USABO Practice Test

What is USABO? The USABO is a four-tier competition that demands mastery of advanced biological concepts. Success in the USABO competition can open doors to prestigious universities and scientific careers. Practice with the free USABO - USA Biology Olympiad practice test on PracticeTestGeeks (11 questions with answer explanations).

USABO Exam at a Glance

Facts verified Nov 7, 2026 against Center for Excellence in Education. Dates that have passed are removed automatically.

Free USABO - USA Biology Olympiad Study Tools

Interactive USABO - USA Biology Olympiad resources on PracticeTestGeeks, free to start:

• Free USABO Anatomy and Physiology Questions and Answers — 11 questions with instant scoring and answer explanations
• USABO - USA Biology Olympiad flashcards — review key terms and concepts card by card
• USABO - USA Biology Olympiad study guide — topic-by-topic overview of what the exam covers
• USABO - USA Biology Olympiad cheat sheet — one-page printable summary for last-minute review

According to Center for Excellence in Education, “All exams will continue to be online at one time and on one day.”^[2]

USABO content outline and where to practise each area

The content areas below are copied from the official USABO content outline published by Center for Excellence in Education, with the share of the exam each area carries. The right-hand column shows which of our practice sets covers it.

Worked examples: how to reason through USABO questions

These are practice questions written for this site, not questions from the real exam. Each explanation shows why the right answer is right and why the others are wrong.

Example 1

Question: Which of the following is incorrect about operons?

1. Operons can be switched off with a repressor.
2. The lac operon is an inducible operon.
3. In the presence of lactose and glucose, the lac operon will not be repressed.
4. CAP is an activator of transcription when not bound to cAMP.
5. A mutation in the operator of the trp operon can lead to the overproduction of tryptophan.

Answer: D. CAP is an activator of transcription when not bound to cAMP.

Explanation:

D is the incorrect statement, so it is the answer. CAP activates transcription only when it is bound to cAMP. Without cAMP, CAP cannot bind the CAP site and does not help RNA polymerase. The other statements are all true. A: a repressor bound to the operator blocks transcription. B: the lac operon is inducible because allolactose takes the repressor off the operator. C: when lactose is present, the repressor is released, so the operon is not repressed. Glucose keeps cAMP low, which weakens activation, but that is not repression. E: if a mutation in the trp operator stops the repressor from binding, the genes stay switched on and tryptophan is overproduced.

Rule to remember: repressors work at the operator and turn genes off. CAP-cAMP is an activator that turns them up. Keep these two controls apart.

Example 2

Question: In tetrapods, neural pathways carrying information from all the senses, except for the sense of smell, pass through and synapse in a particular anatomical structure in the brain, which is embryonically derived from the diencephalon. This structure is the:

1. Medulla
2. Thalamus
3. Amygdala
4. Occipital lobe
5. Somatosensory cortex

Answer: B. Thalamus

Explanation:

B, the thalamus, is correct. The thalamus develops from the diencephalon. It is the relay station where every sensory pathway except smell synapses before reaching the cortex. Smell travels from the olfactory bulb more directly to the cortex. A, the medulla, is part of the brainstem. It controls breathing and heart rate and is not the general sensory relay. C, the amygdala, is a limbic structure in the cerebrum that processes emotion. D, the occipital lobe, is cortex that receives visual input after the thalamus. It does not come from the diencephalon. E, the somatosensory cortex, is the destination for touch signals, not the shared relay point.

Rule to remember: the diencephalon gives rise to the thalamus and hypothalamus. All senses except smell pass through the thalamus.

Example 3

Question: Which of the following are most responsible for carrying and transporting triacylglycerols in the body?

1. IDL and LDL
2. Chylomicrons and LDL
3. Chylomicrons and VLDL
4. HDL and LDL
5. IDL and VLDL

Answer: C. Chylomicrons and VLDL

Explanation:

C, chylomicrons and VLDL, is correct. Chylomicrons carry dietary triacylglycerols from the intestine. VLDL carries triacylglycerols made in the liver. These are the two particles richest in triacylglycerol. A and E include IDL, which is what remains of VLDL after much of its triacylglycerol has been removed. A, B and D include LDL, which mainly carries cholesterol to tissues. D also includes HDL, which carries cholesterol back to the liver. So every option except C names at least one carrier that is mostly about cholesterol.

