrane are A) peripheral proteins. B) phospholipids. C) carbohydrates. D) integral proteins. E) cholesterol molecules. Answer: D 10) Which of the following is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures? A) The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly. B) Unsaturated fatty acids have a higher cholesterol content and therefore more cholesterol in their membranes. C) Unsaturated fatty acids are more polar than saturated fatty acids. D) The double bonds block interaction among the hydrophilic head groups of the lipids. E) The double bonds result in shorter fatty acid tails and thinner membranes. Answer: A 11) Which of the following is true of integral membrane proteins? A) They lack tertiary structure. B) They are loosely bound to the surface of the bilayer. C) They are usually transmembrane proteins. D) They are not mobile within the bilayer. E) They serve only a structural role in membranes. Answer: C 12) The primary function of polysaccharides attached to the glycoproteins and glycolipids of animal cell membranes is A) to facilitate diffusion of molecules down their concentration gradients. B) to actively transport molecules against their concentration gradients. C) to maintain the integrity of a fluid mosaic membrane. D) to maintain membrane fluidity at low temperatures. E) to mediate cell-to-cell recognition. Answer: E 13) A protein that spans the phospholipid bilayer one or more times is A) a transmembrane protein. B) an integral protein. C) a peripheral protein. D) an integrin. E) a glycoprotein. Answer: A 14) Which of these are not embedded in the hydrophobic portion of the lipid bilayer? A) transmembrane proteins B) integral proteins C) peripheral proteins D) integrins E) glycoproteins Answer: C 15) The cell membranes of Antarctic ice fish might have which of the following adaptations? A) very long chain fatty acids B) branched isoprenoid lipids C) a high percentage of polyunsaturated fatty acids D) a higher percentage of trans fatty acids E) no cholesterol Answer: C 16) The formulation of a model for a structure or for a process serves which of the following purposes? A) It asks a scientific question. B) It functions as a testable hypothesis. C) It records observations. D) It serves as a data point among results. E) It can only be arrived at after years of experimentation. Answer: B 17) Why are lipids and proteins free to move laterally in membranes? A) The interior of the membrane is filled with liquid water. B) Lipids and proteins repulse each other in the membrane. C) Hydrophilic portions of the lipids are in the interior of the membrane. D) There are only weak hydrophobic interactions in the interior of the membrane. E) Molecules such as cellulose can pull them in various directions. Answer: D 18) Over the years, the fluid mosaic model has been refined based on recent experimental findings. In the years since the proposal of the fluid mosaic model of the cell membrane, which of the following observations has been added to the model? A) The membrane is only fluid across a very narrow temperature range. B) Proteins rarely move in the membrane. C) Unsaturated lipids are excluded from the membranes and do not contribute to membrane fluidity. D) The concentration of protein molecules appears to be much higher. E) Membrane proteins are made of only acidic amino acids. Answer: D 19) Cell membranes are asymmetrical. Which of the following statements is the most likely explanation for the membrane's asymmetrical nature? A) Because the cell membrane forms a border between one cell and another in tightly packed tissues such as epithelium, the membrane must be asymmetrical B) Because 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) The chemical constitution of the inner and outer layer of the cell membrane is predetermined by genes. E) Proteins only function on the cytoplasmic side of the cell membrane, which results in the membrane’s asymmetrical nature. Answer: C 20) Which of the following is true for the evolution of cell membranes? A) The fluid mosaic nature of cell membranes provides the explanation for the evolution of cell membranes. B) Membrane proteins are the sole component responsible for the evolution of cell membranes. C) The evolution of cell membranes is driven by the evolution of glycoproteins and glycolipids. D) All components of membranes evolve as a result of natural selection. E) An individual organism selects its preferred type of cell membrane for particular functions. Answer: D 21) The movement of the hydrophobic gas nitrous oxide (N2O) (laughing gas) into a cell is an example of A) diffusion across the lipid bilayer. B) facilitated diffusion. C) active transport. D) osmosis. E) cotransport. Answer: A 22) What kinds of molecules pass through a cell membrane most easily? A) large and hydrophobic B) small and hydrophobic C) large polar D) ionic E) monosaccharides such as glucose Answer: B 23) Which of the following is a characteristic feature of a carrier protein in a plasma membrane? A) It