Chapter 7 Bio 1107

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? (eText Concept 7.4) * passive diffusion of Ca2+ into the cell down its electrochemical gradient * movement of Ca2+ into the cell through an ion channel down its concentration gradient * movement of Ca2+ into the cell through a carrier protein down its electrical gradient * facilitated diffusion of Ca2+ into the cell down its electrochemical gradient * cotransport of Ca2+ into the cell with Cl-

facilitated diffusion of Ca2+ into the cell down its electrochemical gradient

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? (eText Concept 7.3) * 0.4 M * distilled water * 1.0 M * 0.8 M * 150 mM.

1.0 M

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? (eText Concept 7.3) * High salt concentration lowers the pH, thus inhibiting bacterial metabolism. * Bacterial cells shrivel up in high salt solutions, causing the cell to burst. * A 30% salt solution is hypertonic to the bacteria, so they lose too much water and plasmolyze. * A 30% salt solution is hypotonic to the bacteria, so they gain too much water and burst. * High salt concentration raises the pH, thus inhibiting bacterial metabolism.

A 30% salt solution is hypertonic to the bacteria, so they lose too much water and plasmolyze.

Which of the following pairs correctly matches a membrane transport process to its primary function? (eText Concept 7.5) * phagocytosis ... secretion of large particles from the cell by fusion of vesicles with the plasma membrane * osmosis ... passive diffusion of water and small solutes across a membrane * pinocytosis ... the uptake of water and small solutes into the cell by formation of vesicles at the plasma membrane * exocytosis ... the movement of water and solutes out of the cell by vesicle fusion with the plasma membrane * None of the above is correct.

pinocytosis ... the uptake of water and small solutes into the cell by formation of vesicles at the plasma membrane No. In phagocytosis (cellular eating), a type of endocytosis, a cell engulfs a particle by wrapping pseudopodia around it and packaging it within a membrane-enclosed sac large enough to be classified as a food vacuole

Which of the following statements about the sodium-potassium pump is correct? (eText Concept 7.4) * The sodium-potassium pump is a symporter that results in a net negative charge outside the cell. * 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 uses an existing proton gradient to drive the movement of sodium and potassium ions. * The sodium-potassium pump is an antiporter that results in a net negative charge inside the cell. * 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.

the sodium-potassium pump is an antiporter that results in a net negative charge inside the cell.

Which statement(s) about the sidedness of the plasma membrane is/are correct? (eText Concept 7.1) * 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. * The two lipid layers may differ in specific lipid composition. * Every integral membrane protein has a specific orientation in the plasma membrane. * The asymmetrical distribution of membrane proteins, lipids, and carbohydrates across the plasma membrane is determined as the membrane is being constructed. * All of the listed responses are correct.

All of the listed responses are correct.

Which of the following is a correct difference between active transport and facilitated diffusion? (eText Concept 7.4) * Facilitated diffusion involves transport proteins, and active transport does not. * Active transport requires energy from ATP, and facilitated diffusion does not. * Facilitated diffusion can move solutes against a concentration gradient, and active transport cannot. * Active transport involves transport proteins, and facilitated diffusion does not. * Active transport can move solutes in either direction across a membrane, but facilitated diffusion can only move in one direction.

Active transport requires energy from ATP, and facilitated diffusion does not.

Cells A and B are the same size, shape, and temperature, but cell A is metabolically less active than cell B; cell B is actively converting oxygen to water in cellular respiration. Oxygen will diffuse more rapidly into cell _____ because _____. (eText Concept 7.3) * B ... the oxygen molecules inside cell B have a higher kinetic energy * A ... the diffusion gradient there is shallower * B ... the gradient of oxygen is oriented in the opposite direction compared to cell A * B ... the diffusion gradient in cell B is steeper * A ... its membrane transport proteins will not be saturated

B ... the diffusion gradient in cell B is steeper

f a red blood cell and a plant cell were placed in seawater, what would happen to the two types of cells? (eText Concept 7.3) * The red blood cell would burst, and the plant cell would shrink. * Both cells would lose water; the red blood cell would shrivel, and the plant plasma membrane would pull away from the cell wall. * Seawater is isotonic to both cells, therefore, neither cell will change as there will be no movement of water into or out of the cells. * The red blood cell would shrink, and the plant cell would gain water. * Both cells would gain water by osmosis; the red blood cell would burst, and the plant cell would increase in turgor pressure.

