Unit 5 Practice Test				Name:_______________________________________

____	1)	Which of the following types of molecules are the major structural components of the cell membrane?
A)	phospholipids and cellulose	D)	proteins and cellulose	
B)	nucleic acids and proteins	E)	glycoproteins and cholesterol	
C)	phospholipids and proteins	

____	2)	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.	

____	3)	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.	

____	4)	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	

____	5)	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.	

____	6)	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.	

____	7)	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, even though they possibly can do so.	
C)	Unsaturated lipids are excluded from the membranes.	
D)	The concentration of protein molecules is now known to be much higher.	
E)	The proteins are known to be made of only acidic amino acids.	

____	8)	What kinds of molecules pass through a cell membrane most easily?
A)	large and hydrophobic	D)	ionic	
B)	small and hydrophobic	E)	monosaccharides such as glucose	
C)	large polar	

____	9)	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.	

____	10)	Nitrous oxide gas molecules diffusing across a cell's plasma membrane is an example of
A)	diffusion across the lipid bilayer.	D)	osmosis.	
B)	facilitated diffusion.	E)	cotransport.	
C)	active transport.	

____	11)	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.	

____	12)	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.	D)	The cell will become flaccid.	
B)	The cell membrane will lyse.	E)	The cell will become turgid.	
C)	Plasmolysis will shrink the interior.	

____	13)	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	D)	exocytosis	
B)	phagocytosis	E)	facilitated diffusion	
C)	active transport pumps	

____	14)	What is the voltage across a membrane called?
A)	water potential	D)	osmotic potential	
B)	chemical gradient	E)	electrochemical gradient	
C)	membrane potential	

____	15)	White blood cells engulf bacteria through what process?
A)	exocytosis	D)	osmosis	
B)	phagocytosis	E)	receptor–mediated exocytosis	
C)	pinocytosis	

For the following questions, match the labeled component of the cell membrane in the figure with its description.

____	16)	Which component is the peripheral protein?
A)	A	B)	B	C)	C	D)	D	E)	E	

____	17)	Which component is the fiber of the extracellular matrix?
A)	A	B)	B	C)	C	D)	D	E)	E	

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.

____	18)	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.	

____	19)	After the system reaches equilibrium, what changes are observed?
A)	The molarity of sucrose and glucose are equal on both sides.	
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.	

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.

____	20)	What would be observed by live–cell fluorescence microscopy immediately after HIV entry if the red fluorescent lipid dye–labeled HIV membrane fuses with the target cell plasma membrane?
A)	A spot of red fluorescence will be visible on the infected cell's plasma membrane, marking the site of membrane fusion and HIV entry.	
B)	The red fluorescent dye–labeled lipids will appear in the infected cell’s interior.	
C)	A spot of red fluorescence will diffuse in the infected cell's cytoplasm.	
D)	A spot of red fluorescence will remain outside the cell after delivering the viral capsid.	
E)	Fluorescence microscopy does not have enough resolution to visualize fluorescently labeled HIV virus particles.	

____	21)	Using live–cell fluorescence microscopy, researchers observed that a red fluorescent spot moved from the plasma membrane into the interior of target cells when red fluorescent dye–labeled HIV was added to the cells. What is the best conclusion from these observations?
A)	The hypothesis that HIV enters the cell via fusion with the target cell plasma membrane is supported.	
B)	The hypothesis that HIV enters the cell via fusion with the target cell plasma membrane is not supported.	
C)	The hypothesis that HIV enters the cell via endocytosis is supported.	
D)	The hypothesis that HIV enters the cell via endocytosis is not supported.	
E)	Neither hypothesis is supported by these results.	

____	22)	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.	

____	23)	Which of the following is true for the signaling system in an animal cell that lacks the ability to produce GTP?
A)	It would not be able to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane.	
B)	It could activate only the epinephrine system.	
C)	It would be able to carry out reception and transduction but would not be able to respond to a signal.	
D)	It would use ATP instead of GTP to activate and inactivate the G protein on the cytoplasmic side of the plasma membrane.	
E)	It would employ a transduction pathway directly from an external messenger.	

____	24)	Which of the following describes the events of apoptosis?
A)	The cell dies, it is lysed, its organelles are phagocytized, and its contents are recycled.	
B)	The cell’s DNA and organelles become fragmented, the cell dies, and it is phagocytized.	
C)	The cell dies, and the presence of its fragmented contents stimulates nearby cells to divide.	
D)	The cell’s DNA and organelles become fragmented, the cell shrinks and forms blebs, and the cell’s parts are packaged in vesicles that are digested by specialized cells.	
E)	The cell’s nucleus and organelles are lysed, and the cell enlarges and bursts.	

The following questions are based on the figure below:

____	25)	Which of the following types of signaling is represented in the figure?
A)	autocrine	B)	paracrine	C)	hormonal	D)	synaptic	E)	long distance	

____	26)	In the figure, the dots in the space between the two structures represent which of the following?
A)	receptor molecules	C)	neurotransmitters	E)	pheromones	
B)	signal transducers	D)	hormones	

____	27)	Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because
A)	they are species specific.	
B)	they always lead to the same cellular response.	
C)	they amplify the original signal manyfold.	
D)	they counter the harmful effects of phosphatases.	
E)	the number of molecules used is small and fixed.	

____	28)	Binding of a signaling molecule to which type of receptor leads directly to a change in the distribution of ions on opposite sides of the membrane?
A)	receptor tyrosine kinase	
B)	G protein–coupled receptor	
C)	phosphorylated receptor tyrosine kinase dimer	
D)	ligand–gated ion channel	
E)	intracellular receptor	

____	29)	In a simple synapse, neurotransmitter chemicals are released by
A)	the dendritic membrane.	D)	cell bodies.	
B) C)	the presynaptic membrane.         axon hillocks.	E)	ducts on the smooth endoplasmic reticulum.	