is a peripheral membrane protein. B) It exhibits a specificity for a particular type of molecule. C) It requires the expenditure of cellular energy to function. D) It works against diffusion. E) It has few, if any, hydrophobic amino acids. Answer: B 24) Which of the following would likely move through the lipid bilayer of a plasma membrane most rapidly? A) CO2 B) an amino acid C) glucose D) K+ E) starch Answer: A 25) Which of the following statements is correct about diffusion? A) It is very rapid over long distances. B) It requires an expenditure of energy by the cell. C) It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration. D) It is an active process in which molecules move from a region of lower concentration to one of higher concentration. E) It requires integral proteins in the cell membrane. Answer: C 26) Water passes quickly through cell membranes because A) the bilayer is hydrophilic. B) it moves through hydrophobic channels. C) water movement is tied to ATP hydrolysis. D) it is a small, polar, charged molecule. E) it moves through aquaporins in the membrane. Answer: E 27) Celery stalks that are immersed in fresh water for several hours become stiff and hard. Similar stalks left in a 0.15 M salt solution become limp and soft. From this we can deduce that A) the fresh water and the salt solution are both hypertonic to the cells of the celery stalks. B) the fresh water and the salt solution are both hypotonic to the cells of the celery stalks. C) the fresh water is hypotonic and the salt solution is hypertonic to the cells of the celery stalks. D) the fresh water is hypertonic and the salt solution is hypotonic to the cells of the celery stalks. E) the fresh water is isotonic and the salt solution is hypertonic to the cells of the celery stalks. Answer: C 28) Mammalian blood contains the equivalent of 0.15 M NaCl. Seawater contains the equivalent of 0.45 M NaCl. What will happen if red blood cells are transferred to seawater? A) Water will leave the cells, causing them to shrivel and collapse. B) NaCl will be exported from the red blood cells by facilitated diffusion. C) The blood cells will take up water, swell, and eventually burst. D) NaCl will passively diffuse into the red blood cells. E) The blood cells will expend ATP for active transport of NaCl into the cytoplasm. Answer: A 29) Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells? A) The animal cell is in a hypotonic solution, and the plant cell is in an isotonic solution. B) The animal cell is in an isotonic solution, and the plant cell is in a hypertonic solution. C) The animal cell is in a hypertonic solution, and the plant cell is in an isotonic solution. D) The animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution. E) The animal cell is in a hypertonic solution, and the plant cell is in a hypotonic solution. Answer: D 30) When a plant cell, such as one from a peony stem, is submerged in a very hypotonic solution, what is likely to occur? A) The cell will burst. B) The cell membrane will lyse. C) Plasmolysis will shrink the interior. D) The cell will become flaccid. E) The cell will become turgid. Answer: E 31) Glucose diffuses slowly through artificial phospholipid bilayers. The cells lining the small intestine, however, rapidly move large quantities of glucose from the glucose-rich food into their glucose-poor cytoplasm. Using this information, which transport mechanism is most probably functioning in the intestinal cells? A) simple diffusion B) phagocytosis C) active transport pumps D) exocytosis E) facilitated diffusion Answer: E 32) Which of the following membrane activities requires energy from ATP hydrolysis? A) facilitated diffusion of chloride ions across the membrane through a chloride channel B) movement of water into a cell C) movement of Na+ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid D) movement of glucose molecules into a bacterial cell from a medium containing a higher concentration of glucose than inside the cell E) movement of carbon dioxide out of a paramecium Answer: C 33) 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) The cotransporter can also transport potassium ions. E) A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose. Answer: E 34) The phosphate transport system in bacteria imports phosphate into the cell even when the concentration of phosphate outside the cell is much lower than the cytoplasmic phosphate concentration. Phosphate import depends on a pH gradient across the membrane–more acidic outside the cell than inside the cell. Phosphate transport is an example of A) passive diffusion. B) facilitated diffusion. C) active transport. D) osmosis. E) cotransport. Answer: E 35) What is the voltage across a membrane called? A) water potential B) chemical gradient C) membrane potential D) osmotic potential E) electrochemical gradient Answer: C 36) The sodium-potassium pump is called an electrogenic pump because it A) pumps equal quantities of Na+ and K+ across the membrane. B) pumps hydrogen ions out