USABO Open Exam Actual EXAM
USABO OPEN EXAM ACTUAL EXAM NEWEST 2025/2026 WITH
COMPLETE QUESTIONS AND CORRECT ANSWERS |ALREADY
GRADED A+||BRAND NEW VERSION!
. Integral transmembrane proteins are proteins imbedded in the cell membrane.
Which of the following amino acids would you MOST expect to find in the
transmembrane region of such proteins?
[ ] A. Lysine
[ ] B. Serine
[ ] C. Tryptophan
[ ] D. Arginine - ANSWER-C Tryptophan
(it is non polar and does not have a charge)
The frequency of individuals affected with an autosomally recessive inherited
disorder is 1 in 4. Assuming that the population affected by this disease is in
Hardy-Weinberg equilibrium, what is the proportion of carrier individuals in this
population?
[ ] A. 12.5%
[ ] B. 25%
[ ] C. 50%
[ ] D. 100% - ANSWER-C 50%
The velocity of action potential conduction across a nerve axon is increased by the
presence of the myelin sheath. In the peripheral nervous system, what cell
myelinates the axon?
1|Page
, USABO Open Exam Actual EXAM
[ ] A. Oligodendocyte
[ ] B. Astrocyte
[ ] C. Schwann cell
[ ] D. Microglial cell - ANSWER-Schwann cell
Rods and cones are associated with _____ and _____ vision, respectively.
[ ] A. Light/dark...color
[ ] B. Color...light/dark
[ ] C. Near...far
[ ] D. Far...near - ANSWER-A
In many types of cancer, the function of the p53 gene is lost. Wild-type p53 is
MOST likely to be a
[ ] A. proto-oncogene
[ ] B. tumor suppressor
[ ] C. positive regulator of cell cycle progression
[ ] D. gene required for DNA replication - ANSWER-B
What glycolytic product is shuttled to the mitochondria in aerobic respiration?
[ ] A. Acetyl-CoA
[ ] B. Fumarate
[ ] C. Succinyl-CoA
[ ] D. Pyruvate - ANSWER-D
2|Page
, USABO Open Exam Actual EXAM
Telomerase is responsible for _____ the size of telomeres, and its function is often
____ in carcinogenesis.
[ ] A. maintaining ... decreased
[ ] B. maintaining ... increased
[ ] C. decreasing ... decreased
[ ] D. decreasing ... increased - ANSWER-B
Which of the following is NOT a mode of natural selection?
[ ] A. stabilizing selection
[ ] B. sexual selection
[ ] C. directional selection
[ ] D. diversifying selection - ANSWER-B
Protostomes have _____ and _____ types of cleavage.
[ ] A. spiral ... determinate
[ ] B. spiral ... indeterminate
[ ] C. radial ... determinate
[ ] D. radial ... indeterminate - ANSWER-A Pg 661
Which of the following is NOT a characteristic of all chordates?
[ ] A. notochord
[ ] B. vertebrae
3|Page
, USABO Open Exam Actual EXAM
[ ] C. pharyngeal slits
[ ] D. postanal tail - ANSWER-B
Unlike most polypeptide hormones, steroid hormones are unique in that they
[ ] A. Activate gene transcription
[ ] B. Diffuse across cell membranes
[ ] C. Can bind proteins
[ ] D. Can be used as therapeutic drugs - ANSWER-B
In superoxide dismutase 1, an enzyme implicated in amyotrophic lateral sclerosis
(Lou Gehrig's disease), a copper ion is bound to the active site and is important for
enzyme activity. In this enzyme, copper most likely functions as a(n)
[ ] A. coenzyme
[ ] B. cofactor
[ ] C. allosteric activator
[ ] D. allosteric inhibitor - ANSWER-B
The order of normal blood flow through the human heart is
[ ] A. right ventricle, right atrium, lungs, left ventricle, left atrium, body
[ ] B. right ventricle, right atrium, body, left ventricle, left atrium, lungs
[ ] C. right atrium, right ventricle, lungs, left atrium, left ventricle, body
[ ] D. right atrium, right ventricle, body, left atrium, left ventricle, lungs - ANSWER-
C
4|Page
USABO OPEN EXAM ACTUAL EXAM NEWEST 2025/2026 WITH
COMPLETE QUESTIONS AND CORRECT ANSWERS |ALREADY
GRADED A+||BRAND NEW VERSION!
