Biology subject test (5)

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 5

Biology Subject Test 5

1.

What is the principal function of NaHCO3?

6.

A.
B.
C.
D.

Dissolves CO2 better
Inactivates bile
Acts as a buffer
Combines with oxygen when hemoglobin is
saturated
E. Combines with CO2 in alveoli

A.
B.
C.
D.
E.
7.

2.

Lacteals absorb
A.
B.

C.
D.
E.

3.

A.
B.
C.
D.
E.

4.

A. It occurs in the cytoplasm.
B. Glycolysis is anaerobic.
C. 1 molecule of glucose breaks down into one
molecule of pyruvate.
D. 1 molecule of glucose results in the formation of 2
net ATP and 2 reduced molecules of NAD+.
E. Glucose is partially oxidized.

5.

Which of the following is NOT true regarding DNA?

Which of the following does not occur immediately after
birth?
The infant begins to produce adult hemoglobin.
Resistance in the pulmonary arteries decreases.

Pressure in the left atrium increases.
Pressure in both the inferior vena cava and the right
atrium increases.
E. The ductus arteriosus constricts.

8.

0%
3.125%
6.25%
12.5%
25%

All of the following statements about the glycolytic
pathway are true EXCEPT

chloroplast.
microbody.
phagosome.
vacuole.
lysosome.

A.
B.
C.
D.

carbohydrates.
proteins.
fatty acids.

salts.
Two of the above

If a strand of DNA underwent four rounds of
replication, what percentage of the total DNA present
would be comprised of the original DNA molecule?

You isolate a membrane bound vesicle containing
hydrolytic enzymes. It is most likely a

In a population in Hardy-Weinberg equilibrium, the
frequency of the dominant allele D is three times that of
the recessive allele d. What is the frequency of
heterozygotes in the population?
A.
B.
C.
D.
E.

9.

6.25%
25%
37.5%
56.25%
75%

Shortly after gastrulation, a teratogen affects the
development of the endoderm. You will most likely see

a deformity in the
A.
B.
C.
D.
E.

lens of the eye.
gonads.
nervous system.
bladder lining.
connective tissue.

10. Which component of blood is involved in clot
formation?

A. Erythrocytes
The basic unit is a nucleotide.
B. Macrophages
Adenine and guanine are pyrimidines.
C. T cells
The strands are anti-parallel.
D. B cells
Guanine always binds with cytosine with three
E. Platelets
hydrogen bonds.
E. The sugar molecule is deoxyribose.
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A.
B.

C.
D.


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11. Which of the following is not secreted by the thyroid?
A.
B.
C.
D.
E.

Thyroxine
Triiodothyronine
TSH
All of the above
None of the above

12. Hypothyroidism is always associated with
A.
B.
C.
D.
E.

high blood pressure.
irritability.
low metabolic rate.
high body temperature.

decreased heart rate.

13. Which of the following cellular substituents is made
within the nucleus?
A.
B.
C.
D.
E.

Lysosome
Golgi apparatus
Ribosome
Smooth endoplasmic reticulum
Cell membrane

14. A capillary has
A. a higher hydrostatic pressure at the arteriole end
and a lower hydrostatic pressure at the venule end.
B. a higher osmotic pressure in its blood plasma than
the osmotic pressure of the interstitial fluid
bathing the tissues.
C. a hydrostatic pressure that results from the beating
of the heart.
D. Choices A and C only
E. Choices A, B and C

15. Which of the following elements is not found in nucleic
acids?
A.

B.
C.
D.
E.

2

Sulfur
Carbon
Oxygen
Nitrogen
Phosphorus

16. A colorblind male XcY is crossed with a normal female
who is a carrier of fragile X and colorblindness (XfXc).
What is the probability that a male child will be
phenotypically normal?
A.
B.
C.
D.
E.

0%
25%
50%
75%
100%

17. Which of the following is NOT true regarding the

cytoskeleton?
A.
B.
C.
D.
E.

It is composed of microtubules and microfilaments.
It gives the cell mechanical support.
It maintains the cell's shape.
It is not required for mitosis.
It is functional in the cell's motility.

