USABO EXAM 2025 NEWEST QUESTIONS AND
CORRECT ANSWERS (VERIFIED ANSWERS)
What enzyme does HIV use to convert RNA to DNA? - ans -Reverse Transcriptase
Questions 9 & 10 refer to the following information. The concentration of ions
inside an amoeba is expressed below as ion-units per milliliter. The composition
of the extracellular environment (ECE) is given for comparison. Assume the
amoeba has been in the environment for some time.
As the number of (+) and (-) ions in the amoeba and in the ECE are not equal, one
might assume that: - ans -other ions are also involved.
Questions 9 & 10 refer to the following information. The concentration of ions
inside an amoeba is expressed below as ion-units per milliliter. The composition
of the extracellular environment (ECE) is given for comparison. Assume the
amoeba has been in the environment for some time.
The differences in concentration of K+ and Na+ inside and outside of the amoeba
indicate that: - ans -energy has been expended.
. Five events occur in a cell constituting a cause-and-effect sequence: 1. an
enzyme is manufactured at the ribosomes 2. cellulose is deposited in a cell wall 3.
a molecule of RNA is transcribed 4. a carbohydrate polymer is synthesized 5. a
nucleic acid migrates from nucleus to ribosome - ans -3,5,1,4,2
When bacterial cells multiply maximally during the logarithmic phase, the total
number of cells (b) after some time interval (t) is equal to the original number of
cells (B) multiplied by 2n , where n is the number of generations formed during
the time interval: n = t/g and b = (B)(2n ). The generation time (g) for type A cells
is 28 minutes (assume no cell death). Estimate the LEAST amount of time required
for a population of type A cells to increase by 300 percent - ans -approximately 42
minutes
A population of 2800 flowers is in Hardy-Weinberg equilibrium, and 2352 of them
are red in color. The red allele [R]is the dominant allele; the allele for white color
[r] is recessive. What would be the frequency of heterozygotes in the population?
- ans -.48
The cause of trisomy 21 is: - ans -error during meiosis
,The molecular weight of fumarate is 160.0. How many grams of fumarate are
there in 200 mL of a 0.1 M fumarate solution? - ans -3.20 grams
Replacement of a lysine with a glycine in a protein could result in all of the
following EXCEPT a : - ans -loss of a negatively charged side chain.
The bacterial genome was sequenced and a mutation found in a gene adjacent to
β-galactoside. How would you best explain these research findings? The: - ans -
mutation renders the enzyme responsible for lactose transport sensitive to high
temperatures.
Researchers found that the arginine code AGG is poorly represented in genes of
E.coli. Interestingly, they also found that this triplet, when present, binds to the
ribosome 7-9 base pairs upstream from the starting ATG triplet (methionine).
What does this information suggest in regard to the AGG codon? - ans -it may
have a regulatory function in the cell
The above pedigree results from a rare SEX-LINKED disease. If individual 1 and 2
have a baby, what is the likelihood that the child, noted with a ?, will have the
disease? - ans -0% if it is a girl; 50% if it is a boy
The diversity of animal and plant species found on the Galapagos Islands differs
from that of the mainland because of: - ans -divergent evolution
In many species of flowering plants, the characteristics of the flower; its scent,
color, time of flowering, time of day it opens, kind and amount of food it offers,
are matched to the pollinating organism's size, form, physiology and reproductive
cycle. The term that describes this relationship is: - ans -coevolution
Mountain goats may have a thicker coat of hair than goats at lower altitudes in
the same general geographical area. This adaptation to the cooler climate of the
mountains most likely arose as a result of: - ans -directional selection.
A given polyclonal antibody molecule can bind to: - ans -more than one molecule
of the same antigen per antibody molecule.
, If a mouse is exposed to cycles of 12 hours of light followed by 12 hours of dark,
the mouse is mostly active in the dark and has a rest-activity cycle of 24 hours. If
the mouse is then kept in a constantly dark environment, the period of the rest-
activity cycle is slightly less than 24 hours. Why does the mouse's cycle shorten in
the dark environment? - ans -the mouse's circadian clock requires environmental
cues to reset it
Why is pepsinogen secreted as a zymogen into the stomach? To: - ans -prevent
digestion of the gastric glands.
The anatomy of an animal from a cold climate differs from that of an animal from
the tropics in that: - ans -the animal from the cold climate has smaller ears.
A person suffering from nerve gas exposure is given atropine to counteract the
effects. Why? - ans -atropine blocks the acetylcholine receptor which blocks the
excess acetylcholine lingering in the synaptic cleft
Which of the following does NOT describe synovial joints? - ans -bones held
together by cartilage
Which of the following processes aid in skeletal muscle relaxation after
contraction? - ans -acetylcholinesterease degrades acetylcholine
In India, "night blindness" is a condition mostly found in children, but it can also
be found in adults. This condition is an early sign of: - ans -vitamin A deficiency
A dog was kept in a room at a temperature of 40°C for two weeks. At the end of
that time, it was determined that the dog was sterile. An investigator conjectured
that the high temperature had caused the animal's sterility. In order to conjecture
this hypothesis, an investigator should be able to show that: - ans -the dog was
not sterile before the experimental period began.
The promoter region of a prokaryotic gene is located to the gene and is
the binding site for . - ans -5'...RNA polymerase
Which of the following is TRUE of prokaryotes?
I. Simultaneous transcription and translation
II. Presence of intron sequences
III. Circular DNA - ans -I and III only
Integral transmembrane proteins are proteins imbedded in the cell membrane.
