USABO Past Papers & Solutions
USA Biology Olympiad
USABO Open Exam and Semifinal past papers with worked solutions across the full IBO content distribution.
- Eligibility
- US high-school students
- Format
- Open Exam: multiple-choice and true/false · Semifinal: multiple-choice and free response
- Duration
- Open Exam: 50 minutes · Semifinal: 2 hours
- Scoring
- Open Exam selects semifinalists; semifinal selects the national finalists
USABO's Open Exam is fast and broad: fifty minutes to cover cell biology, genetics, anatomy, plant biology, ethology and ecology. The semifinal slows down and goes deeper, with free-response questions that expect reasoning from experimental data. Past papers matter here mainly for calibration — they show you the IBO topic weightings that the exam follows, so your reading time goes where the marks actually are.
Past papers by year
Each year page lists the official paper source (paper Open and paper Semifinal), the answer key location, difficulty notes and how to review your solutions.
Stuck on a USABO question?
Send us the question number. A mentor who has sat and medalled in USABO will reply with a step-by-step walkthrough and the faster competition method.
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What the paper tests
Cell & molecular biology
Genetics & evolution
Anatomy & physiology
Plant biology
Ecology & ethology
Where it leads: National finalists attend the training camp that selects the US IBO team. See our coaching programme.
Book personalised USABO classes
Past papers show you the gap; a mentor closes it. Our USABO mentors are medal winners who walk through every solution 1-to-1, then set targeted practice on the archetypes you lost marks on.
Want the full USABO paper pack and score guide?
Tell us your target and we will send the USABO paper list, the official scoring rules and a preparation plan built around the questions you keep losing marks on.
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Frequently asked questions
- How do I qualify for the USABO semifinal?
- By scoring in the top band of the Open Exam; the exact cut-off is set annually against the field. Speed is a real constraint — many students lose marks simply by not finishing.
- What should I study alongside past papers?
- A college-level general biology text used selectively, guided by the topic weightings the past papers reveal, is more efficient than reading cover to cover.