USABO OPEN EXAM (ACTUAL EXAM) | ALL
QUESTIONS AND CORRECT ANSWERS WITH
EXPLANATIONS | GRADED A+ | VERIFIED ANSWERS |
NEWEST EXAM 2025
You examine a leaf cross-section under a microscope and find many
loosely packed cells. These cells have many chloroplasts and relatively thin
cell walls. These cells are:
A. collenchyma.
B. endodermis.
C. parenchyma.
D. schlerenchyma.
E. xylem ---------CORRECT ANSWER-----------------C. parenchyma.
Parenchyma cells have primary walls that are relatively thin and
flexible. Parenchyma cells are often depicted as "typical" plant cells
because they generally are the least specialized. Tissue comprised of
parenchyma may contain few or many air spaces and the cells may or
may not contain chloroplasts. Chloroplast containing parenchyma
cells are often referred to as Chlorenchyma.
Which of the following would be most likely to increase competition among
the members of the vole population in a given area?
A. An increase in the number of hawk predators
B. An increase in the reproduction rate of voles
C. An increase in temperature
D. An increase in the food supply
E. An epidemic of rabies within the vole population ---------CORRECT
ANSWER-----------------B. An increase in the reproduction rate of voles
Resource limitation in crowded populations can stop population
growth. Population density intensifies intraspecific competition for
declining nutrients, resulting in a lower birth rate.
,Tobacco mosaic virus has RNA rather than DNA as its genetic material. If
the RNA genome from a tobacco mosaic virus is mixed with proteins from a
human rhinovirus, the result is a mixed virus. If that virus could infect a cell
and reproduce, what would you expect the resulting viruses to be like?
A. A hybrid including genetic material from tobacco mosaic virus and
proteins from the rhinovirus
B. A hybrid including proteins from tobacco mosaic virus and genetic
material from the rhinovirus
C. Rhinovirus
D. Tobacco mosaic virus
E. No viruses would result because no viral DNA was present ---------
CORRECT ANSWER-----------------D. Tobacco mosaic virus
Virus genomes may consist of double-stranded DNA, single-stranded
DNA, double-stranded RNA, or single-stranded RNA depending on the
specific type of virus. Tobacco mosaic virus has a rigid, rodshaped
capsid. The genetic material from the tobacco mosaic virus serves as
the template for the human rhinovirus to replicate itself and produce
new capsid proteins by transcription and translation. The new viral
DNA and capsid proteins assemble into tobacco mosaic virus
particles, which then leave the cell.
An amphipathic molecule is a molecule that is characterized by:
A. 2 different forms that are mirror images of each other.
B. an amino group.
C. a hydrophilic end and a hydrophobic end.
D. a positively charged end and a negatively charged end.
E. rarely being found in cell membranes. ---------CORRECT ANSWER-------
----------C. a hydrophilic end and a hydrophobic end.
An amphipathic molecule is a phospholipid that has both a
hydrophilic region and a hydrophobic region.
,The function of a molecular chaperone is to:
A. act as an energy source during the polymerization of amino acids into a
polypeptide.
B. act as a carrier molecule and bring "activated" monomers to a polymer
for incorporation.
C. bind to specific structures on the polypeptide in order to assist the
folding of a protein into its correct three dimensional shape.
D. unfold proteins with the incorrect three-dimensional shape and refold
them into the proper shape.
E. transport rRNA from the nucleus to the cytoplasm. ---------CORRECT
ANSWER-----------------C. bind to specific structures on the polypeptide in
order to assist the folding of a protein into its correct three dimensional
shape.
Chaperonins (also called chaperone proteins) are protein molecules
that assist in the proper folding of other proteins. Molecular
chaperones do not actually specify the correct final structure of a
polypeptide. They work instead by keeping the new polypeptide
segregated from "bad influences" in the cytoplasmic environment
while it spontaneously folds.
