Princeton WB BIOL

MCAT SciENCE WoRKBOOK
TABLE OF CONTENTS

PERIODIC TABLE OF THE ELEMENTS .......................................................

4

BIOLOGY
QuESTIONS AND PAssAGEs .................•....................•..•..••....•.•.•.....•
SOLUTIONS..............................................................................

5

139

PHYSICS
QuESTIONS AND pAS SAGES ......••....•...............•..•......•..•..•.......•....

223

SoLUTIONS ..............................................................................

353

GENERAL CHEMISTRY
QuESTIONS AND PASSAGES .........................................................

431

SoLUTIONS .....•...•..•.•.....•.......•..•........•......•........•...•....•.•..........

569

ORGANIC CHEMISTRY
QuESTIONS AND PASSAGES .........................................................

639

SoLUTIONS ..............................................................................

731

MCAT SciENCE

WoRKBOOK

2


PASSAGE GUIDE
BIOLOGY
Chapter
Number

1
2
3
4

5
6

7

8
9

10

MCAT Biological Sciences Review
MCAT Biology Chapter Title

Corresponding MCAT Science Workbook
Passage Numbers

Molecular Biology
Microbiology
Generalized Eukaryotic Cells
Genetics and Evolution
Nervous and Endocrine Systems
Circulatory, Lymphatic, and Immune Systems
Digestive and Excretory Systems
Muscle and Skeletal Systems
Respiratory and Skin Systems
Reproductive Systems and Development

5, 12, 16, 18, 23,25, 27-32,55
13, 17, 19, 20, 21, 26, 34,35
1,2, 4,6, 7,10,24
33,56,62, 63,64, 65,66
8,9, 15,22,38,39,58,59,67-74
40,42,43,44,45, 46,47,61, 75

14,57, 76, 77,78
41,48,49,50,51,60, 79
52,53,54, 80
3, 11, 36,37,81, 82,83

MCAT Physical Sciences Review
MCAT Physics Chapter Title

Correspond;ng MCAT Science Workbook
Passage Numbers

Kinematics
Mechanics I
Mechanics II
Mechanics Ill
Fluids and Elasticity of Solids
Electrostatics
Electricity and Magnetism
Oscillations and Waves
Sound
Light and Geometrical Optics

11 2

PHYSICS
Chapter
Number
1
2
3

4
5
6
7
8
9

10

4

3-9, 15-18
1Q-13, 19-24
31,32
25-30,33-39
14,40,45,46,48-55
42,43,56,57
41,44,47,58-60

GENERAL CHEMISTRY
Chapter
Number
1

2
3
4
5
6
7

8
9
10

MCAT Physical Sciences Review
MCAT General Chemistry Chapter Title

Corresponding MCAT Sqience Workbook
Passage Numbers

Atomic Structure
Periodic Trends and Bonding
Phases
Gases
Solutions
Kinetics
Equilibrium
Acids and Bases
Thermodynamics
Redox and Electrochemistry

1-4,6,9-18,70
5, 7,19-28,43,72
35,57,59, 60,62, 63,65,66
40,61,64, 67
31,41, 42, 45,68, 69
33,44, 71
29,37,39,46
30,32,34,36,38,47-55

58, 73-78
8,56, 79-91

ORGANIC CHEMISTRY
Chapter
Number

1
2
3

4
5
6

MCAT Biological Sciences Review
MCAT Organic Chemistry Chapter Title

Corresponding MCAT Science Workboo}f
Passage Numbers

Structure and Bonding
Substitution and Elimination Reactions
Electrophilic Addition Reactions
Nucleophilic Addition/Cycloaddition Reactions
Lab Techniques and Spectroscopy
Biologically-Important Organic Chemistry

1,2, 3
4,5, 6, 7,8,9, 10

11, 12, 13, 14, 15, 16, 17, 18
19,20,21,22,23,24,25,26,27-30
31,32,33,34,35
36,37,38, 39,40,41,42,43

3

INTRODUCTION


PERIODIC TABLE OF THE ELEMENTS

r--

r--

2
He
4.0

1

H
1.0
3

4

8

Be

B

c

7

Ll

N

0

6.9

9.0

10.8

16.0

12

13

12.0
14

14.0

11

16

Na

Mg

AI

Sl

23.0

24.3

27.0

28.1

15
p
31.0

.5

19

20

21

22

24

26

27

28

29

Ca

Sc:

Ti

v

2S

K

Cr

Mo

Fe

Co

Nl

Cu

39.1
37

40.1

4.5.0

47.9

.50.9

.55.8

40

41

43

44

58.9
4.5

58.7
46

Kb

Sr

Zr

Nb

Mo

Tc:

Ku

Rh

85 •.5

87.6

39
y
88.9

.52.0
42

54.9

38

91.2

92.9

95.9

(98)

101.1

5.5

.56

57

72

73

74

75

76

Cs
132.9

23

Ba

La*

ur

Ta

w

Ke

Os

137.3

138.9

178.5

180.9
10.5

Db
(2621

183.9

186.2
107
Bb
(262)

190.2

87

88

89

104

Fr

Ka

Act

Kf

(223)

226.0

227.0

(261)

•
t

SCIENCE WORKBOOK

s,

_(263)

108
Hs
(265)

Ar

32.1

3.5 . .5

39.9

32

33

34

3.5

36

As

Se

Br

Kr

63.5

69.7

72.6

74.9

79.0

79.9

83.8

47

48

49

50

51

Pd

Ag

52

Cd

lo

So

Sb

Te

102.9

106.4

107.9

112.4

114.8

118.7

121.8

127.6

53
I
126.9

54
Xe
131.3

77
lr
192.2

78

79

80

81

82

83
81
209.0

85

Po

At

(209)

(210)

86
Rn
(222)

175.0
103

Pt

Au

Hg

Tl

Pb

195.1

197.0

200.6

204.4

207.2

84

109

Mt
(267)

61

62

63

64

Sm

Eu

Gd

140.1

144.2

(145)

150.4

152.0

157.3

65
Tb
158.9

90

91·

92

93

94

95

96

97

Tb

Pa

Np

Pu

Am

Cm

Bk

(243)

(241}

(247)

(237)

Cl

Ge

Pm

238.0

s

31

60

(231)

17

10
Ne
20.2
18

Ga

Nd

u

9
F

19.0

30
Zn
65.4

59
Pr
140:9

58

Ce

232.0

MCAT

106

6

(244)

4

66

67

68

69

Dy
162.5
98

Ho

Er

Tm

164.9

167.3

168.9

70
Yb
173.0

cr

99

100

101

Es

102

Fm

Md

No

Lr

(251)

(252)

(257)

(258)

(259)

(260)

7l

Lu

MCAT BIOLOGY
PRACTICE QUESTIONS AND pAS SAGES

5


Passage 1 (Questions 1-9)
Graph IV

Graph III
Many membrane transport processes are not driven
directly by the hydrolysis of A TP. Instead, they are coupled
to the flow of an ion down its electrochemical gradient. For
example, glucose is transported into some animal cells by the
simultaneous entry of Na •. Sodium ions and glucose bind to
a specific transport protein and enter together. A protein
responsible for the concerted movement of two such species
is called a symport. An anti port carries two species in opposite
directions. The rate and extent of glucose transport depends
on the Na +gradient across the plasma membrane. Sodium
ions entering the cell in the company of glucose are pumped
out again by the Na•tK• A TPase pump.

