Deck 5: Membrane Transport and Cell Signaling

Question 1

The presence of cholesterol in the plasma membranes of some animals

A) enables the membrane to stay fluid more easily when cell temperature drops.
B) enables the animal to remove hydrogen atoms from saturated phospholipids.
C) enables the animal to add hydrogen atoms to unsaturated phospholipids.
D) makes the membrane less flexible, allowing it to sustain greater pressure from within the cell.
E) makes the animal more susceptible to circulatory disorders.

Answer 1

A

Question 2

Which of the following types of molecules are the major structural components of the cell membrane?

A) phospholipids and cellulose
B) nucleic acids and proteins
C) phospholipids and proteins
D) proteins and cellulose
E) glycoproteins and cholesterol

Answer 2

C

Question 3

Cell membranes are asymmetrical. Which of the following statements is the most likely explanation for the membrane's asymmetrical nature?

A) Because the cell membrane forms a border between one cell and another in tightly packed tissues such as epithelium, the membrane must be asymmetrical
B) Because cell membranes communicate signals from one organism to another, the cell membranes must be asymmetrical.
C) The two sides of a cell membrane face different environments and carry out different functions.
D) The chemical constitution of the inner and outer layer of the cell membrane is predetermined by genes.
E) Proteins only function on the cytoplasmic side of the cell membrane, which results in the membrane's asymmetrical nature.

Answer 3

C

Question 4

Singer and Nicolson's fluid mosaic model of the membrane proposed that membranes

A) are a phospholipid bilayer.
B) are a phospholipid bilayer between two layers of hydrophilic proteins.
C) are a single layer of phospholipids and proteins.
D) consist of protein molecules embedded in a fluid bilayer of phospholipids.
E) consist of a mosaic of polysaccharides and proteins.

Question 5

According to the fluid mosaic model of cell membranes, which of the following is a true statement about membrane phospholipids?

A) They can move laterally along the plane of the membrane.
B) They frequently flip-flop from one side of the membrane to the other.
C) They occur in an uninterrupted bilayer, with membrane proteins restricted to the surface of the membrane.
D) They are free to depart from the membrane and dissolve in the surrounding solution.
E) They have hydrophilic tails in the interior of the membrane.

Question 6

Over the years, the fluid mosaic model has been refined based on recent experimental findings. In the years since the proposal of the fluid mosaic model of the cell membrane, which of the following observations has been added to the model?

A) The membrane is only fluid across a very narrow temperature range.
B) Proteins rarely move in the membrane.
C) Unsaturated lipids are excluded from the membranes and do not contribute to membrane fluidity.
D) The concentration of protein molecules appears to be much higher.
E) Membrane proteins are made of only acidic amino acids.

Question 7

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.

Question 8

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

Question 9

Which of the following is a reasonable explanation for why unsaturated fatty acids help keep any membrane more fluid at lower temperatures?

A) The double bonds form kinks in the fatty acid tails, preventing adjacent lipids from packing tightly.
B) Unsaturated fatty acids have a higher cholesterol content and therefore more cholesterol in their membranes.
C) Unsaturated fatty acids are more polar than saturated fatty acids.
D) The double bonds block interaction among the hydrophilic head groups of the lipids.
E) The double bonds result in shorter fatty acid tails and thinner membranes.

Question 10

The formulation of a model for a structure or for a process serves which of the following purposes?

A) It asks a scientific question.
B) It functions as a testable hypothesis.
C) It records observations.
D) It serves as a data point among results.
E) It can only be arrived at after years of experimentation.

Question 11

A protein that spans the phospholipid bilayer one or more times is

A) a transmembrane protein.
B) an integral protein.
C) a peripheral protein.
D) an integrin.
E) a glycoprotein.

Question 12

The cell membranes of Antarctic ice fish might have which of the following adaptations?

A) very long chain fatty acids
B) branched isoprenoid lipids
C) a high percentage of polyunsaturated fatty acids
D) a higher percentage of trans fatty acids
E) no cholesterol

Question 13

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.

Question 14

Some regions of the plasma membrane, called lipid rafts, have a higher concentration of cholesterol molecules. At high temperatures, these regions

A) are more fluid than the surrounding membrane.
B) are less fluid than the surrounding membrane.
C) are able to flip from inside to outside.
D) detach from the plasma membrane and clog arteries.
E) have higher rates of lateral diffusion of lipids and proteins into and out of these regions.

