LESSON – 12 and 13MEMBRANES.

A. MEMBRANE STRUCTURE.

A. Objectives.

- Describe and draw schematically a picture of a generic biological membrane; relate the structure to microscopic images of the membrane.Explain how Overton deduced the lipophilic nature of membranes; use Gorter and Grendel’s experiment to deduce that the lipid bilayer is the basis of the membrane streucture; explain the structure of phospholipids and how they form a lipid bilayer.Describe the permeability of a lipid bilayer for oxygen, water, lipids, large hydrophobic molecules, small hydrophobic molecules, ions, charged molecules, (large) polar molecules (e.g., size of amino acids, monosaccharides and up).

- Explain the relationship of proteins and carbohydrates with the membrane; note differences in the Danielli structure and the fluid mosaic model; relate the distribution of amino acids to the different functional domains of transmembrane proteins; explain the nature of glycoproteins.

- Discuss how the nature of membrane lipids (or fatty acid tails) determines the temperature sensitivity of the membrane; define: glycoprotein, glycolipid, spectrin, clathrins, cholesterol

B. Lecture outline.

1. THE LIPID FOUNDATION OF MEMBRANES.

Read: The structure of biological membranes (SBM p107-115).

a. Charles Overton (1895): the importance of lipids.b. Gorter and Grendel (1925): the lipid bilayer.c. Phospholipids.d. Bilayer sheets: permeability of lipid bilayer.

2. MEMBRANE STRUCTURE.

a. Davson—Danielli model (1935): a protein-lipid sandwich.b. Singer and Nicolson (1972): the fluid mosaic model.c. molecular organization of membrane: transmembrane proteins and glycoproteins

3. ADAPTATION OF MEMBRANES TO THE ENVIRONMENT.

LESSON – 14MEMBRANES.

B. MEMBRANE TRANSPORT.Diffusion and Osmosis.

A. Objective.

— List 4 functions of the membrane.— Define diffusion, osmosis, osmotic pressure, hydrostatic pressure, isotonic, hypotonic

and hypertonic medium, and contractile vacuole.— Apply the principles of osmosis to animal cells, plant cells, bacteria, fungi and

protozoa (amoebae, flagellates and ciliates) in fresh water and in sea water.— Use the principles of osmosis to prevent microbial growth in food products; explain

why an antibiotic that destroys the cell wall of bacteria can be used as a cure in human an animal infections.

B. Lecture outline.

1. DIFFUSION AND OSMOSIS.

Read: Diffusion and Osmosis (SBM p116-118).

a. diffusion.b. osmosis.c. isotonic, hypertonic and hypotonic medium.

note: Maintaining osmotic balance.

LESSON-15MEMBRANES

B. MEMBRMIE TRANSPORT.Bulk transport and selective transport of molecules.

A. Objective.

- Explain and draw schematically the principle of endocytosis; compare endocytosis, receptor—mediated endocytosis, phagocytosis, pinocytosis and exocytosis; contrast osmotrophs and phagotrophs structurally and functionally.

- Discuss the importance of the selective permeability of membranes.- Compare passive and active transport, transport by simple diffusion and facilitated

diffusion.- Explain the principle of active transport and apply to the sodium-potassium pump, and

coupled channel.

B. Lecture outline.

2. TRANSPORT OF BULK MATERIAL ACROSS THE MEMBRANE.

a. Endocytosis

Read: Exocytosis amd endocytosis (SBM p123-127).

2. SELECTIVE TRANSPORT OF MOLECULES..

Read: Passive transport (SBM p115-120).Read: Active transport (SBM p120-123).

a. passive transport—diffusion,— facilitated diffusion.

b. active transport— sodium—potassium pump.— co— and counter transport: coupled channels.

C. Study Questions.

1. How many fatty acids are connected to a glycerol in a phospholipid?A. 0.B. 1.C. 2.D. 3.E. 4.

2 What is the most significant property of a phospholipid in terms of its participation in membrane structure?

A. One end is nonpolar; the other is extremely polar.B. The entire molecule is very hydrophobic.C. The entire molecule is extremely polar.D. The entire molecule is extremely nonpolar.E. The entire molecule is very hydrophilic.

3. How do phospholipid molecules line up in the two leaflets of the bilayer that forms spontaneously when the lipids are mixed with water?

A. head-to-head.B. head-to-tail.C. polar end to polar end.D. alternating phosphate and fatty acid groups.E. tail-to-tail.

4. What statement describes the permeability of a lipid bilayer INCORRECTLY? A lipid bilayer is

A. completely impermeable to large water-soluble molecules.B. permeable to glucose and uncharged amino acids.C. permeable to lipids.D. permeable to small, uncharged, polar molecules such as water, carbon dioxide, ammonium and oxygen.E. impermeable to ions.

