USABO USA Biology Olympiad Practice Test PDF (Free Printable 2026 June)

Free USABO Practice Test PDF Download

The USA Biology Olympiad (USABO) is one of the most rigorous science competitions available to high school students in the United States — and it is a direct pathway to the International Biology Olympiad (IBO) for the top performers. The competition tests biology knowledge at the college and university level, far beyond what standard AP Biology covers. Our free printable PDF gives you 2026 practice questions spanning the full USABO content spectrum: cell biology, molecular biology, biochemistry, genetics, plant biology, animal physiology, ecology, evolution, and ethology.

Whether you are preparing for the 50-question Open Exam or targeting a top score on the 120-question Semifinal, this PDF lets you study anywhere — at your desk, in a library, or wherever you do your best thinking. Download it once and use it as many times as you need.

What the USABO Exam Covers

The USABO Semifinal and IBO exams draw from university-level biology across nine major content areas. The Open Exam tests a broad cross-section of the same material at a slightly lower depth. Here is what you need to master for each domain.

Cell Biology

Expect detailed questions on membrane structure and function (fluid mosaic model, membrane proteins, transport mechanisms), signal transduction pathways (receptor tyrosine kinases, G-protein coupled receptors, second messengers), the cell cycle (G1/S/G2/M phases, checkpoints, cyclins and CDKs), mitosis and meiosis in complete mechanistic detail, and organelle function including the detailed machinery of the endomembrane system and mitochondrial structure.

Molecular Biology

DNA replication (origins, helicases, primase, leading and lagging strand synthesis, Okazaki fragments, proofreading), transcription and translation in both prokaryotes and eukaryotes, gene regulation at every level (operon model for prokaryotes, enhancers, silencers, transcription factors, chromatin remodeling for eukaryotes), and biotechnology methods including PCR, gel electrophoresis, Southern/Northern/Western blotting, CRISPR-Cas9 mechanism, and recombinant DNA techniques are all fair game.

Biochemistry

Enzyme kinetics questions require you to interpret Michaelis-Menten curves, calculate Km and Vmax, and understand competitive versus non-competitive inhibition. Metabolic pathway questions cover glycolysis (substrates, products, ATP yield, regulation), the TCA cycle (intermediates, enzyme names, NADH/FADH2 production), the electron transport chain (complexes I–IV, proton gradient, chemiosmosis), oxidative phosphorylation (ATP synthase mechanism), and both the light reactions and the Calvin cycle of photosynthesis in mechanistic detail.

Genetics and Evolution

Mendelian and non-Mendelian inheritance patterns, linkage and recombination frequency calculations, population genetics (Hardy-Weinberg equilibrium calculations, genetic drift, bottleneck and founder effects, natural selection mathematics), phylogenetics (reading and constructing cladograms, maximum parsimony), speciation mechanisms (allopatric, sympatric, parapatric), and the mathematical modeling of evolutionary change are all tested at the Semifinal level.

Plant Biology

Plant anatomy (root, stem, and leaf structure; vascular tissue types — xylem and phloem), meristem types and their roles, hormone functions (auxin in phototropism and cell elongation, gibberellin in stem elongation and seed germination, cytokinin in cell division, ABA in stomatal closure and dormancy, ethylene in fruit ripening), the mechanistic details of both C3 and C4 photosynthesis, transpiration and water potential, and tropisms are all covered.

Animal Physiology

The nervous system (action potential generation and propagation, synaptic transmission, neurotransmitter types), the endocrine system (hormone classes, feedback loops, specific glands and their hormones), the adaptive and innate immune system (B cells, T cells, antibody structure, MHC molecules, complement), circulatory system (cardiac cycle, blood pressure regulation, capillary exchange), and renal function (nephron structure, filtration, reabsorption, secretion, countercurrent multiplication) are all high-frequency Semifinal topics.

Ecology and Ethology

Population dynamics (logistic and exponential growth, carrying capacity, predator-prey oscillations), community ecology (competition, mutualism, succession), energy flow (trophic levels, ecological efficiency), nutrient cycles (nitrogen, carbon, phosphorus), conservation biology concepts, and animal behavior (classical and operant conditioning, imprinting, kin selection, Hamilton rule for altruism, honest signaling) round out the content coverage.

Free USABO Practice Tests Online

The PDF is a powerful study resource, but the best USABO preparation combines offline review with timed online testing. Our USABO practice test platform offers randomized question sets drawn from all nine content domains, with answer explanations that go beyond the correct answer to build the deep mechanistic understanding the Semifinal demands. Use the PDF to diagnose your weakest areas, then return to the online tests to drill those topics under exam-like time pressure.