X

X

time-

time-

Graph V
c

0

·~ .~

~~~

""" c 8

< 8.5

A group of researchers wished to gain information about
a type of bacteria that was known to take in glucose across its
cell membrane by use of a sodium-glucose cotransport
mechanism. The researchers conducted two experiments in
which bacterial cells were placed in glucose-containing media
that differed with respect to relative ion concentration and
ATP content. Glycolysis was inhibited in the cells during
these experiments.

X

time-

Figure 2 Glucose, Na +, and ATP concentrations in
medium

1. Within animal cells, the transport ofNa +'out of the cell
by the Na+fK• ATPase pump involves:

Experiment I:
Bacterial cells with relatively low intracellular sodium
concentration were placed in a glucose-rich medium that had
a relatively high sodium concentration but no ATP. At
regular time intervals, the medium was analyzed for glucose
concentration and sodium concentration. See Figure l.

A.
B.
C.
D.

symport.
antiport.
facilitated diffusion.
active transport.

2. The results of Experiments 1 and 2 suggest that the cells
c

0

':J

e

~si
~8

a 8.s

~
X

time-

take up glucose:
c
0

':J

§

~·-

8§

+
o:l 8
Z u.S

c

A. in exchange for ATP, as long as extracellular
sodium concentration remains constant.

B. in exchange for sodium, as long as ATP
concentration is zero.
C. together with sodium, as long as a favorable sodium
concentration gradient is maintained.
D. together with sodium, as long as extracellular ATP
concentration is increasing.

X

time-

Figure 1 Glucose and N a • concentrations in medium
(no A TP in medium)
3. On the basis of Experiments l and 2, a researcher
hypothesized that all of the cells under study ultimately
depend on energy to operate the sodium-glucose
cotransport mechanism. Is this hypothesis reasonable?

Experiment 2:
Bacterial cells with relatively low intracellular sodium
concentration were placed in a glucose-rich medium that had
a relatively high sodium concentration and that was also rich
in ATP. At regular time intervals, the medium was analyzed
for glucose, sodium, and ATP concentration. See Figure 2.
If radiolabeled A TP is used in this experiment, the majority
of the radiolabel at the end of the experiment is found as ADP
inside the cells.

MCAT

SCIENCE WORKBOOK

A. No; Figure 1 indicates that glucose can cross the
cell membrane indefinitely in the absence of
exogenous energy.
B. No; Figure 2 indicates that extracellular glucose
and A TP concentrations are independent.
C. Yes; Figure 1 indicates that a sodium gradient
drives glucose transport, and Figure 2 indicates
that ATP maintains the sodium gradient.
D. Yes; Figures 1 and 2 indicate that glucose crosses
the ce1l membrane in exchange for phosphate.

6


6. A student postulated that the glucose transport protein
must be located exclusively on the outer surface of the
cell membrane. Is this hypothesis necessarily true?

4. The results of Experiments 1 and 2 indicate that ATP
promotes the cellular uptake of glucose by serving as a
source of:

A.

A.

enzymes.

Yes; transport proteins only occur on the outer
surface of membranes.
Yes; the hydrophobic tails of the lipid bilayer
repel protein molecules.
No; transport proteins are located exclusively on
the inner surface of the lipid bilayer.
No; transport proteins may span the entire width
of the lipid bilayer.

B. metabolic energy.

c.

B.

inorganic phosphate.

D. carbohydrate.

c.

5. If, in Experiment 1, ATP had been added to the medium
at time x, which of the following would represent the
appearance of Graphs I and II?

D.

7. According to Figure 1, as sodium concentration in the

A.

~

~

8
.5

'[

.a8

.!:9

\]
~
~

e
.s
+

::I

]
.5

u

""

B.

.X

~

0

0
::1

time~

~

c.
D.

Graph II

~

e

.5

8. In Figure 1, if the initial Na+ concentration in the
medium were doubled, which graph below would best
depict the glucose concentration in the medium?

+;
~

:§
.X

.X

time-

time~

A.

c.

remain at its original level, because sodium
concentration does not affect glucose
concentration .
increase, because less glucose is transported into
the bacterial cells.
level off, because a sodium gradient is not available
to drive c otrans port.
approach zero, because glucose and sodium are
transported together.

ell

time-

e

A.

6

.X

B.

medium approaches the same concentration found in
the cells, glucose concentration in the medium would:

E!

::I

c.
8

::I

~

~

6
.5
.......
u

""

0

0
::1

:§

]

~

8

~
~

.s

~

~
0

u

u

::I

:§

:§

6

.X

.X

D.
E

:I

Graph I

6
.5

]

8

E

::I

~

.5

.5

u

e

'[

~

0

:I

+

0

:§

ell

u

b

::I

:§

time-

time-

B.
§

.X

.-time-

.X

]

.......

::I

+eli

time-

D.

e

.5

~
0

8

.5

~

~

.X

.X

time-

time-

L

e

.5

u

8
::1

:§
X

time~

7

a

::I

]

v

.X

time-

BIOLOGY


9. Based on the information in the passage, the first step
in the transport of sodium and glucose into a cell is:
A. binding of specific secreted proteins to sodium in
the surrounding medium.
B. direct hydrolysis of ATP in the cytoplasm by the

sodium-glucose cotransporter.
C. direct hydrolysis of ATP on the extracellular
surface by the sodium-glucose cotransporter.
D. binding of specific proteins in the membrane to
sodium and glucose in the surrounding medium.

Passage 2 (Questions 1-7)
Protein synthesis occurs either on free ribosomes or
ribosomes bound to the endoplasmic reticulum (ER).
According to the signal hypothesis, it is the growing
polypeptide that cues the ribosomes to remain free or attach
to the ER. Proteins targetted to the ER, Golgi, lysosomes,
plasma membrane, or to be secreted contain a signal peptide
of 15 or more continuous amino acids. These N-terminus
signal peptides are responsible for the co-translational
insertion of the growing polypeptide into the membrane of
the ER. After the leading end of the protein is inserted into
the ER lumen, the signal peptide is cleaved by an enzyme.
Proteins destined for the secretory pathway are packaged
into vesicles that pinch off from the membrane of the ER and
fuse with the cis face of the Golgi apparatus. Often the
, packaging of a protein into a transport vesicle requires the
. presence of a region on the protein that is recognized by a
receptor in the Golgi membrane. This receptor-protein
complex will localize to a vesicle and target the vesicle to its
destination.
One of the best-characterized pathways of vesi_cular
transport involves proteins destined to become lysosomal
enzymes. These proteins carry a unique mannose-6-phosphate
(M6P) marker that is recognized by the specific M6P receptor

in the membrane of the Golgi apparatus. M6P receptors bind
proteins and sequester them along one region of the Golgi
membrane, facilitating their packaging into vesicles. Once
the vesicle has budded from the Golgi apparatus, it travels to
the lysosome, where it fuses with the lysosomal membrane.
The M6P receptor releases its bound protein when it
encounters the acidic pH of the interior of the lysosome. The
acidity of the lysosome also activates lysosomal enzymes.

1. Proteins that are to be secreted pass through what series
of organelles?

A.
B.
C.
D.

ER ----) Golgi ----) lysosomes ----) plasma membrane
ER ----) Golgi ----) secretory vesicles
cytoplasm ----) Golgi ----) ER ~.secretory vesicles
ER ~ secretory vesicles ~ lysosomes

2. Where in the cell would the M6P receptor be transcribed?
A.
B.
C.
D.

In
In

In
In

the
the
the
the

nucleus
cytoplasm
rough ER
Golgi


Passage 3 (Questions 1-6)

3. The transport of proteins to the lysosomes requires
which of the following?
A.
B.
C.
D.

The circulation of a fetus differs from that of a newborn
infant in several important aspects.

Acidic pH in the ER
Vesicle movement from the roughER to the Golgi
Endocytosis
Inhibition of signal peptidase

First, unlike an infant's anatomy, fetal anatomy does not
