BIOL1113 Membrane Structure and Function Q's

The internal solute concentration of a plant cell is about 0.8 M. To demonstrate plasmolysis, it would be necessary to suspend the cell in what solution? a. distilled water b. 0.4 M c. 1.0 M d. 0.8 M e. 150 mM

1.0 M This solution is hypertonic to the plant cell. Water will leave the cell, and eventually the plasma membrane will pull away from the cell wall, resulting in plasmolysis.

Green olives may be preserved in brine, which is a 30% salt solution. How does this method of preservation prevent microorganisms from growing in the olives? a. High salt concentration lowers the pH, thus inhibiting bacterial metabolism b. A 30% salt solution is hypertonic to the bacteria, so they lose too much water and undergo plasmolysis c. High salt concentration raises the pH, thus inhibiting bacterial metabolism d. Bacterial cells shrivel up in high salt solutions, causing the cell to burst e. A 30% salt solution is hypotonic to the bacteria, so they gain too much water and burst

A 30% salt solution is hypertonic to the bacteria, so they lose too much water and undergo plasmolysis If a cell is placed in a hypertonic solution, it will lose water to its environment, shrivel, and probably die.

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. The sodium ions are moving down their electrochemical gradient while glucose is moving up. b. Glucose entering the cell along 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.

A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose

Which of the following is a correct difference between active transport and facilitated diffusion? a. Active transport involves transport proteins, and facilitated diffusion does not b. Facilitated diffusion requires carrier proteins, but active transport requires channel proteins c. Facilitated diffusion can move solutes against a concentration gradient, and active transport cannot d. Active transport requires energy from ATP, and facilitated diffusion does not e. Facilitated diffusion involves transport proteins, and active transport does not

Active transport requires energy from ATP, and facilitated diffusion does not Active transport can move substances against the concentration gradient, but it requires energy in the form of ATP.

Which of the following is true of the evolution of cell membranes? a. Cell membranes have stopped evolving now that they are fluid mosaics b. Cell membranes cannot evolve if the membrane proteins do not c. The evolution of cell membranes is driven by the evolution of glycoproteins and glycolipids d. All components of membranes evolve in response to natural selection e. An individual organism selects its preferred type of cell membrane for particular functions

All components of membranes evolve in response to natural selection

Which statements about the sidedness of the plasma membrane is correct? a. The two lipid layers may differ in specific lipid composition b. Parts of proteins that are exposed on the cytoplasmic side of the endoplasmic reticulum are also exposed on the cytoplasmic side of the plasma membrane c. Every integral membrane protein has a specific orientation in the plasma membrane d. The asymmetrical distribution of membrane proteins, lipids, and carbohydrates across the plasma membrane is determined as the membrane is being constructed e. All of the listed responses are correct

All of the listed responses are correct All of the listed choices are aspects of the sidedness of the plasma membrane.

Cells A and B are the same size, shape, and temperature, but cell A is metabolically less active than cell B. and cell B is actively converting oxygen to water in cellular respiration. Oxygen will diffuse more rapidly into cell __________ because __________. a. A ... its membrane transport proteins will not be saturated b. A ... the concentration gradient there is shallower c. B ... the diffusion gradient in cell B is steeper d. B ... the oxygen molecules inside cell B have a higher kinetic energy e. B ... the gradient of oxygen is oriented in the opposite direction compared to cell A

B ... the diffusion gradient in cell B is steeper As long as a metabolically active cell converts oxygen to water during cellular respiration shortly after it enters, diffusion into the cell will continue because the concentration gradient favors movement in that direction.

Seawater is hypertonic to cytoplasm in vertebrate cells and in plant cells. If a red blood cell and a plant cell were placed in seawater, what would happen to the two types of cells? a. The red blood cell would shrink, and the plant cell would gain water b. Both cells would gain water by osmosis; the red blood cell would burst, and the plant cell would increase in turgor pressure c. Both cells will gain water, but cell walls will prevent both cells from bursting d. The red blood cell would burst, and the plant cell would shrink e. Both cells would lose water; the red blood cell would shrivel, and the plant plasma membrane would pull away from the cell wall

Both cells would lose water; the red blood cell would shrivel, and the plant plasma membrane would pull away from the cell wall Seawater will cause both cells to lose water.