5. Because phopholipid molecules are free to move laterally, the membrane is said to beA. filmy.B. fluid.C. loose.D. permeable.E. soft.

6. A membrane containing a predominance of phospholipids with highly unsaturated fatty acid chains is likely

A. fluid only at high temperatures.B. quite fluid even at low temperatures.C. rather stiff and inflexible at high temperatures only.D. permissive to protein movement only at high temperatureE. solid at any temperature.

7. Molecules that penetrate through the membrane are calledA. doughnut molecules.B. penetration molecules.C. pore molecules.

D. transmembrane molecules.E. thoroughfare molecules.

8. What type of macromolecules form transmembrane molecules?A. lipids.B. polysaccharides.C. proteins.D. nucleic acids.E. prostaglandins.

9. How thick is a typical membrane? AboutA. 25 angstrom.B. 75 angstrom.C. 75 nanometer.D. 25 micrometer.E. 75 millionth of an inch.

10. How thick is the hydrophobic part of a typicsj. membrane? AboutA. 25 millimeter.B. 25 micrometer.C. 25 nanometer.D. 25 angstrom.E. 25 picometer.

11. Rank the chemical composition of a typical membrane in order of abundance?A. polysaccharide > nucleic acid > phospholipid > protein.B. protein > polysaccharide > phospholipid > nucleic acid.C. phospholipid > nucleic acid > protein > polysaccharide.D. phospholipid > polysaccharide > nucleic acid > protein.E. phospholipid > protein > polysaccharide.

12. What is the principal objection against the Danielli-Dawson model of a membrane? It does not

A. describe a fluid structure.B. account for the bilayer of lipids that surrounds the cells as was shown earlier (1925

Gortel and Grendel).C. explain the trilayered structure seen electron microscopically.D. allow entrance of sugars, amino acids or nitrogen bases in the cell.E. explain the important role of phospholipids in the membrane.F.

13. What molecules in addition to proteins can function as surface markers of cells?A. ATP.B. linear or branching oligosaccharide groups.C. cholesterol.D. sodium ion.E. water.

14. What bond(s) is(are) NOT found in phospholipids?A. R-CH=CH-R.B. R-O-OPOH-O-R.C. R-CH2-CH2-R.D. R-O-CO-R.

E. R-CO-NH-R’.

15. What are the components of a glycolipid?A. a protein with attached carbohydrate moiety.B. a chain of amino acids with a fatty acid chain attached.C. a chain of amino acids with a polysaccharide attached.D. lipids connected to a repeating ribose-phosphate backbone.E. a lipid to which an oligosaccharide is linked.

16. The part of the protein that extends in the lipid bilayer is composed of amino acids that areA. highly polar.B. negatively charged.C. hydrophobic.D. positively charged.E. water soluble.

17. The interior of the transmembrane, anion channel is lined by amino acids that are NOTA. highly polar.B. negatively charged.C. hydrophobic.D. positively charged.D. water soluble.

18. What is the likely function of a transmembrane protein that is neither a channel component or a carrier molecule? Its function is to

A. anchor glycolipids.B. participate in active transport.C. drive cell motility.D. transduce signals.E. provide surface identification.

19. Receptor molecules bind their specific 1igandsA. on the exterior of the membrane.B. in the midst of fatty acid tails.C. at the cytoplasmic side of the membrane.D. in a hydrophobic environment.E. surrounded by a meshwork of scaffolding proteins

20. Which of the following properties of the lipid bilayer make the membrane more fluid at colder temperatures?

A. short—chained fatty acid tails.B. polyunsaturated fatty acid chain.C. kinks in the fatty acid tails.D. presence of complex lipids such as cholesterol.E. all of the above.

21. Surface marker proteins can moveA. laterally in the plane of the membrane.B. flip-flop between the two leaflets of the membrane.C. hardly within the of the solid lipid boundary.D. across tight junctions.E. in and out of the membrane.

22. The fluid mosaic model of membranes dates fromA. 1830 (independence of Belgium).B. 1925.C. 1935.D. 1972.E. 1990.

23. In addition to accentuating the physical state of the membrane as fluid, what function of the membrane is stressed by the fluid mosaic model of Singer and Nicholson?

A. endocytosis.B. transmembrane communication.C. self identification.D. the structure of junctions.E. physical boundary properties.

24. The movement of a material from a region of high concentration toward a region of low concentration by the random movement of molecules is called

A. active transport.B. diffusion.C. osmosis.D. migration.E. Brownian movement.

25. The random saltatory movement of molecules is calledA. active transport.B. diffusion.C. osmosis.D. migration.E. Brownian movement.

26. What type of movement across the plasma membrane is(are) considered (an) example(s) of passive transport?A. the sodium-potassium pump.B. endocytosis.C. coupled channels.D. facilitated diffusion.E. cell identification.