. Integral transmembrane proteins are proteins imbedded in the cell membrane.
Which of the following amino acids would you MOST expect to find in the
transmembrane region of such proteins?
[ ] A. Lysine
[ ] B. Serine
[ ] C. Tryptophan
[ ] D. Arginine - ANSWER-C Tryptophan
(it is non polar and does not have a charge)
The frequency of individuals affected with an autosomally recessive inherited
disorder is 1 in 4. Assuming that the population affected by this disease is in
Hardy-Weinberg equilibrium, what is the proportion of carrier individuals in this
population?
[ ] A. 12.5%
[ ] B. 25%
[ ] C. 50%
[ ] D. 100% - ANSWER-C 50%
The velocity of action potential conduction across a nerve axon is increased by the
presence of the myelin sheath. In the peripheral nervous system, what cell
myelinates the axon?
1|Page
, USABO Open Exam Actual EXAM
[ ] A. Oligodendocyte
[ ] B. Astrocyte
[ ] C. Schwann cell
[ ] D. Microglial cell - ANSWER-Schwann cell
Rods and cones are associated with _____ and _____ vision, respectively.
[ ] A. Light/dark...color
[ ] B. Color...light/dark
[ ] C. Near...far
[ ] D. Far...near - ANSWER-A
In many types of cancer, the function of the p53 gene is lost. Wild-type p53 is
MOST likely to be a
[ ] A. proto-oncogene
[ ] B. tumor suppressor
[ ] C. positive regulator of cell cycle progression
[ ] D. gene required for DNA replication - ANSWER-B
What glycolytic product is shuttled to the mitochondria in aerobic respiration?
[ ] A. Acetyl-CoA
[ ] B. Fumarate
[ ] C. Succinyl-CoA
[ ] D. Pyruvate - ANSWER-D
2|Page
, USABO Open Exam Actual EXAM
Telomerase is responsible for _____ the size of telomeres, and its function is often
____ in carcinogenesis.
[ ] A. maintaining ... decreased
[ ] B. maintaining ... increased
[ ] C. decreasing ... decreased
[ ] D. decreasing ... increased - ANSWER-B
Which of the following is NOT a mode of natural selection?
[ ] A. stabilizing selection
[ ] B. sexual selection
[ ] C. directional selection
[ ] D. diversifying selection - ANSWER-B
Protostomes have _____ and _____ types of cleavage.
[ ] A. spiral ... determinate
[ ] B. spiral ... indeterminate
[ ] C. radial ... determinate
[ ] D. radial ... indeterminate - ANSWER-A Pg 661
Which of the following is NOT a characteristic of all chordates?
[ ] A. notochord
[ ] B. vertebrae
3|Page
, USABO Open Exam Actual EXAM
[ ] C. pharyngeal slits
[ ] D. postanal tail - ANSWER-B
Unlike most polypeptide hormones, steroid hormones are unique in that they
[ ] A. Activate gene transcription
[ ] B. Diffuse across cell membranes
[ ] C. Can bind proteins
[ ] D. Can be used as therapeutic drugs - ANSWER-B
In superoxide dismutase 1, an enzyme implicated in amyotrophic lateral sclerosis
(Lou Gehrig's disease), a copper ion is bound to the active site and is important for
enzyme activity. In this enzyme, copper most likely functions as a(n)
[ ] A. coenzyme
[ ] B. cofactor
[ ] C. allosteric activator
[ ] D. allosteric inhibitor - ANSWER-B
The order of normal blood flow through the human heart is
[ ] A. right ventricle, right atrium, lungs, left ventricle, left atrium, body
[ ] B. right ventricle, right atrium, body, left ventricle, left atrium, lungs
[ ] C. right atrium, right ventricle, lungs, left atrium, left ventricle, body
[ ] D. right atrium, right ventricle, body, left atrium, left ventricle, lungs - ANSWER-
C
4|Page
