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AP® Biology

The Best AP® Biology Review: Topic Summaries, Examples, and Free Practice

Welcome to Albert’s collection of science topic reviews for teaching and reviewing AP® Biology. Teachers and students can explore our easy-to-follow guides below for use at home or in the classroom.

Unit 1 | The Chemistry of Life

What makes water essential for life? How do the structures of biological macromolecules determine their functions?

The review articles below unpack the molecular building blocks of life—carbohydrates, proteins, lipids, and nucleic acids—and how their unique structures enable critical biological processes. From water’s polarity to protein folding and DNA structure, these foundational topics lay the groundwork for mastering Unit 1 of AP® Biology.

1.1 | Structure of Water and Hydrogen Bonding

1.2 | Elements of Life

1.3 | Introduction to Biological Macromolecules

1.4 | Properties of Biological Macromolecules

1.5 | Structure and Function of Biological Macromolecules

1.6 | Nucleic Acids

Unit 2 | Cell Structure and Function

How do organelles work together to keep cells alive? Why is the structure of the cell membrane so important for transport and communication?

The review articles below cover the inner workings of cells, from the specialized roles of mitochondria and ribosomes to the selective permeability of membranes. Learn how compartmentalization, surface area-to-volume ratios, and membrane proteins support essential processes like energy production, molecular transport, and homeostasis.

2.1 | Cell Structure: Subcellular Components

2.2 | Cell Structure and Function

2.3 | Cell Size

2.4 | Plasma Membranes

2.5 | Membrane Permeability

2.6 | Membrane Transport

2.7 | Facilitated Diffusion

2.8 | Tonicity and Osmoregulation

2.9 | Mechanisms of Transport

2.10 | Compartmentalization

2.11 | Origins of Cell Compartmentalization

Unit 3 | Cellular Energetics

How do enzymes speed up chemical reactions in living systems? What cellular processes allow organisms to capture, store, and use energy?

The review articles below explore the role of enzymes, photosynthesis, and cellular respiration in maintaining life’s energy flow. From enzyme structure and function to the electron transport chain and ATP production, this unit breaks down the essential reactions that fuel biological processes.

3.1 | Enzyme Structure

3.2 | Enzyme Catalysis

3.3 | Environmental Impacts on Enzyme Function

3.4 | Cellular Energy

3.5 | Photosynthesis

3.6 | Cellular Respiration

Unit 4 | Cell Communication and Cell Cycle

How do cells send, receive, and respond to signals? What happens when the cell cycle is disrupted?

The review articles below dive into cell communication and the regulation of the cell cycle. Learn how signal transduction pathways guide cellular responses, how feedback mechanisms maintain homeostasis, and how checkpoints ensure healthy cell division. From receptor proteins to mitosis, Unit 4 covers the essential processes that keep organisms functioning and responding to their environments

4.1 | Cell Communication

4.2 | Introduction to Signal Transduction

4.3 | Signal Transduction

4.4 | Changes in Signal Transduction Pathways

4.6 | Cell Cycle

4.7 | Regulation of Cell Cycle

Unit 5 | Heredity

How does meiosis contribute to genetic diversity? What patterns help us predict how traits are inherited?

The review articles below cover the mechanisms of inheritance, from Mendelian genetics to more complex, non-Mendelian patterns. Dive into meiosis, chromosomal inheritance, and genetic variation to understand how traits are passed down and why offspring aren’t identical. Unit 5 sets the foundation for mastering genetics, probability, and patterns of heredity.

5.2 | Meiosis and Genetic Diversity

5.3 | Mendelian Genetics

5.4 | Non-Mendelian Genetics

5.5 | Environmental Effects on Phenotype

5.6 | Chromosomal Inheritance

Unit 6 | Gene Expression and Regulation

How does genetic information flow from DNA to proteins? What happens when mutations or regulatory changes affect gene expression?

The review articles below explore how traits are inherited, expressed, and regulated at the molecular level. From DNA replication and transcription to translation and gene regulation, Unit 6 dives deep into the central dogma of biology. You’ll also learn how mutations, genetic engineering, and changes in genotype influence phenotype and drive variation in populations.

6.1 | DNA and RNA Structure

6.2 | Replication

6.3 | Transcription and RNA Processing

6.4 | Translation

6.5 | Regulation of Gene Expression

6.6 | Gene Expression and Cell Specialization

6.7 | Mutations

6.8 | Biotechnology

Unit 7 | Natural Selection

What drives evolution and speciation over time? How does genetic variation affect survival and biodiversity?

The review articles below explore the mechanisms and evidence behind evolution—from natural selection and genetic drift to phylogenetic trees and extinction events. Learn how mutations, environmental pressures, and reproductive isolation shape species over generations. Unit 7 also covers Hardy-Weinberg equilibrium, common ancestry, and the origin of life to help you connect key evolutionary principles across time and ecosystems.

7.1 | Introduction to Natural Selection

7.2 | Natural Selection

7.3 | Artificial Selection

7.4 | Population Genetics

7.5 | Hardy-Weinberg Equilibrium

7.6 | Evidence of Evolution

7.7 | Common Ancestry

7.8 | Continuing Evolution

7.9 | Phylogeny

7.10 | Speciation

7.11 | Extinction

7.12 | Variations in Populations

7.13 | Origins of Life on Earth

Unit 8 | Ecology

How do organisms interact with each other and their environments? What factors shape ecosystems and influence biodiversity?

The review articles below examine the ecological relationships and environmental factors that impact survival, behavior, and energy use. Explore topics like population dynamics, species interactions, ecosystem stability, and the effects of human activity on biodiversity. Unit 8 connects individual behavior to global systems, helping you understand the balance of life within complex ecological networks.

8.1 | Responses to the Environment

8.2 | Energy Flow Through Ecosystems

8.3 | Population Ecology

8.4 | Effect of Density of Populations

8.5 | Community Ecology

8.6 | Biodiversity

8.7 | Disruptions to Ecosystems