Cell Biology Exam #1-2013
Name______Key___________
Lab Section _____________
Multiple choice. Choose the best answer (2 points each).
1.____C_ Measurements show that the pH of a particular lake is 5.0. What is the hydrogen ion
concentration of the lake? a) 5.0 M ; b) 10-9 M ; c) 10-5 M ; d) 105 M ; e) 5%
2.__X-dropped this question___This property of water explains both why water is a good solvent but
also how it plays an important role in evaporative cooling: a) water has a high specific heat; b) water is
cohesive; c) water has a high heat capacity; d) water is less dense as a solid than a liquid; e) water can
hydrogen bond with other water molecules.
3.__C___When an ionic bonded molecule like NaCl is placed in water, it dissociates. Another name for
this process is: a) pH; b) buffer; c) dissolving; d) amphoteric; e) hydrogen bonding
4.___D__If the blood becomes acidic (acidosis), it is a serious medical condition. Which of these
substances or process prevents this from happening? a)cohesion; b) adhesion; c) denaturation;
d) bicarbonate/carbonic acid; e) electronegativity
5.___E__If the pH of a solution in which a molecule is present changes, this attribute (property) of the
molecule may also change: a) its charge; b) shape; c) its function; d) a and c; e) all of the above
6. __B__Carbon has an atomic number of 6. How many bonds must carbon form with other atoms in
order to be stable? a) 2; b) 4; c) 6; d) 1; e) can’t be determined from the given information.
7. __A__Which action could produce a carbonyl group? a) the replacement of the OH of a carboxyl
group with hydrogen ; b) the addition of a thiol to a hydroxyl; c) the addition of a hydroxyl to a
phosphate; d) the replacement of the nitrogen of an amine with oxygen; e) the addition of a
sulfhydryl to a carboxyl
8.__A___
Which molecule above contains an amino functional group but is not an amino acid?
a) A.; b) B; c)C ; d)D; e)E
9.___B__ Thalidomide and L-dopa are examples of pharmaceutical drugs that occur as enantiomers, or
molecules that: a) have identical three-dimensional shapes; b) are mirror images of one another;
c) lack an asymmetric carbon; d) differ in the location of their double bonds; e) differ in their electrical
charge.
10.___A__The Cell Theory: a) was proposed prior to (before) the formulation of the Davson-Danielli
model of membrane structure; b) depended on the development of the technology of electron
microscopy ; c) applies to eukaryotic cells but not prokaryotic cells; d) depended on the development of
cell fractionation techniques; e) was proposed by Singer and Nicholson.
11.___B__Plant cells are often larger than animal cells. This is possible because this organelle ____often
occupies a large part of the volume of the plant cell’s cytoplasm, effectively decreasing the volume of
plant cell cytoplasm (thus improving its surface area/volume ratio).
a) mitochondria; b) central vacuole; c) cytoskeleton; d) lysosome; e) nucleus
12.__E__Homogenization and differential centrifugation are essential features of this process used to
study cell structure and function: a) phase-contrast microscopy; b) glycosylation; c) pinocytosis;
d) bioluminescence; e) cell fractionation.
13.___C__This cell organelle contains acid hydrolases and may be genetically programmed to selfdestruct during organismal development or apoptosis: a) Golgi apparatus; b) smooth ER; c) lysosome;
d) nucleolus; e) cytoskeleton.
14.___A__Antibodies are glycoproteins secreted into the blood by white blood cells called Blymphocytes. Which of the following cell organelles would be least involved in the process of antibody
production and secretion? a) contractile vacuole; b) rough ER; c) Golgi apparatus; d) cytoskeleton
system;
e) membrane-bound ribosomes.
15.___D__The structure of this cell organelle is directly tied to its function and involves an inner
membrane which separates two compartments (the matrix and the inner membrane space):
a) nucleus; b) rough ER; c) Golgi apparatus; d) mitochondria; e) basal body
16.___A__The function of this cell structure depends on protein conformational change (including
dyneine walking) stimulated by protein phosphorylation/dephosphorylation:
a) flagella; b) plasmodesmata; c) desmosomes; d) sodium potassium ATPase; e) mitochondrial matrix
17.__C___Intracellular protein sorting (which determines where a protein goes once it is synthesized),
involves adding molecular “address tags” to the protein. This addressing process is typically associated
with the: a) nucleolus; b) central vacuole; c) Golgi apparatus; d) free ribosomes; e) stroma
18.___C__Becasue plant cells have a large central vacuole filled with water, it is essential that they also
have this cell structure: a) chloroplast; b) contractile vacuole; c) cell wall; d) gap junctions;
e)desmosomes
19.___A__This cell structure gives cells of a given organisms a unique “cell signature” which is important
in the processes of tissue rejection and the body’s ability to recognize foreign versus self: a) glycocalyx;
b) middle lamella; c)desmosomes; d) cytoskeleton system; e) endomembrane system.
