Biology 2e

Citation

Clark, M. A., Douglas, M., & Choi, J. (2018). Biology 2e (2nd ed.). OpenStax. Free official edition: https://openstax.org/details/books/biology-2e

Chapter Summary

Biology 2e is OpenStax's textbook for the two-semester introductory biology sequence for science majors, about 1,440 pages in the PDF. Its 47 chapters are grouped into eight units, followed by three short appendices (periodic table, geological time, metric system). The preface describes the approach as comprehensive coverage of foundational research and core concepts "through an evolutionary lens". Every chapter follows the same pattern: an introduction built around a photograph, numbered sections each opening with learning objectives, then key terms, a section-by-section chapter summary, Visual Connection questions, review questions and critical thinking questions. Recurring boxes include Evolution Connection, Scientific Method Connection, Career Connection, Everyday Connection and Link to Learning.

Chapter 1: The Study of Life

The opening chapter introduces science and its methods (inductive and deductive reasoning, hypotheses and theories, basic and applied science, peer-reviewed papers) and the themes of biology: the properties shared by living things, the levels of organization from atoms to the biosphere, and evolution as the source of diversity.

Chapters 2–3: The Chemical Foundation of Life; Biological Macromolecules

Unit 1 supplies the chemistry. Chapter 2 covers atoms, isotopes, ions and bonds, the properties of water, pH and buffers, and the chemistry of carbon. Chapter 3 treats how monomers build polymers and then works through carbohydrates, lipids, proteins (with their four levels of structure) and nucleic acids.

Chapters 4–5: Cell Structure; Structure and Function of Plasma Membranes

Unit 2 begins with microscopy and cell theory, prokaryotic and eukaryotic cells, the endomembrane system, the cytoskeleton and the connections between cells. Chapter 5 presents the fluid mosaic model of the membrane and then passive, active and bulk transport.

Chapters 6–8: Metabolism; Cellular Respiration; Photosynthesis

Three chapters on energy. Chapter 6 introduces free and activation energy, the laws of thermodynamics, ATP and enzymes. Chapter 7 follows glycolysis, pyruvate oxidation and the citric acid cycle, oxidative phosphorylation and fermentation, then the links between carbohydrate, protein and lipid metabolism and the regulation of respiration. Chapter 8 covers the light-dependent reactions and the Calvin cycle.

Chapters 9–10: Cell Communication; Cell Reproduction

Chapter 9 treats signalling molecules and receptors, signal propagation through second messengers and phosphorylation, cellular responses, and signalling in single-celled organisms. Chapter 10 covers the cell cycle and its control, cancer as a failure of that control, and prokaryotic cell division.

Chapters 11–13: Meiosis and Sexual Reproduction; Mendel's Experiments and Heredity; Modern Understandings of Inheritance

Unit 3 opens with meiosis and the variety of sexual life cycles. Chapter 12 reconstructs Mendel's experiments with probability, traits and the laws of inheritance. Chapter 13 introduces the chromosomal theory, Sturtevant's use of recombination frequencies to map linked genes, and inherited disorders of chromosome number and structure.

Chapters 14–17: DNA Structure and Function; Genes and Proteins; Gene Expression; Biotechnology and Genomics

The molecular core of the book. Chapter 14 runs from the historical experiments that identified DNA to its structure, sequencing, replication in prokaryotes and eukaryotes, and repair. Chapter 15 treats the genetic code, transcription, RNA processing and translation. Chapter 16 explains gene regulation in prokaryotes and, level by level, in eukaryotes (epigenetic, transcriptional, post-transcriptional, translational), ending with cancer as a disease of gene regulation. Chapter 17 covers laboratory techniques (gel electrophoresis, PCR, blotting, cloning), genome mapping, whole-genome sequencing and the applications of genomics and proteomics.

Chapters 18–20: Evolution and the Origin of Species; The Evolution of Populations; Phylogenies and the History of Life

Unit 4 presents evolution by natural selection and its evidence, speciation and its rates, population genetics (Hardy–Weinberg equilibrium, the forces that change allele frequencies, adaptive evolution), and the reconstruction of phylogenies from morphological and molecular data, including the difficulties posed by horizontal gene transfer.

