Biology subject test (2)

MCAT Subject Tests
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_________________________________________________________________________ B I O L O G Y S U B J E C T T E S T 2

Biology Subject Test 2

1.

Which of the following is in a different chemical
category than the others?
A.
B.
C.
D.
E.

2.

A portal system

6.

The contractile vacuole of Euglena decreases its rate of
contraction when the organism is transferred from fresh
water to sea water. This is explained by
7.

The chromosome number remains unchanged as a result
of
A.
B.
C.
D.
E.

The distance between linked genes is often measured by

A.
B.
C.
D.
E.

A. an increase in the osmotic pressure of the
environment.
B. a decrease in the osmotic pressure of the
environment.
C. the nitrogenous wastes can remain in the cell
because of a higher salt concentration outside the
cell.
D. excess salts are eliminated without the loss of water.
E. salt inhibits the contractile apparatus.
4.

Which of the following is a correct association?
A. Mitochondria : transports materials from the
nucleus to the cytoplasm
B. Golgi apparatus : modification and glycosylation of
proteins
C. Endoplasmic reticulum : selective barrier for the
cell
D. Ribosome : digestive enzymes most active at an acid
pH
E. Lysosomes : membrane-bound organelles which
convert fat into sugars

Cytosine

Thymine
Arginine
Guanine
Uracil

A. receives blood directly from the aorta.
B. carries blood from one set of capillaries through a
vein to another set of capillaries.
C. always empties into the liver.
D. is present in the walls of the ventricles.
E. links the small intestine and kidney.
3.

5.

probability of crossing over.
frequency of silent mutations.
histone concentrations.
distance between ribosomes on mRNA.
AT/GC ratio.

Disjunction is defined as
A. when the paternal chromosomes separate from the
maternal chromosomes.
B. when homologous pairs of chromosomes
recombine.
C. when the spindle apparatus is formed from the
centrioles.
D. when the cell membrane invaginates to form two
daughter cells.

E. None of the above

Questions 8-12 refer to the choices below

meiosis.
mitosis.
fertilization.
non-disjunction in all gametes formed.
None of the above
8.

A. Copulation
B. Fertilization
C. Meiosis
D. Mitosis
E. Gastrulation
Method of replication for epithelial cells.

9.

Tetrads are formed in this process.

10. Fusion of the nuclei of two gametes.
11. May result in the formation of polar bodies.
12. Results in archenteron formation.
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13. Which of the following is (are) derived from the
mesoderm?
A.
B.
C.
D.
E.

Heart
Lung epithelium
Intestinal mucosa
Nerve
Two of the above

18. PGAL
A. is considered the prime end product of
photosynthesis.
B. can be used immediately as food.
C. can be combined and rearranged to form glucose.
D. can be stored as insoluble polysaccharides such as
starch.
E. All of the above

14. Which of the following is NOT a steroid?
19. During what stage of meiosis does crossing over occur?
A.
B.
C.
D.
E.

Cholesterol
Vitamin D
Testosterone
Thyroxine
Cortisol

A.
B.
C.
D.
E.

Prophase I
Metaphase I
Anaphase I
Telophase I
Interkinesis

15. Which of the following cells produce antibodies?
20. The blood group antigens are an example of
A.
B.
C.
D.
E.

Macrophages
B cells
T cells

Neurons
Natural Killer cells

16. The rate of an enzyme catalyzed reaction can be
influenced by all of the following EXCEPT
A.
B.
C.
D.
E.

Substrate concentration
Temperature
Enzyme concentration
Rate constant
pH

17. What is the probability of a white, long tailed mouse
from the cross of a heterozygous black, heterozygous
long-tailed mouse with a homozygous recessive white,
homozygous recessive short tailed mouse?
A.
B.
C.
D.
E.

2

0%

25%
50%
75%
100%

A.
B.
C.
D.
E.

pleiotropy.
incomplete dominance.
codominance.
epistasis.
incomplete penetrance.

21. Sex-linked traits such as hemophilia and colorblindness
A.
B.
C.
D.
E.

are located on autosomes.
are always dominant.
are found in genetic bottlenecks.
have been selected out of the population.
are rarely seen in females.