Question 15

In order for a protein to be an integral membrane protein it would have to be

A) hydrophilic.
B) hydrophobic.
C) amphipathic, with at least one hydrophobic region.
D) completely covered with phospholipids.
E) exposed on only one surface of the membrane.

Question 16

Why are lipids and proteins free to move laterally in membranes?

A) The interior of the membrane is filled with liquid water.
B) Lipids and proteins repulse each other in the membrane.
C) Hydrophilic portions of the lipids are in the interior of the membrane.
D) There are only weak hydrophobic interactions in the interior of the membrane.
E) Molecules such as cellulose can pull them in various directions.

Question 17

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.

Question 18

When biological membranes are frozen and then fractured, they tend to break along the middle of the bilayer. The best explanation for this is that

A) the integral membrane proteins are not strong enough to hold the bilayer together.
B) water that is present in the middle of the bilayer freezes and is easily fractured.
C) hydrophilic interactions between the opposite membrane surfaces are destroyed on freezing.
D) the carbon-carbon bonds of the phospholipid tails are easily broken.
E) the hydrophobic interactions that hold the membrane together are weakest at this point.

Question 19

Which of the following is true for the evolution of cell membranes?

A) The fluid mosaic nature of cell membranes provides the explanation for the evolution of cell membranes.
B) Membrane proteins are the sole component responsible for the evolution of cell membranes.
C) The evolution of cell membranes is driven by the evolution of glycoproteins and glycolipids.
D) All components of membranes evolve as a result of natural selection.
E) An individual organism selects its preferred type of cell membrane for particular functions.

Question 20

Which of these are not embedded in the hydrophobic portion of the lipid bilayer?

A) transmembrane proteins
B) integral proteins
C) peripheral proteins
D) integrins
E) glycoproteins

Question 21

Proton pumps are used in various ways by members of every domain of organisms: Bacteria, Archaea, and Eukarya. What does this most probably mean?

A) Proton pumps must have evolved before any living organisms were present on Earth.
B) Proton gradients across a membrane were used by cells that were the common ancestor of all three domains of life.
C) The high concentration of protons in the ancient atmosphere must have necessitated a pump mechanism.
D) Cells of each domain evolved proton pumps independently when oceans became more acidic.
E) Proton pumps are necessary to all cell membranes.

Question 22

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

Question 23

Which of the following is a characteristic feature of a carrier protein in a plasma membrane?

A) It is a peripheral membrane protein.
B) It exhibits a specificity for a particular type of molecule.
C) It requires the expenditure of cellular energy to function.
D) It works against diffusion.
E) It has few, if any, hydrophobic amino acids.

Question 24

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.

Question 25

The movement of the hydrophobic gas nitrous oxide (N2O) (laughing gas) into a cell is an example of

A) diffusion across the lipid bilayer.
B) facilitated diffusion.
C) active transport.
D) osmosis.
E) cotransport.

Question 26

The phosphate transport system in bacteria imports phosphate into the cell even when the concentration of phosphate outside the cell is much lower than the cytoplasmic phosphate concentration. Phosphate import depends on a pH gradient across the membrane-more acidic outside the cell than inside the cell. Phosphate transport is an example of

A) passive diffusion.
B) facilitated diffusion.
C) active transport.
D) osmosis.
E) cotransport.

Question 27

Which of the following is most likely true of a protein that cotransports glucose and sodium ions into the intestinal cells of an animal?

A) Sodium and glucose compete for the same binding site in the cotransporter.
B) Glucose entering the cell down its concentration gradient provides energy for uptake of sodium ions against the electrochemical gradient.
C) Sodium ions can move down their electrochemical gradient through the cotransporter whether or not glucose is present outside the cell.
D) The cotransporter can also transport potassium ions.
E) A substance that blocks sodium ions from binding to the cotransport protein will also block the transport of glucose.

Question 28

Which of the following membrane activities requires energy from ATP hydrolysis?

A) facilitated diffusion of chloride ions across the membrane through a chloride channel
B) movement of water into a cell
C) movement of Na+ ions from a lower concentration in a mammalian cell to a higher concentration in the extracellular fluid
D) movement of glucose molecules into a bacterial cell from a medium containing a higher concentration of glucose than inside the cell
E) movement of carbon dioxide out of a paramecium

Question 29

Which of the following statements is correct about diffusion?

A) It is very rapid over long distances.
B) It requires an expenditure of energy by the cell.
C) It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.
D) It is an active process in which molecules move from a region of lower concentration to one of higher concentration.
E) It requires integral proteins in the cell membrane.

