The course is structured into 8 widely taught units, all interconnected by 4 Big Ideas. As you progress through the units and build proficiency in 7 key science practices, using a well-structured study guide can help you stay organized and connect concepts more effectively.
AP Environmental Science CED Overview
The APES course is made up of 2 components:
- Course content
- Science practices
The course is structured into 8 widely taught units, all interconnected by 4 Big Ideas. Additionally, you’ll develop proficiency in 7 key science practices as you progress through the units.
AP Environmental Science’s 4 Big Ideas
Big Ideas are the basis of the course and help you make connections between course units and concepts. You can get a deeper understanding of the Big Ideas by applying them in different ways as you go through each unit. The Big Ideas for the course include:
- Big Idea 1: Energy Transfer (ENG)
Energy transformations drive all ecological processes. Energy cannot be created. It can only change forms from 1 type to another (e.g., from potential to kinetic energy). As energy passes through systems, more of it is wasted at each step.
- Big Idea 2: Interactions between Earth Systems (ERT)
The Earth comprises interconnected biochemical systems that work together to create a stable ecosphere. These systems change over time and space, each with a different threshold for recovering from damage or disturbances.
- Big Idea 3: Interactions Between Different Species and the Environment (EIN)
For millions of years, humans have altered Earth’s natural systems, which have had an enormous impact on the environment. The nature and pace of this impact have grown exponentially with the development of technology and population growth.
- Big Idea 4: Sustainability (STB)
To survive and thrive, we need sustainable systems. That means finding the perfect balance between conserving and developing resources. Managing our resources wisely is super important. As we work to develop solutions, we need to understand that cultural, social, and economic factors play a big role in finding solutions.
AP Environmental Science’s 9 Units and Their Topics
While each APES unit is important, some carry more weight, especially in the multiple-choice section, so you’ll encounter more questions from these units than others. The table below outlines the units and their respective weights in Section I of the exam.
| Units | Weighting |
|---|---|
| Unit 1: The Living World: Ecosystems | 6-8% |
| Unit 2: The Living World: Biodiversity | 6-8% |
| Unit 3: Populations | 10-15% |
| Unit 4: Earth Systems and Resources | 10-15% |
| Unit 5: Land and Water Use | 10-15% |
| Unit 6: Energy Resources and Consumption | 10-15% |
| Unit 7: Atmospheric Pollution | 7-10% |
| Unit 8: Aquatic and Terrestrial Pollution | 7-10% |
| Unit 9: Global Change | 15-20% |
Learn more about these AP Environmental Science units by clicking on the unit widgets below:
The Living World: Ecosystems
(Class Period 14-15)
Unit 1 introduces Earth as an interconnected system, focusing on resource distribution, species interactions, biomes, and energy transfer in ecosystems. You’ll learn to quantify energy loss across trophic levels.
You will learn about the following AP Environmental Science topics:
- Introduction to Ecosystems
- Terrestrial Biomes
- Aquatic Biomes
- The Carbon Cycle
- The Nitrogen Cycle
- The Phosphorus Cycle
- The Hydrologic Cycle
- Primary Productivity
- Trophic Levels
- Energy Flow and the 10% Rule
- Food Chains and Food Webs
The Living World: Biodiversity
(Class Periods 11-12)
Biodiversity includes the variety of genes, species, and ecosystems and is essential for maintaining ecological stability. In this unit, you’ll explore key biodiversity concepts and processes, compare related ideas, and clearly explain their differences in writing and discussion. You will learn about the following topics:
- Introduction to Biodiversity
- Ecosystem Services
- Island Biogeography
- Ecological Tolerance
- Natural Disruptions to Ecosystems
- Adaptations
- Ecological Succession
Populations
(Class Period 12-13)
Populations within ecosystems change over time due to various factors. This unit examines how species traits relate to ecosystem changes and includes practice with population growth calculations, the rule of 70, and selecting the correct formulas to analyze data.