of the cell. C) contributes to the membrane potential. D) ionizes sodium and potassium atoms. E) is used to drive the transport of other molecules against a concentration gradient. Answer: C 37) The movement of potassium into an animal cell requires A) low cellular concentrations of sodium. B) high cellular concentrations of potassium. C) an energy source such as ATP. D) a cotransport protein. E) a potassium channel protein. Answer: C 38) Ions diffuse across membranes through specific ion channels A) down their chemical gradients. B) down their concentration gradients. C) down the electrical gradients. D) down their electrochemical gradients. E) down the osmotic potential gradients. Answer: D 39) Which of the following would increase the electrochemical gradient across a membrane? A) a chloride channel B) a sucrose-proton cotransporter C) a proton pump D) a potassium channel E) both a proton pump and a potassium channel Answer: C 40) Proton pumps are used in various ways by members of every domain of organisms: Bacteria, Archaea, and Eukarya. What does this most probably mean? A) Proton pumps must have evolved before any living organisms were present on Earth. B) Proton gradients across a membrane were used by cells that were the common ancestor of all three domains of life. C) The high concentration of protons in the ancient atmosphere must have necessitated a pump mechanism. D) Cells of each domain evolved proton pumps independently when oceans became more acidic. E) Proton pumps are necessary to all cell membranes. Answer: B 41) A bacterium engulfed by a white blood cell through phagocytosis will be digested by enzymes contained in A) peroxisomes. B) lysosomes. C) Golgi vesicles. D) vacuoles. E) secretory vesicles. Answer: B 42) Familial hypercholesterolemia is characterized by which of the following? A) defective LDL receptors on the cell membranes B) poor attachment of the cholesterol to the extracellular matrix of cells C) a poorly formed lipid bilayer that cannot incorporate cholesterol into cell membranes D) inhibition of the cholesterol active transport system in red blood cells E) a general lack of glycolipids in the blood cell membranes Answer: A 43) The difference between pinocytosis and receptor-mediated endocytosis is that A) pinocytosis brings only water molecules into the cell, but receptor-mediated endocytosis brings in other molecules as well. B) pinocytosis increases the surface area of the plasma membrane, whereas receptor-mediated endocytosis decreases the plasma membrane surface area. C) pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis offers more selectivity. D) pinocytosis requires cellular energy, but receptor-mediated endocytosis does not. E) pinocytosis can concentrate substances from the extracellular fluid, but receptor-mediated endocytosis cannot. Answer: C 44) In receptor-mediated endocytosis, receptor molecules initially project to the outside of the cell. Where do they end up after endocytosis? A) on the outside of vesicles B) on the inside surface of the cell membrane C) on the inside surface of the vesicle D) on the outer surface of the nucleus E) on the ER Answer: C 45) When protein membrane receptors are activated, what usually happens? A) A change occurs in intracellular ion concentration. B) The receptors open and close in response to protein signals. C) A change occurs on only one membrane surface: exterior or interior. D) The receptor preferentially binds with lipid or glycolipid signal molecules. E) The receptor changes conformation after binding with signal polypeptides. Answer: E 46) Which of the following is true of steroid receptors? A) The receptor molecules are themselves lipids or glycolipids. B) The receptor may be inside the nuclear membrane. C) The unbound steroid receptors are quickly recycled by lysosomes. D) The concentration of steroid receptors must be relatively high in most cells. E) The receptor molecules are free to move in and out of most organelles. Answer: B 47) What is most likely to happen to an animal's target cells that lack receptors for local regulators? A) They might compensate by receiving nutrients via a factor. B) They could develop normally in response to neurotransmitters instead. C) They could divide but never reach full size. D) They might not be able to multiply in response to growth factors from nearby cells. E) Hormones would not be able to interact with target cells. Answer: D 48) Which of the following is characterized by a cell releasing a signal molecule into the environment, followed by a number of cells in the immediate vicinity responding? A) hormonal signaling B) autocrine signaling C) paracrine signaling D) endocrine signaling E) synaptic signaling Answer: C 49) In which of the following ways do plant hormones differ from hormones in animals? A) Plant hormones interact primarily with intracellular receptors. B) Plant hormones may travel in air or through vascular systems. C) Animal hormones are found in much greater concentration. D) Plant hormones