27. If the concentration of solutes in the fluid surrounding a cell is lower than that inside the cell, the fluid surrounding the cell is

A. atonic.B. hypertonic.C. hypotonic.D. hypnotic.E. isotonic.

28. If the concentration of solutes in the fluid surrounding a cell is higher than that inside the cell, the fluid surrounding the cell is A. atonic.

B. hypertonic.C. hypotonic.D. hypnotic.

E. isotonic.

29. If equal amounts of water enter the cell as leave the cells than the medium surrounding the cell isA. atonic.B. hypertonic.C. hypotonic.D. hypnotic.E. isotonic.

30. If the concentration of solutes in the fluid surrounding a cell is equal to that inside the cell, the fluid surrounding the cell isA. atonic.B. hypertonic.C. hypotonic.D. hypnotic.E. isotonic.

31. The medium surrounding a cell is called hypertonic whenA. the concentration of solutes of the cytoplasm is lower than that of the medium.B. the concentration of solutes of the cytoplasm is higher than that of the medium.C. equal amounts of solutes are dissolved in the cytoplasm and surrounding medium.D. there is a lower concentration of dissolved molecules in the medium than in the

cytoplasm.E. the cytoplasm is surrounded by a semi-permeable membrane.

32. The medium surrounding a cell is called hypotonic whenA. the concentration of solutes of the cytoplasm is lower than that of the medium.B. there is a higher concentration of dissoved molecules in the medium than in the

cytoplasm.C. equal amounts of solutes are dissolved in the cytoplasm and surrounding medium.D. there is a lower concentration of dissolved molecules in the medium than in the

cytoplasm.E. the cytoplasm is surrounded by a semi—permeable membrane.

33. If a cell is placed in a hypertonic solution one event that is sure to occur is thatA. sugars and amino acids will move out of the cells.B. the cell wall will collapse inward.C. the cell will die of lack oxygen.D. the cell will of shrink as water moves out.E. the cell will swell as water moves in.

34. The turgor pressure of a plant cell is positive inA. hypertonic medium.B. isotonic medium.C. hypotonic medium.D. hypnotic medium.E. atonic medium.

35. Cut flowers will stand erect inA. hypotonic medium.B. atonic medium.C. isotonic medium.D. hypertonic medium.

E. hypnotic medium.

36. Unlike plant cells, animal cells in hypotonic mediumA. gain water.B. lose water.C. do not gain or lose water.D. lose valuable solutes.E. lyse (burst).

37. Besides ions an important determinant of the osmotic pressure of blood isA. albumin.B. hemoglobin.C. globulin.D. isotonin.E. isoplasm.

38. Sweet water protozoa, such as Paramecium, have contractile vacuoles thatA. contract to pump water in the cells to prevent dessication.B. contract to remove waste products of cellular

metabolism.C. prevent the cells from shrinking as water is lost.D. remove excess water from the cell.E. take in water to maintain osmotic balance.

39. When leaf cells lose so much water that turgor pressure falls, the plantA. closes up the water channels of the membranes.B. blooms.C. takes in water from the atmosphere.D. uses contractile vacuoles to increase water content.E. wilts.

40. The ability of a cell to engulf particles such as bacteria is calledA. exocytosis.B. endocytosis.C. phagocytosis.D. pinocytosis.E. vesiculation.

41. The membrane that surrounds a phagocytized particle is derived from theA. Golgi complex.B. lysosomes.C. endoplasmic reticulum.D. plasma membrane.E. nuclear envelope.

42. Osmotrophs are cells thatA. are sensitive to osmosis.B. acquire some of their nutrients by facilitated diffusion.C. do not phagocytize.D. are always surrounded by a cell wall.E. feed on osmium.

43. The anion channel of an animal cell passes chloride by

A. active transport.B. diffusion.C. facilitated diffusion.D. pinocytosis.E. expenditure of ATP.

44. A cell takes up or eliminates many kinds of molecules against a concentration gradient by means ofA. active transport.B. diffusion.C. facilitated diffusion.D. pinocytosis.E. expenditure of ATP.

45. The principle active transport channel of the animal cell is theA. ATP pump.B. coupled channel.C. glucose pump.D. proton pump.E. sodium-potassium pump.

46. In the sodium-potassium pumpA. cellular potassium is exchanged for extracellular sodium.B. potassium enters the cell by facilitated diffusion.C. potassium enters the cells by a coupled channel.D. sodium and potassium are both moved against a concentration gradient.E. cellular sodium levels are kept high.

47. What is a typical molecule that would bind to a cell receptor?A. ATP.B. DNA.C. glycolipids.D. hormones.E. surface markers.