22. Cell division
A. is a mechanism by which a cell halves its organelles
and cytoplasm.
B. does not involve DNA replication.
C. is a way for multicellular organisms to grow,
develop, and repair.
D. is also known as mitosis.
E. None of the above

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23. In Drosophila, the gene for red eyes (w+) is dominant
over the gene for white eyes (w). Round eye (B+) is
dominant to Bar eye (B). A fly of an unknown genotype
is crossed against a white bar eyed fly. The phenotypic
ratio of the offspring is
25% Red, round eyed
25% Red, bar eyed
25% White, round eyed
25% White, bar eyed

28. Very early in embryonic development, each cell still has
the ability to develop into a complete organism. This is
known as
A.
B.
C.

D.
E.

indeterminate cleavage.
determinate cleavage.
blastulation.
gastrulation.
None of the above

What is the genotype of the unknown parent?
A.
B.
C.
D.
E.

w+w+ B+B+
w+w B+B+
w+w BB
ww B+B
w+w B+B

24. How many ATP are produced from 2 molecules of
glucose using only substrate level phosphorylation?
A.
B.
C.
D.
E.

4
8
36
38
40

25. In the DNA of C. elegans, 15% of the bases are
guanine, what percentage are thymines?
A.
B.
C.
D.
E.

15%
20%
35%
70%
85%

26. Which of the following does not secrete a hormone?
A.
B.
C.
D.
E.

pituitary gland
salivary gland
hypothalamus

heart
kidney

27. In pedigree analysis, which of the following would lead
you to assume autosomal dominance?
A.
B.
C.
D.
E.

The trait skips every other generation.
The trait shows up in every generation.
The trait shows up mainly in females.
The trait shows up mainly in males.
The trait is always masked by another allele.

29. The insertion or deletion of a single nucleotide base in a
cell’s DNA results in a
A.
B.
C.
D.
E.

thymine dimer.
missense mutation.
frameshift mutation.
nonsense mutation.
degenerate genetic code.

30. According to the theory of blood groups, which of the
following statements is false?
A. Type O blood contains no agglutinins.
B. Agglutinins are antibodies.
C. Type A blood contains agglutinins for type B
agglutinogens.
D. Agglutinogens are antigens.
E. Rh factor is a type of agglutinogen found in human
blood.
31. During what stage of cell division do chromosomes go
from single-stranded to double-stranded?
A.
B.
C.
D.
E.

Interphase
Prophase
Metaphase
Anaphase
Telophase

32. What level(s) of protein structure is characterized by αhelices and β-sheets?
A.
B.
C.
D.
E.

Primary
Secondary
Tertiary
Quaternary
Secondary and tertiary

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33. Axons are sheathed in myelin which
A.
B.
C.
D.
E.

allows faster conduction of impulses.
maintains the resting potential.
allows the pumping of Na+ out of the cell.
initiates the action potential.
determines the threshold of the neuron.

34. How many genetically different gametes can be formed
by a mouse that is genotypically AABbCc? (Assume no
linkage between these genes and that none are lethal.)
A.
B.

C.
D.
E.

4
6
7
8
9

35. Active transport is best defined as
A. diffusion of soluble substances across a membrane
from a region of high concentration to low
concentration.
B. osmosis of water across a semi-permeable
membrane involving the hydrolysis of polypeptides.
C. the movement of materials across a semipermeable
membrane against an electrochemical gradient.
D. the movement of materials across a semipermeable
membrane with an electrochemical gradient.
E. the movement of substances across a membrane in
accordance with the Donnan equilibrium.

38. What is the major difference between prokaryotes and
eukaryotes?
A.
B.
C.
D.
E.

Only eukaryotes have a cell wall
Eukaryotes are all autotrophic.
Eukaryotes lack ribosomes.
Prokaryotes have no nuclear membrane.
Prokaryotes have mitochondria.

39. In which of the following would you find cristae?
A.
B.
C.
D.
E.

Endoplasmic reticulum
Mitochondria
Nucleus
Nucleolus
Ribosomes

40. Which of the following is not a necessary condition for
the Hardy-Weinberg equilibrium?
A.
B.
C.
D.

Random mating
Large gene pool
Random emigration and immigration

Forward mutation rate equals backward mutation
rate
E. No inbreeding

STOP! END OF TEST.

36. Which of the following cells does not have DNA?
A.
B.
C.
D.
E.

Phagocyte
Epithelial cell
Erythrocyte
Osteocyte
Sperm

37. Continuous muscle contraction causes a buildup of lactic
acid because
A. it is a breakdown product of ADP.
B. it is a degredation product of phosphocreatine.
C. it is a metabolic end-product of anaerobic
metabolism.
D. it is a breakdown product of fatty acid degradation.
E. actomyosin contraction releases cross-links of
lactate.