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

Which of the following statements about cotransport of solutes across a membrane is correct? (eText Concept 7.4) * Cotransport involves the hydrolysis of ATP by the transporting protein. * In cotransport, both solutes that are being transported are moving down their chemical gradients. * A cotransport protein is most commonly an ion channel. * The sodium-potassium pump is an example of a cotransport protein. * Cotransport proteins allow a single ATP-powered pump to drive the active transport of many different solutes.

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

Which of these statements describes some aspect of facilitated diffusion? (eText Concept 7.3) * Facilitated diffusion of solutes may occur through channel or transport proteins in the membrane. * Facilitated diffusion of solutes occurs through phospholipid pores in the membrane. * Facilitated diffusion requires energy to drive a concentration gradient. * There is only one kind of protein pore for facilitated diffusion. * Facilitated diffusion is another name for osmosis.

Facilitated diffusion of solutes may occur through channel or transport proteins in the membrane. No. Facilitated diffusion occurs through integral membrane transport proteins.

Which of the following is false in regard to facilitated diffusion? (eText Concept 7.3) * Facilitated diffusion requires the hydrolysis of ATP. * Facilitated diffusion requires a concentration gradient. * Facilitated diffusion can occur using transport proteins. * Facilitated diffusion can move ions across membranes. * Facilitated diffusion can occur through protein channels.

Facilitated diffusion requires the hydrolysis of ATP.

The discomfort associated with irritable bowel syndrome can be alleviated with low doses of the class of antidepressants that block the reuptake of serotonin from the synaptic cleft (the space between adjacent neurons). Serotonin is a relatively small polar neurotransmitter used to transmit nerve impulses in the nerve tissue in the gut and central nervous system. Serotonin is transported back into the releasing neuron up its concentration gradient and down a sodium gradient. How might an antidepressant block serotonin reuptake by the releasing neuron? (eText Concept 7.4) * It could promote exocytosis of serotonin. * It could block active transport of serotonin back into the cell by blocking a serotonin-sodium symporter. * It could block receptor-mediated endocytosis. * It could block a cotransporter involved in facilitated diffusion * It could block the passive diffusion of serotonin back into the cell by chemically modifying serotonin.

It could block active transport of serotonin back into the cell by blocking a serotonin-sodium symporter.

Which of the following statements about diffusion is true? (eText Concept 7.3) * It always requires integral proteins of the cell membrane. * It requires expenditure of energy by the cell. * It is a passive process. * It occurs when molecules move from a region of lower concentration to a region of higher concentration. * It is very rapid over long distances.

It is a passive process.

Which of the following statements concerning carbohydrates associated with the plasma membrane is correct? (eText Concept 7.1) * Carbohydrates on the plasma membrane are typically short chains of between two and five monosaccharides. * Carbohydrates are only found associated with the membranes of prokaryotic cells. * The carbohydrate composition of most eukaryotic plasma membranes is quite similar. * Carbohydrates associated with the plasma membrane are located on both surfaces of the membrane. * Membrane carbohydrates function primarily in cell-cell recognition.

Membrane carbohydrates function primarily in cell-cell recognition.

Which of the following is a function of membrane proteins and also facilitates tissue formation during embryogenesis? (eText Concept 7.1) * Membrane proteins attach the membrane to the cytoskeleton. * Membrane proteins with short sugar chains form identification tags that are recognized by other cells. * Membrane proteins form channels, which move substances across the membrane. * Membrane proteins provide receptors for chemical messengers. * All of the listed responses are correct.