48. Examples of molecules to which cell surface receptors respond include all of the following EXCEPT

A. adrenalin.B. thyroxine.C. insulin.D. acetylcholine.E. water.

49. A cell takes up or eliminates many kinds of molecules against a concentration gradient by means ofA. coupled channels.B. diffusion.C. facilitated diffusion.D. pinocytosis.E. expenditure of ATP.

50. What component is NOT a part of the plasma membrane?

A. ribosomes.B. exterior glycoproteins and glycolipids.C. supporting cytoplasmic fibers.D. a lipid bilayer foundation.E. transmembrane proteins.

51. What description does NOT characterize a cell membrane?A. fluid.B. unable to repair itself.C. asymmetrical regarding molecular composition.D. thin.E. flexible.

52. What description does NOT apply to the cell membrane?A. protects the cytoplasm.B. regulates the passage of materials into and out of the cell.C. allows communication with other cells.D. is a rigid, static structure.E. is unresponsive to changes in its outside environment.

53. What characteristic of proteins is most important for their functioning as a receptor?A. size.B. amino acid sequence.C. amphipathic nature.D. tertiary structure.E. all of the above.

54. The left side of the U-shaped tube contains 20 ml of an 8% protein, 2% sugar solution. The right side contains 20 ml of a 2% protein, 8% sugar solution. The membrane between the sides is permeable to sugar and water but NOT to protein. After 1 day it is found that in the left side

A. the volume of liquid has increased and the concentration of sugar decreased.B. the volume of liquid increased, the concentration of sugar decreased, and the

concentration of protein remained unchanged.C. there has been no change.D. the volume of liquid increased, the concentration of sugar increased and the number

of protein molecules stayed the same same.E. the volume of liquid increased but the concentration of sugar and protein remained

the same.

55. In order to pass through a cell membrane a hydrophilic molecule binds to a membrane protein which subsequently

A. rotates through the membrane and releases the molecule in the cytoplasm.B. undergoes a conformational change forcing the molecule through a channel into the

cytoplasm.C. diffuses laterally in the membrane.D. dissolves in the hydrophobic interior of the lipid bilayer.E. changes the polar character of the molecule.

56. What bond(s) is(are) most important for membrane structure?A. ionic bonds.B. covalent bonds.

C. hydrophobic bonds.D. hydrogen bonds.E. many weak bonds.

57. Compared to the cell membrane of an organism living at 4C, the membrane of an organism living at 40C would

A. be identical.B. have more proteins and proportionately less phospholipid.C. have longer chained and more saturated fatty acids.D. have more lipids and proportionately less protein.E. is richer in carbohydrates.

58. What metaphor describes best the arrangement of proteins and lipids in the cell membrane?A. a chocolate layer cake with sugar frosting.B. an apple pie.C. a cheese cake with graham cracker crust.D. jello with fruit.E. an Oreo cooky

59. Which of the following functional classes of proteins would have segments rich in hydrophobic amino acids?

A. signal receptors.B. transport proteins.C. channel proteins.D. membrane pore proteins.E. all of the above.

60. Which solution has the highest osmotic pressure?A. 1 M glucose.B. 0.1 M glucose.C. 0.1 M sucrose.D. 0.05 M glucose.E. 0.05 M NaC1.

61. Plant cells are placed in a 4% salt solution. Which of the following statements is true?A. the salt solution is hypotonic.B. the cell undergoes plasmolysis.C. the cell will burst.D. the turgor pressure in the cell will burst.E. the osmotic pressure of the central vacuole is less than that of the cytoplasm.

62. Which of the following processes is most adversely affected when a cell is poisoned by a toxin that inhibits ATP synthesis? Transmembrane movement of

A. sodium.B. water.C. sugar.D. oxygen.E. chloride anion.

63. All of the following are functions of the cell membrane EXCEPT:A. transmitting signals.B. participating in energy transfer.

C. being freely permeable to all substances.D. regulating the passage of materials.E. participating in chemical reactions.

64. Which of the following statements concerning phospholipids is FALSE?A. They have two distinct regions, one strongly hydrophobic and the other strongly

hydrophilic.B. They are amphipathic molecules.C. They have cylindrical shapes that allow them to associate with water most easily as

a bilayer structure.D. They contain a polar organic group attached to a phosphate group.E. They contain three fatty acids chains.

65. In a lipid bilayer, ___________ fatty acid tails face each other within the bilayer and form a region that excludes water.

A. hypertonicB. hyperosmoticC. hypotonicD. hydrophilicE. hydrophobic

66. If phospholipids form a spherical structure when placed in water, then which of the following is the most logical conclusion about those phosopholipid molecules?

A. They are not amphipathic.B. They contain two fatty acid chains.C. They are cone-shaped.D. They form a bilayer.E. Both their ends are hydrophilic.