provide direct contact between the fetus and the external
environment. The lungs of the fetus are collapsed and fluidfilled, and do not function in respiration. Fetal respiration,
nutritional and excretory functions are all performed by the
placenta, which is essentially composed of interwoven fetal
and maternal capillaries. Maternal blood, however, does not
normally mix with fetal blood.

4. Which of the following enzymes would be expected to
function well within an acidic environment?
A.
B.
C.
D.

Signal peptidase
Trypsin
Pepsin
Pancreatic lipase

Second, both sides of the fetal heart supply blood to the
systemic circulation; hence, they work largely in parallel,
rather than in series as in an infant. While the lungs are fluidfilled, the pulmonary vascular resistance is higher than the·
systemic vascular resistance. Shunts between the left and
right atria· and between the great arteries permit most of the
blood to bypass the lungs.

5. Which of the following processes would be disrupted in
a cell that failed to label proteins with the M6P marker?

A.
B.
C.
D.

Intracellular digestion of macromolecules
Protein synthesis
Oxidative phosphorylation
Golgi formation

Third, the fetus exists in hypoxic conditions relative to
those that exist after birth. To reach the fetal blood, oxygen
must diffuse through the placenta from the maternal blood
which has already oxygenated a substantial portion of
maternal body tissue. The blood that perfuses the fetus is
about 67% saturated with oxygen. In the normal person. this
is the approximate saturation of mixed venous blood returning
to the lungs to be oxygenated. Blood that leaves the lungs of
the normal adult is about 95% to 98% saturated with oxygen.
The lowest oxygen saturation of blood in the fetal circulation
occurs in blood in the lower inferior vena cava. In the fetal
lamb, which furnishes a good model for the study of human
fetal circulation, oxygen saturation of blood in the lower
inferior vena cava is 26%. Blood in the superior vena cava,
which comes mostly from the head, is only 31% saturated in
the human fetus.

6 •. If a protein that is destined to become a lysosomal
enzyme were synthesized without a signal peptide, in
which of the following cellular regions would it

ultimately reside?
A.
B.
C.
D.

The
The
The
The

cytosol
cell surface
mitochondria
peroxisomes

7. The ER lumen corresponds most closely to which ofthe
following compartments?
A.
B.
C.
D.

The
The
The
The

The fetus has two adaptations for survt vmg relative
hypoxia: its cellular enzymes can function at low oxygen

tensions, and fetal hemoglobin can deliver oxygen to the
tissues despite low levels of oxygen saturation. These special
properties are lost within a few days after birth, when normal
respiratory activities begin.

interior of the nucleus
cytoplasm
extracellular environment
intermembrane space in mitochondria

The brain of the human fetus is large relative to the rest
of the body, and its supply of oxygen is very important. The
fetal brain is perfused with highly-saturated blood from the
left ventricle. The output of the right ventricle, which is less
saturated, supplies the limbs and internal organs of the fetus.

9

BIOLOGY


l. At the placenta, C0 2 should normally:

5. Blood delivered to the fetus has a lower oxygen
concentration than does blood leaving the adult lung
because, before it reaches the placenta, maternal blood:

A. diffuse from the fetal side to the maternal side.
B. diffuse from the maternal side to the fetal side.
C. be of equal concentration on both the maternal and

fetal sides.
D. be of higher concentration on the maternal side
with no net diffusion between the maternal and
fetal sides.

A. mixes with fetal blood of lower oxygen
concentration.
B. releases oxygen to the mother's own tissues.
C. gives up nutrients to the fetal circulation.
D. must pass through the right atrium and ventricle.

2. Some children persist in forming fetal hemoglobin for
months or even years after birth. Such children would
likely:

6. Which of the following chambers of the fetal heart
supply blood to the systemic circulatory system?
A.
B.
C.
D.

A. be able to withstand environments having low
oxygen content.
B. be able to shunt blood from the right to the left side
of the heart.
C. be unable to survive in the absence of an artificial
oxygen supply.
D. be unable to bear children.

3. A newborn infant is able to survive the loss of fetal
hemoglobin within a few days after birth because the
infant's:
A. blood continues to bypass the fluid-filled lungs.
B. circulatory system is independent of the mother's.
C. lungs have direct contact with oxygen in the
environment.
D. digestive and excretory systems become active.

4. In a pregnant woman with healthy lungs but impaired
circulation, her fetus may be at risk of suffering birth
defects because:
A. the placenta will show increased material perfusion.
B. the fetus cannot tolerate any compromising of the
blood supply to its internal organs.
C. the maternal alveoli may be deficient in oxygen
partial pressure.
D. fetal oxygen supply depends on maternal
circulation.

MCAT

SciENCE WoRKBOOK

10

Right atrium and right ventricle
Right atrium and left atrium
Left ventricle and right ventricle
Left ventricle and right atrium

Passage 4 (Questions 1-6)

1. Across which of the following cell types would the
inward diffusion of water be most pronounced under
normal conditions?

The selective permeability of cell membranes plays an
important role in regulating the intracellular environment.
Ions can be transported across cell membranes by passive,
active, or facilitated processes.

A.
B.
C.
D.

Ionophores are small hydrophobic molecules that dissolve
in the lipid bilayer and increase its ion permeability. Most
are synthesized by microorganisms, presumably as biological
weapons, and some have been used as antibiotics. They have
been widely employed by cell biologists to increase membrane
permeability to specific ions in studies on synthetic bilayers,
cells, and cell organelles.

Epithelial cells of the stomach
Epithelial cells of the large intestine
Endothelial cells of the alveolar capillaries
Cornified cells of the skin

2. If, in Experiment 1, the cells were placed in a hypotonic
medium, and if the cells were permeable to water and
magnesium, then the cells would most likely have:
A. increased in calcium concentration to compensate
for a deficit in positive charge.
B. decreased in calcium concentration by intake of
water.
C. decreased in size by losing both calcium and
magnesium ions.
D. decreased in size by losing water passively along
a concentration gradient.

It is known th.at ionophores may be substance-specific.
That is, a given ionophore may promote cell membrane
permeability to one substance, but not to another.
An investigator sought to learn more about the characteristics of a particular ionophore termed Ionophore A.
Experiment 1:
Cells with relatively high internal calcium concentration
and low internal magnesium concentration were placed in an
aqueous medium of relatively low calcium concentration and
high magnesium concentration.

3. A graduate ~tudent suggested that a neuron at resting
potential might be induced to undergo an action potential
by exposure to a sodium-specific ionophore. Is this a
reasonable hypothesis?

After several seconds had elapsed, the cells' internal ion
concentrations were evaluated, and it was found that internal

concentrations of calcium and magnesium had remained the
same.

A. Yes, the ionophore would excite a threshold
reaction in· the neuron's Schwann cells.
B. Yes, an action potential occurs when threshold
depolarization causes voltage-gated channels to
open.
C. No, an action potential requires a reduced
permeability to sodium ions.
D. No, an action potential is triggered by active
transport of sodium along the myelin sheath.

Experiment 2:
Experiment 2 was identical to Experiment 1 except that
the cell medium was infused, also, with Jonophore A.
The cells' internal ion concentrations were evaluated,
and it was found that the internal concentration of calcium
had remained the same but that the internal concentration of
magnesium had increased substantially.

4. If, in either Experiment 1 or Experiment 2, the cells had
decreased their internal concentration of magnesium, it
would indicate that they had undergone a process in
which:
A. ATP had been converted to ADP.
B. Ca 2+ entered the cell.
C. carbohydrates had been synthesized.
D. voltage.,.gated ion channels had opened.

11

BIOLOGY


..
S. The results of Experiments 1 and 2 would most justify
the researcher's conclusion that:

Questions 1 through 11 are NOT based on a
descriptive passage.

A. Ionophore A would not be a useful antibiotic.
B. lonophore A is specific to positively-charged ions,
since it altered sodium permeability but not
magnesium permeability.
C. ionophores facilitate movement only in accordance
with existing concentration gradients.
D. in order to be effective, ionophores require the
active assistance of the cell's sodium-potassium
pump.

1. All of the following are key processes in the production
of energy in the mitochondrion EXCEPT:
A.
B.
C.
D.

2. When it is time to breed, salmon travel from saltwater,

in which they are hypotonic, to freshwater, in which
they are hypertonic. They maintain solute balance by
reversing their osmoregulatory machinery when moving
between the two environments. Failure to reverse this
machinery when moving to their breeding grounds would
most likely result in:

6. If a given cell were persistently engaged in active
transport, its cytoplasm would most likely be rich in:
A.
B.
C.
D.

glycolysis.
the citric acid cycle.
electron transport.
oxidative phosphorylation.

smooth endoplasmic reticulum.
lysosomes.
centrioles.
mitochondria.

A. death, as cells became too concentrated to carry
out normal metabolism.
B. death, as cells underwent lysis due to water influx.
C. improved metabolic activity, as enzyme
concentrations increased.
D. no change, because movement from a hypertonic

to a hypotonic medium does not present osmotic
challenges.

3. A hormone is discovered that rapidly accumulates inside
renal cells in the absence of endocytosis when
administered to mice intravenously. The hormone is
most likely a:
A.
B.
C.
D.

polypeptide.
steroid.
second messenger.
neurotransmitter.

4. The ratio of guanine-cytosine (G-C) pairs to adeninethymine (A-T) pairs is useful in laboratory manipulation
of double-stranded DNA. If a segment of DNA has a
low G-C: A-T ratio, it would be reasonable to assume
that this segment would:
A. contain more guanine than cytosine.
B. contain more adenine than thymine.
C. require more energy to separate the two DNA
strands than would a comparable segment of DNA
having a high G-C : A-T ratio.
D. require less energy to separate the two DNA strands
than would a comparable segment of DNA having
a high G-C : A-T ratio.

MCAT

SciENCE WoRKBOOK

12


5. What organelle would be most closely associated with
exocytosis of newly synthesized secretory protein?
A.
B.
C.
D.

9. In Kartagener' s syndrome, defective dyne in is produced
causing a paralysis of microtubule-based movement of
flagellae and cilia. One could expect to find all of the
following outcomes EXCEPT:

Lysosomes
Golgi apparatus
Peroxisomes
Ribosomes

A.
B.
C.
D.

6. It is known that the developing frog embryo requires

greater protein production than the adult organism. If
cells from a developing frog embryo and from a mature
frog were examined, would the investigator find the
greater rate of translation in cells of the embryo or of
the adult?

10. If erythrocytes are placed into a hypertonic solution,
they will:
A.
B.
C.
D.

A. Embryo, because a developing organism requires
a higher rate of translation than does an adult
B. Embryo, because ribosomal production is not yet
under regulatory control by DNA
C. Adult, because ribosomal production is more
efficient in a mature organism
D. Adult, because a mature organism has more
complex metabolic requirements

hemolyze.
remain the same.
swell up.
shrivel.

11. A codon is a segment of an mRNA molecule that codes
for one amino acid in a polypeptide chain formed
during protein synthesis. Which of the following

correctly describes the chain of events that occurs in
the synthesis of a polypeptide?

7. Colchicine is a compound which interferes with the
formation of microtubules. Which of the following
would be affected LEAST by the administration of
colchicine?
A.
B.
C.
D.

male infertility.
ectopic pregnancy in women.
chronic lung infections.
failure to ovulate in women.

A. Specific RNA codons cause amino acids to line up
in a specific order; tRNA anticodons attach to
mRNA codons; rRNA codons cause protein
molecules to cleave into specific amino acids.
B. DNA generates mRNA in the nucleus; mRNA
moves to the cytoplasm and attaches to a tRNA
anticodon; an operon regulates the sequence of
events that causes amino acids to line up in their
appropriate order.
C. DNA generates tRNA; the tRNA anticodon attaches
to the mRN A codon in the cytoplasm; tRNA is
carried by mRNA to the ribosomes, causing amino
acids to join together in a specific order.

D. DNA generates mRNA; mRNA moves to the
ribosomes, where a tRNA anticodon binds to an
mRNA codon, causing amino acids to join together
in their appropriate order.

Mitotic spindles
Flagellae
Organelle movement
Amoeboid motility of cells

8. Clathrin, a substance that aggregates on the cytoplasmic
side of cell membranes, is responsible for the
coordinated pinching off of membrane in receptormediated endocytosis. A lipid-soluble toxin that
inactivates clathrin would be associated with:
A. reduced delivery of polypeptide hormones to
endosomes.
B. increased secretion of hormone into the
extracellular fluid.
C. increased protein production on the rough
endoplasmic reticulum.
D. an increase in ATP consumption.

13

BIOLOGY


Passage 5 (Questions 1-8)

1. The reaction of glucose-6-phosphate to ribulose-5-

phosphate is a(n):
The pentose phosphate pathway (PPP) produces ribose5-phosphate from glucose-6-phosphate, and generates
NADPH, which is used by the cell in biosynthetic pathways
(such as fatty acid biosynthesis) as a reducing agent. Ribose5-phosphate is converted to 5-phosphoribosyl-1pyrophosphate (PRPP) by the enzyme ribose phosphate
pyrophosphokinase. PRPP is an essential precursor in the
biosynthesis of all nucleotides. Ribose phosphate
pyrophosphokinase is inhibited by high levels of both purine
or pyrimidine nucleotides. The committed step in purine
nucleotide synthesis is catalyzed by the enzyme
amidophosphoribosyl transferase, which uses glutamine and
PRPP as substrates. This enzyme is inhibited by AMP and
GMP and is activated by high concentrations of PRPP. An
intermediate in purine biosynthesis is inosine monophosphate
(IMP). The conversion of IMP to AMP is inhibited by AMP,
and the conversion of IMP to GMP is inhibited by GMP. An
essential precursor in pyrimidine biosynthesis is carbamoyl
phopshate, which is generated by the enzyme carbamoyl
phosphate synthase. This enzyme is inhibited by UTP and
activated by ATP and.PRPP. The production of CTP from
UTP is inhibited by CTP. These reactions are summarized in
Figure 1.

A.
B.
C.
D.

2. Synthesis of which of the following are subject to endproduct inhibition?

A. ATP and GTP only
B. UTP and CTP only
C. ATP, GTP, and CTP only
D. ATP. GTP, CTP, and UTP

3. The presence of high concentrations of ATP stimulates
produetion of:
A. ribose-5-phosphate.
B. pyrimidines.
C. purines.
D. both pyrimidines and purines.

4. Which of the following is the balanced equation for the
conversion of 1 mole of glucose-6-phosphate (G6P)
into PRPP?

2NADPH+2W

___

Glucose-6-P --)>__::~~<(c:;._

Ribulose-5-P