18. One molecule of glucose is catabolized via cellular
respiration. How many molecules of ATP are produced
by oxidative phosphorylation?
A.
B.
C.
D.
E.

2
4
32
36
40

19. Drosophila melanogaster can have several eye colors.
Red eyes are dominant over white eyes and sepia eyes. If

a red eyed fly that resulted from a mating of red eyed
and sepia eyed parents is crossed with a sepia eyed fly,
what percentage of the offspring will have sepia eyes?
A.
B.
C.
D.
E.

0%
25%
50%
75%
100%

20. The retina of the eye is a derivative of the
A.
B.
C.
D.
E.

endoderm.
ectoderm.
mesoderm.
ectoderm and mesoderm.
mesoderm and endoderm.

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21. Vitamin K absorption occurs mainly in the
A.
B.
C.
D.
E.

duodenum.
jejunum.
stomach.
large intestine.
mouth.

22. All of the following are characteristics of osmosis
EXCEPT
A. Passive transport
B. Occurs with water
C. Solvent will spontaneously move from a hypertonic
environment to a hypotonic environment
D. Solvent spontaneously moves from an area of high
solvent concentration to low solvent concentration
E. Is a special form of diffusion

23. What region of the brain controls the breathing rate?
A.
B.
C.

D.
E.

Medulla oblongata
Hypothalamus
Cerebrum
Cerebellum
Pituitary gland

26. All of the following occur in the mouth except
A.
B.
C.
D.
E.

mechanical digestion.
moistening of food.
chemical digestion of proteins.
bolus formation.
chemical digestion of starch.

27. Which of the following is TRUE about the role of LH in
the menstrual cycle?
A. LH inhibits the secretion of GnRH
B. LH is secreted by the ovary
C. LH induces the ruptured follicle to become the
corpus luteum and secrete progesterone and
estrogen
D. LH stimulates the development and maintenance of

the endometrium in preparation for implantation of
the embryo
E. LH stimulates milk production after birth

28. Cardiac muscle
A.
B.
C.
D.
E.

Is innervated by the somatic motor nervous system
Is not striated
Is multi-nucleated
Has voluntary contraction
Does not require Ca2+

24. Which type of muscle is always multinucleated?
A.
B.
C.
D.
E.

Cardiac muscle
Skeletal muscle
Smooth muscle
A and B
B and C

25. Which of the following hormones is released from the
posterior pituitary?
A.
B.
C.
D.
E.

Oxytocin
FSH
Glucagon
Estrogen
Calcitonin

29. Which of the following statements about the glycolytic
pathway is true?
A. Oxygen serves as a major reactant in glycolysis.
B. During glycolysis, glucose is partially reduced.
C. For each molecule of glucose that undergoes
glycolysis, two net molecules of ATP and two
molecules of reduced NAD are produced.
D. For each molecule of glucose that undergoes
glycolysis, one molecule of pyruvic acid is formed.
E. Pyruvic acid, the final product of the Krebs cycle,
serves as the immediate fuel for the next series of
cellular reactions.
30. Which region of the kidney has the lowest solute
concentration?
A.
B.

C.
D.
E.

Nephron
Cortex
Medulla
Pelvis
Epithelia

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31. Which of the following hormones raises the
concentration of blood calcium?
A.
B.
C.
D.
E.

Glucagon
Insulin
Parathyroid hormone
Aldosterone
Anti-diuretic hormone

32. If a person lacks gamma globulin, he would have

A.
B.
C.
D.
E.

severe allergies.
low resistance to infection.
diabetes.
hemophilia.
None of the above

33. Resting membrane potential depends on
A. The differential distribution of ions across the axon
membrane
B. Active transport
C. Selective permeability
D. The Na+/K+ pump
E. All of the above

36. Which of the following is NOT made of cartilage?
A.
B.
C.
D.
E.

Nose
Middle ear
Outer ear

Skeletal Joint
Larynx

37. Which of the following hormones directly affects blood
sugar level?
A.
B.
C.
D.
E.

Oxytocin
Calcitonin
Estrogen
Glucagon
Thyrotropin

38. At the arterial end of a capillary bed, the osmotic
pressure
A.
B.
C.
D.
E.

Is greater than the hydrostatic pressure
Results in a net outflow of fluid
Is less than the hydrostatic pressure
Two of the above
None of the above

39. Which of the following is NOT true about aldosterone?
34. Which of the following is generally a passive process
A.
B.
C.
D.
E.