67. A key discovery that weakened the Davson-Danielli “sandwich” model of cell membranes was that:

A. membrane proteins form a solid sheet on either side of the phospholipid bilayer.B. membrane proteins form a solid sheet separating the phospholipid layer.C. the phospholipids do not associate with each other in the hydrophobic region of

membranes.D. membrane proteins were not uniform and did not form flattened sheets.E. membrane proteins occurred in regular organized patterns on the surface of

membranes.

68. Who proposed the fluid mosaic model of cell membrane structure in 1972?A. Davson and SingerB. Frye and EdidinC. Brown and GoldsteinD. Singer and Nicholson

E. Davson and Danielli

69. What is meant by the term “fluid mosaic model”?A. It is the diffusion of lipid-soluble substances through the lipid bilayer.B. It is the movement of lipids and integral proteins within the lipid bilayer.C. It is the solubility of water in the membrane.D. It is the method of substance transport across the membrane.E. It is the movement of surface proteins through the membrane.

70. In the experiment in which Frye and Edidin fused the plasma membranes of a mouse and a human cell, what happened to the membrane proteins?

A. They formed a spherical structure.B. They formed a bilayer.C. They moved laterally across the cell surface.D. They flip-flopped from one layer to the other.E. They reacted with cholesterol molecules on the membrane surface.

71. Vegetable oil is different from animal fat in that the phospholipids in vegetable oil have fatty acid tails that:

A. solidify at room temperature.B. lack double bonds.C. are saturated.D. interact via van der Waals forces.E. bend.

72. Cholesterol within membranes functions as a(n) ____________ through its interactions with both hydrophobic and hydrophilic parts of phospholipids.

A. water blockerB. pH bufferC. energy sourceD. temperature controllerE. fluidity buffer

73. Which of the following statements about lipid bilayers is FALSE?A. They are self-sealing.B. They are inflexible.C. They spontaneously form closed vesicles.D. They can fuse with other bilayers.E. They resist forming free ends.

74. Integral proteins: A. are weakly bound to the surface of the membrane.B. are strongly bound to the cytosolic surface of the membrane.C. have no hydrophobic portions.

D. are completely embedded within the lipid bilayer.E. are amphipathic.

75. A transmembrane protein differs from other membrane proteins because it:A. is covalently linked to the outer surface of the plasma membrane.B. is a glycoprotein with carbohydrates attached.C. is attached to the inside of the membrane by an ionic bond.D. completely extends through the membrane. E. is completely embedded within the membrane.

76. Peripheral proteins are linked to either surface of the plasma membrane by: A. covalent disulfide bonds.B. associating with fatty acids through hydrophobic interactions.C. embedding in one side of the membrane and, thus, not extending through to the

other side. D. associating with glycoproteins on the inner membrane surface.E. bonding to integral proteins through noncovalent interactions.

77. Which of the following functions best explains the reason for the asymmetrically oriented structure of the proteins in the cell membrane?

A. These proteins are manufactured by free ribosomes.B. Each type of protein has its own function.C. These proteins pass through the ER membrane into the ER lumen.D. Enzymes are needed to modify the carbohydrate chains on these proteins.E. These proteins are initially formed by ribosomes on the rough ER.

78. Proteins that are destined to become associated with the inner surface of the plasma membrane are:

A. manufactured in the same way as protein hormones.B. manufactured in the same way as proteins destined to become external peripheral

proteins.C. made on free ribosomes in the cytoplasm.D. made on ribosomes located on the rough endoplasmic reticulum.E. transported to the plasma membrane within a secretory vesicle.

79. Which of the following statements explaining the differences in number and types of peripheral proteins found on the inner and outer surfaces of cell membranes is correct?

A. The functions of the membrane differ on the inside and outside of the cell.B. Not all proteins can pass through the membrane and, thus, more accumulate on the

inside.C. Proteins on the outside of the membrane are synthesized at a slower rate than

proteins on the inside of the membrane.D. Proteins on the outside of membrane are made extracellularly and are unable to

penetrate the phospholipid bilayer and enter the cell.

E. The external peripheral proteins are weakly attached to the membrane and are readily washed away.

80. Biological membranes are normally permeable to:A. large, hydrophilic molecules.B. small, hydrophilic molecules.C. large, hydrophobic molecules.D. small, hydrophobic molecules.E. None of these.

81. Which of the following molecules is least likely to cross a cellular membrane by simple diffusion?

A. carbon dioxideB. nitrogenC. oxygen D. potassium ionE. water

82. An ABC transporter:A. is a type of water channel.B. uses the energy of ATP to transport solutes.C. uses gated channels to transport ADP.D. is present in kidney tubules and prevents dehydration.E. is a type of porin.