You will learn about the following topics:
- Generalist and Specialist Species
- K-Selected and r-Selected Species
- Survivorship Curves
- Carrying Capacity
- Population Growth and Resource Availability’
- Age Structure Diagrams
- Total Fertility Rate
- Human Population Dynamics
- Demographic Transition
Earth Systems and Resources
(Class Period 11-12)
This unit examines Earth systems and life-sustaining resources. Changes to Earth’s systems at convergent and divergent boundaries can cause mountains, island arcs, earthquakes, volcanoes, and seafloor spreading. In this unit, you can practice analyzing and understanding qualitative models and representations of environmental issues. You should be able to identify and describe environmental processes that are visibly displayed.
You will learn about the following topics:
- Tectonic plates
- Soil Formation and Erosion
- Earth’s Atmosphere
- Global Wind Patterns
- Watersheds
- Solar Radiation and Earth’s Seasons
- Earth’s Geography and Climate
- El Niño and La Niña
Land and Water Use
(Class Period 18-19)
This unit explores human activities that disrupt ecosystems in both beneficial and negative ways, as well as the measures used to mitigate their effects. It examines how people use natural resources, such as mining and clear-cutting, and how that affects the environment. In this unit, you can practice naming environmental problems such as pollution, ozone layer depletion, and global climate change.
You will learn about the following topics:
- The Tragedy of the Commons
- Clearcutting
- The Green Revolution
- Impacts of Agricultural Practices
- Irrigation Methods
- Pest Control Methods
- Meat Production Methods and Overfishing
- Impacts of Overfishing
- The Impacts of Mining
- Impacts of Urbanization
- Ecological Footprints
- Introduction to Sustainability
- Methods to Reduce Urban Runoff
- Integrated Pest Management
- Sustainable Agriculture
- Aquaculture
- Sustainable Forestry
Energy Resources and Consumption
(Class Period 16-17)
This unit will analyze the effects that human consumption of renewable and nonrenewable energy sources has on the surrounding ecosystem. Energy consumption varies around the world, and the availability of energy resources is determined by the region’s geologic history. In this unit, you will learn how to locate natural energy resources such as coal, crude oil, and ore on a world map.
You will learn about the following topics:
- 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 Cells
- Wind Energy
- Energy Conservation
Atmospheric Pollution
(Class Period 11-12)
Air is a natural resource that covers the whole planet and flows through many systems. The air quality is affected by what people do both inside and outside. In this unit, you can practice comparing and predicting patterns and trends in a graph or table to explain how the data or the representation illustrates environmental concepts. You can also practice finding ways to fix the health problems caused by air pollution.
You will learn about the following topics:
- Introduction to Air Pollution
- Photochemical Smog
- Thermal Inversion
- Atmospheric CO2 and Particulates
- Indoor Air Pollutants
- Reduction of Air Pollutants
- Acid Rain
- Noise Pollution
Aquatic and Terrestrial Pollution
(Class Period 19-20)
Human actions that cause pollution have a direct effect on ecosystems in the air, on land, and in water. Sometimes it’s easy to figure out where pollution comes from, but other times it’s hard to tell. Numerous problems affecting human health have been connected to pollution. You should be able to look at an environmental problem with a critical eye and evaluate a given solution, pointing out its pros and cons.
You will learn about the following topics:
- Sources of Pollution
- Human Impact 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
- Pathogens and infectious diseases
Global Change
(Class Period 19-20)
Environmental science examines how local and regional human activities impact the planet. Unsustainable resource use can deplete stratospheric ozone and increase greenhouse gases, affecting both human health and the environment. In this unit, you’ll analyze the causes and impacts of global environmental change and apply prior skills to evaluate and propose solutions.
You will learn about the following AP Environmental Science topics:
- Stratospheric Ozone Depletion
- Reducing Ozone Depletion
- The Greenhouse Effect
- Increases in the Greenhouse Gases
- Global Climate Change
- Ocean Warming
- Ocean Acidification
- Invasive Species
- Endangered Species
- Human Impacts on Biodiversity
APES Science Practices
The APES Science Practices define the key skills students are expected to build throughout the course and apply on the exam. These practices focus on explaining environmental concepts, analyzing data and visual information, designing and evaluating investigations, performing mathematical calculations, interpreting texts, and proposing evidence-based solutions. Exam questions often require you to use one or more of these science practices to demonstrate your understanding and problem-solving abilities.
| Science Practices | MCQ Weightage | FRQ Weightage |
|---|---|---|
| Concept Explanation | 30%–38% | 13%–20% |
| Visual Representations | 12%–19% | 6%–10% |
| Text Analysis | 6%–8% | Not assessed in FRQ |
| Scientific Experiments | 2%–4% | 10%–14% |
| Data Analysis | 12%–19% | 6%–10% |
| Mathematical Routines | 6%–9% | 20% |
| Environmental Solutions | 17%–23% | 26%–34% |
Science Practices: Multiple Choice Question (MCQ) & Free Response Question (FRQ) Weighting
Science Practice 1: Concept Explanation
You’ll learn to explore environmental concepts, processes, and models in written form.