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THE ANSWER KEY AND EXPLANATIONS BEGIN ON THE FOLLOWING PAGE.

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BIOLOGY SUBJECT TEST 2

ANSWER KEY

6

1. C

9. C

17. B

25. C

33. A

2. B

10. B

18. E

26. B

34. A

3. B

11. C

19. A

27. B

35. C

4. B

12. E

20. C

28. A

36. C

5. B

13. A

21. E

29. C

37. C

6. A

14. D

22. C

30. A

38. D

7. A

15. B

23. E

31. A

39. B

8. D

16. D

24. B

32. B

40. C

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EXPLANATIONS

1.

C
Of the compounds listed, answer choices A, B, D, and E are all nitrogenous bases. They are present in such
compounds as RNA and DNA. The nitrogenous bases guanine and adenine are purines, and the nitrogenous bases
cytosine, thymine, and uracil are pyrimidines. Answer choice C, arginine, is an amino acid and not a nitrogenous base.
Amino acids are the building blocks for proteins.

2.

B
Portal systems are unusual circulatory arrangements in the body in which there are two interconnected capillary beds.
In normal non-portal circulation, blood travels from arteries to a capillary bed and back to a vein. In portal systems,
however, blood travels from an artery to a capillary bed, to a vein, to a second capillary bed, and back to a second vein.

The two most well-known portal systems in the human body are the hepatic portal system and the hypothalamic portal
system. In the hepatic portal system, blood leaving the capillary bed of the small intestine, which has picked up digested
food, passes through the hepatic portal vein to a capillary bed in the liver before returning to a normal venous system. In
the hypothalamic portal system, the two capillary beds are contained in the hypothalamus and the anterior pituitary. This
portal system brings releasing factors from the hypothalamus to the anterior pituitary. Answer choice A is incorrect; a
portal system may receive blood from the aorta, but this is not its definition. Answer choice C is incorrect; a portal system
may involve the liver, but there are other systems as previously described. Answer choice D is incorrect; there is no portal
system within the ventricles of the heart. Answer choice E is incorrect; there is no portal system connecting the small
intestine and the kidney.

3.

B
The contractile vacuole of Euglena removes excess water from the organism after it comes through the cell
membrane osmotically. In fresh water, the osmotic pressure drives water inside the organism due to a higher solute
concentration with the Euglena. The organism must use energy (ATP) to force the water back out. When this organism is
transferred to salt water, the solute concentration is greater outside the cell, thus the osmotic pressure is smaller. This
causes water to leave the Euglena. The contractile vacuole no longer has to remove water.

4.

B
Mitosis is cellular division that results in the formation of two daughter cells that are genetically identical to each
other and to the parent cell. The two daughter cells are also diploid (2n). Answer choice A is incorrect because meiosis
results in a reduction of chromosome number from 2n to n. It is a process of cell division in which two successive nuclear
divisions produce four haploid gametes from one diploid germ cell. Answer choice C is incorrect because fertilization is
the fusion of two haploid (n) gametes into one diploid (2n) zygote. Answer choice D is incorrect because non-disjunction
results from the failure of homologous chromosomes to separate during meiosis and has chromosome numbers of n+1 or
n–1.

5.

B
The Golgi apparatus consists of a stack of membrane-enclosed sacs. The Golgi receives vesicles and their contents
from the ER, modifies them (e.g. glycosylation) and repackages them into vesicles, and distributes them. Answer choice A
is incorrect because mitochondria are involved in cellular respiration, and answer choice C is incorrect because the ER
transports polypeptides around the cell and to the Golgi apparatus for packaging. Answer choice D is incorrect because
the ribosome is the site of protein synthesis, and answer choice E is incorrect because lysosomes are membrane-bound
organelles containing digestive enzymes, and typically have a low pH.

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6.

A
The degree of genetic linkage is a measure of how far apart two genes are on the same chromosome. The probability
of a crossover and exchange occurring between two points is generally directly proportional to the distance between the
points. For example, pairs of genes that are far apart from each other on a chromosome have a higher probability of being
separated during crossover than pairs of genes that are located close to each other. Thus, the frequency of genetic
recombination between two genes is related to the distance between them. Recombination frequencies can be used to
construct a genetic map. One map unit is defined as a 1 percent recombinant frequency. Recombination frequencies are
roughly additive.