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

CO2

In what way do the membranes of a eukaryotic cell vary? a. Only certain membranes of the cell are selectively permeable b. Certain proteins are unique to each membrane c. Phospholipids are found only in certain membranes 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

Certain proteins are unique to each membrane

Which of the following statements about cotransport of solutes across a membrane is correct? a. The sodium-potassium pump is an example of a cotransport protein b. Cotransport proteins allow a single ATP-powered pump to drive the active transport of many different solutes c. Cotransport involves the hydrolysis of ATP by the transporting protein d. A cotransport protein is most commonly an ion channel e. In cotransport, both solutes that are being transported are moving down their chemical gradients

Cotransport proteins allow a single ATP-powered pump to drive the active transport of many different solutes The electrochemical gradient created by a single ATP-dependent pump can drive the transport of many different solutes using cotransport proteins.

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. 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

D and E

Which of the following correctly describes a general property of all electrogenic pumps? a. Electrogenic pumps result in a cell with a high internal concentration of protons b. Electrogenic pumps pump sodium out of the cell and potassium into the cell c. Electrogenic pumps create a voltage difference across the membrane d. Electrogenic pumps result in a cell with an interior that is positively charged relative to the outside of the cell e. Electrogenic pumps can pump a large variety of solutes across a membrane against their concentration gradient

Electrogenic pumps create a voltage difference across the membrane An electrogenic pump creates a net charge difference across a membrane (a membrane potential).

Which of these statements describes some aspect of facilitated diffusion? a. There is only one kind of protein pore for facilitated diffusion b. Facilitated diffusion requires energy to drive a concentration gradient c. Facilitated diffusion of solutes may occur through channel or transport proteins in the membrane d. Facilitated diffusion is another name for osmosis e. Facilitated diffusion of solutes occurs through phospholipid pores in the membrane

Facilitated diffusion of solutes may occur through channel or transport proteins in the membrane The passageways for facilitated diffusion may be either protein pores or carrier proteins.

Which of the following is FALSE in regard to facilitated diffusion? a. Facilitated diffusion requires the hydrolysis of ATP b. Facilitated diffusion requires a concentration gradient c. Facilitated diffusion can occur through protein channels d. Facilitated diffusion can move ions across membranes e. Facilitated diffusion can occur by means of transport proteins

Facilitated diffusion requires the hydrolysis of ATP This statement is false. Facilitated diffusion, like simple diffusion, needs only a concentration gradient—no energy input is required.

Human immunodeficiency virus (HIV. infects cells that have both CD4 and CCR5 cell surface molecules. The viral nucleic acid molecules are enclosed in a protein capsid, and the protein capsid is itself contained inside an envelope consisting of a lipid bilayer membrane and viral glycoproteins. One hypothesis for viral entry into cells is that binding of HIV membrane glycoproteins to CD4 and CCR5 initiates fusion of the HIV membrane with the plasma membrane, releasing the viral capsid into the cytoplasm. An alternative hypothesis is that HIV gains entry into the cell via receptor-mediated endocytosis, and membrane fusion occurs in the endocytotic vesicle. To test these alternative hypotheses for HIV entry, researchers labeled the lipids on the HIV membrane with a red fluorescent dye. If HIV first enters the cell in an endocytotic vesicle, instead of directly fusing with the plasma membrane, then a. HIV infection should be hindered by microtubule polymerization inhibitors such as nocodazole b. HIV infection should be more efficient at lower temperatures c. intact cortical actin microfilaments should interfere with HIV infection d. cells lacking integrins should be resistant to HIV infection e. addition of ligands for other cell-surface receptors to stimulate their endocytosis should increase the efficiency of HIV infection

HIV infection should be hindered by microtubule polymerization inhibitors such as nocodazole

Which of the following statements about diffusion is true? a. It involves only the movement of water molecules b. It requires expenditure of energy by the cell c. It is a passive process d. It occurs when molecules move from a region of lower concentration to a region of higher concentration e. It always requires integral proteins of the cell membrane

It is a passive process Diffusion is the tendency of molecules to spread out in the available space. A substance will diffuse from an area of higher concentration to an area of lower concentration without energy input.

