AP Environmental Science (College Board): complete guide to the nine units, the science practices and the exam

College Board AP Environmental Science (APES) is designed to be the equivalent of a one-semester, introductory college environmental science course. The course is interdisciplinary, drawing on biology, chemistry, earth science and the social sciences, and the content is organized into nine units. There is no coursework, but data analysis and quantitative skills are examined directly in both sections of the exam. This page is the index: below is a map of the nine units, the exam structure, and how to study each one. This library covers all nine units in full.

The nine AP Environmental Science units

The College Board organizes the content into nine units. Each carries an exam weighting (the approximate share of multiple-choice questions it tends to contribute).

Unit 1 The Living World: Ecosystems (6 to 8%)

Species interactions, terrestrial and aquatic biomes, the carbon, nitrogen, phosphorus and hydrologic cycles, primary productivity, trophic levels, energy flow and the 10% rule, and food chains and food webs.

Unit 2 The Living World: Biodiversity (6 to 8%)

The levels of biodiversity, ecosystem services, island biogeography, ecological tolerance, natural disruptions to ecosystems, adaptations, and ecological succession.

Unit 3 Populations (10 to 15%)

Generalist and specialist species, survivorship curves, carrying capacity, population growth and resource availability, age structure diagrams, and human population dynamics.

Unit 4 Earth Systems and Resources (10 to 15%)

Plate tectonics, soil formation and properties, the atmosphere, global wind patterns, watersheds, and solar radiation and the seasons.

Unit 5 Land and Water Use (10 to 15%)

Agriculture, irrigation, pest control, meat production, the green revolution, mining, ecological footprints, and sustainable land and water management.

Unit 6 Energy Resources and Consumption (10 to 15%)

Renewable and non-renewable energy, fossil fuels, nuclear power, energy efficiency, and the environmental effects of each energy source.

Unit 7 Atmospheric Pollution (7 to 10%)

Sources of air pollution, photochemical smog, thermal inversions, indoor air pollution, acid rain, and pollution control.

Unit 8 Aquatic and Terrestrial Pollution (7 to 10%)

Sources and types of pollution, point and non-point sources, endocrine disruptors, human health hazards, solid and hazardous waste, and pollution control measures.

Unit 9 Global Change (15 to 20%)

Stratospheric ozone depletion, climate change, the greenhouse effect, ocean warming and acidification, invasive species, endangered species, and human impacts on biodiversity.

Exam structure

The AP Environmental Science exam is 3 hours and has two sections. A four-function calculator (with square root) is allowed throughout.

• Section I, multiple choice - 80 questions, 1 hour 30 minutes, 60%. Discrete questions and sets, many built on data, graphs, models and text or visual sources.
• Section II, free response - 3 questions, 1 hour 10 minutes, 40%. One question on designing an investigation, one on analyzing an environmental problem and proposing a solution (with calculations), and one on analyzing an environmental problem and proposing a solution using data and calculations.

The free-response questions are written from the science practices, so they ask you to explain concepts, design and analyze experiments, perform calculations (showing your work), interpret data, and propose and justify solutions using AP task verbs (Describe, Explain, Identify, Calculate, Justify, Propose, Make a claim).

How to study AP Environmental Science

AP Environmental Science rewards clear conceptual explanation, confident calculation, and the ability to connect topics to real environmental problems.

1. Work from the Course and Exam Description. Each topic (for example 1.4 The Carbon Cycle) maps to specific learning objectives and essential knowledge that exam questions are written from.
2. Master the quantitative toolkit. Practice percentages and percentage change, dimensional analysis, scientific notation, the rule of 70, primary productivity, and the 10% rule until they are automatic, and always show your working.
3. Learn the science practices. Rehearse designing investigations, reading data and graphs, and proposing evidence-based solutions, because the free-response questions are scored on these skills.
4. Connect topics to the big themes. Tie each topic to energy transfer, systems interactions, biodiversity, sustainability and human impact; examiners reward these connections.
5. Rehearse the free-response format. Time yourself on the three free-response questions and make sure every calculation shows its steps and every solution is justified.

The units, topic by topic

Each topic has a Course-and-Exam-Description-level answer page with worked exam questions and cross-links, plus an overview guide and quiz. Browse the set at /ap/environmental-science/syllabus. This library covers all nine units in full:

• Unit 1: introduction to ecosystems, terrestrial biomes, aquatic biomes, the carbon cycle, the nitrogen cycle, the phosphorus cycle, the hydrologic (water) cycle, primary productivity, trophic levels, energy flow and the 10% rule, food chains and food webs.
• Unit 2: introduction to biodiversity, ecosystem services, island biogeography, ecological tolerance, natural disruptions to ecosystems, adaptations, ecological succession.
• Unit 3: generalist and specialist species, survivorship curves, carrying capacity, population growth and resource availability, age structure diagrams, total fertility rate, human population dynamics, demographic transition.
• Unit 4: plate tectonics, soil formation and erosion, soil composition and properties, Earth's atmosphere, global wind patterns, watersheds, solar radiation and Earth's seasons, Earth's geography and climate.
• Unit 5: the tragedy of the commons, clearcutting, the Green Revolution, impacts of agricultural practices, irrigation methods, pest control methods, meat production methods, impacts of overfishing, impacts of mining, urbanization, ecological footprints, introduction to sustainability, methods to reduce urban runoff, integrated pest management, sustainable agriculture, aquaculture, sustainable forestry.
• Unit 6: renewable and nonrenewable resources, global energy consumption, fuel types and uses, distribution of natural energy resources, fossil fuels, nuclear power, energy from biomass, solar energy, hydroelectric power, geothermal energy, hydrogen fuel cell, wind energy, energy conservation.
• Unit 7: introduction to air pollution, photochemical smog, thermal inversion, atmospheric CO2 and particulates, indoor air pollutants, reduction of air pollutants, acid rain, noise pollution.
• Unit 8: sources of pollution, human impacts on ecosystems, endocrine disruptors, human impacts on wetlands and mangroves, eutrophication, thermal pollution, persistent organic pollutants (POPs), bioaccumulation and biomagnification, solid waste disposal, waste reduction methods, sewage treatment, lethal dose 50% (LD50), dose-response curve, pollution and human health.
• Unit 9: stratospheric ozone depletion, reducing ozone depletion, the greenhouse effect, increases in greenhouse gases, global climate change, ocean warming, ocean acidification, invasive species, endangered species, human impacts on biodiversity.

For the official Course and Exam Description

The College Board publishes the full Course and Exam Description, released free-response questions, scoring guidelines and the lab manual at apcentral.collegeboard.org. Always study from the current Course and Exam Description and the College Board's own released exams, because question style and the science practices are board-specific.