Which of the following amino acids would you MOST expect to find in the
CORRECT ANSWERS (VERIFIED ANSWERS)
What enzyme does HIV use to convert RNA to DNA? - ans -Reverse Transcriptase
Questions 9 & 10 refer to the following information. The concentration of ions
inside an amoeba is expressed below as ion-units per milliliter. The composition
of the extracellular environment (ECE) is given for comparison. Assume the
amoeba has been in the environment for some time.
As the number of (+) and (-) ions in the amoeba and in the ECE are not equal, one
might assume that: - ans -other ions are also involved.
Questions 9 & 10 refer to the following information. The concentration of ions
inside an amoeba is expressed below as ion-units per milliliter. The composition
of the extracellular environment (ECE) is given for comparison. Assume the
amoeba has been in the environment for some time.
The differences in concentration of K+ and Na+ inside and outside of the amoeba
indicate that: - ans -energy has been expended.
. Five events occur in a cell constituting a cause-and-effect sequence: 1. an
enzyme is manufactured at the ribosomes 2. cellulose is deposited in a cell wall 3.
a molecule of RNA is transcribed 4. a carbohydrate polymer is synthesized 5. a
nucleic acid migrates from nucleus to ribosome - ans -3,5,1,4,2
When bacterial cells multiply maximally during the logarithmic phase, the total
number of cells (b) after some time interval (t) is equal to the original number of
cells (B) multiplied by 2n , where n is the number of generations formed during
the time interval: n = t/g and b = (B)(2n ). The generation time (g) for type A cells
is 28 minutes (assume no cell death). Estimate the LEAST amount of time required
for a population of type A cells to increase by 300 percent - ans -approximately 42
minutes
A population of 2800 flowers is in Hardy-Weinberg equilibrium, and 2352 of them
are red in color. The red allele [R]is the dominant allele; the allele for white color
[r] is recessive. What would be the frequency of heterozygotes in the population?
- ans -.48
The cause of trisomy 21 is: - ans -error during meiosis
,The molecular weight of fumarate is 160.0. How many grams of fumarate are
there in 200 mL of a 0.1 M fumarate solution? - ans -3.20 grams
Replacement of a lysine with a glycine in a protein could result in all of the
following EXCEPT a : - ans -loss of a negatively charged side chain.
The bacterial genome was sequenced and a mutation found in a gene adjacent to
β-galactoside. How would you best explain these research findings? The: - ans -
mutation renders the enzyme responsible for lactose transport sensitive to high
temperatures.
Researchers found that the arginine code AGG is poorly represented in genes of
E.coli. Interestingly, they also found that this triplet, when present, binds to the
ribosome 7-9 base pairs upstream from the starting ATG triplet (methionine).
What does this information suggest in regard to the AGG codon? - ans -it may
have a regulatory function in the cell
The above pedigree results from a rare SEX-LINKED disease. If individual 1 and 2
have a baby, what is the likelihood that the child, noted with a ?, will have the
disease? - ans -0% if it is a girl; 50% if it is a boy
The diversity of animal and plant species found on the Galapagos Islands differs
from that of the mainland because of: - ans -divergent evolution
In many species of flowering plants, the characteristics of the flower; its scent,
color, time of flowering, time of day it opens, kind and amount of food it offers,
are matched to the pollinating organism's size, form, physiology and reproductive
cycle. The term that describes this relationship is: - ans -coevolution
Mountain goats may have a thicker coat of hair than goats at lower altitudes in
the same general geographical area. This adaptation to the cooler climate of the
mountains most likely arose as a result of: - ans -directional selection.
A given polyclonal antibody molecule can bind to: - ans -more than one molecule
of the same antigen per antibody molecule.
, If a mouse is exposed to cycles of 12 hours of light followed by 12 hours of dark,
the mouse is mostly active in the dark and has a rest-activity cycle of 24 hours. If
the mouse is then kept in a constantly dark environment, the period of the rest-
activity cycle is slightly less than 24 hours. Why does the mouse's cycle shorten in
the dark environment? - ans -the mouse's circadian clock requires environmental
cues to reset it
Why is pepsinogen secreted as a zymogen into the stomach? To: - ans -prevent
digestion of the gastric glands.
The anatomy of an animal from a cold climate differs from that of an animal from
the tropics in that: - ans -the animal from the cold climate has smaller ears.
A person suffering from nerve gas exposure is given atropine to counteract the
effects. Why? - ans -atropine blocks the acetylcholine receptor which blocks the
excess acetylcholine lingering in the synaptic cleft
Which of the following does NOT describe synovial joints? - ans -bones held
together by cartilage
Which of the following processes aid in skeletal muscle relaxation after
contraction? - ans -acetylcholinesterease degrades acetylcholine
In India, "night blindness" is a condition mostly found in children, but it can also
be found in adults. This condition is an early sign of: - ans -vitamin A deficiency
A dog was kept in a room at a temperature of 40°C for two weeks. At the end of
that time, it was determined that the dog was sterile. An investigator conjectured
that the high temperature had caused the animal's sterility. In order to conjecture
this hypothesis, an investigator should be able to show that: - ans -the dog was
not sterile before the experimental period began.
The promoter region of a prokaryotic gene is located to the gene and is
the binding site for . - ans -5'...RNA polymerase
Which of the following is TRUE of prokaryotes?
I. Simultaneous transcription and translation
II. Presence of intron sequences
III. Circular DNA - ans -I and III only
Integral transmembrane proteins are proteins imbedded in the cell membrane.
Which of the following amino acids would you MOST expect to find in the