The sodium-potassium pump in animal cells requires cytoplasmic ATP to pump ions across the plasma membrane. When the proteins of the pump are first synthesized in the rough ER, what side of the ER membrane will the ATP binding site be on? a. It will be on the cytoplasmic side of the ER b. It will be on the side facing the interior of the ER c. It could be facing in either direction because proteins are properly reoriented in the Golgi apparatus d. It doesn't matter, because the pump is not active in the ER

It will be on the cytoplasmic side of the ER

Which of the following statements concerning carbohydrates associated with the plasma membrane is correct? a. The carbohydrate composition of most eukaryotic plasma membranes is quite similar b. Membrane carbohydrates function primarily in cell-cell recognition c. Carbohydrates associated with the plasma membrane are located on both surfaces of the membrane d. Carbohydrates are found associated with the membranes of prokaryotic cells only e. Carbohydrates on the plasma membrane are typically long, complex chains of several dozen monosaccharides

Membrane carbohydrates function primarily in cell-cell recognition Variations in carbohydrate structure distinguish one species from another, one individual from another, and even one cell type from another.

Which of the following functions of membrane proteins is important in tissue formation during embryonic development in animals? a. Membrane proteins with short sugar chains form identification tags that are recognized by other cells b. Membrane proteins possess enzymatic activity c. Membrane proteins attach the membrane to the cytoskeleton d. Membrane proteins form channels, which move substances across the membrane e. All of the listed responses are correct

Membrane proteins with short sugar chains form identification tags that are recognized by other cells Cell-cell recognition is an important function of membrane proteins, and this cell-cell recognition is important in tissue formation during embryogenesis.

A selectively permeable membrane separates two solutions. Water is able to pass through this membrane; however, sucrose (a disaccharide) and glucose (a monosaccharide) cannot pass. The membrane separates a 0.2-molar sucrose solution from a 0.2-molar glucose solution. With time, how will the solutions change? a. Water will leave the sucrose solution because the sucrose molecule is a disaccharide and, thus, larger than the monosaccharide glucose b. Water will enter the sucrose solution because the sucrose molecule is a disaccharide and, thus, larger than the monosaccharide glucose c. The sucrose solution is hypertonic and will gain water because the total mass of sucrose is greater than that of glucose d. After the sucrose dissociates into two monosaccharides, water will move via osmosis to the side of the membrane that contains the dissociated sucrose e. Nothing will happen, because the two solutions are isotonic to one another

Nothing will happen, because the two solutions are isotonic to one another Osmotic pressure is produced by the concentration of dissolved substances and is not influenced by the relative sizes of the solutes.

Which of the following statements about passive transport is correct? a. In passive transport, solute movement stops when the solute concentration is the same on both sides of the membrane b. Passive transport operates independently of diffusion c. Passive transport does not occur in the human body d. Passive transport operates independently of the concentrations of the moving solute e. Passive transport permits the solute to move in either direction, but the net movement of solute molecules occurs down the concentration gradient of the molecule

Passive transport permits the solute to move in either direction, but the net movement of solute molecules occurs down the concentration gradient of the molecule Passive transport can occur in either direction, but the direction of net diffusion is down the concentration gradient of the solute.

Which of the following statements about the role of phospholipids in the structure and function of biological membranes is correct? a. Phospholipids are completely unable to interact with water b. Phospholipids form a structure in which the hydrophobic portion faces outward c. Phospholipids form a selectively permeable structure d. They are triacylglycerols, which are commonly available in foods e. Phospholipids form a single sheet in water

Phospholipids form a selectively permeable structure Their structure allows some substances to penetrate easily and blocks others.

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. In the small airways of the lung, a thin layer of liquid is needed between the epithelial cells and the mucus layer in order for cilia to beat and move the mucus and trapped particles out of the lung. One hypothesis is that the volume of this airway surface liquid is regulated osmotically by transport of sodium and chloride ions across the epithelial cell membrane. How would the lack of a functional chloride channel in cystic fibrosis patients affect sodium ion transport and the volume of the airway surface liquid? a. Sodium ion transport will increase; higher osmotic potential will increase airway surface liquid volume b. Sodium ion transport will increase; higher osmotic potential will decrease airway surface liquid volume c. Sodium ion transport will decrease; lower osmotic potential will decrease airway surface liquid volume d. Sodium ion transport will decrease; lower osmotic potential will increase the airway surface liquid volume e. Sodium ion transport will be unaffected; lack of chloride transport still reduces osmotic potential and decreases the airway surface liquid volume

