USABO Open Exam 2023 Questions
And Answers.
Sunflower chromosomes have been isolated and their DNA/NT analyzed. It was
found that chromosome 2 has unusually high content of Adenine (40%). How many
percent of Guanine is present in chromosome 2?
A. 10%
B. 20%
C. 30%
D. 40 %
E. 50% - Answer A. 10%
Sunflower chromosomes have been isolated and their DNA/NT analyzed. It was
found that chromosome 2 has unusually high content of Adenine (40%). Assume that
the entire sequence of the chromosome is transcribed. Which of the following is true
for the content of Adenine in the transcribed RNA?
A. Adenine is 40% of the RNA.
B. Adenine is 20% of the RNA.
C. Adenine is at least 20% of the RNA.
D. Adenine is at least 40% of the RNA.
E. The content of Adenine is not possible to determine based on the information
provided. - Answer E. The content of Adenine is not possible to determine based on
the information provided.
Which of the following is a primary organ or structure of the immune system?
A. Spleen
B. Thymus
C. Tonsils
D. Lymph nodes
E. Appendix - Answer B. Thymus
"Hairs" (such as trichomes) on the surface of leaves may limit:
A. photosynthesis.
B. intake of carbon dioxide.
C. evapotranspiration.
D. drought adaptations.
E. movement of water in the vessels. - Answer C. evapotranspiration.
You discover a worm-like organism that inhabits soil samples that has the following
characteristics: segmented body and few bristle-like extensions. To which one of the
following groups will you assign this organism?
A. Cestoda
B. Polychaeta
C. Oligochatea
D. Onychophora
E. Myriapoda - Answer C. Oligochatea
, USABO Open Exam 2023 Questions
And Answers.
Evolution is a product of:
A. realized niche and biomagnification.
B. phenotypic variation and selective pressures.
C. rainfall and temperature.
D. adaptability within one generation.
E. extinction and landscape variability. - Answer B. phenotypic variation and
selective pressures.
Which of the following is NOT true of allosterically regulated enzymes?
A. Their activity can be modulated by effector molecules.
B. They demonstrate cooperativity.
C. Their activity can be modulated by substrate concentration.
D. They follow Michaelis-Menten kinetics. E. Plots of their rate of product formation
versus substrate concentration are sigmoidal in shape. - Answer D. They follow
Michaelis-Menten kinetics. E. Plots of their rate of product formation versus substrate
concentration are sigmoidal in shape.
Why can glycolysis proceed under anaerobic or aerobic conditions while the citric
acid cycle only proceeds under aerobic conditions?
A. Oxygen is a byproduct of the conversion of the glycolytic intermediate glucose-6-
phosphate to fructose-6-phosphate.
B. Enzymes of glycolysis do not use oxygen as cofactors, while enzymes of the citric
acid cycle require oxygen for proper folding.
C. Enzyme catalysis during the citric acid cycle is regulated by allosteric effectors,
which include oxygen.
D. NAD+ is produced during three steps of glycolysis and only one step of the citric
acid cycle.
E. Under anaerobic conditions, NAD+ (for glycolysis) can be regenerated through
the conversion of pyruvate into lactate. - Answer E. Under anaerobic conditions,
NAD+ (for glycolysis) can be regenerated through the conversion of pyruvate into
lactate.
If a child is blood type O, which of the following blood types is IMPOSSIBLE for
either parent?
A. A
B. B
C. O
D. AB
E. None are impossible - Answer D. AB
Which of the following initiates blood clotting?
A. Mechanical or chemical damage to blood vessel endothelium
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