are synthesized from two or more distinct molecules. E) Animal hormones are primarily for mating and embryonic development. Answer: B 50) When a neuron responds to a particular neurotransmitter by opening gated ion channels, the neurotransmitter is serving as which part of the signal pathway? A) receptor B) relay molecule C) transducer D) signal molecule E) endocrine molecule Answer: D 51) Testosterone functions inside a cell by A) acting as a signal receptor that activates tyrosine kinases. B) binding with a receptor protein that enters the nucleus and activates specific genes. C) acting as a steroid signal receptor that activates ion channel proteins. D) becoming a second messenger that inhibits nitric oxide. E) coordinating a phosphorylation cascade that increases spermatogenesis. Answer: B 52) Which of the following is true of transcription factors? A) They regulate the synthesis of DNA in response to a signal. B) They transcribe ATP into cAMP. C) They initiate the epinephrine response in animal cells. D) They control gene expression. E) They regulate the synthesis of lipids in the cytoplasm. Answer: D 53) In general, a signal transmitted via phosphorylation of a series of proteins A) brings a conformational change to each protein. B) requires binding of a hormone to a cytosol receptor. C) cannot occur in yeasts because they lack protein phosphatases. D) requires phosphorylase activity. E) allows target cells to change their shape and therefore their activity. Answer: A 54) Which of the following most likely would be an immediate result of a growth factor binding to its receptor? A) protein kinase activity B) adenylyl cyclase activity C) GTPase activity D) protein phosphatase activity E) phosphorylase activity Answer: A 55) Which of the following statements is true of signal molecules? A) When signal molecules first bind to receptor tyrosine kinases, the receptors phosphorylate a number of nearby molecules. B) In response to some G-protein-mediated signals, a special type of lipid molecule associated with the plasma membrane is cleaved to form IP3 and calcium. C) In most cases, signal molecules interact with the cell at the plasma membrane and then enter the cell and eventually the nucleus. D) Toxins such as those that cause botulism and cholera interfere with the ability of activated G proteins to hydrolyze GTP to GDP, resulting in phosphodiesterase activity in the absence of an appropriate signal molecule. E) Protein kinase A activation is one possible result of signal molecules binding to G-protein-coupled receptors. Answer: E 56) Which of the following is a correct association? A) kinase activity and the addition of a tyrosine B) phosphodiesterase activity and the removal of phosphate groups C) GTPase activity and hydrolysis of GTP to GDP D) phosphorylase activity and the catabolism of glucose E) adenylyl cyclase activity and the conversion of cAMP to AMP Answer: C 57) The function of phosphatases in signal transduction is best described as to A) move the phosphate group of the transduction pathway to the next molecule of a series. B) prevent a protein kinase from being reused when there is another extracellular signal. C) amplify the transduction signal so it affects multiple transducers. D) amplify the second messengers such as cAMP. E) inactivate protein kinases and turn off the signal transduction. Answer: E 58) In which of the following ways could signal transduction most probably be explored in research to treat cancer? A) removal of serine/threonine phosphate acceptors from transduction pathways in colon pre-cancerous growths B) alteration of protein kinases in cell cycle regulation in order to slow cancer growth C) increase in calcium ion uptake into the cytoplasm in order to modulate the effects of environmental carcinogens D) expansion of the role of transduction inhibitors in the cells before they give rise to cancer E) increase in the concentration of phosphor diesterases in order to produce more AMP Answer: B 59) A drug designed to inhibit the response of cells to testosterone would almost certainly result in which of the following? A) lower cytoplasmic levels of cAMP B) an increase in receptor tyrosine kinase activity C) a decrease in transcriptional activity of certain genes D) an increase in cytosolic calcium concentration E) a decrease in G-protein activity Answer: C 60) At puberty, an adolescent female body changes in both structure and function of several organ systems, primarily under the influence of changing concentrations of estrogens and other steroid hormones. How can one hormone, such as estrogen, mediate so many effects? A) Estrogen is produced in very large concentration and therefore diffuses widely. B) Estrogen has specific receptors inside several cell types, but each cell responds in the same way to its binding. C) Estrogen is kept away from the surface of any cells not able to bind it at the surface. D) Estrogen binds to specific receptors inside many kinds of cells, each of which have different