Rule to remember: lipoprotein density rises as triacylglycerol is removed. The least dense particles, chylomicrons and VLDL, carry the most fat. The denser LDL and HDL mainly carry cholesterol.

How to use these practice tests

Start by reading the official USABO exam pages at usabo-trc.org to confirm your exam date, the exam format and your school's registration status. Then take one short practice set from each content area to find your weak spots.

• Map your gaps. List each content area and mark it strong, shaky or weak based on that first round. Animal anatomy and physiology, Cell Biology, and Genetics and Evolution carry the most weight in the official outline, so spend more time on them.
• Work by topic. Do one set at a time, such as Classical and Mendelian Genetics or Cellular Respiration and Metabolism. Read every explanation, including on questions you got right.
• Write the rule. After each miss, write the general rule in one line, like the rules in the worked examples above. Review those notes often.
• Practise under time. The Open Exam lasts 50 minutes, so do some mixed sets with a timer to practise your pacing.
• Use official material. Work through any past exams or sample questions on the official site. Our questions are practice questions we wrote, not real exam questions.

In the last days before the exam, redo the questions you missed and reread your rule notes. Learn less new material.

• Topics: Mendelian genetics, biotech, population genetics
• Questions: ~12 questions on Open Exam

Reviewing past usabo exams is the single most effective way to prepare. The question style is unique and often repeats concepts from previous years.

USABO Award Levels

Understanding USABO score benchmarks and recognition levels.

Becoming a USABO semifinalist is a significant academic achievement recognized by top universities. National Finalists often gain admission to Ivy League institutions.

1. Find a Test Center - Check if your school is registered for the USABO competition.
2. Register Online - Create an account on the AoPS/USABO portal before the deadline.
3. Pay Fees - Ensure your school has paid the USABO registration fee ($125/school).
4. Prepare for Exam - Use our usabo practice test resources to study.
5. Take Open Exam - Log in to take the 50-minute usabo open exam in February.
6. Check Results - Scores are released about 3 weeks after the exam.
7. Advance - If you qualify, prepare for the usabo semifinal exam in March.

The USABO competition is one of the most affordable high-impact extracurriculars. A single $125 fee covers an unlimited number of students from one school.

Ace the USABO Competition

Join thousands of students using our USABO practice test resources to prepare for the open exam. Start your journey to becoming a semifinalist today.

Sample USABO - USA Biology Olympiad Practice Questions

Try these questions from our free USABO - USA Biology Olympiad practice tests. The correct answer and an explanation follow each question.

1. What is a best practice in USA Biology Olympiad immunology and disease?

   • A. A method or technique recognized as superior based on evidence and expert consensus
   • B. Any practice that is easy to implement
   • C. The cheapest available approach
   • D. A practice used only by large organizations

   Answer: A. A method or technique recognized as superior based on evidence and expert consensus

Best practices are methods, techniques, or approaches that are recognized through evidence, research, and expert consensus as producing superior results and are recommended for adoption.

• A. In the presence of oxygen and an uncoupler of oxidative phosphorylation.
• B. In the absence of oxygen.
• C. In the presence of oxygen.
• D. In the presence of a high concentration of ATP.

Answer: C. In the presence of oxygen.

Facultative anaerobes can produce ATP through both aerobic respiration and fermentation. Aerobic respiration, which occurs in the presence of oxygen, yields significantly more ATP (approximately 30-32 ATP per glucose) than anaerobic respiration or fermentation (typically 2 ATP per glucose). An uncoupler would disrupt the proton gradient, severely reducing ATP synthesis. A high concentration of ATP would inhibit key enzymes in respiration through negative feedback.

Take the full USABO - USA Biology Olympiad practice test

If you want more targeted practice, the usabo past exams page covers the same material with additional questions and explanations.

If you want more targeted practice, the usabo practice test page covers the same material with additional questions and explanations.

Official Resources

• USA Biolympiad (USABO) — Center for Excellence in Education: the official USABO program site with the exam calendar, rules, eligibility, and registration details.
• Center for Excellence in Education (CEE): the nonprofit that sponsors and administers the USABO competition in the United States.
• International Biology Olympiad (IBO): the global competition where the four-student USABO national team represents the USA each year.