Ethidium Bromide is used in electrophoresis of DNA fragments because it:
A. makes the fragments visible under UV light.
B. makes the DNA fragments more mobile in the gel.
C. increases the conductivity of electricity through the gel.
D. helps determine the size of the fragments.
E. maintains a stable pH. ---------CORRECT ANSWER-----------------A.
makes the fragments visible under UV light.
Gel electrophoresis separates macromolecules - nucleic acids or
proteins - on the basis of size, electrical charge and other physical
properties. It sorts a mixture of DNA molecules into bands, each
consisting of DNA molecules of the same length. Ethidium Bromide is
a DNA-binding dye that fluoresces the DNA restriction fragments
under UV light.
, The species Homo sapiens first appeared in which geologic epoch?
A. Miocene
B. Paleocene
C. Pleistocene
D. Pliocene
E. Eocene ---------CORRECT ANSWER-----------------C. Pleistocene
In the Cenozoic era, quaternary period, Homo sapiens first appeared
in the Pleistocene epoch (about 1.8 million years ago).
Which statement describing plant structure is appropriate?
A. Sclerenchyma cells provide support for the plant body
B. Collenchyma cells may form the outer cell layer of the plant
C. Wood is formed from old epidermal cells
D. Stomates are pores in the roots that allow nutrients to enter
E. Parenchyma cells have thicker cell walls than other plant cells ---------
CORRECT ANSWER-----------------A. Sclerenchyma cells provide support
for the plant body
Parenchyma cells are relatively unspecialized cells with thin, flexible
primary walls. Collenchyma cells have unevenly thickened primary
walls and provide support to parts of the plant that are still growing.
Sclerenchyma cells are specialized for plant support and have
secondary walls hardened with lignin. They may be dead at functional
maturity and are much more rigid than collenchyma cells. Mature
sclerenchyma cells cannot elongate. They occur in regions of the
plant that have stopped growing in length.
The Hardy-Weinberg equilibrium principle assumes all of the following
statements EXCEPT:
QUESTIONS AND CORRECT ANSWERS WITH
EXPLANATIONS | GRADED A+ | VERIFIED ANSWERS |
NEWEST EXAM 2025
You examine a leaf cross-section under a microscope and find many
loosely packed cells. These cells have many chloroplasts and relatively thin
cell walls. These cells are:
A. collenchyma.
B. endodermis.
C. parenchyma.
D. schlerenchyma.
E. xylem ---------CORRECT ANSWER-----------------C. parenchyma.
Parenchyma cells have primary walls that are relatively thin and
flexible. Parenchyma cells are often depicted as "typical" plant cells
because they generally are the least specialized. Tissue comprised of
parenchyma may contain few or many air spaces and the cells may or
may not contain chloroplasts. Chloroplast containing parenchyma
cells are often referred to as Chlorenchyma.
Which of the following would be most likely to increase competition among
the members of the vole population in a given area?
A. An increase in the number of hawk predators
B. An increase in the reproduction rate of voles
C. An increase in temperature
D. An increase in the food supply
E. An epidemic of rabies within the vole population ---------CORRECT
ANSWER-----------------B. An increase in the reproduction rate of voles
Resource limitation in crowded populations can stop population
growth. Population density intensifies intraspecific competition for
declining nutrients, resulting in a lower birth rate.
,Tobacco mosaic virus has RNA rather than DNA as its genetic material. If
the RNA genome from a tobacco mosaic virus is mixed with proteins from a
human rhinovirus, the result is a mixed virus. If that virus could infect a cell
and reproduce, what would you expect the resulting viruses to be like?