20.___A__These animal cell structures are basically the equivalent of plasmodesmata in plant cells.
Heart cells have these structures to allow ions to flow from one heart muscle cell to another which
propagates the contraction of heart muscle tissue: a) gap junctions; b) desmosomes; c) glycocalyx;
d) tight junctions; e) intermediate filaments.
21.___E__Cytokenesis and cytoplasmic streaming are functions associated with this cell
structure/organelle: a) cell wall; b) nucleolus; c) endomembrane system; d) chloroplasts;
e) cytoskeletal system
22.__A___ This cell organelle contains enzymes that are involved in lipid synthesis as well as enzymes
involved in drug detoxification (so there is a lot of this cell organelle in liver cells): a) smooth ER;
b) nucleus; c) vesicles; d) matrix; e)plasmodesmata
23.___A__ According to the fluid-mosaic model of cell membranes, which of the following is a true
statement about membrane phospholipids? a) they move laterally (side to side) along the plane of the
membrane; b) they frequently flip-flop from one side of the membrane to the other; c) they occur as an
uninterrupted bilayer with membrane proteins restricted to the surface of the membrane; d) they have
hydrophilic tails in the interior of the membrane.
24.__C___ Cells poisoned so that their ATP manufacturing system cannot work are unable to maintain a
proper sodium-potassium balance. Which of the following methods must be involved in maintaining
sodium-potassium balance in the cell? a) diffusion; b) facilitated diffusion; c) active transport;
d) exocytosis; e) endocytosis.
25.___E__ Which of the following statements about the Na+/K+ ion pump is false?
a) it pumps more positive ions out of the cell than into the cell; b) it is important in the functioning of
nerve cells; c) conformational changes resulting from dephosphorylation of the carrier molecule are
involved in its action; d) conformation changes resulting from phosphorylation of the carrier molecule
are involved in its action; e) it moves ions from their high to low concentrations.
26.__C___ People with a genetic defect (hypercholesterolemia) that results in a very high concentration
of cholesterol in their blood have a defect in this cellular transport process: a) pinocytosis; b) exocytosis;
c) receptor mediated endocytosis; d) phagocytosis; e) active trasnport
27.___B__ Some protozoans have special organelles called contractile vacuoles that continually
eliminate excess water from the cell. The presence of these organelles tells you that the environment:
a) is isotonic to the protozoan b) is hypotonic to the protozoan c) is hypertonic to the protozoan
d) contains a higher concentration of solutes than the protozoan e) both c and d
28.___E__Proton pumps: a) actively transport H+ ions; b) are coupled to a sucrose co-transport system
in plants; c) can be used an energy source to power flagella in prokaryotic cells; d) move H+ ions from
areas of low to high concentration; e) all of the above are correct.
29.__C___ Facilitated diffusion differs from simple diffusion in that facilitated diffusion: a) moves
substances from areas of low to high free energy; b) is a spontaneous process; c) requires the presence
of a "carrier molecule"; d) is primarily responsible for moving water into cells; e) moves ions against
their concentration gradient (from low to high concentration).
30.___C__ Which of the following is a reasonable explanation for why unsaturated fatty acids help keep
any membrane more fluid at lower temperatures?
a) Unsaturated fatty acids have a higher cholesterol content.
b) Unsaturated fatty acids permit more water in the interior of the membrane.
c) The double bonds form a kink in the fatty acid tail, forcing adjacent lipids to be further apart.
d) The double bonds block interaction among the hydrophilic head groups of the lipids.
e) The double bonds result in a shorter fatty acid tail.
31.__B___ In what way do the membranes of a eukaryotic cell vary?
a) Phospholipids are found only in certain membranes ; b) Certain proteins are unique to each
membrane; c) Only certain membranes of the cell are selectively permeable; d) Some membranes have
hydrophobic surfaces exposed to the cytoplasm, while others have hydrophilic surfaces facing the
cytoplasm.