A. G6P + ATP

C
H20

ppp

Xylutose-5-P

~

PRPP +AMP

B. G6P + H20 + 2 NADP•-+
PRPP + C0 2 + 2 NADPH + H•

C. G6P + H20 + 2 NADP• + ATP ~
PRPP + C0 2 + AMP+ 2 NADPH + 2 H•

Fructose-6-P ----/-=-=~--­ RibOse-5-P
Glyceraldehyde-3-P

carboxylation of G6P.
reduction of G6P.
oxidation of G6P.
isomerization of G6P.

~

ATP Ribose
·
phosphate
pyrophosphokinase
AMP

D. G6P

+ H 20 + 2 NADP• + ATP ~
PRPP + glyceraldehyde-3-phosphate +
F6P + C0 2 + AMP+ 2 NADPH + 2 H+

PRPP
(5-Phosphoribosyl-1-pyrophosphate)
S. Which of the following result(s) from the pentose
phosphate pathway?

Glutamine
Carbamoyl
phosphate
synthase

Intermediate 1
(IMP)

~

-

I. Production of NADPH
II. Production of glycolytic intermediates
III. Production of ribose-5-phosphate

ATP

Carbamoyl
phosphate

r,~
GMP) "AMP
CTP

r

C02

A. I only
B. II only
C. I and III only
D. I, II, and III

UTP - - - Intermediate 2

Figure 1 Biosynthetic pathway
MCAT

SciENCE WoRKBOOK

14


Passage 6 (Questions 1-7)

6. According to the diagram, which of the following are
reactants for the production of purines?
A.
B.

C.
D.

The cytoskeleton of eukaryotic cells is composed of three
elements: microtubules, microfilaments, and intermediate
filaments. Microtubules are hollow tubes composed of
tubulin a{J heterodimers and are the largest of the three
cytoskeletal structures. They function in cell structure,
movement of cilia and flagella, transportation of organelles,
and sister chromatid separation during mitosis. They are
anchored to the microtubule organizing center, which contains
the centrioles. Microfilaments are fibrous polymers of the
globular protein actin which are essential for amoeboid
motility, cell-cell adhesion, and contractile processes. The
function of microtubules and microfilaments in the eukaryotic
cell·depends on a dynamic equilibrium between monomeric
and polymerized forms of the proteins. Microtubules and
microfi laments are constantly depolymeri zing and
repolymerizing, and it is thought that this is the mechanism
whereby they mediate motility, for example in the extension
of a pseudopod due to formation of long actin polymers.

Glutamine and PRPP only
Carbamoyl phosphate and PRPP only
Glutamine, carbamoyl phosphate, and PRPP only
Glutamine, C0 2 , ATP, and PRPP only

7. Which of the following is/are true of the pentose
phosphate pathway?

I. It is more active in adipose tissue than muscle.
II. NADPH is produced and can be used to generate
ATP through oxidative phosphorylation.

III. It is a s·eries of isomerizations of six carbon
sugars.
A.
B.
C.
D.

I only
I and II only
II and III only
I, II and III

The following experiment was conducted to study the
functions of microtubules and microfilaments in eukaryotic
cells:

8. It can be inferred from the passage that TTP is made
from:

Three groups of cultured cells were placed in media
containing all necessary growth requirements. To Group A,
nothing was added. To Groups Band C, the drugs cytochalasin
and vinblastine, respectively, were added. Cells were
observed over time for changes in morphology and function.
The results are summarized below:

I. glutamine.
II. carbamo.yl phosphate.

III. intermediate 1.
IV. intermediate 2.
A.
B.
C.
D.

III only
I and II only
I and III only
I, II, and IV only

Group

Drug

Effect

A

None

5% of cells in mitosis at any one time;
normal morphology/function

B

Cytochalasin Cells arrested in cytokinesis;
inhibition of amoeboid motility

c

Vinblastine

.Cells arrested in metaphase of mitosis;
no effect on amoeboid motility

1

1. If mitosis takes one hour, what is the total cell cycle
time for these cells?
A. 5 hours
B. 10 hours
C. 20 hours
D. 50 hours

15

BIOLOGY


6. Which of the following is NOT true of eukaryotic
flagella?

2. The drug cytochalasin affects:
A.
B.

C.
D.

microtubules.
microfilaments.
both microfilaments and microtubules.
Cannot be determined from the information given

A. They are structurally identical to prokaryotic
flagella.
B. They are cytoplasmic extensions with a 9 + 2
arrangement of microtubules.
C. ATP hydrolysis is required for their movement.
D. They are similar in structure to cilia.

3. Which of the following accurately describes the role of
cytoskeletal proteins in mitosis?
I. Microtubules known as polar fibers radiate from
the centrioles to connect with kinetochore fibers,
also composed of microtubules, emanating from
the centromere.
II. Contraction of microtubules is responsible for
formation of the cleavage furrow during
anaphase.
III. After recombination between homologous
chromosomes, homologous chromosomes are
pulled to opposite poles by microtubules.
A.
B.
C.

D.

7. Which of the following best describes the cells of
Group Cas viewed under the microscope?
A. A set of chromosomes can be seen at either end of
the cells; no nuclear envelope is visible.
B. Chromosomes are aligned in the middle of the cell;
no nuclear envelope is visible.
C. The chromosomes are partially thickened, and the
nuclear envelope is partially disintegrated.
D. No. chromosomes are visible, and the nuclear
envelope is fully intact.

I only
I and II only
I and III only
I, II, and III

4. A researcher stains actin of cells in interphase with a
fluorescent anti-actin antibody .. As seen under the
microscope, the fluorescence would be:
A. seen as two star-shaped structures near the nucleus.
B. uniformly dispersed throughout the cell, giving it
an even color.
C. concentrated in the cytoplasm.
D. concentrated solely inside the nucleus.

5. A researcher studies the effect of phalloidin, a chemical
that prevents actin depolymerization. Which of the
following is a likely effect of phalloidin?

A.
B.
C.
D.

MCAT

Inhibition of organelle movement within the cell
Inhibition of mitotic spindle formation
Inhibition of protein synthesis
Cessation of amoeboid movement

SCIENCE WORKBOOK

16


Passage 7 (Questions 1-7)

1. In Experiment 1, the substance in control of G 1 arrest
must be present:

Dividing eukaryotic cells pass through a regular sequence
of growth and division, known as the cell cycle. The cycle
consists of four major phases: mitosis, G I, S, and G2. G 1
is a period of general growth and replication of cytoplasmic
organelles and proteins. In the S phase, chromosomal material
is replicated, and in the G2 phase the structures associated
with mitosis are assembled. See Figure 1.

A. in the nucleus.
B. someplace within the cell, but a more specific
location cannot be determined from this
experiment.
C. outside the cell wall.
D. in the cytoplasm.

2. In Experiment 2, the first sign of mitosis would be:

Cell Division
~

A.
B.
C.
D.

the formation of nuclear membranes.
the disappearance of the nuclear membrane.
condensing of the chromosomes.
splitting of the centromeres.

3. Mitosis occurs in which of the following human cell
types?
I. Primary spermatocyte
II. Bone marrow cells
III. Mature. erythrocytes

Figure 1
A.

B.
C.
D.

The duration of the cell cycle varies from one species to
another, and from one cell type to another. The G I phase
varies the most. For example, embryonic cells can pass
through the GI phase so quickly that it hardly exists. On the
other hand, differentiated skeletal muscle cells and nerve
cells are arrested in the cell cycle and normally do not divide.

II only
I and III only
II and III only
I, II, and III

4. Interphase corresponds to which phase of the cell cycle?
A.
B.
C.
D.

Two experiments were conducted to determine the causes
of G 1 and G2 arrest.

S phase
Mitosis
G l plus S plus G2
Cytokinesis

Experiment 1
The nucleus of a cell in the S phase is removed, and the
nucleus of a cell in G 1 arrest is transplanted into the
enucleated cell in S phase. The transplanted nucleus soon
becomes activated itself and enters the S phase.

S. Which of the following meiotic characteristics does
mitosis share?
A. Crossing over occurs between paired homologues
