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Biology 2e

OpenStax · 257 sections in 48 chapters. Each section is its own page.

Front matter

• Preface

• Measurements and the Metric System

The Study of Life

• Introduction

• The Science of Biology

• Themes and Concepts of Biology

The Chemical Foundation of Life

• Introduction

• Atoms, Isotopes, Ions, and Molecules: The Building Blocks

• Water

• Carbon

Biological Macromolecules

• Introduction

• Synthesis of Biological Macromolecules

• Carbohydrates

• Lipids

• Proteins

• Nucleic Acids

Cell Structure

• Introduction

• Studying Cells

• Prokaryotic Cells

• Eukaryotic Cells

• The Endomembrane System and Proteins

• The Cytoskeleton

• Connections between Cells and Cellular Activities

Structure and Function of Plasma Membranes

• Introduction

• Components and Structure

• Passive Transport

• Active Transport

• Bulk Transport

Metabolism

• Introduction

• Energy and Metabolism

• Potential, Kinetic, Free, and Activation Energy

• The Laws of Thermodynamics

• ATP: Adenosine Triphosphate

• Enzymes

Cellular Respiration

• Introduction

• Energy in Living Systems

• Glycolysis

• Oxidation of Pyruvate and the Citric Acid Cycle

• Oxidative Phosphorylation

• Metabolism without Oxygen

• Connections of Carbohydrate, Protein, and Lipid Metabolic Pathways

• Regulation of Cellular Respiration

Photosynthesis

• Introduction

• Overview of Photosynthesis

• The Light-Dependent Reactions of Photosynthesis

• Using Light Energy to Make Organic Molecules

Cell Communication

• Introduction

• Signaling Molecules and Cellular Receptors

• Propagation of the Signal

• Response to the Signal

• Signaling in Single-Celled Organisms

Cell Reproduction

• Introduction

• Cell Division

• The Cell Cycle

• Control of the Cell Cycle

• Cancer and the Cell Cycle

• Prokaryotic Cell Division

Meiosis and Sexual Reproduction

• Introduction

• The Process of Meiosis

• Sexual Reproduction

Mendel's Experiments and Heredity

• Introduction

• Mendel’s Experiments and the Laws of Probability

• Characteristics and Traits

• Laws of Inheritance

Modern Understandings of Inheritance

• Introduction

• Chromosomal Theory and Genetic Linkage

• Chromosomal Basis of Inherited Disorders

DNA Structure and Function

• Introduction

• Historical Basis of Modern Understanding

• DNA Structure and Sequencing

• Basics of DNA Replication

• DNA Replication in Prokaryotes

• DNA Replication in Eukaryotes

• DNA Repair

Genes and Proteins

• Introduction

• The Genetic Code

• Prokaryotic Transcription

• Eukaryotic Transcription

• RNA Processing in Eukaryotes

• Ribosomes and Protein Synthesis

Gene Expression

• Introduction

• Regulation of Gene Expression

• Prokaryotic Gene Regulation

• Eukaryotic Epigenetic Gene Regulation

• Eukaryotic Transcription Gene Regulation

• Eukaryotic Post-transcriptional Gene Regulation

• Eukaryotic Translational and Post-translational Gene Regulation

• Cancer and Gene Regulation

Biotechnology and Genomics

• Introduction

• Biotechnology

• Mapping Genomes

• Whole-Genome Sequencing

• Applying Genomics

• Genomics and Proteomics

Evolution and the Origin of Species

• Introduction

• Understanding Evolution

• Formation of New Species

• Reconnection and Speciation Rates

The Evolution of Populations

• Introduction

• Population Evolution

• Population Genetics

• Adaptive Evolution

Phylogenies and the History of Life

• Introduction

• Organizing Life on Earth

• Determining Evolutionary Relationships

• Perspectives on the Phylogenetic Tree

Viruses

• Introduction

• Viral Evolution, Morphology, and Classification

• Virus Infections and Hosts

• Prevention and Treatment of Viral Infections

• Other Acellular Entities: Prions and Viroids

Prokaryotes: Bacteria and Archaea

• Introduction

• Prokaryotic Diversity

• Structure of Prokaryotes: Bacteria and Archaea

• Prokaryotic Metabolism

• Bacterial Diseases in Humans

• Beneficial Prokaryotes

Protists

• Introduction

• Eukaryotic Origins

• Characteristics of Protists

• Groups of Protists

• Ecology of Protists

Fungi

• Introduction

• Characteristics of Fungi

• Classifications of Fungi

• Ecology of Fungi

• Fungal Parasites and Pathogens

• Importance of Fungi in Human Life

Seedless Plants

• Introduction

• Early Plant Life

• Green Algae: Precursors of Land Plants

• Bryophytes

• Seedless Vascular Plants

Seed Plants

• Introduction

• Evolution of Seed Plants

• Gymnosperms

• Angiosperms