You will learn how to:
- Describe and explain environmental concepts and processes in applied contexts.
Science Practice 2: Visual Representations
You’ll learn to explore visual representations of environmental concepts and processes.
You will learn how to:
- Describe and explain how the visual representation of an environmental concept, process, or model relates to broader environmental challenges.
Science Practice 3: Text Analysis
You’ll learn to analyze sources of information about environmental issues.
You will learn how to:
- Define the author’s point of view.
- Describe the author’s viewpoint, assumptions, and reasoning.
- Analyze the reliability of a source and assess the soundness of a study’s findings.
Science Practice 4: Scientific Experiments
You’ll learn how to analyze research studies focusing on environmental principles.
You will learn how to:
- Find a hypothesis or scientific question before conducting an investigation.
- Specify the methodology, design, and/or measurement employed.
- Describe an aspect of the employed study method, design, or measure.
- Observe laboratory settings or collect data from them.
- Describe alterations to a procedure that will affect the results.
Science Practice 5: Data Analysis
You’ll learn to analyze and interpret quantitative data presented in tables, charts, and graphs.
You will learn how to:
- Describe data-based patterns.
- Describe connections between variables represented in data.
- Explain data trends and patterns to draw a conclusion.
- Analyze experimental data and outcomes in light of the specified hypothesis.
- Explain what the evidence suggests or indicates regarding environmental concerns.
Science Practice 6: Mathematical Routines
You’ll learn how to use quantitative methods to talk about ideas about the environment.
You will learn how to:
- Identify a strategy or method that corresponds to the problem to be tackled.
- Utilize relevant mathematical relationships, such as dimension analysis, to solve an issue.
- Calculate a precise numerical answer using the correct units.
Science Practice 7: Environmental Solutions
You’ll learn how to identify solutions to environmental problems.
You will learn how to:
- Describe and explain environmental problems.
- Describe potential solutions or methods for environmental issues.
- Describe downsides, advantages, or unforeseen consequences for suggested solutions.
- Use information and evidence to support a prospective solution.
- In an applied context, make a claim that provides a remedy to an environmental issue.
- Clarify a suggested solution by describing its potential benefits.
Frequently Asked Questions (FAQs)
How many topics are there in AP Environmental Science?
The AP Environmental Science course has 9 units. Each unit is divided into teachable segments known as topics. Each unit has approximately 10 topics.
What are the most important units in AP Environmental Science?
The top 5 units with the most number of questions on the APES MCQ section of the exam can be considered more important than other units. These units are:
- Unit 9: Global Change (15-20%)
- Unit 3: Populations (10-15%)
- Unit 4: Earth Systems and Resources (10-15%)
- Unit 5: Land and Water Use (10-15%)
- Unit 6: Energy Resources and Consumption (10-15%)
Does AP Environmental Science have a lab requirement like AP Biology or AP Chemistry?
Unlike AP Biology or AP Chemistry, AP Environmental Science does not have a strict, separate lab hour requirement set by College Board®. However, hands-on investigations and field-based activities are strongly encouraged. Students are expected to design experiments, collect and analyze data, and apply scientific reasoning to real-world environmental issues. These labs may include field studies, simulations, and data analysis activities. While the format varies by school, inquiry-based learning and practical investigation remain important to mastering course concepts and preparing for the exam.
References
- AP Environmental Science Course And Exam Description. (2025). apstudents.collegeboard.org.
https://apcentral.collegeboard.org/media/pdf/ap-environmental-science-course-and-exam-description.pdf - Course Content. AP Environmental Science. (2026). apstudents.collegeboard.org. Retrieved on
https://apstudents.collegeboard.org/courses/ap-environmental-science
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