Membrane proteins with short sugar chains form identification tags that are recognized by other cells.

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? (eText Concept 7.3) * Water enters the sucrose solution because the sucrose molecule is a disaccharide and thus larger than the monosaccharide glucose. * After the sucrose dissociates into two monosaccharides, water will move via osmosis to the side of the membrane that contains the dissociated sucrose. * The sucrose solution is hypertonic and will gain water because the total mass of sucrose is greater than that of glucose. * Nothing happens because the two solutions are isotonic to one another. * Water leaves the sucrose solution because the sucrose molecule is a disaccharide and thus larger than the monosaccharide glucose.

Nothing happens because the two solutions are isotonic to one another. Correct. 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? (eText Concept 7.3) * Passive transport operates independently of the concentrations of the moving solute. * Passive transport operates independently of diffusion. * Passive transport does not occur in the human body. * Passive transport permits the solute to move in either direction, but the net movement of the population of solute occurs down the concentration gradient of the molecule. * In passive transport, solute movement stops when the solute concentration is the same on both sides of the membrane.

Passive transport permits the solute to move in either direction, but the net movement of the population of solute occurs down the concentration gradient of the molecule. Correct. 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? (eText Concept 7.1) * Phospholipids form a structure in which the hydrophobic portion faces outward. * They are triacylglycerols, which are commonly available in foods. * Phospholipids are completely insoluble in water. * Phospholipids form a selectively permeable structure. * Phospholipids form a single sheet in water

Phospholipids form a selectively permeable structure.

The plasma membrane is referred to as a "fluid mosaic" structure. Which of the following statements about that model is true? (eText Concept 7.1) * Only phospholipids are capable of moving in the membrane. * 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. * The fluid aspect of the membrane is due to the behavior of phospholipids, and the mosaic aspect is due to the presence of carbohydrates. * The mosaic aspect of the membrane is due to the glycosylation of inner leaflet phospholipids. * The fluid aspect of the membrane is due to the lateral and rotational movement of phospholipids, and embedded proteins account for the mosaic aspect.

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

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, don't protons move back into the cell through the sucrose-proton cotransport protein? (eText Concept 7.4) * The movement of protons through the cotransport protein cannot occur unless sucrose also moves at the same time. * In the absence of sucrose, the ATP-powered proton pump does not function, so there is no proton gradient. * Protons, unlike other substances, do not diffuse down their concentration gradient. * Protons are freely permeable through the phospholipid bilayer, so no transport protein is needed for protons. * Protons cannot move through membrane transport proteins.

The movement of protons through the cotransport protein cannot occur unless sucrose also moves at the same time.

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? (eText Concept 7.4) * 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 charge of +1 outside the cell membrane. * Active transport moves solutes down their concentration gradients and always uses ATP as the source of energy to do this. * Active transport uses channel proteins and ensures that the interior of the cell is always positive compared to the exterior of the cell. * 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

The sodium/potassium pump hydrolyzes ATP and results in a net charge of +1 outside the cell membrane.

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? (eText Concept 7.3) * There would be no osmotic movement of water in response to the added salt. * The added salt would enter the cell, causing the cell to take up water and swell. * The added salt makes the solution hypotonic compared to the cell. Water will enter the cell by osmosis. * Water would leave the cell by osmosis, causing the volume of the cytoplasm to decrease. * 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. Correct. The added salt makes the solution hypertonic compared to the cell. Water will leave the cell by osmosis.