7.

A
Disjunction is defined as the separation of maternal and paternal chromosomes during meiosis. Each tetrad is

separated into two halves. One of each pair of chromosomes, each containing two chromatids, is pulled to opposite ends
of the cell. Note that some of the maternal chromosomes can go to one end and some to the other end. The distribution
homologues between the two resultant nuclei are random.

8.

D
Epithelial cells are constantly shed from the body and have to be replaced. Epithelial cells are indentical to one
another, and are produced via mitosis.

9.

C
During prophase I of meiosis I, homologous chromosomes come together and intertwine in a process called synapsis.
Since at this stage each chromosome consists of two sister chromatids, each synaptic pair of homologous chromosomes
contains four chromatids, and is therefore often called a tetrad.

10.

B
Fertilization is defined as the fusion of nuclei of two gametes to form a zygote capable of becoming an adult
organism.

11.

C
Oogenesis is a type of meiosis that produces eggs. Meiosis I of this process results in two daughter cells known as
the secondary oocyte and a small polar body. The polar body is formed by an unequal distribution of cytoplasm during
splitting of the primary oocyte.

12.

E
Gastrulation results in the formation of the tree primary germ layers and the primitive digestive tract, called the
archenteron.

13.

A
The ectodermal germ layers give rise to the epidermis of the skin and also the nervous system. The endodermis, or
endodermal germ layer, gives rise to the lining of the digestive system, its associated glands and organs (such as the liver
and pancreas), and the lungs. Most of the other organs and systems of the body are mesodermal, including the excretory
system, the reproductive system, the muscular and skeletal systems, and the circulatory system. Many of the human body
tissues are derived from the mesoderm. In answering questions of this type, if you review and eliminate tissues derived

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from the ectoderm and endoderm, you find that the remaining tissues are mesodermal. In this question, answer choices B
and C are endodermal tissues. Answer choice D, nerve, is an ectodermal derivative.
14.

D
Thyroxine is a hormone released from the thyroid gland. It is not a steroid, but a derivative of the amino acid
tyrosine. All of the other answer choices are steroids and belong to a class of lipid-derived molecules with a characteristic
ring structure. Steroid hormones pass through the cell membrane with ease because they are lipid-soluble.

15.

B
Antibodies are produced as a response to the detection of foreign material (e.g. viral coat proteins, bacterial cell
walls) in the body. These antigens are detected by T cells which set the immune response in motion. Among their many
actions, T cells stimulate B cells to become antibody producing plasma cells, making choice B the correct answer. B cells
can also be stimulated to become memory cells, which remain dormant in the interstitial fluid and lymphatics until the
same antigen is detected again, upon which they can quickly initiate a humoral response.
Choice A is incorrect because macrophages are phagocytic cells that engulf foreign material (such as bacterial cells)
and digest it. Choice C, T cells, are the immune response organizers. They can become cytotoxic cells (which kill
invading cells), helper T cells (which recruit other T and B cells into the battle) and suppresser T cells (which turn the
response off when the antigen has been cleared). Choice D is a throw away--neurons play no role in the immune response.
Choice E, natural killer cells, are rouge cells that destroy invading cells that they come across.

16.

D
The rate constant (k) which appears in the rate law is a temperature dependent constant. For a given temperature
nothing will change k, so it can have no influence on an enzyme catalyzed reaction.
We can eliminate choice A with the understanding that if the substrate concentration increases the reaction rate will
also increase, until you hit a maximum rate (at which point the enzymes become saturated with substrate).
Choices B and E are incorrect because all enzymes have an optimal temperature and pH (for most enzymes it is body
temperature and plasma pH; 37oC and 7.2 respectively) under which they operate most efficiently. If the temperature or
pH is increased or decreased from the optimal point, the reaction rate will decrease.
Choice C is incorrect because an increase in enzyme concentration will cause an increase in reaction rate, so we are
left with choice D.

17.

B
Let B = black coat color and b = white coat color and L = long tail and l = short tail. So, what is the probability of a
white, long-tailed mouse from the cross of BbLl x bbll? Let's construct the Punnett square.

bl
(only
possible
gamete)

BL
Bl
BbLl
Bbll
(black, long) (Black,
short)

bL
bl
bbLl
bbll
(white, long) (white,
short)

So, 25% of the offspring will be black with long tails, 25% of the offspring will be black with short tails, 25% of the
offspring will be white with long tails (what we're looking for), and 25% of the offspring will be white with short tails.
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18.