Chapters 21–24: Viruses; Prokaryotes: Bacteria and Archaea; Protists; Fungi

Unit 5 surveys biological diversity, starting with viruses (structure, infection, prevention and treatment, prions and viroids), then bacteria and archaea (diversity, structure, metabolism, bacterial diseases, beneficial prokaryotes), the eukaryotic origins and groups of protists, and fungi including their ecology and their importance to people.

Chapters 25–26: Seedless Plants; Seed Plants

The evolution of land plants from green algae through bryophytes and seedless vascular plants, then gymnosperms and angiosperms and the role of seed plants in ecosystems and human life.

Chapters 27–29: Introduction to Animal Diversity; Invertebrates; Vertebrates

The features used to classify animals and animal phylogeny, then the invertebrate phyla organized by superphylum (Lophotrochozoa, Ecdysozoa, Deuterostomia), and the vertebrates from fishes to mammals, ending with the evolution of primates.

Chapters 30–32: Plant Form and Physiology; Soil and Plant Nutrition; Plant Reproduction

Unit 6 covers the plant body (stems, roots, leaves), water and solute transport, plant sensing and responses, plant nutrition and soil, and sexual and asexual reproduction in plants.

Chapters 33–43: Animal Structure and Function

Unit 7 is the longest. Chapter 33 introduces animal form, the four primary tissues and homeostasis. It is followed by chapters on nutrition and digestion (34), the nervous system (35), sensory systems (36), the endocrine system (37), the musculoskeletal system (38), the respiratory system (39), the circulatory system (40), osmotic regulation and excretion (41), the immune system (42), and animal reproduction and development (43). The chapters are comparative in principle but, as the preface says, keep a focus on human anatomy and physiology.

Chapters 44–47: Ecology and the Biosphere; Population and Community Ecology; Ecosystems; Conservation Biology and Biodiversity

Unit 8 moves from biogeography, biomes and climate change (44), through population demography, life histories, human population growth, community ecology and behavioural biology (45), to energy flow and biogeochemical cycles (46), and finally the biodiversity crisis, threats to biodiversity and its preservation (47).

Key Concepts

Units 1–2: Chemistry and the cell (Chapters 1–10)

• Levels of organization: life is organized hierarchically from atoms and molecules to cells, organisms, populations, communities, ecosystems and the biosphere.
• Structure and function of macromolecules: carbohydrates, lipids, proteins and nucleic acids are built from monomers; for proteins, shape determines function.
• Fluid mosaic model: the membrane as a phospholipid bilayer with embedded, mobile proteins controlling transport.
• Free energy and enzymes: reactions release or consume free energy; enzymes lower activation energy.
• Cellular respiration and photosynthesis: complementary pathways for capturing and releasing energy, linked through ATP and electron carriers.
• Signal transduction: how a signal at a receptor is relayed by second messengers to a cellular response.

Unit 3: Genetics (Chapters 11–17)

• Mendelian inheritance and linkage: segregation and independent assortment, and their modification by genes lying close together on chromosomes.
• Central dogma: DNA is replicated and transcribed into RNA, which is translated into protein.
• Levels of gene regulation: in eukaryotes, expression is controlled from chromatin through transcription and RNA processing to translation and protein modification.
• Genomics: the study of whole genomes through mapping and sequencing.

Units 4–5: Evolution and diversity (Chapters 18–29)

• Natural selection and speciation: adaptation of populations and the origin of new species through reproductive isolation.
• Hardy–Weinberg equilibrium: the null model for detecting evolutionary change in allele frequencies.
• Phylogeny: evolutionary relationships inferred from homologous traits and molecular data.
• Three domains: the division of life into Bacteria, Archaea and Eukarya based on molecular evidence.