before they separate into two different nuclei.
B. It occurs only in diploid cells.
C. Each cell divides twice, producing a total of four
cells.
D. Replic~tion of chromosomes occurs prior to
prophase.

Experiment 2
A cell in G2 arrest is fused with a mitotic cell. The
nucleus originally in G2 arrest promptly shows signs of
entering mitosis.
Adapted from Biological Science by William T. Keeton and James L. Gould. Cl986 by W.W.
Norton&. Company, and Biology, by Helena Curtis, Ct983 by Worth Publishers, Inc.

17

BIOLOGY


6. Chloroplasts and mitochondria have their own chromosomes. The genomes of chloroplasts and mitochondria
must replicate during:

A.
B.
C.
D.

the S phase.
the G I phase.
mitosis.
cytokinesis.

7. Which of the following gives the correct order of the
phases of mitosis?
A.
B.
C.
D.

MCAT

Prophase, metaphase. anaphase, telophase
Prophase, anaphase, telophase, metaphase
Anaphase, prophase, metaphase, telophase
Telophase, anaphase, metaphase. prophase

SciENCE WoRKBOOK

18


Passage 8 (Questions 1-8)

1. Treatment of cells with ouabain, an inhibitor of the
Na+fK+ ATPase, causes cells to swell and burst. Which
of the following is the most likely explanation for this?

The Na+/K+ ATPase found in the plasma m.embrane of
cells throughout the body pumps Na+ out of cells and K+ into
cells, using the energy of ATP hydrolysis to drive the transport
of these ions against concentration gradients. Hydrolysis of
one ATP to ADP +Pi drives the transport of 3 Na+ out of the
cell and 2 K+ into the cell at the same time. The Na +JK+
ATPase consists of a catalytic transmembrane subunit with a
molecular weight of 100,000 daltons and an associated
45,000-dalton glycoprotein. The ATP hydrolysis which
fuels the pump can account for a significant fraction of a
cell's energy usage, as great as 70% of the energy needs of
cells that transmit action potentials.

A. Ouabain prevents proteins from leaving the cell.
B. The movement of sodium ions out of the cell is
decreased by ouabain.
C. The movement of potassium ions into the cell is
increased by ouabain.
D. Ouabain also opens potassium leak channels.

2. A drug that blocks the passage of potassium ions through
potassium leak channels would be most likely to have
what effect on the electric potential across the plasma
membrane?

The plasma membrane is impermeable to the passive
diffusion of sodium and potassium ions. However, animal
ce-lls have potassium ion leak channels that allow potassium
ions to diffuse down a concentration gradient out of the cell.
The more potassium that diffuses out of the cell, the greater
the negative charge remaining in the cellular interior. When
the negative transmembrane potential becomes large enough
to counterbalance the K+ concentration gradient and halt the
net flow of K+ ions, the transmembrane electric potential is
the resting membrane potenial. The resting membrane
potential plays a key role in propagating action potentials.
During an action potential, the resting membrane potential
helps to drive sodium movement into the cell and depolarize
the membrane. After depolarization, theN a +JK+ A TPase and
potassium leak channels help to re-establish the resting
membrane potential.

A. The resting membrane potential would become
more negative in the cellular interior relative to
the extracellular environment.
B. The resting membrane potential would become
less negative in the cellular interior relative to the
extracellular environment.
C. The resting membrane potential would become
positive in the cellular interior relative to the
extracellular environment.
D. The drug would have no effect on membrane
potential.

3. The membrane-spanning regions of the ATPase would

most likely consist of amino acids with side groups that
are:

The Na+/K+ ATPase is also important in other processes,
such as balancing the osmotic pressure in the cell with the
extracellular environment. The cell contains many
macromolecular ions such as nucleic acids and proteins. The
net movement of ions out of the cell created by the Na +/K+
ATPase ensures that the osmotic pressure within the cell
created by these ions is not greater than the extracellular
osmotic pressure. The concentration gradient of sodium
created by the Na+JK+ ATPase is also used to drive several
different transmembrane transport processes. In the small
intestine, for example, the absorption of glucose into the
intestinal epithelium against a gradient is driven by
cotransport of sodium down a concentration gradient.

I. hydrophobic.
II. basic.
III. nonpolar.

A.
B.
C.
D.

19

II only
I and II only

I and III only
I, II, and.-III

BIOLOGY


4. In isolated membrane-bound vesicles composed of
plasma membrane from human cells, the Na +fK+ ATPase
can synthesize ATP if the concentration of ions is
manipulated. If the exterior vesicle surface is equivalent
to the exterior surface of the plasma membrane, which
of the following conditions will result in ATP production
rather than ATP hydrolysis?

7. Linking ATP hydrolysis to Na +and K+ transport affects
ion transport in which of the following ways?
A. The equilibrium and llG for Na• and K+ transport
are altered.
B. The equilibrium for Na+ and K• transport are not
affected, but !:J.G is made negative.
C. The equilibrium for Na• and K• transport are
altered, but AG remains unchanged.
D. Neither the equilibrium nor llG for Na• and K•
transport is affected.

A. Increased ADP in the exterior and increased ATP
in the interior of the vesicle, with high sodium and
potassium both inside and outside of the vesicle
B. Decreased ADP in the exterior and decreased ATP
in the interior of the vesicle, with high sodium and

potassium both inside and outside of the vesicle
C. Increased K+ in the exterior and increased Na+ in
the interiQr of the vesicle, with ADP and P1 high
both inside and outside of the vesicle
D. Increased K+ in the interior and increased Na+ in
the exterior of the vesicle, with ADP and Pi high
both inside and outside of the vesicle

8. If a single N a+fK+ ATPase were inserted into ·an
artificial membrane impermeable to all ions, with high
concentrations of ATP, N a+, and K+ on both sides of the
membrane, which of the following would result?
I. Substantial ATP hydrolysis on both sides of the
membrane
II. Substantial ATP hydrolysis on only one side of
the membrane, with accumulation of potassium
on the opposite side
III. Substantial ATP hydrolysis on only one side of
the membrane, with accumulation of sodium on
the opposite side

5. The membrane density of the ATPase complex can be
measured experimentally by the binding of a radiolabeled compound. The largest signal would be expected
to come from:
A.
B.
C.
D.

A.

B.
C.
D.

bone marrow.
nerve cells.
epithelial cells.
skin cells.

6. In the generation of the resting membrane potential,
high concentrations of lithium, cesium, rubidium, or
thallium can substitute for potassium outside the cell,
but they cannot substitute for sodium inside the cell.
This suggests which of the following concerning the
Na•JK+ ATPase?
A. The internal ion binding site is specific for sodium.
B. The external ion binding site is specific for
potassium.
C. The Na+JK+ ATPase is poisoned by those ions.
D. The Na+JK+ ATPase performs a vital function in
transporting a wide variety of positive ions.

MCAT

SCIENCE WORKBOOK

20

I only
II only

III only
II and III only


Passage 9 (Questions 1-8)

A. Control

t •

Lipid bilayer membranes are impermeable to passive
diffusion by ions such as chloride (Cl-), sodium (Na+), and
potassium (K+). To diffuse across the plasma membrane,
ions travel through transmembrane proteins that act as ion
channels. Each type of ion channel allows specific ions to
diffuse through the membrane down a concentration gradient.
The frequency and duration of ion-channel opening are
regulated by different receptors in several different ways.
Voltage-gated ion channels open and close in response to