A. A hybrid including genetic material from tobacco mosaic virus and
proteins from the rhinovirus
B. A hybrid including proteins from tobacco mosaic virus and genetic
material from the rhinovirus
C. Rhinovirus
D. Tobacco mosaic virus
E. No viruses would result because no viral DNA was present ---------
CORRECT ANSWER-----------------D. Tobacco mosaic virus
Virus genomes may consist of double-stranded DNA, single-stranded
DNA, double-stranded RNA, or single-stranded RNA depending on the
specific type of virus. Tobacco mosaic virus has a rigid, rodshaped
capsid. The genetic material from the tobacco mosaic virus serves as
the template for the human rhinovirus to replicate itself and produce
new capsid proteins by transcription and translation. The new viral
DNA and capsid proteins assemble into tobacco mosaic virus
particles, which then leave the cell.
An amphipathic molecule is a molecule that is characterized by:
A. 2 different forms that are mirror images of each other.
B. an amino group.
C. a hydrophilic end and a hydrophobic end.
D. a positively charged end and a negatively charged end.
E. rarely being found in cell membranes. ---------CORRECT ANSWER-------
----------C. a hydrophilic end and a hydrophobic end.
An amphipathic molecule is a phospholipid that has both a
hydrophilic region and a hydrophobic region.
,The function of a molecular chaperone is to:
A. act as an energy source during the polymerization of amino acids into a
polypeptide.
B. act as a carrier molecule and bring "activated" monomers to a polymer
for incorporation.
C. bind to specific structures on the polypeptide in order to assist the
folding of a protein into its correct three dimensional shape.
D. unfold proteins with the incorrect three-dimensional shape and refold
them into the proper shape.
E. transport rRNA from the nucleus to the cytoplasm. ---------CORRECT
ANSWER-----------------C. bind to specific structures on the polypeptide in
order to assist the folding of a protein into its correct three dimensional
shape.
Chaperonins (also called chaperone proteins) are protein molecules
that assist in the proper folding of other proteins. Molecular
chaperones do not actually specify the correct final structure of a
polypeptide. They work instead by keeping the new polypeptide
segregated from "bad influences" in the cytoplasmic environment
while it spontaneously folds.
Ethidium Bromide is used in electrophoresis of DNA fragments because it:
A. makes the fragments visible under UV light.
B. makes the DNA fragments more mobile in the gel.
C. increases the conductivity of electricity through the gel.
D. helps determine the size of the fragments.
E. maintains a stable pH. ---------CORRECT ANSWER-----------------A.
makes the fragments visible under UV light.
Gel electrophoresis separates macromolecules - nucleic acids or
proteins - on the basis of size, electrical charge and other physical
properties. It sorts a mixture of DNA molecules into bands, each
consisting of DNA molecules of the same length. Ethidium Bromide is
a DNA-binding dye that fluoresces the DNA restriction fragments
under UV light.
, The species Homo sapiens first appeared in which geologic epoch?
A. Miocene
B. Paleocene
C. Pleistocene
D. Pliocene
E. Eocene ---------CORRECT ANSWER-----------------C. Pleistocene
In the Cenozoic era, quaternary period, Homo sapiens first appeared
in the Pleistocene epoch (about 1.8 million years ago).
Which statement describing plant structure is appropriate?
A. Sclerenchyma cells provide support for the plant body
B. Collenchyma cells may form the outer cell layer of the plant
C. Wood is formed from old epidermal cells
D. Stomates are pores in the roots that allow nutrients to enter
E. Parenchyma cells have thicker cell walls than other plant cells ---------
CORRECT ANSWER-----------------A. Sclerenchyma cells provide support
for the plant body
Parenchyma cells are relatively unspecialized cells with thin, flexible
primary walls. Collenchyma cells have unevenly thickened primary
walls and provide support to parts of the plant that are still growing.
Sclerenchyma cells are specialized for plant support and have
secondary walls hardened with lignin. They may be dead at functional
maturity and are much more rigid than collenchyma cells. Mature
sclerenchyma cells cannot elongate. They occur in regions of the
plant that have stopped growing in length.
The Hardy-Weinberg equilibrium principle assumes all of the following
statements EXCEPT:
