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AP® Biology CED | Units, Topics & Key Concepts

AP® Biology builds your college-ready science foundation through labs and real practice. Get ready to score well in your class and on your exam with our guide.

Home » AP Course Exam » AP Biology » AP® Biology CED | Units, Topics & Key Concepts

AP Biology is designed to build a strong foundation in college-level biology through a combination of conceptual understanding, data analysis, and hands-on investigation. Throughout the course, students apply biological principles across different contexts while preparing for an exam that includes 60 multiple-choice questions and 6 free-response questions, each weighted across the eight instructional units.

AP Biology Curriculum Framework & Components

The AP® Biology curriculum is structured around a clear framework outlined in the official AP Biology Course and Exam Description (CED). This framework defines what students learn, how they apply biological knowledge, and how those skills are assessed on the AP Bio exam. Understanding this structure helps students see how individual topics connect across the course rather than treating each unit as isolated content.

At a high level, the AP Biology curriculum consists of 2 core components:

Science Practices, which emphasize how biologists think, investigate, and analyze data
Course Content, organized into 8 instructional units

This course content is grounded in Big Ideas, which serve as unifying themes across all AP Biology units and topics. Together, these components explain what AP Biology covers, how students are expected to engage with the material, and why concepts reappear in different contexts throughout the course.

AP Biology Science Practices

Science Practices are essential skills outlined in the AP Biology course and exam description that foster critical thinking and analysis. There are 6 practices you will master by the end of your AP Biology course as part of the broader AP Biology curriculum.

Science Practice	Concept Explanation
Concept Explanation	Describe and explain biological concepts and processes, including their application in various contexts.
Visual Representations	Describe and explain characteristics of visual representations of biological concepts and processes, including their relationships to theoretical and applied contexts. Represent and analyze relationships within biological models, such as diagrams, flowcharts, systems, and mathematical models, and relate them to larger biological principles.
Questions and Methods	Formulate or identify a testable question grounded in an observation, data, or model. Define the null hypothesis and predict potential outcomes of an experiment. Design experimental procedures that align with the question, ensuring: Proper identification of dependent and independent variables. Selection and justification of appropriate control groups. Suggest a revised investigation based on the assessment of the experimental design or evidence.
Representing and Describing Data	Create visual representations of data, such as graphs, scatter plots, or charts (e.g., bar graphs, histograms, line graphs, pie charts, box-and-whisker plots), ensuring: Selection of the appropriate graph type for the dataset Accurate labeling of axes with appropriate units and legends Proper scaling of axes Precise plotting of data points, including error bars Addition of trend lines to illustrate patterns Interpret data from tables or graphs by: Identifying specific data points Highlighting trends and patterns within the dataset Explaining relationships between variables
Statistical Tests and Data Analysis	Conduct mathematical calculations, including: Applying equations outlined in the curriculum Calculating means, rates, ratios, percentages, and percent changes Utilize statistical tools such as confidence intervals and error bars to assess whether sample means differ significantly. Perform chi-square tests to evaluate hypotheses. Analyze data to assess hypotheses or predictions, determining whether to reject or fail to reject the null hypothesis.
Argumentation	Make a claim Support claims using evidence Reason Explain relationships Predict causes and effects

AP Biology Course Content

The 8 AP Biology units are based on 4 Big Ideas. The Big Ideas are introduced first, followed by a breakdown of the individual units.

To enhance your understanding of these concepts, explore our AP Biology Study Guide, available in both print and digital formats, featuring 120+ end-of-topic Check for Understanding questions designed to solidify your knowledge.

4 Big Ideas in AP Biology Curriculum

Big Ideas are the themes explored throughout the curriculum. These AP Biology key concepts are interwoven throughout each of the course’s units because they apply in different ways.

Big Ideas

Big Idea 1: Evolution (EVO)

The process that drives diversity and unity of life
Change of gene frequencies in a population over time leading to biodiversity within and among species
Charles Darwin's theory of natural selection explains how populations evolve through accumulating changes in their genes
Environmental changes, natural catastrophes, and human-induced events alter gene pools, leading to further evolution

Units: Cell Structure and Function, Heredity, Natural Selection, and Ecology

Big Idea 2: Energetics (ENE)

Biological systems depend on energy and molecules to grow, reproduce, and maintain homeostasis
Living systems employ various methods to attain, use, and store energy
Energy deficiencies can have detrimental effects on populations and ecosystems

Units: Chemistry of Life, Cell Structure and Function, Cellular Energetics, Cell Communication and Cell Cycle, and Ecology

Big Idea 3: Information Storage and Transmission (IST)

Living systems store, retrieve, transmit, and respond to information essential to life processes
Genetic information stored in DNA is passed from parent to offspring, influencing survival, growth, and reproduction
Non-inheritable information influences behavior between cells, organisms, and populations, crucial for evolution and natural selection

Units: Chemistry of Life, Cell Communication and Cell Cycle, Heredity, Gene Expression and Regulation, and Ecology

Big Idea 4: Systems Interactions (SYI)

Biological systems interact with each other exhibiting complex properties
Interactions occur at molecular and ecosystem levels, enhancing diversity and resilience to environmental changes

Units: Chemistry of Life, Cell Communication and Cell Cycle, Cellular Energies, Heredity, Natural Selection, and Ecology

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AP Biology Units and Their Topics

The AP Biology course is divided into 8 units, each aligned with the 4 Big Ideas. Below is a breakdown of AP Biology units, their exam weightage, and the key topics covered in each

Unit 1: Chemistry of Life

(8%-11% Exam Weighting | 5-7 Class Periods)

Unit 1 covers the chemical building blocks of life, focusing on elements for carbon-based systems and topics such as water significance, energy acquisition, and macromolecule exchange.

The Big Ideas explored in this unit:

Big Idea 2: Energetics: The role of energy in the synthesis and breakdown of polymers.
Big Idea 3: Information Storage & Transmission: The transmission of information between living systems to ensure survival.
Big Idea 4: Systems Interactions: The importance of water’s polarity in living systems.

Unit 2: Cell Structure and Function

(10%-13% Exam Weighting | 11-13 Class Periods)

Unit 2 dives into topics including the cell membrane, homeostasis, organelles, and cellular products and explores the connection between organelles and other cellular components.

The Big Ideas explored in this unit:

Big Idea 1: Evolution: The eukaryotic cell’s origin.
Big Idea 2: Energetics: The advantages and disadvantages of cellular compartmentalization and the role of transport mechanisms involving the cell membrane in the conservation of energy.
Big Idea 4: Systems Interactions: The effect of the presence or absence of subcellular components on living systems.

Unit 3: Cellular Energetics

(12%-16% Exam Weighting | 14-17 Class Periods)

Unit 3 explores how cells capture, store, and use energy through processes such as photosynthesis and cellular respiration.

The Big Ideas explored in this unit:

Big Idea 2: Energetics: The accumulation and usage of energy by a living system.

Unit 4: Cell Communication and Cell Cycle

(10%-15% Exam Weighting | 9-11 Class Periods)

Unit 4 covers cell communication, transduction pathways, and energy utilization for growth and replication.

The Big Ideas explored in this unit:

Big Idea 2: Energetics: How cells use energy to communicate with each other.
Big Idea 3: Information Storage and Transformation: How the cell cycle helps with the retention of genetic information and why cells communicate with each other.

Unit 5: Heredity

(8%-11% Exam Weighting | 9-11 Class Periods)

Unit 5 explores the topic of heredity, specifically focusing on the biological concepts and processes involved.

The Big Ideas explored in this unit:

Big Idea 1: Evolution: The influence of genetics on our understanding of evolution.
Big Idea 3: Information Storage and Transmission: The importance of characteristics suppression from one generation to the next and arguing Mendel’s laws.
Big Idea 4: Systems Interactions: Influence of the diversity of a species on inheritance.

Unit 6: Gene Expression and Regulation

(12%-16% Exam Weighting | 18-21 Class Periods)

Unit 6 explores the role of nucleic acids in gene expression and investigates the structural differences between DNA and RNA.

The Big Idea explored in this unit:

Big Idea 3: Information Storage and Transmission: The relationship between gene regulation and the continuity of life and the diversification of genetic information from one generation to the next.

Unit 7: Natural Selection

(13%-20% Exam Weighting | 20-23 Class Periods)

Unit 7 delves into the concept of natural selection and its role in driving evolution. The main focus is on how populations adapt to their environments to ensure survival and successful reproduction.

The Big Ideas explored in this unit:

Big Idea 1: Evolution: Defend the theory of evolution in scientific terms and discuss the conditions that could possibly make a population less or more likely to evolve.
Big Idea 4: Systems Interactions: Identify how species interactions can hamper or encourage evolution.

Unit 8: Ecology

(10%-15% Exam Weighting | 18-21 Class Periods)

Unit 8 examines ecology, with a focus on the interconnections among biological systems.

The Big Ideas explored in this unit:

Big Idea 1: Evolution: Biodiversity is essential to the survival and evolution of the species within that ecosystem.
Big Idea 2: Energetics: The relationship between energy and a biological system's health.
Big Idea 3: Information Storage and Transmission: The effect of disruptions in a biological system on the storage and transmission of genetic information.
Big Idea 4: Systems Interactions: The effect of interactions among species on the survival of an ecosystem.

Each of these AP Biology units and topics help build a comprehensive understanding of the subject while preparing you for success on the AP Bio exam. Get a sense of how you might be tested on these with our AP Biology practice tests. You can customize each test by selecting the units you want questions from and choose the number of questions you’d like. You’ll get detailed and illustrated answer explanations for each question, plus the ability to create flashcards using spaced repetition.

Key Concepts Students Learn Across AP Biology Units

While each AP Biology unit focuses on specific topics, several key concepts recur throughout the course. These concepts help students connect ideas across units and apply biological principles in different contexts, which is a central expectation of the AP Biology Course and Exam Description.

Across the AP Biology curriculum, students develop a deeper understanding of:

Structure and function, including how the shape and organization of molecules, cells, and systems influence biological processes.
Energy flow and transformation, such as how energy is captured, stored, transferred, and used to sustain life.
Information storage, transmission, and expression, covering how genetic information is stored in DNA, expressed through gene regulation, and passed across generations.
Evolution and adaptation, explaining how genetic variation and environmental pressures shape populations over time.
Systems interactions, emphasizing how components within biological systems interact, respond to feedback, and maintain stability.

These key concepts appear repeatedly across AP Biology units rather than being confined to a single topic. Understanding how they connect helps students analyze unfamiliar scenarios, interpret data, and construct evidence-based explanations on the AP Bio exam.

AP Biology Labs: An Outline

Lab experiments are part of the AP Biology CED. Labs allow you to create scientific questions, perform experiments, and delve into course subjects. 13 labs covering ideas such as artificial selection, diffusion, osmosis, and cellular processes, as outlined in the AP Biology labs, improve your scientific reasoning and analysis skills. They also will help you:

Master the subject matter
Understand the empirical work
Develop practical skills
Learn the nature of science
Drive your interest in scientific learning
Develop your teamwork skills

As part of your labs, you will need to ask questions, design experiments to test your hypotheses, conduct experiments, analyze your findings, and reach conclusive results. To enhance your understanding and prepare effectively, explore our AP Bio review course, which offers detailed explanations and practice tools tailored to AP Biology topics.

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Frequently Asked Questions (FAQs)

What are the most important topics in AP Biology?

Here is a list of the most important AP Biology topics based on their exam weighting:

Unit 7: Natural Selection (13%-20%)
Unit 3: Cellular Energetics (12%-16%)
Unit 6: Gene Expression and Regulation (12%-16%)
Unit 4: Cell Communication and Cell Cycle (10%-15%)
Unit 8: Ecology (10%-15%)
Unit 2: Cell Structure and Function (10%-13%)
Unit 1: Chemistry of Life (8%-11%)
Unit 5: Heredity (8%-11%)

Can I take AP Biology without taking regular biology?

In most schools, students are expected to complete a high school biology course before enrolling in AP Biology. The AP Biology curriculum builds on foundational concepts such as cell structure, basic genetics, and biological processes that are typically introduced in an introductory biology class. Without this background, students may find it difficult to keep pace with the course. Taking regular biology first helps ensure students are prepared for the depth and analytical skills required in AP Biology.

Is AP Biology an easy subject?

AP Biology could be considered one of the easier AP science subjects. However, it depends on your aptitude for studying biology, the amount of time you can dedicate to studying, etc.To make it easier, the UWorld AP Bio online course provides step-by-step guidance, review tools, and practice questions to build confidence.

What is the hardest unit of AP Biology?

Unit 7: Natural Selection is often considered the hardest unit in AP Biology because it requires students to apply multiple concepts at once, including evolutionary mechanisms, population genetics, and data analysis. Many exam questions in this unit involve interpreting experimental data and defending scientific explanations, which can be challenging without a strong conceptual foundation. However, the difficulty of any unit depends on a student’s strengths. Students who are comfortable with data interpretation and scientific reasoning may find this unit more manageable.

What is the easiest unit of AP Biology?

Unit 1: Chemistry of Life is often considered the easiest unit in AP Biology, especially for students with prior exposure to basic chemistry concepts. This unit focuses on foundational topics such as water properties, macromolecules, and enzyme activity, which are typically more familiar and less abstract than later units. That said, building a strong understanding in Unit 1 is essential, as many concepts introduced here appear throughout the AP Biology curriculum.