Sodium ion transport will decrease; lower osmotic potential will decrease airway surface liquid volume

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

The cell will become turgid

The plasma membrane is referred to as a "fluid mosaic" structure. Which of the following statements about that model is true? a. The fluid aspect of the membrane describes its structure at normal temperatures, and the mosaic aspect describes the behavior of the membrane as the temperature is lowered b. Only phospholipids are capable of moving in the membrane c. The fluid aspect of the membrane is due to the behavior of phospholipids, and the mosaic aspect is due to the presence of carbohydrates d. The fluid aspect of the membrane is due to the lateral and rotational movement of phospholipids, and embedded proteins account for the mosaic aspect e. The mosaic aspect of the membrane is due to the glycosylation of phospholipids on the cytoplasmic side of the membrane

The fluid aspect of the membrane is due to the lateral and rotational movement of phospholipids, and embedded proteins account for the mosaic aspect This is what the term "fluid mosaic" refers to.

Consider the transport of protons and sucrose into a plant cell by the sucrose-proton cotransport protein. Plant cells continuously produce a proton gradient by using the energy of ATP hydrolysis to pump protons out of the cell. Why, in the absence of sucrose, do protons not move back into the cell through the sucrose-proton cotransport protein? a. Protons are freely permeable through the phospholipid bilayer, so no transport protein is needed for protons b. In the absence of sucrose, the ATP-powered proton pump does not function, so there is no proton gradient c. Protons cannot move through membrane transport proteins d. Protons, unlike other substances, do not diffuse down their electrochemical gradient e. The movement of protons through the cotransport protein cannot occur unless sucrose moves at the same time

The movement of protons through the cotransport protein cannot occur unless sucrose moves at the same time The obligate coupling of proton movement to sucrose movement prevents the energy of the proton gradient from being lost if sucrose is not present.

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. 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

The patient's red blood cells will swell because the blood fluid has become hypotonic compared to the cells

Active transport requires an input of energy and can also generate voltages across membranes. Based on this information, which of the following statements is true? a. Active transport uses channel proteins and ensures that the interior of the cell is always positive compared to the exterior of the cell b. The sodium-potassium pump hydrolyzes ATP and results in a net positive change outside the cell membrane c. The source of energy for active transport of a solute up its gradient can be ATP or a concentration gradient of a second solute. This second gradient of solutes maintains no net difference in voltage across the membrane d. Active transport moves solutes down their concentration gradients and always uses ATP as the source of energy to do this e. Active transport can use ATP as its energy source and ensures that there is no voltage across the cell membrane

The sodium-potassium pump hydrolyzes ATP and results in a net positive change outside the cell membrane This is how the sodium-potassium pump generates voltage across the cell membrane.

Which of the following statements about the sodium-potassium pump is correct? a. The sodium-potassium pump moves Na+ and K+ in the same direction, resulting in a net negative charge outside the cell b. The sodium-potassium pump moves sodium out of the cell and co-transports protons into the cell, which is the source of energy for the movement of the potassium into the cell c. The sodium-potassium pump moves Na+ and K+ in opposite directions, resulting in a net negative charge inside the cell d. The sodium-potassium pump uses an existing proton gradient to drive the movement of sodium and potassium ions e. The sodium-potassium pump transports Na+ and K+ across the plasma membrane in the same direction at the expense of ATP hydrolysis

The sodium-potassium pump moves Na+ and K+ in opposite directions, resulting in a net negative charge inside the cell This is a true statement. An electrogenic pump creates a net movement of charge across a membrane. The sodium-potassium pump moves three Na+ out and two K+ in for a net transport of one positive charge out of the cell.