83. Which of the following is not a characteristic of aquaporins?A. They are transmembrane proteins.B. They facilitate the rapid transport of water through the plasma membrane.C. They are located in mammalian kidney tubules.D. They respond to specific hormones.E. They cause dehydration.

84. Catalysts are reusable. Enzymes are protein catalysts, and are reusable. Select the protein(s) below that is (are) not used up by the process carried out:

A. Na+/K+ pump carrier proteinsB. aquaporinsC. proteins involved in facilitated diffusionD. Na+/K+ pump carrier proteins and also aquaporinsE. Na+/K+ pump carrier proteins, aquaporins, and also proteins involved in facilitated

diffusion

85. A bottle of perfume is opened on the opposite side of the room and within minutes you begin to smell the perfume. This phenomenon is a classic example of:

A. dialysis.B. osmosis.C. active transport.D. facilitated diffusion.E. simple diffusion.

86. The passive movement of a substance along its concentration gradient is termed:A. active transport.B. dialysis.C. diffusion.D. exocytosis.E. osmosis.

87. Simple diffusion may involve the movement of ______________________ through the plasma membrane down a concentration gradient.

A. small polar moleculesB. small nonpolar moleculesC. large polar moleculesD. large nonpolar moleculesE. water

88. Which of the following membrane activities does NOT require the expenditure of energy by the cell?

A. active transportB. osmosisC. endocytosisD. exocytosisE. synthesis of more membrane

89. If the concentration of solutes in a cell is less than the concentration of solutes in the surrounding fluid, then the extracellular fluid is said to be:

A. hypertonic.B. hypotonic.C. isotonic.D. stable.E. amphipathic.

90. The higher the concentration of solute in a solution, the _________ the effective water concentration and the ________ the osmotic pressure.

A. lower; lowerB. lower; higherC. higher; higher

D. higher; lowerE. Answer cannot be determined from the information provided.

91. Consider a U-tube that initially contains pure water on one side of a selectively permeable membrane and water plus solute on the other side. Which of the following best describes what will happen next?

A. Solute molecules diffuse across the membrane faster than water molecules.B. The fluid level rises on the side containing the pure water.C. The diffusion of water molecules causes an osmotic pressure to build up in the tube.D. Solute molecules are transported across the membrane by facilitated diffusion.E. Some water molecules become “bound up” with solute molecules and do not

diffuse freely.

91. Solutions that are isotonic:A. are not in dynamic equilibrium.B. have equal concentrations of solute and water.C. have equal concentrations of solute but not water.D. have equal concentrations of water but not solute.E. will exhibit no net movement of water from one solution to the other.

92, 93. Use the figure to answer the corresponding questions.

92. Which of the following statements about the red blood cells in Figure B is true?

A. These red blood cells have been placed in an isotonic solution.

B. These red blood cells have swollen in response to a hypertonic external solution.

C. These red blood cells have swollen in response to a hypotonic external solution.

D. These red blood cells have shrunken in response to a hypertonic external solution.

E. These red blood cells have shrunken in response to a hypotonic external solution.

93. Which of the following statements about the red blood cells in Figure A is true?

A. There has been no net water movement.B. There has been a net flow of water out of the cell.C. There has been a net flow of water into the cell.D. Pinocytosis has occurred.E. Plasmolysis has occurred.

94. A patient who has had a severe hemorrhage accidentally receives a large transfusion of

distilled water directly into a major blood vessel. You would expect this mistake to:A. have no unfavorable effect as long as the water is free of bacteria.B. have serious, perhaps fatal consequences because there would be too much fluid to

pump.C. have serious, perhaps fatal consequences because the red blood cells could shrink.D. have serious, perhaps fatal consequences because the red blood cells could swell

and burst.E. have no serious effect because the kidney could quickly eliminate excess water.

95. A plant cell placed in a hypertonic solution will:A. remain unchanged.B. undergo lysis.C. undergo plasmolysis.D. swell slightly.E. become crenated.

96. Penicillin is toxic to certain dividing bacterial cells because it prevents cell wall formation, causing the cells to burst. This indicates that the bacteria live in:

A. a hypotonic medium.B. a hypertonic medium.C. an isotonic medium.D. a medium with a higher osmotic pressure than the cell.E. Both a hypertonic medium and a medium with a higher osmotic pressure than the

cell.

97. A wilted flower placed in a vase of water for several hours became stiff and stood erect. When it was placed in a salt solution, it wilted. From this information we can say that the cells of the flower are:

A. hypotonic to both fresh water and the salt solution.B. hypertonic to both the fresh water and the salt solution.C. hypertonic to fresh water but hypotonic to the salt solution.D. hypotonic to fresh water but hypertonic to the salt solution.E. isotonic to fresh water but hypotonic to the salt solution.