• The Role of Seed Plants

Introduction to Animal Diversity

• Introduction

• Features of the Animal Kingdom

• Features Used to Classify Animals

• Animal Phylogeny

• The Evolutionary History of the Animal Kingdom

Invertebrates

• Introduction

• Phylum Porifera

• Phylum Cnidaria

• Superphylum Lophotrochozoa: Flatworms, Rotifers, and Nemerteans

• Superphylum Lophotrochozoa: Mollusks and Annelids

• Superphylum Ecdysozoa: Nematodes and Tardigrades

• Superphylum Ecdysozoa: Arthropods

• Superphylum Deuterostomia

Vertebrates

• Introduction

• Chordates

• Fishes

• Amphibians

• Reptiles

• Birds

• Mammals

• The Evolution of Primates

Plant Form and Physiology

• Introduction

• The Plant Body

• Stems

• Roots

• Leaves

• Transport of Water and Solutes in Plants

• Plant Sensory Systems and Responses

Soil and Plant Nutrition

• Introduction

• Nutritional Requirements of Plants

• The Soil

• Nutritional Adaptations of Plants

Plant Reproduction

• Introduction

• Reproductive Development and Structure

• Pollination and Fertilization

• Asexual Reproduction

The Animal Body: Basic Form and Function

• Introduction

• Animal Form and Function

• Animal Primary Tissues

• Homeostasis

Animal Nutrition and the Digestive System

• Introduction

• Digestive Systems

• Nutrition and Energy Production

• Digestive System Processes

• Digestive System Regulation

The Nervous System

• Introduction

• Neurons and Glial Cells

• How Neurons Communicate

• The Central Nervous System

• The Peripheral Nervous System

• Nervous System Disorders

Sensory Systems

• Introduction

• Sensory Processes

• Somatosensation

• Taste and Smell

• Hearing and Vestibular Sensation

• Vision

The Endocrine System

• Introduction

• Types of Hormones

• How Hormones Work

• Regulation of Body Processes

• Regulation of Hormone Production

• Endocrine Glands

The Musculoskeletal System

• Introduction

• Types of Skeletal Systems

• Bone

• Joints and Skeletal Movement

• Muscle Contraction and Locomotion

The Respiratory System

• Introduction

• Systems of Gas Exchange

• Gas Exchange across Respiratory Surfaces

• Breathing

• Transport of Gases in Human Bodily Fluids

The Circulatory System

• Introduction

• Overview of the Circulatory System

• Components of the Blood

• Mammalian Heart and Blood Vessels

• Blood Flow and Blood Pressure Regulation

Osmotic Regulation and Excretion

• Introduction

• Osmoregulation and Osmotic Balance

• The Kidneys and Osmoregulatory Organs

• Excretion Systems

• Nitrogenous Wastes

• Hormonal Control of Osmoregulatory Functions

The Immune System

• Introduction

• Innate Immune Response

• Adaptive Immune Response

• Antibodies

• Disruptions in the Immune System

Animal Reproduction and Development

• Introduction

• Reproduction Methods

• Fertilization

• Human Reproductive Anatomy and Gametogenesis

• Hormonal Control of Human Reproduction

• Human Pregnancy and Birth

• Fertilization and Early Embryonic Development

• Organogenesis and Vertebrate Axis Formation

Ecology and the Biosphere

• Introduction

• The Scope of Ecology

• Biogeography

• Terrestrial Biomes

• Aquatic Biomes

• Climate and the Effects of Global Climate Change

Population and Community Ecology

• Introduction

• Population Demography

• Life Histories and Natural Selection

• Environmental Limits to Population Growth

• Population Dynamics and Regulation

• Human Population Growth

• Community Ecology

• Behavioral Biology: Proximate and Ultimate Causes of Behavior

Ecosystems

• Introduction

• Ecology of Ecosystems

• Energy Flow through Ecosystems

• Biogeochemical Cycles

Conservation Biology and Biodiversity

• Introduction

• The Biodiversity Crisis

• The Importance of Biodiversity to Human Life

• Threats to Biodiversity

• Preserving Biodiversity

Attribution. Biology 2e, OpenStax, Rice University, and the contributing authors credited in the book. Licensed under Creative Commons Attribution 4.0 International. Source revision d2779c2edf of openstax/osbooks-biology-bundle (2026-02-03). CC BY 4.0. Original source ↗. Text edition of a pinned CC BY 4.0 source revision of the OpenStax book, converted from CNXML by the EvidenceHelix importer. Original prose, learning objectives, tables, exercises, glossary and captions are preserved; images are not copied (figures link to the original source and keep their credits). No new content was added. Later revisions of this book can carry different licence terms and are not used.