____	30)	The "threshold" potential of a membrane
A)	is the point of separation from a living to a dead neuron.	
B)	is the lowest frequency of action potentials a neuron can produce.	
C)	is the minimum hyperpolarization needed to prevent the occurrence of action potentials.	
D)	is the minimum depolarization needed to operate the voltage–gated sodium and potassium channels.	
E)	is the peak amount of depolarization seen in an action potential.	

____	31)	A toxin that binds specifically to voltage–gated sodium channels in axons would be expected to
A)	prevent the hyperpolarization phase of the action potential.	
B)	prevent the depolarization phase of the action potential.	
C)	prevent graded potentials.	
D)	increase the release of neurotransmitter molecules.	
E)	have most of its effects on the dendritic region of a neuron.	

____	32)	The following steps refer to various stages in transmission at a chemical synapse.
1.   Neurotransmitter binds with receptors associated with the postsynaptic membrane.
2.   Calcium ions rush into neuron's cytoplasm.
3.   An action potential depolarizes the membrane of the axon terminal.
4.   The ligand–gated ion channels open.
5.   The synaptic vesicles release neurotransmitter into the synaptic cleft.
Which sequence of events is correct?
A)	1 ® 2 ® 3 ® 4 ® 5	D)	4 ® 3 ® 1 ® 2 ® 5	
B)	2 ® 3 ® 5 ® 4 ® 1	E)	5 ® 1 ® 2 ® 4 ® 3	
C)	3 ® 2 ® 5 ® 1 ® 4	

____	33)	Neurotransmitters affect postsynaptic cells by
A)	initiating signal transduction pathways in the cells.	
B)	causing molecular changes in the cells.	
C)	affecting ion–channel proteins.	
D)	altering the permeability of the cells.	
E)	All of these options are correct.	

For the following questions, refer to the graph of an action potential.

____	34)	The membrane potential is closest to the equilibrium potential for potassium at label
A)	A.	B)	B.	C)	C.	D)	D.	E)	E.	

____	35)	The cell is not hyperpolarized; however, repolarization is in progress, as the sodium channels are closing or closed, and many potassium channels have opened at label
A)	A.	B)	B.	C)	C.	D)	D.	E)	E.	

____	36)	What happens when a resting neuron's membrane depolarizes?
A)	There is a net diffusion of Na+ out of the cell.	
B)	The equilibrium potential for K+ (EK) becomes more positive.	
C)	The neuron's membrane voltage becomes more positive.	
D)	The neuron is less likely to generate an action potential.	
E)	The cell's inside is more negative than the outside.	

Unit 5 Summative Questions
Answer Section

MULTIPLE CHOICE

	1)	ANS:	C	PTS:	1	TOP:	Concept 7.1	

	2)	ANS:	A	PTS:	1	TOP:	Concept 7.1	

	3)	ANS:	A	PTS:	1	TOP:	Concept 7.1	

	4)	ANS:	A	PTS:	1	TOP:	Concept 7.1	

	5)	ANS:	C	PTS:	1	TOP:	Concept 7.1	

	6)	ANS:	C	PTS:	1	TOP:	Concept 7.1	

	7)	ANS:	D	PTS:	1	TOP:	Concept 7.1	

	8)	ANS:	B	PTS:	1	TOP:	Concept 7.2	

	9)	ANS:	B	PTS:	1	TOP:	Concept 7.2	

	10)	ANS:	A	PTS:	1	TOP:	Concept 7.2	

	11)	ANS:	C	PTS:	1	TOP:	Concept 7.3	

	12)	ANS:	E	PTS:	1	TOP:	Concept 7.3	

	13)	ANS:	E	PTS:	1	TOP:	Concept 7.4	

	14)	ANS:	C	PTS:	1	TOP:	Concept 7.4	

	15)	ANS:	B	PTS:	1	TOP:	Concept 7.5	

	16)	ANS:	D	PTS:	1	TOP:	Concept 7.1	

	17)	ANS:	A	PTS:	1	TOP:	Concept 7.1	

	18)	ANS:	C	PTS:	1	TOP:	Concept 7.3	

	19)	ANS:	C	PTS:	1	TOP:	Concept 7.3

	20)	ANS:	A	TOP:	Concept 6.1| Concept 6.4| Concept 7.1| Concept 7.5

	21)	ANS:	B	TOP:	Concept 6.1| Concept 6.4| Concept 7.1| Concept 7.5	

	22)	ANS:	C	PTS:	1	TOP:	Concept 7.3	

	23)	ANS:	A	PTS:	1	TOP:	Concept 11.2		

	24)	ANS:	D	PTS:	1	TOP:	Concept 11.5		

	25)	ANS:	D	PTS:	1	TOP:	Concept 11.1		

	26)	ANS:	C	PTS:	1	TOP:	Concept 11.1		

	27)	ANS:	C	PTS:	1	TOP:	End–of–Chapter Questions

	28)	ANS:	D	PTS:	1	TOP:	End–of–Chapter Questions

	29)	ANS:	B	PTS:	1	TOP:	Concept 48.1		

	30)	ANS:	D	PTS:	1	TOP:	Concept 48.2		

	31)	ANS:	B	PTS:	1	TOP:	Concept 48.2		

	32)	ANS:	C	PTS:	1	TOP:	Concept 48.4		

	33)	ANS:	E	PTS:	1	TOP:	Concept 48.4		

	34)	ANS:	D	PTS:	1	TOP:	Concept 48.2		

	35)	ANS:	C	PTS:	1	TOP:	Concept 48.2		

	36)	ANS:	C	PTS:	1	TOP:	End–of–Chapter Questions