98. Facilitated diffusion:A. requires a transmembrane protein.B. requires ATP.C. can move molecules against a concentration gradient.D. is typically used to transport small nonpolar molecules.E. All of these.

99. Which of the following are forms of carrier-mediated transport?A. Facilitated diffusion onlyB. Carrier-mediated active transport only

C. Osmosis onlyD. Both facilitated diffusion and carrier-mediated active transportE. Facilitated diffusion, carrier-mediated active transport, and osmosis

100. Although glucose molecules constantly diffuse into a cell along their concentration gradient, equilibrium is never reached and glucose continues to enter the cell. This is a direct result of:

A. the very fast turnover rate of glucose metabolism.B. the continuous excretion of glucose from other parts of the cell.C. the rapid and continuous intracellular formation of glucose phosphates.D. the active transport of glucose.E. the ability of the cell to engulf glucose by pinocytosis.

101. Studies of glucose transport in liposomes have revealed that:A. glucose is transported against a concentration gradient.B. the binding of glucose triggers a conformational change in the carrier protein.C. the transport of solutes via carrier proteins is faster than via channel proteins.D. glucose phosphates move readily across the membrane by simple diffusion.E. glucose moves readily across the membrane by simple diffusion.

102. A bacterium containing sodium ions at a concentration of 0.1 mM lives in a pond that contains sodium ions at 0.005 mM. Evidently, sodium ions are entering the cell by:

A. active transport.B. endocytosis.C. diffusion.D. facilitated diffusion.E. osmosis.

103. Which of the following describes how facilitated diffusion is powered?A. Facilitated diffusion is “free of cost.”B. Facilitated diffusion is powered by the potential energy of the concentration

gradient.C. ATP is required directly.D. Both A and B.E. A, B, and C.

104. Which of the following statements about the sodium-potassium pump is true?A. It transports hydrogen ions out of the cell.B. It transports 3 sodium ions out of the cell in exchange for 2 potassium ions.C. It transports 2 sodium ions out of the cell in exchange for 2 potassium ions.D. It transports 2 sodium ions out of the cell in exchange for 3 potassium ions.E. It transports water directly out of the cell.

105. In the mechanism of action of a proton pump, the role of ATP is to:

A. cause a proton to bind to a carbohydrate.B. cause a cell to take up protons by endocytosis.C. cause a cell to release protons by exocytosis.D. transfer protons to the inside of a cell.E. transfer protons to the outside of a cell.

106. In the coupled transport of glucose and sodium ions:A. glucose molecules are transported down their concentration gradient.B. sodium ions are transported down their concentration gradient.C. the transport of glucose powers the transport of sodium.D. ATP causes a conformational change in the carrier protein.E. an antiport carrier protein is involved.

107. A human white blood cell engulfs a bacterial cell by:A. carrier-mediated facilitated diffusion.B. exocytosis.C. phagocytosis.D. pinocytosis.E. the sodium-potassium pump.

108. A person has a genetic disease that prevents the phospholipids in the plasma membrane of the white blood cells from freely fusing with the other membranes within the cell. How would this disease affect phagocytosis?

A. Lysosomes would not be formed.B. Facilitated diffusion would not occur.C. Lysosomes would be formed lacking hydrolytic enzymes.D. The phagocytic vacuole would not fuse with the lysosome.E. Endocytosis would not occur.

109. Pinocytosis:A. is engulfment of large particles by the cell.B. occurs in protozoans and algae but not in more complex organisms.C. involves the specific binding of molecules to receptors on the cell surface.D. is the nonspecific uptake of fluids by pinching inward of the plasma membrane.E. is movement of molecules against the concentration gradient through a permeable

membrane.

110. Receptor-mediated endocytosis:A. is a passive process.B. involves only membrane transport proteins.C. brings about the selective uptake of materials by enclosing them in membranous

vesicles.D. does not require energy.E. is most likely to be found in cells that release large amounts of hormones.

111, 112. Use the figure to answer the corresponding questions.

111. The process illustrated in the accompanying figure is called:A. facilitated diffusion.B. pinocytosis.C. cotransport.D. lysis.E. exocytosis.

112. The process illustrated in the accompanying figure would most likely be used to transport:

A. glucose.B. hormones.C. potassium ions.D. carbon dioxide.E. bacteria.

113. Select the receptor mediated endocytosis events that are in the correct (before, after) order:A. Endosome fuses with lysosome; receptors are transported to plasma membrane and

recycled.B. Ligand binds to receptors; coated vesicle forms by endocytosis.C. Contents are digested and released in the cytoplasm; ligand separates from its

receptor.D. Endosome fuses with lysosome; receptors are transported to plasma membrane and

recycled.E. None of the events are listed in the correct order.

114. In cells that are constantly involved in secretion, an equivalent amount of membrane must be returned to the interior of the cell for each vesicle that fuses with the plasma membrane; if this does not occur, then what would happen?

