The USABO Open Exam
Fifty questions. Fifty minutes. The same paper sat by thousands of students worldwide — and the deepest past-paper archive in China to prepare you for it.
USABO preparation hub
- USABO Past Papers (2003–2025)
- USABO Exams — Format & Syllabus (you are here)
- USABO Prep Resources
- USABO China Region
Scan the QR on the past-papers page to get the full free pack.
50 questions · 50 minutes · one sitting
The USABO Open Exam consists of 50 multiple-choice questions completed in 50 minutes. The paper is in English and there is no negative marking — every question is worth attempting.
In China, students sit the exam on paper at a partnering school. An online option is available on request. This is the BIOUS (BioOlympiad Initiative USA–China) exam, run by ASDAN using USABO’s own questions and judging standard.
The format is identical to the US Open Exam — the same questions, the same time limit, the same scoring benchmark.
How to register →
The Open Exam syllabus
Questions draw from seven topic areas spanning the full breadth of modern biology. All are tested at the level of genuine understanding, not rote recall.
Cell Biology & Molecular Biology
Cell structure and function, membranes, organelles, metabolism, DNA replication, transcription and translation.
Genetics & Evolution
Inheritance patterns, mutation, population genetics, natural selection, speciation and evolutionary mechanisms.
Plant Anatomy & Physiology
Tissue systems, photosynthesis, transport, reproduction, hormones and plant responses to the environment.
Animal Anatomy & Physiology
Organ systems, homeostasis, the nervous and endocrine systems, circulation, immunity and thermoregulation.
Animal Behaviour (Ethology)
Innate and learned behaviour, communication, social organisation, foraging and the evolution of behaviour.
Ecology
Populations, communities, ecosystems, energy flow, nutrient cycling, biomes and conservation biology.
Biosystematics
Classification, phylogenetics, the major kingdoms and phyla, and the characteristics that distinguish taxonomic groups.
How the exam is scored
US Open Exam recognitions
In the United States, USABO awards two national recognitions for the Open Exam:
- Honorable Mention — Top 20% of all US participants
- Certificate of Merit — Top 30% of all US participants
China-region awards
China-region awards are determined by percentile rank among all BIOUS participants, with five tiers from Bronze to Top Gold. China-region awards →
2026 raw-score cutoffs (out of 50): Gold 40 · Silver 33 · Bronze 25. Exact thresholds published each season.
2003–2025: the deepest practice library in China
Our archive of USABO Open Exam papers spans more than two decades — the most comprehensive practice library available to students in China. Working through real past papers is the most direct route to exam readiness.
Browse the full past-paper archive →
Two habits that matter most
Work through past Open Exam papers systematically — the archive stretches from 2003 to 2025, giving you more than 20 real sittings to learn from. Pair that with a thorough study of the seven core topic areas to fill any gaps the papers reveal.
Full preparation guide →Questions about the exam or past papers?
Our advisors can help you find the right papers and build a preparation plan.