Question 30

The movement of potassium into an animal cell requires

A) low cellular concentrations of sodium.
B) high cellular concentrations of potassium.
C) an energy source such as ATP.
D) a cotransport protein.
E) a potassium channel protein.

Question 31

Which of the following would increase the electrochemical gradient across a membrane?

A) a chloride channel
B) a sucrose-proton cotransporter
C) a proton pump
D) a potassium channel
E) both a proton pump and a potassium channel

Question 32

Which of the following statements correctly describes the normal tonicity conditions for typical plant and animal cells?

A) The animal cell is in a hypotonic solution, and the plant cell is in an isotonic solution.
B) The animal cell is in an isotonic solution, and the plant cell is in a hypertonic solution.
C) The animal cell is in a hypertonic solution, and the plant cell is in an isotonic solution.
D) The animal cell is in an isotonic solution, and the plant cell is in a hypotonic solution.
E) The animal cell is in a hypertonic solution, and the plant cell is in a hypotonic solution.

Question 33

Ions diffuse across membranes through specific ion channels

A) down their chemical gradients.
B) down their concentration gradients.
C) down the electrical gradients.
D) down their electrochemical gradients.
E) down the osmotic potential gradients.

Question 34

Water passes quickly through cell membranes because

A) the bilayer is hydrophilic.
B) it moves through hydrophobic channels.
C) water movement is tied to ATP hydrolysis.
D) it is a small, polar, charged molecule.
E) it moves through aquaporins in the membrane.

Question 35

Celery stalks that are immersed in fresh water for several hours become stiff and hard. Similar stalks left in a 0.15 M salt solution become limp and soft. From this we can deduce that

A) the fresh water and the salt solution are both hypertonic to the cells of the celery stalks.
B) the fresh water and the salt solution are both hypotonic to the cells of the celery stalks.
C) the fresh water is hypotonic and the salt solution is hypertonic to the cells of the celery stalks.
D) the fresh water is hypertonic and the salt solution is hypotonic to the cells of the celery stalks.
E) the fresh water is isotonic and the salt solution is hypertonic to the cells of the celery stalks.

Question 36

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

Question 37

The sodium-potassium pump is called an electrogenic pump because it

A) pumps equal quantities of Na+ and K+ across the membrane.
B) pumps hydrogen ions out of the cell.
C) contributes to the membrane potential.
D) ionizes sodium and potassium atoms.
E) is used to drive the transport of other molecules against a concentration gradient.

Question 38

What is the voltage across a membrane called?

A) water potential
B) chemical gradient
C) membrane potential
D) osmotic potential
E) electrochemical gradient

Question 39

Mammalian blood contains the equivalent of 0.15 M NaCl. Seawater contains the equivalent of 0.45 M NaCl. What will happen if red blood cells are transferred to seawater?

A) Water will leave the cells, causing them to shrivel and collapse.
B) NaCl will be exported from the red blood cells by facilitated diffusion.
C) The blood cells will take up water, swell, and eventually burst.
D) NaCl will passively diffuse into the red blood cells.
E) The blood cells will expend ATP for active transport of NaCl into the cytoplasm.

Question 40

What kinds of molecules pass through a cell membrane most easily?

A) large and hydrophobic
B) small and hydrophobic
C) large polar
D) ionic
E) monosaccharides such as glucose

Question 41

A drug designed to inhibit the response of cells to testosterone would almost certainly result in which of the following?

A) lower cytoplasmic levels of cAMP
B) an increase in receptor tyrosine kinase activity
C) a decrease in transcriptional activity of certain genes
D) an increase in cytosolic calcium concentration
E) a decrease in G-protein activity

Question 42

The difference between pinocytosis and receptor-mediated endocytosis is that

A) pinocytosis brings only water molecules into the cell, but receptor-mediated endocytosis brings in other molecules as well.
B) pinocytosis increases the surface area of the plasma membrane, whereas receptor-mediated endocytosis decreases the plasma membrane surface area.
C) pinocytosis is nonselective in the molecules it brings into the cell, whereas receptor-mediated endocytosis offers more selectivity.
D) pinocytosis requires cellular energy, but receptor-mediated endocytosis does not.
E) pinocytosis can concentrate substances from the extracellular fluid, but receptor-mediated endocytosis cannot.

Question 43

In which of the following ways do plant hormones differ from hormones in animals?