A. The ratio of cell surface would decrease, compared to cell volume.B. The cell surface would shrivel.C. The surface area would remain constant.D. The number of membrane receptor proteins would decrease.E. The cell surface will keep expanding.

115. Which of the following statements is not true? Biological membranes A. are composed partly of amphipathic lipids.B. have hydrophobic and hydrophilic regions.C. are typically in a fluid state.D. are made mainly of lipids and of proteins that lie in thin sheets on the membrane

surface.E. function in signal transduction.

116. According to the fluid mosaic model, membranes consist ofA. a lipid-protein sandwichB. mainly phospholipids with scattered nucleic acidsC. a fluid phospholipid bilayer in which proteins are embeddedD. a fluid phospholipid bilayer in which carbohydrates are embeddedE. a protein bilayer that behaves as a liquid crystal

117. Transmembrane proteinsA. are peripheral proteinsB. are receptor proteinsC. extend completely through the membraneD. extend along the surface of the membraneE. are secreted from the cell

118. Which of the following is not a function of the plasma membrane?A. transports materialsB. helps structurally link cells C. manufactures proteinsD. anchors the cell to the extracellular matrixE. has receptors that relay signals

119. ABC transportersA. use the energy of ATP hydrolysis to transport certain ions and sugarsB. are important in facilitated diffusion of certain ionsC. are a small group of channel proteinsD. are found mainly in plant cell membranesE. permit passive diffusion through their channels

120. When plant cells are in a hypotonic environment, theyA. undergo plasmolysisB. build up turgor pressureC. wiltD. decrease pinocytosisE. lose water to the environment

121. A laboratory technician accidently places red blood cells in a hypertonic solution. What happens?A. they undergo plasmolysisB. they build up turgor pressureC. they swellD. they pump solutes outE. they become dehydrated and shrunken

122. Which of the following processes requires the cell to expend metabolic energy directly (for example, from ATP)?

A. active transportB. facilitated diffusionC. all forms of carrier-mediated transportD. osmosisE. simple diffusion

123. Which of the following requires a transport protein?A. simple diffusionB. facilitated diffusionC. establishment of turgor pressureD. osmosisE. osmosis when a cell is in a hypertonic solution

124. The action of sodium-potassium pumps is an example of A. direct active transportB. pinocytosisC. aquaporin transportD. exocytosisE. facilitated diffusion

125. Electrochemical gradientsA. power simple diffusionB. are established by pinocytosisC. are necessary for transport by aquaporinsD. are established by concentration gradientsE. are a result of both an electric charge difference and a concentration difference

between the two sides of the membrane

126. Which carrier protein is a symporter?A. one that co-transports glucose and sodiumB. one that carries on facilitated diffusionC. one that moves two substances in opposite directionsD. an ion channelE. the sodium-potassium pump

127. In indirect transportA. a uniporter moves a solute across a membrane against its concentration gradientB. a channel protein moves ions by facilitated diffusionC. the movement of one solute down its concentration gradient provides energy for

transport of some other solute up its concentration gradientD. osmosis powers the movement of ions against their concentration gradientE. sodium is directly transported in one direction, and potassium is indirectly

transported in the same direction

128. A cell takes in dissolved material by forming tiny vesicles around fluid droplets tapped by folds of the plasma membrane. This process is called

A. indirect active transportB pinocytosisC. receptor-mediated endocytosisD. exocytosisE. facilitated diffusion.

True/False

129. Biological membranes are one dimemsional fluids. _______

130. In cell membranes, glycoproteins and glycolipids are exposed to the extracellular surface for cell recognition and adhesion to other cells._______

131. Mutations to ABC transporter genes contribute to cystic fibrosis. _______

132. Osmotic pressure of a solution is the amount of pressure exerted on the side of a selectively permeable membrane containing a higher concentration of solute to prevent diffusion of solute. _________

133. If solution of A is hypotonic to B, then the direction of net movement of water is B to A. ___

134. Plasmolysis occurs in plant cells when the soil or water contains low concentrations of salts or fertilizers.______

135. Sodium-potassium pumps maintain and electrochemical gradient._______

136. In the sodium-potassium pump, sodium ion release causes two K+ ions to be released into the cell. ______

137. Coupled transport systems directly provide energy for active transport of solutes._____

138. LDL cholesterol is taken into the cell by receptor-mediated endocytosis. _______

Matching.

A. Transmit information into the cell.B. Catalysed reactions which take place within or along membrane surface.C. Allow selective transport of ions or molecules.D. Use ATP to transport solutes.E. Anchor cell to extracellular matrix.

139. Integrins.

140. Channels

141. Protein pumps.

142. Signal transduction receptors.

143. Membrane-bound enzymes.