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

They are usually transmembrane proteins

Glucose can be moved into cells via an active transport mechanism when the concentration of glucose inside the cell is higher than the concentration of glucose outside of the cell. This active transport mechanism moves glucose and sodium into the cell at the same time. The glucose moves up its gradient and the sodium moves down its gradient. Which of the following statements about this mechanism is accurate? a. The distribution of sodium ions across the membrane forms an electrochemical gradient that drives this mechanism b. Sodium and glucose move together into the cell via facilitated diffusion c. To pump glucose up its concentration gradient, sodium moves down its concentration gradient d. Sodium and glucose move together into the cell via facilitated diffusion, and to pump glucose up its concentration gradient, sodium moves down its concentration gradient e. To pump glucose up its concentration gradient, sodium moves down its concentration gradient, and the distribution of sodium ions across the membrane forms an electrochemical gradient that drives this mechanism

To pump glucose up its concentration gradient, sodium moves down its concentration gradient, and the distribution of sodium ions across the membrane forms an electrochemical gradient that drives this mechanism The movement of sodium down its gradient drives glucose up its gradient, and because sodium is at different concentrations on either side of the membrane and as sodium has a +1 charge, an electrochemical gradient also exists.

A single plant cell is placed in an isotonic solution. Salt is then added to the solution. Which of the following would occur as a result of the salt addition? a. There would be no osmotic movement of water in response to the added salt b. The added salt makes the solution hypotonic compared to the cell. Water will enter the cell by osmosis c. The added salt would enter the cell, causing the cell to take up water and swell d. Water would leave the cell by osmosis, causing the volume of the cytoplasm to decrease e. Water would enter the cell by osmosis, and the cell would swell

Water would leave the cell by osmosis, causing the volume of the cytoplasm to decrease The added salt makes the solution hypertonic compared to the cell. Water will leave the cell by osmosis.

Which of the following factors would tend to increase membrane fluidity? a. a greater proportion of saturated phospholipids b. a lower temperature c. a greater proportion of unsaturated phospholipids d. a relatively high protein content in the membrane e. a greater proportion of relatively large glycolipids compared with lipids having smaller molecular masses

a greater proportion of unsaturated phospholipids

The concentration of solutes in a red blood cell is about 2%, but red blood cells contain almost no sucrose or urea. Sucrose cannot pass through the membrane, but water and urea can. Osmosis would cause red blood cells to shrink the most when immersed in which of the following solutions? a. a hypotonic urea solution b. a hypotonic sucrose solution c. a hypertonic urea solution d. pure water e. a hypertonic sucrose solution

a hypotonic sucrose solution When a cell is placed in a hypertonic environment, water will leave the cell, causing it to shrink.

Which of the following would be LEAST likely to diffuse through a plasma membrane without the help of a transport protein? a. dissolved gases such as oxygen or carbon dioxide b. a small, nonpolar molecule c. a large, nonpolar molecule d. a large, polar molecule e. Any of the listed molecules would easily diffuse through the membrane

a large, polar molecule The combination of being polar and large means that this molecule will be the slowest one from the choices to move across the membrane.

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

by increasing the percentage of unsaturated phospholipids in the membrane

Which of the following molecules is most likely to passively diffuse across the plasma membrane? a. carbon dioxide b. glucose c. sodium ion d. DNA e. Hemoglobin

carbon dioxide Hydrophobic molecules, such as hydrocarbons, carbon dioxide, and oxygen, can dissolve in the membrane and cross it with ease.

According to the fluid mosaic model of membrane structure, proteins of the membrane are mostly a. free to depart from the fluid membrane and dissolve in the surrounding solution b. confined to the hydrophobic interior of the membrane c. randomly oriented in the membrane, with no fixed inside-outside polarity d. spread in a continuous layer over the inner and outer surfaces of the membrane e. embedded in a lipid bilayer

embedded in a lipid bilayer

A nursing infant is able to obtain disease-fighting antibodies, which are large protein molecules, from its mother's milk. These molecules probably enter the cells lining the baby's digestive tract via which process? a. active transport b. passive transport c. osmosis d. endocytosis e. exocytosis

endocytosis Endocytosis is the procedure that cells use to import large molecules across their plasma membrane.

Which of the following is NOT a function of membrane proteins? a. enzymatic activity b. intercellular joining c. cell-cell recognition d. transport e. energy, carbon, and nitrogen storage

energy, carbon, and nitrogen storage Proteins are not present in biological membranes to act as stores of energy, carbon, and nitrogen.