responses to its binding. E) The subcomponents of estrogen, when metabolized, can influence cell response. Answer: D 61) In research on aging (both cellular aging and organismal aging), it has been found that aged cells do not progress through the cell cycle as they had previously. Which of the following would provide evidence that this is related to cell signaling? A) Growth factor ligands do not bind as efficiently to receptors. B) Their lower hormone concentrations elicit a lesser response. C) cAMP levels change very frequently. D) Enzymatic activity declines. E) ATP production decreases. Answer: A 62) Sutherland discovered that the signaling molecule epinephrine A) brings about a decrease in levels of cAMP as a result of bypassing the plasma membrane. B) causes lower blood glucose by binding to liver cells. C) interacts with insulin inside muscle cells. D) interacts directly with glycogen phosphorylase. E) elevates cytosolic concentrations of cyclic AMP. Answer: E 63) Which of the following is the greatest advantage of having multiple steps in a transduction pathway? A) Many of the steps can be used in multiple pathways. B) Having multiple steps in a pathway requires the least amount of ATP. C) Having multiple steps provides for greater possible amplification of a signal. D) Each individual step can remove excess phosphate groups from the cytoplasm. E) Each step can be activated by several G proteins simultaneously. Answer: C 64) GTPase activity is important in the regulation of signal transduction because it A) increases the available concentration of phosphate. B) decreases the amount of G protein in the membrane. C) hydrolyzes GTP to GDP, thus shutting down the pathway. D) converts cGMP to GTP. E) phosphorylates protein kinases. Answer: C 5.2 Art Questions Figure 5.1 For the following questions, match the labeled component of the cell membrane in Figure 5.1 with its description. 1) Which component is the peripheral protein? A) A B) B C) C D) D E) E Answer: D 2) Which component is cholesterol? A) A B) B C) C D) D E) E Answer: E 3) Which component is the fiber of the extracellular matrix? A) A B) B C) C D) D E) E Answer: A 4) Which component is a microfilament of the cytoskeleton? A) A B) B C) C D) D E) E Answer: C 5) Which component is a glycolipid? A) A B) B C) C D) D E) E Answer: B Figure 5.2 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. 6) Initially, in terms of tonicity, the solution in side A with respect to that in side B is A) hypotonic. B) plasmolyzed. C) isotonic. D) saturated. E) hypertonic. Answer: C 7) 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 molarity of glucose is higher in side A than in side B. C) The water level is higher in side A than in side B. D) The water level is unchanged. E) The water level is higher in side B than in side A. Answer: C Figure 5.3 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 to answer the following questions. 8) At the beginning of the experiment, side A A) is hypertonic to side B. B) is hypotonic to side B. C) is isotonic to side B. D) is hypertonic to side B with respect to glucose. E) is hypotonic to side B with respect to sodium chloride. Answer: B 9) If you examine side A after three days, you should find A) a decrease in the concentration of NaCl and glucose and an increase in the water level. B) a decrease in the concentration of NaCl, an increase in water level, and no change in the concentration of glucose. C) no net change in the system. D) a decrease in the concentration of NaCl and a decrease in the water level. E) no change in the concentration of NaCl and glucose and an increase in the water level. Answer: D Figure 5.4 Five dialysis bags, constructed from a semipermeable membrane that is impermeable to sucrose, were filled with various concentrations of sucrose and then placed in separate beakers containing an initial concentration of 0.6 M sucrose solution. At 10-minute intervals, the bags were massed (weighed) and the percent change in mass of each bag was graphed. 10) Which line in the graph represents the bag that contained a solution isotonic to the 0.6 M solution at the beginning of the experiment? A) A B) B C) C D) D E) E Answer: C 11) Which line in the graph represents the bag with the highest initial concentration of sucrose? A) A B) B C) C D) D E) E Answer: A 12) Which line or lines in the graph represent(s) bags that contain a solution that is hypertonic at 50 minutes? A) A and B B) B C) C D) D E) D and E Answer: B Figure 5.5 The following questions are based on Figure 5.5. 