E
PGAL is generally considered the prime end-product of photosynthesis and it can be used as an immediate food
nutrient, combined and rearrange to form monosaccharide sugars, such as glucose, which can be transported to other cells,
or packaged for storage as insoluble polysaccharides such as starch.

19.

A
During prophase I, the chromatin condenses into chromosomes, the spindle apparatus forms, and the nucleoli and
nuclear membrane disappear. Homologous chromosomes come together and intertwine in a process called synapsis.
Sometimes chromatids of homologous chromosomes break at corresponding points and exchange equivalent pieces of
DNA; this process is called crossing over.
Choice B is incorrect. During Metaphase I, homologous pairs align at the equatorial plane and each pair attaches to a
separate spindle fiber by its kinetochore.
Choice C is incorrect. During Anaphase I, the homologous pairs separate and are pulled to opposite poles of the cell.
This process is called disjunction and it accounts for a fundamental Mendelian law.
Choice D is incorrect. During Telophase I, a nuclear membrane forms around each new nucleus. At this point each
chromosome still consist of sister chromatids joined at the centromere. The cell divides into two daughter cells, each
receiving a nucleus containing the haploid number of chromosomes.
Choice E is incorrect because interkinesis is a short rest period between the two cell divisions of meiosis and during
which the chromosomes partially uncoil.

20.

C
The blood group antigens are an example of codominance. Codominance occurs when multiple alleles exist for a
given gene, and more than one is dominant. When the genotype is heterozygous for codominant alleles, the phenotype is
the result of the expression of both alleles simultaneously.

The classic example of codominance and multiple alleles is the inheritance of ABO blood groups in humans. Blood
type is determined by three different alleles, IA, IB, and i. Only two alleles are present in any single individual, but the
population contains all three alleles. IA and IB are both dominant to i. Individuals who are homozygous IA or
heterozygous IAi have blood type A; individuals who are homozygous IB or heterozygous IBi have blood type B; and
individuals who are homozygous ii have blood type O. However, IA and IB are codominant; individuals who are
heterozygous IAIB have a distinct blood type, AB, which combines characteristics of both the A and B blood groups.
Choice A is incorrect because pleiotropy is the ability of a single gene to have multiple effects.
Choice B is incorrect. Some progeny phenotypes are apparently blends of the parental phenotypes. This is known as
incomplete dominance.
Choice D is incorrect: Epistasis is a phenomenon in which one gene alters the expression of another gene that is
independently inherited.
Choice E is incorrect. Penetrance is the proportion of individuals who show the phenotype that is expected from their
genotype. One example of incomplete penetrance is a type of eye tumor called retinoblastoma, which is due to a dominant
allele. Not all individuals who inherit the allele develop the tumor. Furthermore, the severity of the tumor varies among
those individuals who show the retinoblastoma phenotype.

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21.

E
Sex-linked traits, such as hemophilia and color-blindness, are found on the X chromosome. In humans, females have
two X chromosomes and males have only one. As a result recessive genes that are carried on the X chromosome will
produce the recessive phenotypes whenever they occur in males, since no dominant allele is present to mask them. The
recessive phenotype will thus be much more frequently found in males.

Choice A is incorrect because the definition of sex-linked traits is that they are located on the sex chromosomes,
typically the X chromosome.
Choice B is incorrect because sex-linked traits that cause disease or some other deleterious condition are usually
recessive. The normal trait will be a dominant allele. Other sex-linked traits that do not cause disease will have both
dominant and recessive alleles.
Choice C is incorrect. Sex-linked traits can be found in genetic bottlenecks if one of the founders had a sex-linked
trait but are not necessarily always found in genetic bottlenecks.
Choice D is incorrect as sex-linked traits have obviously not been selected out of the population as we still have cases
of hemophilia and color blindness.

22.

C
For unicellular organisms, cell division is a means of reproduction, while for multicellular organisms, it is a method
of growth, development, and replacement of worn-out cells.
Choice A is incorrect because cell division is a process by which a cell doubles its organelles and cytoplasm.
Choice B is incorrect because during cell division, a cell replicates its DNA, then divides in two.
Choice D is incorrect because cell division can follow two different courses: mitosis and meiosis.

23.

