What is on the exam

USABO SyllabusThe full content scope, area by area

The USA Biology Olympiad (USABO), run by the Center for Excellence in Education (CEE), draws on the same seven subject areas as the International Biology Olympiad: cell biology, genetics and evolution, plant anatomy and physiology, animal anatomy and physiology, ethology, ecology, and biosystematics. Below is each area, its approximate IBO-style weighting, the Campbell Biology chapters that cover it, and exactly where it reaches beyond AP Biology.

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The seven subject areas

Weightings shown are approximate IBO-style planning figures that USABO content broadly tracks — not an official per-exam mark scheme. Use them to allocate study time, not to predict an exact question count.

Cell Biology

~20–25% of theory

Membrane structure and transport, organelles, the cytoskeleton, cell signaling, the cell cycle and its control, bioenergetics (respiration and photosynthesis at the mechanistic level), and the chemistry of life — proteins, nucleic acids, enzyme kinetics.

Campbell mapping: Campbell Units 1–3 (chemistry of life, the cell, cellular energetics).

Beyond AP: AP stops at the overview; USABO probes mechanism — proton gradients, signal-transduction cascades, checkpoint control. Depth here often comes from Alberts and Lehninger.

Genetics & Evolution

~20% of theory

Classical and molecular genetics, gene expression and regulation, recombination, mutation, population genetics (Hardy–Weinberg and its assumptions), natural selection, speciation, and molecular evolution.

Campbell mapping: Campbell Units 3–5 (genetics, molecular biology of the gene, evolution).

Beyond AP: USABO expects you to solve multi-step genetics and population-genetics problems and to reason quantitatively about allele frequencies — well past AP-level recognition.

Plant Anatomy & Physiology

~15% of theory

Plant tissue and organ structure, water and solute transport, transpiration, mineral nutrition, photosynthesis in context, plant hormones, growth, development, and reproduction.

Campbell mapping: Campbell Unit 6 (plant form and function).

Beyond AP: Plant biology is barely covered in AP but carries real weight in USABO and the IBO. Raven Biology of Plants is the standard reference for the depth required.

Animal Anatomy & Physiology

~25% of theory

Nutrition and digestion, gas exchange, circulation, osmoregulation and excretion, the endocrine and nervous systems, sensory systems, muscle and movement, immunity, and reproduction and development.

Campbell mapping: Campbell Unit 7 (animal form and function, roughly chapters 40–49).

Beyond AP: The single largest content block. USABO asks why a mechanism works — countercurrent exchange, the loop of Henle gradient, action-potential dynamics — not merely that it exists.

Ethology

~5% of theory

Animal behavior: fixed action patterns, learning, communication, kin selection, optimal foraging, mating systems, and the evolutionary logic of behavior.

Campbell mapping: Campbell Unit 8 (chapters on behavioral ecology).

Beyond AP: Often under-taught entirely in AP. A small but reliably present slice that rewards reading classic behavioral-ecology material.

Ecology

~10% of theory

Population and community ecology, ecosystem energetics and nutrient cycling, biogeochemical cycles, succession, biomes, and conservation biology — plus the statistics to interpret ecological data.

Campbell mapping: Campbell Unit 8 (ecology).

Beyond AP: USABO ecology questions frequently embed data interpretation — reading population models and significance tests — which AP under-trains.

Biosystematics

~5% of theory

Phylogenetics, cladistics, reading and building evolutionary trees, taxonomy, and the diversity and defining features of the major groups of life.

Campbell mapping: Campbell diversity-of-life chapters (Units 4–5 evolution/diversity).

Beyond AP: AP touches phylogeny lightly; USABO expects you to interpret cladograms and recognize defining traits across kingdoms and major clades.

How the syllabus goes beyond AP Biology

AP Biology is a solid foundation, but the USABO syllabus is broader and far deeper in four specific ways:

Depth of mechanism — USABO asks why a process works at the molecular level, where AP asks you to recognize that it happens.
Plant biology, ethology, and biosystematics — barely present in AP, but each carries real weight in USABO and the IBO.
Biostatistics and data interpretation — reading significance tests, p-values, and experimental figures is assumed throughout; AP under-trains this.
Problem-solving over recall — multi-step genetics and population-genetics problems reward reasoning, not memorization.

For the resources that cover each area at the right depth, see our best USABO books guide; for the exam ladder itself, see how to qualify for USABO.

Frequently Asked Questions

What topics are on the USABO exam?

USABO covers the same broad subject areas as the International Biology Olympiad: cell biology; genetics and evolution; plant anatomy and physiology; animal anatomy and physiology; ethology (animal behavior); ecology; and biosystematics. Animal physiology and cell biology carry the most weight, with plant biology, genetics, ecology, ethology, and biosystematics filling out the rest. Every area assumes mechanistic understanding and the ability to interpret experimental data, not just recall.