A) Plant hormones interact primarily with intracellular receptors.
B) Plant hormones may travel in air or through vascular systems.
C) Animal hormones are found in much greater concentration.
D) Plant hormones are synthesized from two or more distinct molecules.
E) Animal hormones are primarily for mating and embryonic development.

Question 44

Which of the following is true of transcription factors?

A) They regulate the synthesis of DNA in response to a signal.
B) They transcribe ATP into cAMP.
C) They initiate the epinephrine response in animal cells.
D) They control gene expression.
E) They regulate the synthesis of lipids in the cytoplasm.

Question 45

When a neuron responds to a particular neurotransmitter by opening gated ion channels, the neurotransmitter is serving as which part of the signal pathway?

A) receptor
B) relay molecule
C) transducer
D) signal molecule
E) endocrine molecule

Question 46

When protein membrane receptors are activated, what usually happens?

A) A change occurs in intracellular ion concentration.
B) The receptors open and close in response to protein signals.
C) A change occurs on only one membrane surface: exterior or interior.
D) The receptor preferentially binds with lipid or glycolipid signal molecules.
E) The receptor changes conformation after binding with signal polypeptides.

Question 47

At puberty, an adolescent female body changes in both structure and function of several organ systems, primarily under the influence of changing concentrations of estrogens and other steroid hormones. How can one hormone, such as estrogen, mediate so many effects?

A) Estrogen is produced in very large concentration and therefore diffuses widely.
B) Estrogen has specific receptors inside several cell types, but each cell responds in the same way to its binding.
C) Estrogen is kept away from the surface of any cells not able to bind it at the surface.
D) Estrogen binds to specific receptors inside many kinds of cells, each of which have different responses to its binding.
E) The subcomponents of estrogen, when metabolized, can influence cell response.

Question 48

A bacterium engulfed by a white blood cell through phagocytosis will be digested by enzymes contained in

A) peroxisomes.
B) lysosomes.
C) Golgi vesicles.
D) vacuoles.
E) secretory vesicles.

Question 49

In general, a signal transmitted via phosphorylation of a series of proteins

A) brings a conformational change to each protein.
B) requires binding of a hormone to a cytosol receptor.
C) cannot occur in yeasts because they lack protein phosphatases.
D) requires phosphorylase activity.
E) allows target cells to change their shape and therefore their activity.

Question 50

Which of the following is a correct association?

A) kinase activity and the addition of a tyrosine
B) phosphodiesterase activity and the removal of phosphate groups
C) GTPase activity and hydrolysis of GTP to GDP
D) phosphorylase activity and the catabolism of glucose
E) adenylyl cyclase activity and the conversion of cAMP to AMP

Question 51

Which of the following most likely would be an immediate result of a growth factor binding to its receptor?

A) protein kinase activity
B) adenylyl cyclase activity
C) GTPase activity
D) protein phosphatase activity
E) phosphorylase activity

Question 52

Which of the following statements is true of signal molecules?

A) When signal molecules first bind to receptor tyrosine kinases, the receptors phosphorylate a number of nearby molecules.
B) In response to some G-protein-mediated signals, a special type of lipid molecule associated with the plasma membrane is cleaved to form IP3 and calcium.
C) In most cases, signal molecules interact with the cell at the plasma membrane and then enter the cell and eventually the nucleus.
D) Toxins such as those that cause botulism and cholera interfere with the ability of activated G proteins to hydrolyze GTP to GDP, resulting in phosphodiesterase activity in the absence of an appropriate signal molecule.
E) Protein kinase A activation is one possible result of signal molecules binding to G-protein-coupled receptors.

Question 53

Familial hypercholesterolemia is characterized by which of the following?

A) defective LDL receptors on the cell membranes
B) poor attachment of the cholesterol to the extracellular matrix of cells
C) a poorly formed lipid bilayer that cannot incorporate cholesterol into cell membranes
D) inhibition of the cholesterol active transport system in red blood cells
E) a general lack of glycolipids in the blood cell membranes

Question 54

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

Question 55

The function of phosphatases in signal transduction is best described as to

A) move the phosphate group of the transduction pathway to the next molecule of a series.
B) prevent a protein kinase from being reused when there is another extracellular signal.
C) amplify the transduction signal so it affects multiple transducers.
D) amplify the second messengers such as cAMP.
E) inactivate protein kinases and turn off the signal transduction.

Question 56

Which of the following is characterized by a cell releasing a signal molecule into the environment, followed by a number of cells in the immediate vicinity responding?