13) Which of the following types of signaling is represented in Figure 5.5? A) autocrine B) paracrine C) hormonal D) synaptic E) long distance Answer: D 14) In Figure 5.5, the dots in the space between the two structures represent which of the following? A) receptor molecules B) signal transducers C) neurotransmitters D) hormones E) pheromones Answer: C 5.3 Scenario Questions 1) Cystic fibrosis is a genetic disease in humans in which the CFTR protein, which functions as a chloride ion channel, is missing or nonfunctional in cell membranes. The CFTR protein belongs to what category of membrane proteins? A) gap junctions B) aquaporins C) electrogenic ion pumps D) cotransporters E) hydrophilic channels Answer: E 2) A patient has had a serious accident and lost a lot of blood. In an attempt to replenish body fluids, distilled water–equal to the volume of blood lost–is transferred directly into one of his veins. What will be the most probable result of this transfusion? A) It will have no unfavorable effect as long as the water is free of viruses and bacteria. B) The patient's red blood cells will shrivel up because the blood fluid has become hypotonic compared to the cells. C) The patient's red blood cells will swell because the blood fluid has become hypotonic compared to the cells. D) The patient's red blood cells will shrivel up because the blood fluid has become hypertonic compared to the cells. E) The patient's red blood cells will burst because the blood fluid has become hypertonic compared to the cells. Answer: C 3) You are working on a team that is designing a new drug. In order for this drug to work, it must enter the cytoplasm of specific target cells. Which of the following would be a factor that determines whether the molecule selectively enters the target cells? A) blood or tissue type of the patient B) hydrophobicity of the drug molecule C) lack of charge on the drug molecule D) similarity of the drug molecule to other molecules transported by the target cells E) lipid composition of the target cells' plasma membrane Answer: D Use this description to answer the following question. A major group of G-protein-coupled receptors contains seven transmembrane α helices. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior face or on the cytosol face of the membrane. The loop on the cytosol side between helices 5 and 6 is usually substantially longer than the others. 4) The coupled G protein most likely interacts with this receptor A) at the NH3 end. B) at the COO- end. C) along the exterior margin. D) along the interior margin. E) at the loop between H5 and H6. Answer: E 5) If an animal cell suddenly lost the ability to produce GTP, what might happen to its signaling system? A) It would not be able to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane. B) It could activate only the epinephrine system. C) It would be able to carry out reception and transduction but would not be able to respond to a signal. D) It would use ATP instead of GTP to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane. E) It would employ a transduction pathway directly from an external messenger. Answer: A 5.4 End-of-Chapter Questions 1) 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 kind of membrane. C) Only certain membranes of the cell are selectively permeable. D) Only certain membranes are constructed from amphipathic molecules. E) Some membranes have hydrophobic surfaces exposed to the cytoplasm, while others have hydrophilic surfaces facing the cytoplasm. Answer: B 2) Which of the following factors would tend to increase membrane fluidity? A) a greater proportion of unsaturated phospholipids B) a greater proportion of saturated phospholipids C) a lower temperature D) a relatively high protein content in the membrane E) a greater proportion of relatively large glycolipids compared with lipids having smaller molecular masses Answer: A 3) Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because A) they are species specific. B) they always lead to the same cellular response. C) they amplify the original signal manifold. D) they counter the harmful effects of phosphatases. E) the number of molecules used is small and fixed. Answer: C 4) Lipid-soluble signaling molecules, such as testosterone, cross the membranes of all cells but affect only target cells because A) only target cells retain the appropriate DNA segments. B) intracellular receptors are present only in target cells. C) most cells lack the Y chromosome required. D) only target cells possess the cytosolic enzymes that transduce the testosterone. E) only in target cells is testosterone able to initiate a phosphorylation cascade. Answer: B 5) Which of the following processes includes all the others? A) osmosis B) diffusion of a solute across a membrane C) facilitated diffusion D) passive transport E) transport of an ion down its electrochemical gradient Answer: D 6) Based on the figure given below, which of these experimental treatments would increase the rate of sucrose transport into the cell? A) decreasing extracellular sucrose concentration B) decreasing extracellular pH C) decreasing cytoplasmic pH D) adding an inhibitor that blocks regeneration of ATP E) adding a substance that makes the membrane more permeable to hydrogen ions Answer: B Test Bank for Campbell Biology in Focus Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson, Jane B. Reece 9780321813664, 9780321962751, 9780134710679

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