E
In this dihybrid problem, a doubly recessive individual is crossed with an individual of unknown genotype. This is
known as a test cross. The white bar eyed fly is a homozygous recessive, wwBB and can only produce one type of gamete:
wB. Looking at the offspring, there are both recessive and dominant traits present for each loci. This means that there
must be both recessive alleles (w and B) and dominant alleles (w+ and B+) in the unknown parent. Therefore, the
genotype of the unknown parent must be w+w B+B, choice E.

24.

B
Substrate level phosphorylation occurs when ATP synthesis is directly coupled with theta degradation of glucose
without the participation of an intermediate molecule such as NAD+. Degradation of one glucose molecule yields a net of
2 ATP from glycolysis and 1 ATP for each turn of the citric acid cycle. Thus a total of 4 ATP are produced by substrate
level phosphorylation for one molecule of glucose. For two molecules, it would be 8 ATP.

25.

C
If 15% are guanine, then another 15% must be cytosine. That leaves 70% to be adenine and thymine. One half of the
70% is adenine (35%) and the other half is thymine (35%).

26.

B
Salivary glands secrete saliva which contains salivary amylase which hydrolyzes complex carbohydrates into maltose.
Amylase is an enzyme, not a hormone.

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Choice A is incorrect because the pituitary gland secretes a number of hormones including ACTH, TSH, and FSH.
Choice C is incorrect because the hypothalamus produces several hormones, including GnRH, oxytocin and
vasopressin.
Choice D is incorrect because the heart secretes atrial natriuretic hormone which is involved in osmoregulation and
blood pressure regulation.
Choice E is incorrect because the kidney secretes renin, which is involved in the regulation of aldosterone secretion,
and erythropoietin, which stimulates the bone marrow to produce red blood cells.

27.

B
A quick and dirty method for analyzing pedigrees states that if a trait shows up in every generation and shows no
gender skewing, then it is probably an autosomal dominant trait.
Choice A is incorrect: If a trait skips generations and does not show gender skewing, it is probably an autosomal
recessive.
Choice C is incorrect: Traits do not typically show up mainly in females because they have two copies of the X
chromosome and can therefore usually mask any deleterious genes they may inherit.
Choice D is incorrect: If a trait shows up typically in males it is probably a recessive allele on the X chromosome. It
doesn't show up in females very often because they typically have another X to mask it.
Choice E is incorrect: If a trait is always masked, it is probably a recessive trait although it would not be masked
when it is homozygous.

28.

A
An indeterminate cleavage is one that results in cells that maintain the ability to develop into a complete organism.
Choice B is incorrect because determinate cleavage results in cells whose future differentiation pathways are
determined at an early developmental stage.
Choice C is incorrect because blastulation begins when the morula develops a fluid-filled cavity called the blastocoel,
which by the fourth day becomes a hollow sphere of cells called the blastula.
Choice D is incorrect. Once implanted in the uterus, cell migrations transform the single cell layer of the blastula
into a three-layered structure called a gastrula.

29.

C
An insertion or deletion of single nucleotide in the cell's DNA will cause a corresponding insertion or deletion in the

mRNA. Since mRNA is "read" by the ribosome three nucleotides at a time (3 nucleotides = a codon), an addition or
deletion will result in the shift in the codon reading frame, hence the term frameshift mutation. For example, if the DNA
had the sequence 5'-CAT CAT CAT-3', and an Adenine were inserted, the DNA would now read 5'-CAA ATC
ATC ATC-3'....a very jumbled message. The mRNA will be similarly effected (assuming the mutation is in a coding
region, i.e. exon), and every codon downstream of the mutation will be different. Every amino acid being joined to the
polypeptide downstream of the mutation will be incorrect, and the resulting protein will be completely dysfunctional.
Thymine dimers, choice A, result from UV radiation cross linking adjacent thymines. When the cells enzymes attempt to
repair the damage, there is the possibility that DNA polymerase will replace the thymines with an incorrect nucleotide,
resulting in a point mutation. So, thymine dimers are a possible cause of point mutations, not frameshift mutations. A
point mutation is when a nucleotide is replaced by an incorrect nucleotide. There are three possible outcomes of a point
mutation:
1) silent mutation: the codon that results codes for the same amino acid, so the mutation has no effect,
or is "silent." This is because the genetic code is degenerate. 2) missense mutation: the resulting codon codes for a

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different amino acid (e.g. sickle cell anemia). 3) nonsense mutation: the resulting codon is a stop codon, and translation
is terminated prematurely.