alterations in the electric potential across the plasma
membrane. Ligand-gated ion channels open in response to
the binding of small molecules on the extracellular surface of
the protein. Mechanical stimuli can also trigger the opening
of ion channels. For example, stretch-activated channels
open in response to stretching of the cell and plasma
membrane. Other ion channels, such as potassium leak
channels, are always open.

(/}

.9=

c:J

. . Closed

-

Open

-

4-1

0

.....

s=
11)

4)

>
0

:g

Time------------------------------------~

I•.. I-.

B. More frequent opening

t•
~

r-- r-

r--

r--

r-

-

r-

r--

.9

The net flux of ions across a plasma membrane is related
to the concentration gradient of ion across the membrane and
to the electrical gradient across the membrane. The net flux
of ions is also related to a membrane permeability constant.
The permeability constant describes the ability of ions to
traverse the membrane in a particular state of closing and
opening of ion channels. For a given electrochemical gradient,

the number of ions crossing a membrane through a single
channel depends on how frequently the channel opens and
how long the channel stays open each time. The surface area
of the membrane is also an important determinant in ion flux,
but only when the membrane is significantly permeable to
ions.

-8=

~
11)

>

0

:g
Time------------------------~

- -

C. Longer open interval

t•

The movement of ions across a plasma membrane can be
analyzed by the placement of microelectrodes into the
cytoplasm of cells to measure changes in voltage across the
membrane. In an experiment, the voltage across a section of
membrane was measured either in the absence of a drug

(Figure lA) or with the same section of membrane in the
presence of Drug B (Figure lB) or Drug C (Figure lC). The
increased movement of ions across the membrane in response
to the opening of ion channels is indicated by empty boxes,
and the closing of ion channels is indicated by filled boxes.

•

...
Time------------------~~

Figure 1

1. The difference between Figure lA and Figure lB would
best support which of the following conclusions?
A. Net flux of ions is greater in Figure lB than in
Figure lA.
B. The transmembrane potential is more negative in
the cytoplasm in Figure lA than in Figure lB.
C. The membrane has more ion channels in Figure lB
than in Figure lA.
D. The membrane has more inhibitory ion channels in
Figure lA than in Figure lB.

21

BIOLOGY


2. The concentration of K+ on one side of a membrane

populated by potassium leak channels is 1 m M and
10 mM on the other side. Which of the following will
increase net potassium ion flux across the membrane?

6. Which observation would be the best evidence that
active transport was responsible for moving a particular
substance into a cell?
A. An inverse relationship between the amount of
substance taken in and oxygen uptake
B. A transmembrane protein is required for the
substance to cross the plasma membrane.
C. Equal concentrations inside and outside the cell
D. A correlation between the amount of the substance
taken in and ATP hydrolysis

I. Increasing the K+ concentration on one side of
the membrane from 10 mM to 11 mM
II. Increasing the K+ concentration on both sides of
the membrane by 10 mM
III. Increasing the density of potassium leak
channels in the membrane

A.
B.
C.
D.

III only
I and II only
I and III only

II and III only

7. The following is a graph of the change in concentration
over time of Substance X as it diffuses across the
plasma membrane of a cell:

3. Most animal cells have approximately 27 times more
chloride in the extracellular fluid than in the cytoplasm.
If the plasma membrane of a postsynaptic neuron is
populated with ligand~ gated chloride ion channels which
open in response to binding of GABA (y-aminobutyric
acid). which of the following will occur upon release of
GABA into the synaptic cleft?

concentration
time--

A. The ci- concentration in the cytoplasm of the
postsynaptic cell will decrease.
B. The number of GABA receptors in the postsynaptic
membrane will increase.
C. The postsynaptic membrane will be hyperpolarized.
D. Net ion flux across the presynaptic memrane will
increase.

This curve suggests that:
A. the plasma membrane is permeable to this
substance.
B. this cell is regulating the influx of Substance X.
C. efflux is slow at first~ and increases over time.

D. proteins required for Substance X transport are
inactivated with increasing time.

4. Due to the presence of protein channels, ions such as
Na+, K+, ci-, and Ca2+ diffuse across plasma membranes
at rates that are much faster than would be predicted
from:
A.
B.
C.
D.

8. Neurons often possess acetylcholine-gated sodium
channels. If researchers found that the flow of sodium
across the membrane of a particular neuron under study
is not altered by the presence of acetylcholine, which of
the following is the best explanation?

the fact that they are nonpolar.
concentration differences across the membrane.
their very low solubility in lipids.
net ion flux.

A. The neuron has a different lipid composition in its
plasma membrane.
B. The gene for the acetylcholine-gated ion channel
in the neuron contained a premature stop codon.
C. The cytoplasm of the neuron contains acetylcholine.
D. Sodium is present at a higher concentration in the
extracellular environment than in the neuron's

cytoplasm.

S. The flow of sodium ions down a concentration gradient
across a lipid bilayer membrane is an indication of
which of the following?
A.
B.
C.
D.

MCAT

Simple diffusion
Facilitated diffusion
Osmosis
Active transport

SCIENCE WORKBOOK

22


Passage 10 (Questions 1-8)
Table 2: Combined Effect of Alcohol & Tobacco on RR

Cancer cells are recognized by their ability to escape
normal regulation of cell division, proliferating out of control,
and often invading local tissues or metastasizing to distant
locations. Most cancers are thought to originate from a
single cell which has undergone a change in its genetic

sequence. However, many cancers require two genetic
aberrations. In these cases a defect in the genome is thought
to predispose the cell to malignant transformation, which
then takes place only after further genetic disturbance. Tumor
progression, whereby a benign tumor becomes a malignant
one, is accelerated by mutagenic agents (tumor initiators)
and nonmutagenic agents (tumor promoters). Both types of
agents affect gene expression, stimulate cell proliferation,
and alter the balance of mutant and nonmutant cells.

gAlcohol

Number of Cigarettes per day

per day

0-7

8-15

16-25

26+

Endolarynx
0-40

1.0

7.0

12.9

15.0

41-80

2.8

8.3

16.1

18.7

12.8

24.8

28.9

18.7

36.5

42.5

~

81-120

121+

....

6.3

Epilarynx

The following tables show the relative risks (RR) of
tobacco and alcohol use for cancer of the endolarynx,
epilarynx, and hypopharynx. A relative risk greater than 1.0
indicates increased risk relative to a control group.

0-40

1.0

12.4

17.7

17.9

41-80

9.1

23.9

33.9

34.4

81-120

20.9

54.6

77.6

78.6

121+

45.2

118.3

168.2

170.5

Adap!Cd from ltllerntllional Joumal of C011cer: C011cer of the f.Aryru;l
Hypopho.ryiiX, Tobacco and Alcolwl, 01988

Table 2

1. Based on the passage, tobacco and alcohol would be
classified as:

Table 1: RR for Alcohol & Tobacco by Site

0

1.0

1.0

1.0

1-7

2.5

2.3

5.5

8-15

7.5

6.7

13.7

14.6

11.0

18.0

17.0

9.4

20.0

25
26+

0-20

1.0

1.0

1.0

21-40

0.88

0.87

1.57

41-80

1.08

1.53

3.15

81-120

1.71

5.10

5.59

121+

2.50

10.6

A.
B.
C.
D.

tumor initiators.
tumor promoters.
mutagens.
Cannot be determined from the information given

2. The direct role of tumor initiators is to cause:
A.
B.
C.
D.

changes in the DNA sequence of a cell.
noncancerous cells to become cancerous.
changes in the metastatic potential of a cell.