Inhalation
Exhalation
Gas exchange
A and B
B and C

A.
B.
C.
D.
E.

Stimulates reabsorption of Na+
Stimulates secretion of K+
Results in the production of concentrated urine
Produced by the adrenal cortex
Known as vasopressin

40. The function of the lymph nodes is to
35. Which of the following is NOT true regarding the
circulatory system?

A.
B.
C.
D.

Mammals have a four chambered heart
Veins have a strong pulse
Arteries typically carry oxygenated blood
The lymphatic system intersects with the circulatory
system at the thoracic duct
E. The pumping chambers of the heart are called
ventricles

4

A.
B.
C.
D.
E.

Filter lymph
Break down hemoglobin
Increase glucose concentrations in blood
Facilitate the absorption of amino acids
Carry oxygen

STOP! END OF TEST.

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THE ANSWER KEY AND EXPLANATIONS BEGIN ON THE FOLLOWING PAGE.

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B I O L O G Y S U B J E C T T E S T 5 ____________________________________________________________________________

BIOLOGY SUBJECT TEST 5

ANSWER KEY

6

1. C

9. D

17. D

25. A

33. E

2. C

10. E

18. C

26. C

34. E

3. C

11. C

19. C

27. C

35. B

4. C

12. C

20. B

28. D

36. B

5. B

13. C

21. D

29. C

37. D

6. E

14. E

22. C

30. B

38. D

7. D

15. A

23. A

31. C

39. E

8. C

16. A

24. B

32. B

40. A

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Explanations
1.

C
The principal function of sodium bicarbonate in the blood is to serve as a buffer to maintain a slightly basic (7.2) pH
of the blood. NaHCO3 is the conjugate base to H2CO3, which results from the combination of carbon dioxide and water:
→ +
–
CO2 + H2O →
← H2CO3 ← H + HCO3

2.

C
The small intestine are lined with finger-like projections called villi which serve to increase the absorptive surface
area. Within the core of the villi are capillaries and lacteals, which are lymphatic vessels. Amino acids and glucose pass
through the villi walls into the capillary. Large fatty acids and glycerol pass into the lacteals and are then reconverted into
fats. Lymph and the absorbed fats will later empty into the central circulatory system.

3.

C
With each round of replication the original DNA material gets halved. After 4 rounds of replication the amount of
1
1
original DNA will = (2)4 = 16 = 6.25%.
The original strand of DNA is comprised of two sister strands. After four rounds of replication, you would have 16
strands of DNA comprised of 32 sister strands. The two original sister strands are 6.25% of the 32 sister strands that you
have at the end of the replication.

4.

C
The statement in choice C is false: One molecule of glucose (6 carbon sugar) breaks down into two molecules of
pyruvate (pyruvate is a 3 carbon molecule). Hence this is the choice we are looking for.
Choice A is a true statement and therefore NOT the correct response: Glycolysis occurs in the cytoplasm.
Choice B is also true. Glycolysis is anaerobic and occurs in both eukaryotes and prokaryotes. In anaerobic conditions
or in anaerobic bacteria, it is the first step in fermentation. In eukaryotes, pyruvate is reduced to lactic acid and in
prokaryotes, it is reduced to ethanol.
Choice D is an accurate statement. In glycolysis, one molecule of glucose is broken down and 4 ATP are formed.
However, due to the initial investment of 2 ATP, the net production of ATP is 2. Also, two molecules of NAD+ are
reduced to NADH. These molecules will later enter the electron transport chain to produce ATP.

5.

B
Adenine and guanine are purines while cytosine, uracil and thymine are pyrimidines.
Choice A is an accurate statement. The basic unit of DNA is a nucleotide which is made up of a phosphate group, a

deoxyribose sugar, and a nucleic acid.
Choice C is also a true statement: The strands are antiparallel, that is, one strand has a 5’ ∅ 3’ polarity and its
complementary strand has a 3’ ∅ 5’ polarity.
Choice D is correct. Guanine always bonds with cytosine with three hydrogen bonds. Adenine will bond with either
thymine or uracil with two hydrogen bonds.
Choice E is correct. The sugar molecule in DNA is deoxyribose while in RNA it is ribose.