30

A
Agglutinins are the antibodies that recognize the different blood types, and are so called because the antibodies cause
agglutination or clumping of blood. Agglutinogens are the antigens that determine blood type. The agglutinogen is found
on the surface of red blood cells, and there are two types involved as discussed in question #20. If a person has the A

agglutinogen they will make agglutinins to type B (anti-B). A type B person has the B agglutinogen and makes anti-A. A
type AB person has both agglutinogens, so makes no agglutinins (otherwise that person will coagulate their own blood).
Type O blood has neither the A or B agglutinogen on the surface of the RBCs, but has agglutinins to both type A and type
B. Rh factor (named after the creature it was first studied in-the rhesus monkey) is another RBC agglutinogen and is
completely independent of the ABO types.
Type A
Surface Antigen

A

A

+

A

A

A

A
Red Blood Cell
31.

A antibody

Agglutinated RBCs

A
Chromosomes go from single-stranded to double-stranded when they replicate. This occurs during the synthesis (S)

phase of interphase.

32.

B
Primary structure is the unique sequence of amino acids. Tertiary structure involves interactions between various
kinds of side chains of amino acids. Quaternary structure involves the interaction of two or more polypeptides. Secondary
structure is the repetitious twisting or folding of the polypeptide backbone; including both α helices and β pleated sheets.

33.

A
Myelin, produced by glial cells, allows axons to conduct impulses faster. The myelin acts as an insulator, preventing
ions from passing through the axon membrane. Ions can only permeate through channels located in small gaps in the
sheath, called nodes of Ranvier. The action potential "jumps" from node to node, making saltatory conduction much faster
than conduction through a non-insulated neuron.
Choices B and C are both achieved by the Na+/K+ pump, not myelin.
Choice D is incorrect because the action potential is initiated by a stimulus that causes depolarization of the axon
hillock.
Choice E is incorrect because it is the voltage regulated ion channels that determine the threshold of a neuron.

34.

A
The gametes that can form from an AABbCc mouse are: ABC, ABc, AbC, and Abc. Therefore the correct answer is
four. Alternatively, using the formula 2n, where n = # of heterozygous genes, n = 2, and 22 = 4.

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35.

C
Active transport is defined as the use of energy to move a substance across a membrane against a concentration
gradient.

36.

C
All of the cells have genetic material with the exception of the erythrocyte, a biconcave disk-shaped cell that contains
hemoglobin and has no nucleus.

37.

C
Continuous muscle contraction utilizes all the available oxygen, and causes the muscle fiber to depend on anaerobic
respiration for energy. NAD+ must be regenerated for glycolysis to continue in the absence of O2. This is accomplished by
reducing pyruvate into lactic acid and only produces two ATP per glucose.

38.

D
Prokaryotes are unicellular organisms with a simple cell structure. They have an outer cell membrane but does not
contain any membrane-bound organelles. There is no true nucleus; the genetic material consists of a single circular
molecule of DNA concentrated in an area of the cell called the nucleoid region. They have a cell wall, a cell membrane,
cytoplasm, ribosomes (different from those found in eukaryotes), and sometimes flagella. Eukaryotes are bounded by cell
membranes and contain cytoplasm. Cytoplasm contains organelles suspended in a semifluid medium called the cytosol.
The genetic material consists of linear strands of DNA organized into chromosomes and located within a membraneenclosed organelle called the nucleus.

39.

B
Mitochondria are the sites of aerobic respiration within the cell and hence the suppliers of energy. Each
mitochondrion is bound by an outer and an inner phospholipid bilayer membrane. The outer membrane is smooth and
acts as a sieve, allowing molecules through on the basis of size. The area between the inner and outer membranes is
known as the intermembrane space. The inner membrane has many convolutions called cristae and a high protein content
that includes the proteins of the electron transport chain. The area bounded by the inner membrane is known as the
mitochondrial matrix and is the site of many of the reactions in cell respiration. Mitochondria are different from the other
organelles in that they are semiautonomous; that is, they contain their own circular DNA and ribosomes, which enables
them to produce some of their own proteins and to self-replicate by binary fission.

40.

C
The Hardy-Weinberg law states that gene ratios and allelic frequencies remain constant through the generations in a
nonevolving population. Four criteria must be met for this to occur: 1. Random mating; 2. a large population; 3. no
migration into or out of the population; and 4. a lack of mutation. If all four of these are met, the gene frequencies will
remain constant. Anytime all four of these are not met, the gene frequencies will change and evolution may occur.

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