tumors to develop in normal tissue.

3. The likelihood of cancer in a person consuming 21-40
g/day of alcohol, compared to the likelihood in a
nondrinker, is:

12.5

A. decreased for endolarynx, epilarynx,
hypopharynx.
B. decreased for endolarynx and epilarynx,
increased for the hypopharynx.
C. decreased for endolarynx, but increased
epilarynx and hypopharynx.
D. increased for endolarynx, epilarynx,
hypopharynx.

Table 1

{

23

and
but
for
and

BIOLOGY


4. Upon which site does tobacco have the greatest adverse
effect?
A.
B.
C.
D.

Passage 11 (Questions 1-7)
The eggs of sea urchins and amphibians have two
mechanisms that prevent polyspermy during fertilization,
the fast block and the slow block.

Endolarynx
Epilarynx
Hypopharynx
All three sites are equally affected.

When the cell membranes of the egg and sperm fuse,
sodium channels in the egg cell membrane open, and
depolarization results. This depolarization prevents other

sperm from entering. It is known as the fast block because it
occurs very rapidly and also because the depolarization lasts
less than a minute.

S. Overall, the combined effects of tobacco and alcohol
on the relative risk for cancer are:
A.
B.
C.
D.

additive.
multiplicative.
independent of each other.
mutually antagonistic because alcohol lowers the
risk produced by tobacco consumption.

However, the effects of the depolarization have permanent
results. These are due to ion fluxes that are caused by the
initial depolarization. First. the depolarization leads to an
influx of Ca 2 •. This, in turn, causes the cortical granules to
release proteolytic enzymes, which destroy bindin receptors
in the vitelline layer. The bindin receptors are the cell
surface proteins to which sperm attach, using the acrosomal
protein bindin. Other proteins exocytosed by the cortical
granules crosslink proteins in the vitelline layer, hardening
it, and cause the vitelline layer to move away from the
plasma membrane of the egg. These permanent changes
prevent other sperm from entering the egg, and constitute the
slow block to polyspermy.

6. ·Which of the following may be seen in cancerous cells?
I. Changes in the cell cycle
II. Changes in gene expression
III. Ability to respond to hormonal control

A.
B.
C.
D.

I and II only
I and III only
II and III only
I, II. and III

The second ion flux which results from the initial
depolarization is an exit of protons. A Na+-H+ exchanger in
the plasma membrane exports one proton for each sodium ion
it imports. Alkalinization of the egg cytoplasm results. The
increase in pH is thought to be responsible for activation of
protein synthesis and initiation of DNA replication in the
egg. Drugs known to interfere with translation block initial
protein synthesis in fertilized eggs, but inhibitors of
transcription do not.

7. What is the relative risk for developing cancer of the
epilarynx in an individual who smokes 8-15 cigarettes
per day and drinks more than 121 g of alcohol per day
(compared to a nonsmoking, nondrinker)?

A.
B.

c.

D.

6.7
10.6
18.7
118.3

1. Where are the bindin receptors located in sea urchin
eggs?

8. Each of the following could cause cancer EXCEPT:
A.
B.
C.
D.

A. a mutation in the gene coding for a cell surface
receptor.
B. a mutation in the gene coding for a steroid receptor.
C. an error in translation of a cell-surface receptor.
D. deletion of the gene coding for a receptor's
regulatory subunit.

2. Primary oocytes are found at what stage of meiosis?

A.
B.
C.
D.

MCAT

SCIENCE WORKBOOK

Vitelline layer
Jelly coat
Cortical granules
Perivitelline space

24

Interphase
Meiotic prophase· I
Meiotic anaphase I
Meiotic prophase II


7. Which of the following hormones stimulate(s)
spermatogenesis in humans?

3. Which of the following might result from fertilization
in a medium that had an abnormally low Na+
concentration?

I. LH

II. FSH
III. Testosterone

I. Polyspermy
II. Failure of bindin receptors to be degraded

III. Alkalinization of the cytoplasm of the fertilized
A.
B.
C.
D.

ovum
A.
B.
C.
D.

I only
II only
I and II only
II and III only

III only
I and III only
II and III only
I, II, and III

4. What would be the effect of artificially depolarizing
the plasma membrane of an unfertilized egg?

A.
B.
C.
D.

Polyspermy
Inhibition of fertilization
Inhibition of postfertilization protein synthesis
Adherence of the vitelline layer to the plasma
membrane

5. Which of the following can be inferred from the passage
about postfertilization events in the sea urchin egg?
A. Messenger RNA coding for proteins which are
normally made after fertilization is synthesized
before fertilization occur-s.
B. Special ribosomes are used for initial postfertilization protein synthesis.
C. RNA polymerases are in place at the initiation
sites for transcription of the mRNA for initial
postfertilization proteins before fertilization
occurs, and immediately begin transcribing when
the fertilized egg becomes alkalinized.
D. Ribosomes are not used in the synthesis of initial
post~fertilization proteins.

6. Which of the following is NOT a characteristic of the
acrosomal reaction that occurs in sperm of sea urchins
during fertilization?
A. Actin is polymerized to create an acrosomal process
in the sperm.

B. Hydrolytic enzymes are released that digest the
jelly coat.
C. Specific proteins are exposed that can bind
receptors on the egg.
D. It is mediated by a decrease in intracellular pH and
Ca2+ concentration.

25

BIOLOGY


Passage 12 {Questions 1-8)
Bacterial glycolysis involves the oxidation of simple
sugars, resulting in a net production of ATP. Aerobic bacteria
generate further ATP in a process similar to that which
occurs on the electron transport chain along the mitochondrial
membrane in animal cells. Anaerobic bacteria use some of
the ATP derived from glycolysis to establish a transmembrane
proton-motive force that drives a variety of cellular functions.
Both systems are illustrated in Figure 1.

(A) Aerobic conditions
respiratory chain

Vibrio alginolyticus is an alkali-tolerant marine bacterium
with an internal salt concentration less than that of its normal
surrounding medium. In studying the activity of various
transport systems in V. alginolyticus, researchers devised
the following experiment: One batch of V. alginolyticus was

grown in a sodium-free environment, enriched with
radio labeled lysine, while another batch was exposed to both
hypertonic sodium and radiolabeled lysine. The bacteria
were removed from the media and then analyzed for
radioactivity. The researchers discovered that the uptake of
basic amino acids by V. alginolyticus is dependent on the
activity of the cation-driven transport mechanism shown in
Figure 2. Only the bacteria grown in a sodium-enriched
environment took up the labeled lysine.

A TP synthetase

I

H+

Inside

Outside

Na+
~~------------~rumno

acid

Figure 2

(B) Anaerobic conditions

1. Any conclusions derived from the experiment are

justified only with the assumption that the radioactive
labeling technique:
A. increases the uptake of neutral amino acids.
B. does not affect the transport mechanism.
C. decreases the uptake of aspartate.
D. increases the rate of acidic amino acid uptake.

2. None of the following is supported by the information
in the passage EXCEPT:

Figure 1

MCAT

SCIENCE WoRKBOOK

A. aerobes only import hydrogen ions, while strict
anaerobes must import and export hydrogen ions.
B. anaerobes have an ATP synthetase that is only
active when bound to a phosphate group, whereas
aerobic ATP synthetase is active when it loses a
phosphate group.
C. anaerobic ATP synthetase functions identically to
aerobic ATP synthetase, but anaerobes lack a fully. \.
functioning respiratory chain.
D. aerobes establish a proton gradient to gene.rate
ATP from ADP and inorganic phosphate I while
:If
anaerobes hydrolyze ATP to generate a proton
gradient.