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6.

E
The lysosome is like the stomach of the cell and is characterized as a membrane bound organelle that stores
hydrolytic enzymes.
Choice A is incorrect because chloroplasts are found only in algae an plant cells. They contain chlorophyll and are
the site of photosynthesis. Chloroplasts contain their own DNA and ribosomes and may have evolved by symbiosis.
Choice B is incorrect because microbodies are membrane bound organelles specialized as containers for metabolic
reactions.
Choice C is incorrect because phagosomes are vesicles that are involved in the transport and storage of materials that
are ingested by the cell through phagocytosis.
Choice D is incorrect. Vacuoles and vesicles are membrane bound sacs involved in the transport and storage of
materials that are ingested secreted, processed, or digested by the cells. Vacuoles are larger than vesicles and are more
likely to be found in plant cells.

7.

D

After birth, a number of changes occur in the circulatory system as the fetus adjusts to breathing on its own. The
lungs expand with air and rhythmic breathing begins. Resistance in the pulmonary blood vessels decreases, causing an
increase in blood flow through the lungs. When the umbilical blood flow stops, blood pressure in the inferior vena cava
decreases, causing a decrease in pressure in the right atrium. In contrast, left atrial pressure increases due to increased
blood flow from the lungs. Increased left atrial pressure coupled with decreased right atrial pressure causes the foramen
ovale to close. In addition, the ductus arteriosus constricts and later closes permanently. The ductus venosus degenerates
over a period of time, completely closing in most infants three months after birth. The infant begins to produce adult
hemoglobin, and by the end of the first year of life, little fetal hemoglobin can be detected in the blood.

8.

C
If the frequency of the dominant allele is three times that of the recessive allele, then p = 3q. According to HardyWeinberg equilibrium, p + q = 1 so 3q + q =1. Solving for q we get 4q = 1; q = 0.25 and p = 0.75. Again according to
Hardy-Weinberg, the frequency of the heterozygotes is equal to 2pq. Substituting in our values for p and q we have the
equation 2(0.75)(0.25) which equals 0.375 or 37.5%.

9.

D
The endoderm will develop into the epithelial linings of the digestive and respiratory tracts, parts of the liver,
pancreas, thyroid, and the bladder lining.
Choice A is incorrect because the lens of the eyes will develop from the ectoderm.
Choice B is incorrect because the gonads are developed from the mesoderm.
Choice C is incorrect because the nervous system is developed from the ectoderm.
Choice E is incorrect because the connective tissue is developed from the mesoderm.

10.

E
Platelets are cell fragments that lack nuclei and are involved in clot formation.

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Choice A, erythrocytes, are the oxygen carrying components of the blood. They contain hemoglobin which can bind
up to four molecules of oxygen
Choice B, macrophages, carry out phagocytosis of foreign particles and bacteria, digest them, and present the
fragments on their cell surface.
Choice C, T cells, lyse virally infected cells or secrete proteins which stimulate the development of B or other types of
T cells.
Choice D, B cells, mature into memory cells or antibody producing cells during immune responses.

11.

C
The thyroid hormone, thyroxine, or tetraiodothyronine, is simply an amino acid containing four atoms of iodine.
Another thyroid hormone, triiodothyronine, contains three atoms of iodine. Both of these hormones accelerate oxidative
metabolism throughout the body. Thyroid-stimulating hormone (TSH) is secreted by the anterior pituitary to stimulate the
thyroid gland.

12.

C
Hypothyroidism is caused by inflammation of the thyroid or iodine deficiency. Thyroid hormones are undersecreted
or not secreted at all. Common symptoms of hypothyroidism include a slowed heart rate and respiratory rate, fatigue, cold
intolerance, and weight gain. In newborns, it is termed cretinism and is characterized by mental retardation and short

stature. Hyperthyroidism occurs when the thyroid is over-stimulated, and symptoms often include increased metabolic
rate, feelings of excessive warmth, profuse sweating, palpitations, weight loss, and protruding eyes.