Which of the following processes and organelles account for the replacement of lipids and proteins lost from the plasma membrane? a. endocytosis and Golgi b. exocytosis and smooth ER and rough ER c. active transport and the rough ER d. flip-flop of phospholipids from one side of the plasma membrane to the other and the Golgi e. receptor-mediated endocytosis and smooth ER and Golgi

exocytosis and smooth ER and rough ER In exocytosis, vesicles derived from the endomembrane system fuse with the plasma membrane, thus increasing the number of phospholipids in the plasma membrane and increasing its surface area. The smooth ER is largely responsible for production of lipids destined for the membrane, and the rough ER produces proteins destined for the plasma membrane.

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

facilitated diffusion

A cell has a membrane potential of -100 mV (more negative inside than outside) and has 1,000 times more calcium ions outside the cell than inside. Which of the following best describes a mechanism by which Ca2+ enters the cell? a. movement of Ca2+ into the cell through a carrier protein down its electrical gradient b. facilitated diffusion of Ca2+ into the cell down its electrochemical gradient c. movement of Ca2+ into the cell through an ion channel down its concentration gradient d. passive diffusion of Ca2+ into the cell down its electrochemical gradient e. cotransport of Ca2+ into the cell with Cl-

facilitated diffusion of Ca2+ into the cell down its electrochemical gradient Both the electrical and chemical (concentration) gradients contribute the energy to move Ca2+ into the cells by facilitated diffusion as long as there is a channel or carrier that is specific for Ca2+.

Consider the currently accepted fluid mosaic model of the plasma membrane. Where in the plasma membrane would cholesterol most likely be found? a. on the outside (external) surface of the membrane b. on either surface of the membrane, but not in the interior of the membrane c. in the interior and on the inside surface, but not on the outside surface d. in the interior of the membrane e. on the inside (cytoplasmic) surface

in the interior of the membrane The steroid cholesterol, wedged between phospholipid molecules in the plasma membranes of animals, helps stabilize the membrane.

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

integral proteins

Initially, in terms of tonicity, the solution in side A with respect to that in side B is 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. a. hypotonic b. plasmolyzed c. isotonic d. saturated e. hypertonic

isotonic

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

on the inside surface of the vesicle

Consider the currently accepted fluid mosaic model of the plasma membrane. Where in the membrane would carbohydrates most likely be found? a. Carbohydrates are rarely associated with plasma membranes b. on both hydrophilic surfaces of the membrane but not in the hydrophobic interior c. in the interior of the membrane d. on the outside (external) surface of the membrane e. on the inside (cytoplasmic) surface of the membrane

on the outside (external) surface of the membrane Membrane carbohydrates are covalently bonded to lipids or proteins and extend out from the external side of the plasma membrane as a means of cell identification.

Which of the following processes includes all others? a. transport of an ion down its electrochemical gradient b. passive transport c. diffusion of a solute across a membrane d. facilitated diffusion e. osmosis

passive transport

An organism with a cell wall would most likely be unable to take in materials through a. diffusion b. osmosis c. active transport d. phagocytosis e. facilitated diffusion

phagocytosis

Which of the following pairs correctly matches a membrane transport process to its primary function? a. phagocytosis: secretion of large particles from the cell by fusion of vesicles with the plasma membrane b. exocytosis: the movement of water and solutes out of the cell by vesicle fusion with the plasma membrane c. osmosis: passive diffusion of water and small solutes across a membrane d. pinocytosis: the uptake of water and small solutes into the cell by formation of vesicles at the plasma membrane e. None of the listed responses is correct

pinocytosis: the uptake of water and small solutes into the cell by formation of vesicles at the plasma membrane Pinocytosis is the uptake of liquid and the solutes dissolved in the liquid.

Which of the following enables a cell to pick up and concentrate a specific kind of molecule? a. channel proteins b. osmosis c. facilitated diffusion d. receptor-mediated endocytosis e. passive transport

receptor-mediated endocytosis In receptor-mediated endocytosis, only a specific molecule, called a ligand, can bind to the receptor. Without receptor binding occurring first, endocytosis does not proceed.

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. 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

similarity of the drug molecule to other molecules transported by the target cells

Which of the following cell structures exhibits selective permeability between a cell and its external environment? a. the plasma membrane b. mitochondria c. endoplasmic reticulum d. lysosomes e. chloroplasts

the plasma membrane The plasma membrane allows some substances to cross into a cell more easily than others.

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

to mediate cell-to-cell recognition