32.__E___ Receptor mediated endocytosis: a) is a form of active transport; b) is a form of facilitated
diffusion; c)describes the method by which vacuoles from the ER fuse to the membranes of the Golgi
apparatus ; d) is a specialized type of exocytosis; e) is a way to transport specific substances from the
environment in to the cell.
33. (4 points each). Agree or disagree with the following statements. In either case, fully defend your
answer.
A. The only basis of the selective action of antibiotics (they kill bacteria but not human cells) is the result
of bacteria having cell walls while human cells do not.
Disagree-While one class of antibiotics (including penicillins) selectively degrade bacterial cell walls,
(which bacteria have and humans don’t), there is a second major class of antibiotics. These antibiotics
(including tetracyclines) selectively kill bacteria because they inhibit protein synthesis on 70 s
ribosomes (bacteria) but not on 80 s ribosomes (human cytoplasmic ribosomes).
Note-many people seemed to have confused antibiotics and antiobodies.
B. There are at least 2 conformational changes that must take place in the Na+/K+ ATPase membrane
protein in order for this pump to carry out its intended function.
Agree-There are several (more than 2) conformational changes. These include:
A. When sodium binds to the ATPase, it changes shape so that the ATPase activity is acitvated and
ATP is hydrolyzed.
B. When ATP phosphorylates the pump, the carrier openS outside and the sites that bind sodium
change shape so sodium is released. Sites that bind K+ also change shape so now K+ can bind.
C. When K+ binds to the pump, the pump changes shape so it loses a phosphate (its
dephosphorylated).
D. When the pump is dephosphorylated, it openS inward and the shape of its K+ sites changes so the
K+ can no longer bind and the shape of its Na+ sites change so that Na+ can now bind.
Note-I told them in class that they would have to be able to describe at least 2 of these
conformational changes for the exam.
C. The fact that water is a molecule with poplar covalent bonds between hydrogen and oxygen helps to
explain why water is so essential to so many life processes.
Agree-Because water has poplar covalent bonds, Oxygen has a slight negative charge and Hydrogen a
slight positive charge. This allow water molecules to hydrogen bond. Hydrogen bonding is
responsible for most of the properties of water that sustain life including high heat of vaporization,
high heat capacity, cohesion, adhesion, and ice floating.
D. A chloroplast’s structure is directly related to the chloroplast’s function.
Agree-Chloroplasts function is photosynthesis which involves converting light energy into chemical
bond energy. This requires chlorophyll and the ability to make ATP by chemiosmosis. The structure
of the chloroplast allows this. Internal membranes , thylakoids (where the light absorbing chlorophyll
is attached) are numerous and stacked (grana) to give lots of surface area for chlorophyll molecules.
The space inside the thylakoid membrane is separated from the stroma by the thylakoid membrane (2
compartments separated by a space) which allows ATP to be produced by chemiosmosis.
34. (10 points). What roles do white blood cells play in your body? Describe 4 cellular structures
(organelles or systems) that are involved in white blood cell function and explain how the
organelle/system you are describing contribute to these white blood cell functions.
White blood cells play a protective role in your body by destroying invading bacteria and
virus as well as cancer cells. They do this by 1) phagocytosis (engulfing) and 2) producing
antibodies.
Any 4 of the following cellular structures would be acceptable.
The following cell organelles play a role in phagocytosis:
a) cytoskeletal system which allows the cell to move by crawling (amoeboid movement)
b) mitochondria which produce ATP necessary for amoeboid movement
c) Vacuoles which contain the engulfed material and are produced by endocytosis
d) lysosomes, which fuse with the engulfed vacuoles and release digestive enzymes that
break down the engulfed material
The following cell organelles play a role in antibody production:
a) the nucleus contains the antibody genes
b) RER produces the antibody and may slightly modify it
c) vesicles transport the antibody to the Golgi
d) the Golgi modifies the antibody by glycosylating it.
e) the mitochondria makes ATP necessary for synthesizing the antibody (translation) or
cell movement.
Note-This questions was on the cell web site on Exam #1 2010
35. (10 points). A) Describe what it means when we say a membrane is fluid? B) Why is it important for
a membrane to maintain a proper level of fluidity? C) What is a specific piece of experimental evidence
that demonstrates that cell membranes are indeed fluid? D) Specifically describe 2 factors that
determine how fluid a membrane is and explain how they do so.