13.

C.
The two ribosomal subunits are manufactured in the nucleolus, a region within the nucleus. The ribosomes are the
sites of protein production. The fact that ribosomes are partly composed of RNA could have clued you in to the correct
answer. Choices A, B, D, and E are all incorrect because they refer to organelles that are composed of phospholipid
membranes and protein, so they are not manufactured in the nucleus. Rather, they are synthesized in regions of the cell
(specifically the smooth endoplasmic reticulum and the ribosomes) other than the nucleus. Choice A, the lysosome,
contains hydrolytic enzymes involved in digestion. Choice B, the Golgi apparatus, is a membrane-bound organelle that
sorts and packages proteins made by the ribosomes. Choice D, the smooth endoplasmic reticulum, is a portion of the
endoplasmic reticulum that does not have ribosomes and is involved in lipid synthesis and drug detoxification. Choice E,
the cell membrane, is a barrier between the interior and exterior of the cell.

14.

E
Choices A, B, and C are all true statements about capillaries. Choice A is correct because a capillary has a higher
hydrostatic pressure at the arteriole end and a lower hydrostatic pressure at the venule end. As blood flows from arterioles
to capillaries, blood pressure gradually drops due to friction between the blood and the walls of the vessels and the increase
in cross-sectional areas provided by numerous capillary beds. Choice B is correct as well. Blood plasma in the capillaries
has a higher osmotic pressure than the pressure in interstitial fluid. This is a result of the greater amount of dissolved
solutes in the blood plasma of the capillaries. Choice C is correct because the pumping force of the heart through the
blood vessels creates hydrostatic pressure. Hydrostatic pressure is defined as the force per area that blood exerts on the
walls of the blood vessels. Again, choice E is the correct answer because choices A, B, and C are all true statements.

15.

A
Sulfur is sometimes found in proteins but never in nucleic acids. The famous Hershey-Chase experiment took
advantage of this to determine whether proteins or nucleic acids carried the genetic information of the cell.

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The other choices are incorrect: Nucleic acids contain the elements C, H, O, N and P. They are polymers of subunits
called nucleotides and code all the information needed by an organism to produce proteins and replicate.

16.

A
Any male born from that mating will receive an X chromosome from his mother and a Y from his father. The X he
receives will either carry fragile X syndrome or colorblindness, so he has a 50% chance of having fragile X syndrome and
a 50% chance of being color blind, neither of which are phenotypically normal.

17.

D
The cytoskeleton forms the mitotic spindle, which is responsible for separating sister chromatids during cell division.
It is integral in proper cell division.
All the other choices are true of the cytoskeleton: The cytoskeleton is composed of microtubules and microfilaments
and gives the cell mechanical support, maintains its shape and functions in cell motility.

18.

C

32 ATP are produced by the electron transport chain and oxidative phosphorylation. Ultimately, 1 molecule of
glucose will be catalyzed to produce 36 ATP (32 from oxidative phosphorylation, 2 from the citric acid cycle, and 2 from
glycolysis).

19.

C
Before considering the Punnett square for the offspring, we will determine the phenotype of the parents. A red eyed
fly with red eyed and sepia eyed parents must be heterozygous because its sepia eyed parent can only contribute the
recessive sepia allele. If this heterozygous fly is crossed with a homozygous recessive (sepia) eyed fly, 1/2 the offspring
will be red eyed because they will receive the red, dominant allele from the heterozygous fly. The Punnett square will look
like this:

Red eyed parent

20.

Sepia eyed

r

parent

r

R

r

Rr

(red)
Rr
(red)

rr
(sepia)
rr
(sepia)

B
The retina develops from the ectoderm. The ectoderm develops into the nervous system, the epidermis, the lens of
the eye, and the inner ear. The endoderm develops into the lining of the digestive tract, lungs, liver, and pancreas. The
mesoderm develops into the muscles, skeleton, circulatory system, gonads, and kidneys.

21.

