USABO Open Exam Questions with

USABO Open Exam  Questions with Complete Solutions (Latest 2025) 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 %

• 50% - Correct Answers ✅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?

• Adenine is 40% of the RNA.
• Adenine is 20% of the RNA.
• Adenine is at least 20% of the RNA.
• Adenine is at least 40% of the RNA.
• The content of Adenine is not possible to determine based

on the information provided. - Correct Answers ✅E. The content of Adenine is not possible to determine based on the information provided. 1 / 3

USABO Open Exam  Questions with Complete Solutions (Latest 2025) Which of the following is a primary organ or structure of the immune system?

• Spleen
• Thymus
• Tonsils
• Lymph nodes
• Appendix - Correct Answers ✅B. Thymus

"Hairs" (such as trichomes) on the surface of leaves may

limit:

• photosynthesis.
• intake of carbon dioxide.
• evapotranspiration.
• drought adaptations.
• movement of water in the vessels. - Correct Answers

✅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? 2 / 3

USABO Open Exam  Questions with Complete Solutions (Latest 2025)

• Cestoda
• Polychaeta
• Oligochatea
• Onychophora
• Myriapoda - Correct Answers ✅C. Oligochatea

Evolution is a product of:

• realized niche and biomagnification.
• phenotypic variation and selective pressures.
• rainfall and temperature.
• adaptability within one generation.
• extinction and landscape variability. - Correct Answers

✅B. phenotypic variation and selective pressures.Which of the following is NOT true of allosterically regulated enzymes?

• Their activity can be modulated by effector molecules.
• They demonstrate cooperativity.
• Their activity can be modulated by substrate

concentration.

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