A. A fluid membrane is a dynamic not a static structure (like dialysis tubing). It can change
composition and its components phospholipids and proteins (at least those that aren’t anchored to
the cytoskeleton) are free to move within the bilayer.
B. If a membrane were not fluid, it would lose its selective permeability. Also, dynamic processes like
endo/exocytosis could not occur.
C. Experimental evidence that demonstrates fluidity includes physical measurements of phospholipid
molecules in the bilayer (1 um sec) and the mouse human cell fusion experiments (with green and red
fluorescently labeled proteins).
D. As temperature increases, fluidity increases and as temperature decreases, fluidity decreases. The
ratio of sat/unsat phospholipids helps to regulate fluidity. The more unsat phospholipids, the more
fluid the membrane (this is important at colder temperatures). Cholesterol allows buffers fluidity by
restricting phospholipid movement at high temperatures and preventing phospholipid packing at
lower temperatures. If a membrane were not fluid, it would lose its selective permeability. Also,
dynamic processes like endo/exocytosis could not occur.
Note-This questions was on the cell web site on Exam #2 2010 ( I warned that that they
should look at both exam #1 and 2 since cell membranes was covered on exam 2 on the old
exams)
Bonus (not optional points)-Each question is worth 1 point. The total bonus points are determined by
subtracting the number of questions answered incorrectly (X 0.5) from the number of correct answers
(an unanswered question is not counted as being incorrect). Therefore, there is a penalty for guessing
when your bonus points are determined. However, the lowest grade you can get on the bonus
section is 0 (so it can’t hurt your final exam score). Any bonus you receive on this exercise will be
added to your final grade.
Synaptic transmission of a nerve impulse between 2 neurons begins when Na+ moves into
the cell, causing depolarization of the axon-terminal membrane. Membrane depolarization in
turn causes the voltage-regulated Ca2+ channel proteins to change from the closed to the open
conformation. The opened channels allow Ca2+ to enter the axon terminal passively, following
the existing Ca2+ gradient (Figure 1). Membrane hyperpolarization caused by the outward flux
of K+ ions, closes the Ca2+ channel.
The neurotransmitter is synthesized and packaged into vesicles by the neuron's
endoplasmic reticulum and Golgi apparatus. Vesicles containing neurotransmitter molecules are
located near the cytoplasmic side of the presynaptic membrane of the axon. The protein
synapsin is thought to hold the vesicles near the presynaptic membrane by attaching them to
microtubules and microfilaments (Figure 1). Elevated Ca2+ levels in the cytoplasm cause release
of the vesicles from the cytoskeleton. The vesicles then undergo exocytosis; that is, they fuse
with the presynaptic membrane, burst open, and release their contents into the synaptic cleft.
_____1.All of the following are required for neurotransmitter release EXCEPT:
a. microtubules and microfilaments; b. synapsin; c. elevated Ca2+ levels; d. closed
Ca2+ channels.
_____2.A neuron that is exposed to a Ca2+ channel blocker will be: a. unable to hyperpolarize;
b. unable to depolarize; c. able to hyperpolarize, but no Ca2+ will enter the presynaptic
membrane; d. able to depolarize, and Ca2+ will enter the presynaptic membrane.
_____3.Synaptic transmission of a nerve impulse is important because it allows the impulse to be
transmitted: a. in 1 direction only; b. in many directions at once; c. more rapidly than
by electrical transmission; d. whether or not electrical transmission is occurring.
____4. Which of the following experimental observations would provide the best evidence that
synapsin is necessary for exocytosis? a. synapsin is found only in neurons; b. synapsin
is found in other cell types known to export material by exocytosis; c. the rate of
exocytosis is directly correlated with the amount of synapsin present per cell; d. a
mutant cell line of neurons lacks only synapsin and is incapable of exocytosis.
____5. The exocytosis of a neurotransmitter vesicle involves all of the following processes
EXCEPT: a. initial packaging of the neurotransmitter into vesicles at the Golgi
apparatus; b. fusion of the microtubules with the presynaptic membrane; c. opening of
the Ca2+ channel; d. attachment of the neurotransmitter vesicles to the cytoskeleton.
____6. What is the most likely function of synapsin in the process of neurotransmitter release?
a. to prevent premature exocytosis by binding secretion vesicles to cytoplasmic
structures; b. to make the secretion process independent of diffusion; c. to decrease the
dependency of the synaptic process on Ca2+; d. to initiate the synthesis of vesicles
containing neurotransmitter.