D
The large intestine is primarily involved in water reabsorption. Salts and minerals are reabsorbed with this water,
and bacteria within the large intestine produce vitamin K, which is also absorbed in the large intestine. Answer choice A
is incorrect because the duodenum is the anterior section of the small intestine, which connects to the posterior end of the
stomach. Answer choice B is incorrect because the jejunum is the second section of the small intestine. It connects to the

10

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duodenum on its anterior end and to the ileum on its posterior end. Answer choice C is incorrect because the stomach is

primarily a food-holding organ. Some small amount of protein digestion occurs there. Answer choice E is incorrect
because the mouth does not absorb water, but it does chew and moisten food and convert a small amount of starch to
maltose through the enzyme salivary amylase.
22.

C
Osmosis is a special type of diffusion involving water and is a form of passive transport. Hypertonic means high
solute and low solvent. Hypotonic means high solvent and low solute. Solvent always flows spontaneously from an area
of high solvent concentration to an area of low solvent concentration. Therefore, water will flow from a hypotonic
environment to a hypertonic environment.

23.

A
The medulla controls many vital functions, including breathing, heart rate and gastrointestinal activity.
Choice B is wrong because the hypothalamus controls such things as hunger, thirst, sex drive, water balance, blood
pressure and temperature regulation. It also plays an integral role in controlling the endocrine system.
Choice C is wrong because the cerebrum (usually referred to as the cerebral cortex) processes and integrates sensory
input and motor responses, and is important for memory and creative thought.
Choice D is wrong because the cerebellum is important in coordinating muscles. It aids in balance (it receives input
from the inner ear), hand-eye coordination, and the timing of rapid movements.
Choice E is wrong because the pituitary gland, along with the hypothalamus, plays an integral role in controlling the
endocrine system.

24.

B
Skeletal muscle is responsible for voluntary movement and is innervated by the somatic nervous system. A muscle is
a bundle of parallel fibers. Each fiber is a multinucleated cell created by the fusion of several mononucleate embryonic
cells. Answer choice C is incorrect because smooth muscle is responsible for involuntary action and is innervated by the

autonomic nervous system. It is found in the digestive tract, bladder, uterus, and blood vessel walls and possesses one
centrally located nucleus. Answer choice A is incorrect because cardiac muscle composes the muscle tissue of the heart.
These muscle fibers possess characteristics of both skeletal and smooth muscle fibers. As in skeletal muscle, the cardiac
muscle has a striated appearance; however, cardiac muscle cells generally have only one or two centrally located nuclei.
Cardiac muscle is innervated by the autonomic nervous system, which serves only to modulate its inherent beat.

25.

A
The posterior pituitary releases two hormones; oxytocin and antidiuretic hormone (ADH, also called vasopressin).
Choice B, FSH, is released by the anterior pituitary. Choice C, glucagon, is released by the alpha cell of the islets of
Langerhans in the pancreas. Choice D, estrogen, is released by the graafian follicle within the ovary during the menstrual
cycle. Choice E, calcitonin, is released by the thyroid gland.

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26.

C
The oral cavity is where mechanical and chemical digestion of food begins. Mechanical digestion is the breakdown
of large food particles into smaller particles through the biting and chewing action of teeth increasing the total surface
area. Chemical digestion begins in the mouth when the salivary glands secrete saliva, which contains the enzyme salivary
amylase, which hydrolyzes starch into simple sugars. Saliva also lubricates the food to facilitate swallowing and provides
a solvent for food particles. The muscular tongue manipulates the food during chewing and rolls it into a ball called a
bolus and pushes the bolus into the pharynx.

27.

C
Luteinizing hormone (LH) is first released as a surge midway through the menstrual cycle. This surge causes the
mature follicle to burst, releasing the ovum from the ovary. Following ovulation, LH induces the ruptured follicle to
develop into the corpus luteum (hence the name), which then secretes estrogen and progesterone.
Choice A is incorrect because it is progesterone and estrogen that inhibits GnRH release (thereby inhibiting FSH and
LH release, thus preventing additional follicles from maturing).
Choice B is incorrect because LH is secreted by the anterior pituitary. The ovary secretes estrogen and progesterone.
Choice D is describing the function of progesterone, not LH.
Choice E is describing the function of prolactin, not LH.

28.