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? (eText Concept 7.3) * a hypotonic urea solution * pure water * a hypotonic sucrose solution * a hypertonic urea solution * a hypertonic sucrose solution

a hypertonic sucrose solution Correct. 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? (eText Concept 7.2) * a large polar molecule * dissolved gases such as oxygen or carbon dioxide * a small nonpolar molecule * a large nonpolar molecule * Any of the above would easily diffuse through the membran

a large polar molecule

Which of the following molecules is most likely to passively diffuse across the plasma membrane? (eText Concept 7.2) * carbon dioxide * glucose * hemoglobin * DNA * sodium ion

carbon dioxide

Which of the following correctly describes a general property of all electrogenic pumps? (eText Concept 7.4) * create a voltage difference across the membrane * pump sodium out of the cell and potassium into the cell * can pump a large variety of solutes across a membrane against their concentration gradient * a cell with a high internal concentration of protons * a cell with an interior that is positively charged relative to the outside of the cell

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

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? (eText Concept 7.5) * passive transport * active transport * endocytosis * exocytosis * osmosis

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

Which of the following functional processes is not a consequence of the association of proteins with biological membranes? (eText Concept 7.1) * cell-cell communication * intercellular joining * enzymatic activity * cell-cell recognition * energy, carbon, and nitrogen storage

energy, carbon, and nitrogen storage

Which of the following processes and organelle(s) accounts for the replacement of lipids and proteins lost from the plasma membrane? (eText Concept 7.5) * flip-flop of phospholipids from one side of the plasma membrane to the other and the Golgi * active transport and the rough endoplasmic reticulum * endocytosis and Golgi * receptor-mediated endocytosis and smooth ER and Golgi * exocytosis and smooth and rough ER

exocytosis and smooth and rough ER No. Although the Golgi is involved in the shipment of phospholipids to the plasma membrane, endocytosis is a process that removes phospholipids from the plasma membrane by budding off of small vesicles.

Consider the currently accepted fluid mosaic model of the plasma membrane. Where in the plasma membrane would cholesterol most likely be found? (eText Concept 7.1) * in the interior and on the inside surface, but not on the outside surface * on the inside (cytoplasmic) surface * in the interior of the membrane * on the outside (external) surface of the membrane * on either surface of the membrane, but not in the interior of the membrane

in the interior of the membrane No. Cholesterol is hydrophobic and will be found in the interior of the bilayer membrane.

Consider the currently accepted fluid mosaic model of the plasma membrane. Where in the membrane would carbohydrates most likely be found? (eText Concept 7.1) * Carbohydrates are rarely associated with plasma membranes. * on the inside (cytoplasmic) surface of the membrane * on both hydrophilic surfaces of the membrane but not in the hydrophobic interior * on the outside (external) surface of the membrane * in the interior of the membrane

on the outside (external) surface of the membrane

Which of the following types of information is/are most likely to be derived from freeze-fracture of biological samples? (eText Concept 7.1) * number of ribosomes associated with the rough endoplasmic reticulum * the information coded for by DNA * patterns of movement in living cells * proteins embedded in membrane bilayers * the structure of pili

proteins embedded in membrane bilayers No. A freeze-fracture does not sequence DNA nucleotides.

Which of the following structural arrangements of the components in biological membranes is most consistent with membrane's property of selective permeability? (eText Concept 7.2) * proteins embedded in two layers of phospholipid * a layer of protein coating a layer of phospholipid * a phospholipid bilayer with proteins scattered on the surfaces of the membranes * phospholipids sandwiched between two layers of protein * proteins sandwiched between two layers of phospholipid

proteins embedded in two layers of phospholipid

Which of the following enables a cell to pick up and concentrate a specific kind of molecule? (eText Concept 7.5) * receptor-mediated endocytosis * channel proteins * passive transport * facilitated diffusion * osmosis

receptor-mediated endocytosis Correct. 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.

Which of the following cell structures exhibits selective permeability between a cell and its external environment? (eText Overview) * lysosomes * chloroplasts * endoplasmic reticulum * mitochondria * plasma membrane

the plasma membrane

Glucose can be moved into cells via two mechanisms. An active transport mechanism can be used 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 most true? (eText Concept 7.4) * The protein that moves the sodium and glucose into the cell is an antiporter. * To pump glucose up its concentration gradient, sodium is moving down its concentration gradient. * The sodium forms an electrochemical gradient in this mechanism. * The first two responses are correct. * The second and third responses are correct.

the second and third responses are correct. Correct. 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 electrical gradient also exists.