A) hormonal signaling
B) autocrine signaling
C) paracrine signaling
D) endocrine signaling
E) synaptic signaling

Question 57

Testosterone functions inside a cell by

A) acting as a signal receptor that activates tyrosine kinases.
B) binding with a receptor protein that enters the nucleus and activates specific genes.
C) acting as a steroid signal receptor that activates ion channel proteins.
D) becoming a second messenger that inhibits nitric oxide.
E) coordinating a phosphorylation cascade that increases spermatogenesis.

Question 58

What is most likely to happen to an animal's target cells that lack receptors for local regulators?

A) They might compensate by receiving nutrients via a factor.
B) They could develop normally in response to neurotransmitters instead.
C) They could divide but never reach full size.
D) They might not be able to multiply in response to growth factors from nearby cells.
E) Hormones would not be able to interact with target cells.

Question 59

In which of the following ways could signal transduction most probably be explored in research to treat cancer?

A) removal of serine/threonine phosphate acceptors from transduction pathways in colon pre-cancerous growths
B) alteration of protein kinases in cell cycle regulation in order to slow cancer growth
C) increase in calcium ion uptake into the cytoplasm in order to modulate the effects of environmental carcinogens
D) expansion of the role of transduction inhibitors in the cells before they give rise to cancer
E) increase in the concentration of phosphodiesterases in order to produce more AMP

Question 60

Which of the following is true of steroid receptors?

A) The receptor molecules are themselves lipids or glycolipids.
B) The receptor may be inside the nuclear membrane.
C) The unbound steroid receptors are quickly recycled by lysosomes.
D) The concentration of steroid receptors must be relatively high in most cells.
E) The receptor molecules are free to move in and out of most organelles.

Question 61

Figure 5.1
For the following questions, match the labeled component of the cell membrane in Figure 5.1 with its description.
Which component is a microfilament of the cytoskeleton?

A) A
B) B
C) C
D) D
E) E

Question 62

Figure 5.2
The solutions in the two arms of this U-tube are separated by a membrane that is permeable to water and glucose but not to sucrose. Side A is half-filled with a solution of 2 M sucrose and 1 M glucose. Side B is half-filled with 1 M sucrose and 2 M glucose. Initially, the liquid levels on both sides are equal.
After the system reaches equilibrium, what changes are observed?

A) The molarity of sucrose is higher than that of glucose on side A.
B) The molarity of glucose is higher in side A than in side B.
C) The water level is higher in side A than in side B.
D) The water level is unchanged.
E) The water level is higher in side B than in side A.

Question 63

Figure 5.5
The following questions are based on Figure 5.5.
Which of the following types of signaling is represented in Figure 5.5?

A) autocrine
B) paracrine
C) hormonal
D) synaptic
E) long distance

Question 64

Figure 5.4
Five dialysis bags, constructed from a semipermeable membrane that is impermeable to sucrose, were filled with various concentrations of sucrose and then placed in separate beakers containing an initial concentration of 0.6 M sucrose solution. At 10-minute intervals, the bags were massed (weighed) and the percent change in mass of each bag was graphed.
Which line in the graph represents the bag with the highest initial concentration of sucrose?

A) A
B) B
C) C
D) D
E) E

Question 65

Figure 5.5
The following questions are based on Figure 5.5.
In Figure 5.5, the dots in the space between the two structures represent which of the following?

A) receptor molecules
B) signal transducers
C) neurotransmitters
D) hormones
E) pheromones

Question 66

Figure 5.5
The following questions are based on Figure 5.5.
Cystic fibrosis is a genetic disease in humans in which the CFTR protein, which functions as a chloride ion channel, is missing or nonfunctional in cell membranes. The CFTR protein belongs to what category of membrane proteins?

A) gap junctions
B) aquaporins
C) electrogenic ion pumps
D) cotransporters
E) hydrophilic channels

Question 67

Figure 5.1
For the following questions, match the labeled component of the cell membrane in Figure 5.1 with its description.
Which component is cholesterol?

A) A
B) B
C) C
D) D
E) E

Question 68

In research on aging (both cellular aging and organismal aging), it has been found that aged cells do not progress through the cell cycle as they had previously. Which of the following would provide evidence that this is related to cell signaling?

A) Growth factor ligands do not bind as efficiently to receptors.
B) Their lower hormone concentrations elicit a lesser response.
C) cAMP levels change very frequently.
D) Enzymatic activity declines.
E) ATP production decreases.

Question 69

Figure 5.1
For the following questions, match the labeled component of the cell membrane in Figure 5.1 with its description.
Which component is the fiber of the extracellular matrix?