D
If a piece of cardiac muscle were placed in a petri dish and nourished properly, it would contract at intrinsic beat.
Cardiac muscle, unlike any other muscle type, is capable of depolarizing spontaneously, which causes a contraction. Other
muscle types require some type of stimulation to cause depolarization and contraction (usually a neurotransmitter).
Choice A is incorrect because cardiac muscle is innervated by the autonomic nervous system. The somatic motor
system controls voluntary actions--walking, running, etc.
Cardiac muscle is striated, eliminating choice B, and has only one or two centrally located nuclei, eliminating choice
C.

29.

C
During glycolysis, 2 net molecules of ATP are produced by substrate-level phosphorylation, and 2 molecules of
NAD+ are reduced to form NADH. Choice A is incorrect because glycolysis is an anaerobic process. Thus, oxygen plays
no part in glycolysis. Choice B is incorrect because during glycolysis, glucose is partially oxidized, not reduced. Choice D
is also incorrect because two molecules of pyruvic acid are formed for each molecule of glucose that undergoes glycolysis.
Choice E is incorrect because pyruvic acid is produced during glycolysis, not during the Krebs cycle. After pyruvic acid is

produced in glycolysis, it is subsequently converted to acetyl coenzyme A, which then enters the Krebs cycle.

30.

B
The area in the kidney with the lowest solute concentration is the cortex. Filtrate that the enters the nephron travels
through the proximal convoluted tubule, then through the loop of Henle, followed by the distal convoluted tubule,
collecting duct, renal pelvis then out of the kidney to the bladder. The convoluted tubules are within the cortex, and the
loop of Henle, collecting duct and pelvis are in the medulla. As filtrate travels from the cortex to the medulla, it constantly
experiences an increasing concentration gradient, the purpose of which is to reabsorb water, so that the urine be
concentrated.

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Choice A is incorrect because the solute concentration within the nephron varies according to the region of the
kidney through which the filtrate is traveling.
Choice C is incorrect because the medulla has a very high concentration gradient, which is necessary in order for an
organism to produce concentrated urine.
Choice D is incorrect because the pelvis, which is in the medulla, has a very high concentration gradient, so that
water can be reabsorbed.
Choice E is incorrect because epithelia does not refer to a region within the kidney.

31.

C

The parathyroid glands are four small pea-shaped structures embedded in the posterior surface of the thyroid. These
glands synthesize and secrete parathyroid hormone, which together with calcitonin and vitamin D, regulates plasma Ca2+
concentration. In turn, the plasma Ca2+ concentration regulates PTH secretion by means of a negative feedback
mechanism. PTH raises the Ca2+ concentration in the blood by increasing bone resorption and decreasing Ca2+ excretion
in the kidneys. In addition, PTH converts vitamin D into its active form, which stimulates intestinal calcium absorption.
Glucagon, choice A, stimulates the conversion of glycogen to glucose in the liver and therefore increases blood glucose.
Insulin, choice B, lowers blood glucose and increases storage of glycogen. Aldosterone, choice D, regulates plasma levels
of sodium and potassium and consequently the total extracellular water volume. It causes the active reabsorption of
sodium and passive reabsorption of water in the nephron. ADH, choice E, stimulates water reabsorption by the kidneys by
increasing the nephron’s permeability to water.

32.

B
With no gamma globulins (antibodies), an organism cannot produce a specific immune response to pathogens.
Clinical manifestations of this are frequent, severe, prolonged infections by organisms of typically low pathogenicity.

33.

E
The resting membrane potential across a nerve cell membrane depends on the physiology of two ions; Na+ and K+.
The Na+/K+ pump is an active transport protein that maintains an electrochemical gradient across the membrane by
pumping 3 Na+ out and 2 K+ in. This unequal pumping causes: (1) the cell to be negative on the inside relative to the
outside; (2) a high concentration of Na+ outside the cell relative to the inside; (3) a high concentration of K+ inside relative
to the outside. The membrane is more permeable to K+ than Na +, and it is the balance between the pump and the "leaky"
membrane that determines the cell's resting potential.

34.