Is the USABO syllabus like AP Biology or the IBO?

It sits between the two in scope but is far closer to the IBO in depth. USABO broadly tracks the IBO subject areas and IBO-style weightings, but at a level a determined US high schooler can reach with the right reading. Compared with AP Biology, USABO goes much deeper on mechanism, adds serious plant biology, ethology, biosystematics, and biostatistics, and expects genuine problem-solving rather than recognition. AP is a useful foundation but covers only a fraction of the USABO scope.

What books cover the USABO syllabus?

Campbell Biology is the core text and covers the large majority of the content map. Beyond it, the standard references are Molecular Biology of the Cell (Alberts) for cell and molecular depth, Raven Biology of Plants for plant biology, an animal-physiology reference for that large block, and Lehninger Principles of Biochemistry for metabolism and enzyme kinetics. See our best USABO books guide for what each one is best for and the order to buy them in.

Are the weightings on this page official?

No. The percentages shown are approximate, IBO-style planning figures that USABO content broadly tracks — they are not an official per-exam mark scheme. USABO sets its own emphasis each year, and a given Open or Semifinal paper may lean more heavily on some areas than others. Use the weightings to allocate study time sensibly, not to predict an exact question count.

How much of the syllabus does Campbell Biology cover?

Campbell Biology covers the large majority of the USABO content map and is the single most important text. It will, however, run out of depth in cell and molecular mechanisms, biochemistry, and plant physiology — which is where reference texts like Alberts, Lehninger, and Raven Biology of Plants take over. Most students master Campbell first, then dig into the references where past papers expose a gap.

Not sure which areas are your weakest?

A free diagnostic maps your strengths across all seven subject areas and shows where to spend your time first. We coach the full syllabus in US time zones.

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USABO SyllabusThe full content scope, area by area

Live online in your US time zone (ET/CT/MT/PT); pricing in USD.

The seven subject areas

Cell Biology

~20–25% of theory

Campbell mapping: Campbell Units 1–3 (chemistry of life, the cell, cellular energetics).

Beyond AP: AP stops at the overview; USABO probes mechanism — proton gradients, signal-transduction cascades, checkpoint control. Depth here often comes from Alberts and Lehninger.

Genetics & Evolution

~20% of theory

Campbell mapping: Campbell Units 3–5 (genetics, molecular biology of the gene, evolution).

Beyond AP: USABO expects you to solve multi-step genetics and population-genetics problems and to reason quantitatively about allele frequencies — well past AP-level recognition.

Plant Anatomy & Physiology

~15% of theory

Plant tissue and organ structure, water and solute transport, transpiration, mineral nutrition, photosynthesis in context, plant hormones, growth, development, and reproduction.

Campbell mapping: Campbell Unit 6 (plant form and function).

Beyond AP: Plant biology is barely covered in AP but carries real weight in USABO and the IBO. Raven Biology of Plants is the standard reference for the depth required.

Animal Anatomy & Physiology

~25% of theory

Nutrition and digestion, gas exchange, circulation, osmoregulation and excretion, the endocrine and nervous systems, sensory systems, muscle and movement, immunity, and reproduction and development.

Campbell mapping: Campbell Unit 7 (animal form and function, roughly chapters 40–49).

Beyond AP: The single largest content block. USABO asks why a mechanism works — countercurrent exchange, the loop of Henle gradient, action-potential dynamics — not merely that it exists.

Ethology

~5% of theory

Animal behavior: fixed action patterns, learning, communication, kin selection, optimal foraging, mating systems, and the evolutionary logic of behavior.

Campbell mapping: Campbell Unit 8 (chapters on behavioral ecology).

Beyond AP: Often under-taught entirely in AP. A small but reliably present slice that rewards reading classic behavioral-ecology material.

Ecology

~10% of theory

Population and community ecology, ecosystem energetics and nutrient cycling, biogeochemical cycles, succession, biomes, and conservation biology — plus the statistics to interpret ecological data.

Campbell mapping: Campbell Unit 8 (ecology).

Beyond AP: USABO ecology questions frequently embed data interpretation — reading population models and significance tests — which AP under-trains.

Biosystematics

~5% of theory

Phylogenetics, cladistics, reading and building evolutionary trees, taxonomy, and the diversity and defining features of the major groups of life.

Campbell mapping: Campbell diversity-of-life chapters (Units 4–5 evolution/diversity).

Beyond AP: AP touches phylogeny lightly; USABO expects you to interpret cladograms and recognize defining traits across kingdoms and major clades.

Frequently Asked Questions

What topics are on the USABO exam?

Is the USABO syllabus like AP Biology or the IBO?

What books cover the USABO syllabus?

Are the weightings on this page official?

How much of the syllabus does Campbell Biology cover?