A) A
B) B
C) C
D) D
E) E

Question 70

Figure 5.5
The following questions are based on Figure 5.5.
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.

Question 71

Sutherland discovered that the signaling molecule epinephrine

A) brings about a decrease in levels of cAMP as a result of bypassing the plasma membrane.
B) causes lower blood glucose by binding to liver cells.
C) interacts with insulin inside muscle cells.
D) interacts directly with glycogen phosphorylase.
E) elevates cytosolic concentrations of cyclic AMP.

Question 72

Figure 5.4
Five dialysis bags, constructed from a semipermeable membrane that is impermeable to sucrose, were filled with various concentrations of sucrose and then placed in separate beakers containing an initial concentration of 0.6 M sucrose solution. At 10-minute intervals, the bags were massed (weighed) and the percent change in mass of each bag was graphed.
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

Question 73

GTPase activity is important in the regulation of signal transduction because it

A) increases the available concentration of phosphate.
B) decreases the amount of G protein in the membrane.
C) hydrolyzes GTP to GDP, thus shutting down the pathway.
D) converts cGMP to GTP.
E) phosphorylates protein kinases.

Question 74

Figure 5.1
For the following questions, match the labeled component of the cell membrane in Figure 5.1 with its description.
Which component is a glycolipid?

A) A
B) B
C) C
D) D
E) E

Question 75

Which of the following is the greatest advantage of having multiple steps in a transduction pathway?

A) Many of the steps can be used in multiple pathways.
B) Having multiple steps in a pathway requires the least amount of ATP.
C) Having multiple steps provides for greater possible amplification of a signal.
D) Each individual step can remove excess phosphate groups from the cytoplasm.
E) Each step can be activated by several G proteins simultaneously.

Question 76

Figure 5.1
For the following questions, match the labeled component of the cell membrane in Figure 5.1 with its description.
Which component is the peripheral protein?

A) A
B) B
C) C
D) D
E) E

Question 77

Figure 5.3
The solutions in the arms of a U-tube are separated at the bottom of the tube by a selectively permeable membrane. The membrane is permeable to sodium chloride but not to glucose. Side A is filled with a solution of 0.4 M glucose and 0.5 M sodium chloride (NaCl), and side B is filled with a solution containing 0.8 M glucose and 0.4 M sodium chloride. Initially, the volume in both arms is the same. Refer to the figure to answer the following questions.
At the beginning of the experiment, side A

A) is hypertonic to side B.
B) is hypotonic to side B.
C) is isotonic to side B.
D) is hypertonic to side B with respect to glucose.
E) is hypotonic to side B with respect to sodium chloride.

Question 78

Figure 5.2
The solutions in the two arms of this U-tube are separated by a membrane that is permeable to water and glucose but not to sucrose. Side A is half-filled with a solution of 2 M sucrose and 1 M glucose. Side B is half-filled with 1 M sucrose and 2 M glucose. Initially, the liquid levels on both sides are equal.
Initially, in terms of tonicity, the solution in side A with respect to that in side B is

A) hypotonic.
B) plasmolyzed.
C) isotonic.
D) saturated.
E) hypertonic.

Question 79

Figure 5.3
The solutions in the arms of a U-tube are separated at the bottom of the tube by a selectively permeable membrane. The membrane is permeable to sodium chloride but not to glucose. Side A is filled with a solution of 0.4 M glucose and 0.5 M sodium chloride (NaCl), and side B is filled with a solution containing 0.8 M glucose and 0.4 M sodium chloride. Initially, the volume in both arms is the same. Refer to the figure to answer the following questions.
If you examine side A after three days, you should find

A) a decrease in the concentration of NaCl and glucose and an increase in the water level.
B) a decrease in the concentration of NaCl, an increase in water level, and no change in the concentration of glucose.
C) no net change in the system.
D) a decrease in the concentration of NaCl and a decrease in the water level.
E) no change in the concentration of NaCl and glucose and an increase in the water level.

Question 80

Figure 5.4
Five dialysis bags, constructed from a semipermeable membrane that is impermeable to sucrose, were filled with various concentrations of sucrose and then placed in separate beakers containing an initial concentration of 0.6 M sucrose solution. At 10-minute intervals, the bags were massed (weighed) and the percent change in mass of each bag was graphed.
Which line in the graph represents the bag that contained a solution isotonic to the 0.6 M solution at the beginning of the experiment?

A) A
B) B
C) C
D) D
E) E