E

Exhalation is generally a passive process involving elastic recoil of the lungs and relaxation of both the diaphragm
and the external intercostal muscles. However, during vigorous exercise, active muscle contraction assists in expiration.
Gas exchange is also a passive process; gases diffuse down their partial pressure gradients. Inhalation is an active process
requiring contraction of the diaphragm and the external intercostals.

35.

B
Veins do not have a strong pulse. They are thin-walled inelastic vessels that usually conduct deoxygenated blood
(the exception being the pulmonary vein) toward the heart. Blood flow depends on compression by neighboring skeletal
muscles rather than a smooth muscular wall lining as found in arteries. Answer choice A is a correct statement, as it is a
characteristic of mammals to have a four chambered heart. Arteries (choice C) are thick walled, muscular elastic vessels
the transport blood away from the heart. This blood is usually oxygenated (except for the pulmonary arteries). The
lymphatic system (choice D) an open circulatory system that transports excess interstitial fluid (lymph) to the
cardiovascular system and keeps fluid levels constant. Lymph enters the bloodstream at the thoracic duct, which connects
to the superior vena cava. The pumping chambers of the heart are called ventricles. The atria are collecting chambers.

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36.

B
The middle ear is made of three bones; the malleus, incus, and stapes. They amplify the vibrations of the tympanic
membrane ("ear drum") and transmit it to the oval window, which leads to the inner ear and receptors on the auditory
nerve. The nose, outer ear, skeletal joints, and the larynx are all made of cartilage. Cartilage is not innervated or
vascularized.

37.

D
Glucagon, secreted by the pancreatic Islet of Langerhans cells in response to a low glucose blood level, stimulates
gluconeogenesis and the conversion of glycogen into glucose, thereby raising blood sugar levels. Choice A is incorrect
because oxytocin, which is produced by the hypothalamus and secreted by the posterior pituitary, stimulates uterine
contractions during labor, and milk secretion during lactation. Choice B is incorrect because calcitonin, secreted by the
thyroid gland, lowers blood calcium levels. Choice C is incorrect because estrogen, secreted by the ovaries, is responsible
for the maintenance of female secondary sex characteristics and maintenance of the endometrium. Choice E is incorrect
because thyrotropin is an anterior pituitary hormone that stimulates the thyroid to release thyroxine and triiodothyronine.
The functions of thyroxine and triiodothyronine are to increase metabolic rate.

38.

D.
Choices B and C are correct. At the arteriole end of the capillary bed the hydrostatic pressure is approximately 36
mmHg while the opposing osmotic pressure is approximately 25 mmHg. The larger hydrostatic pressure forces fluid out
of the capillaries. At the venule end of the capillary bed, the osmotic pressure across the wall is greater than the
hydrostatic pressure, which has dropped to 15 mmHg. This difference tends to draw fluid into the capillaries (osmosis).
Hence, most of the fluid is forced out of the capillaries at the arteriole end, and is reabsorbed by the capillaries at the
venule end. [Note: the specific pressures discussed above need not be memorized; understand the relative values at both
ends of the capillary]

39.

E
Aldosterone is produced by the adrenal cortex and stimulates both the reabsorption of Na+ from the collecting duct,
and the secretion of K+ (it causes Na+/K+ pumps to be turned on at the distal convoluted tubule). The Na+ reabsorption
pulls water with it, leading to a rise in blood volume, and hence a rise in blood pressure and the production of more
concentrated urine. Its release is stimulated by angiotensin II, which was formed as a result of the action of renin (the

renin-angiotensin system). Answer choice E is NOT true about aldosterone, so is the correct answer choice. Vasopressin
(ADH; antid diuretic hormone) is produced by the hypothalamus and stored in the posterior pituitary. It increases water
reabsorption by opening water channels in the nephron (as opposed to the indirect action of aldosterone which increases
salt reabsorption).

40.

A
Lymph nodes are swellings along lymph vessels containing phagocytic cells (leukocytes) that filter the lymph,
removing and destroying foreign particles and pathogens. The liver breaks down hemoglobin and use the components to
produce bile salts. Glucagon, produced by the pancreas, increases the blood concentration of glucose. Lymphatic fluid
absorbs fat and fat soluble vitamins and does not absorb amino acids from the digestive tract. Hemoglobin, found in red
blood cells, carries oxygen.

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