Units 6–8: Organisms and ecology (Chapters 30–47)

• Plant transport: movement of water and solutes through xylem and phloem.
• Homeostasis: the dynamic maintenance of internal conditions around set points by animal organ systems.
• Innate and adaptive immunity: nonspecific defences and specific, memory-forming responses.
• Population growth and carrying capacity: exponential and logistic growth and the limits environments impose.
• Energy flow and biogeochemical cycles: how energy passes through and matter cycles within ecosystems.

Critical Analysis

Strengths

• Complete and free. The book covers the full scope of a majors sequence, from chemistry to conservation, in a single openly licensed text (CC BY-NC-SA 4.0) available free in web view and PDF. Instructors can reorder or omit chapters without penalty to students.
• Consistent, study-friendly structure. Every chapter has the same apparatus: learning objectives for each section, key terms, a section-by-section summary and three tiers of questions. The preface reports more than 350 new review and critical thinking questions in the second edition. Answers to odd-numbered questions are available to students in a separate solution manual.
• Science as a process. Chapter 1 sets out the scientific method, and the Scientific Method Connection boxes walk through experiments (the preface's examples include determining the time spent in cell-cycle stages and testing independent assortment). Several chapters, notably 12–14, build their content from the historical experiments that established it.
• Breadth in organismal biology. Unlike many shorter introductions, it gives full units to plant structure and function (Chapters 30–32) and to animal physiology system by system (Chapters 33–43), and treats invertebrate diversity in some detail.

Limitations

• Very long. At 47 chapters and more than 1,400 pages it holds far more than two semesters of material. Students working alone need a plan for what to skip.
• Uneven revision. The preface explains that the second edition made "very targeted changes at the section level" with no chapter reorganization: about twenty chapters were wholly revised and about fifteen revised mainly for readability. Some phrasing remains loose. The Chapter 18 summary, for example, describes evolution as allowing "more desirable characteristics" to pass to the next generation, wording that can encourage the teleological misconceptions the same unit warns against.
• US-centred examples and a dated base. The chapter openers draw heavily on American cases (Asian carp in Illinois rivers, the 1993 hantavirus outbreak in the southwestern United States, Chesapeake Bay). The book's structure dates from the 2012 first edition, so fast-moving areas such as genomics may need supplementing from current sources.
• Ancillaries partly restricted. Answers to even-numbered questions and other instructor resources require a verified instructor account.

Where It Fits in the Course

Biology 2e sits alongside the major commercial majors' textbooks in this course. Campbell Biology is the standard comprehensive introduction and covers essentially the same ground. Sadava and colleagues' Life: The Science of Biology and Freeman's Biological Science are comprehensive introductions with a stronger emphasis on experiments and inquiry. Any of these can replace or supplement Biology 2e chapter for chapter. For students who need a lighter text, OpenStax's own Concepts of Biology covers the same topics in 21 chapters for non-majors. Several of its chapters were adapted from the same material, so it works as a gentler first reading of difficult topics.

Two books in the course go further rather than wider. Molecular Cell Biology by Lodish and colleagues takes the cell and molecular content of Units 2–3 to research depth, built on the experiments behind each model. Milo and Phillips's Cell Biology by the Numbers teaches cell biology through quantitative estimates, a good companion for students who finish Chapters 4–10 wanting to know how big, how many and how fast. Both are natural next steps after the first year rather than substitutes for it.

How to Use This Book

The book is written for first-year science majors. High-school biology and chemistry are enough; Chapter 2 reviews the needed chemistry, and the appendices give the periodic table, geological time and metric units.

A practical plan for a two-semester sequence:

• Semester 1 (core): Chapters 1–20 — chemistry, the cell, energy, genetics, molecular biology and evolution. Chapters 6–8 and 14–16 are the hardest and deserve the most time.
• Semester 2 (select): Unit 5 diversity (Chapters 21–29), then either the plant unit (30–32) or the animal physiology unit (33–43), or a selection of both, and the ecology unit (44–47). Most courses cannot cover all 27 of these chapters.
• Optional depth: Chapter 9 (cell communication), Chapter 17 (biotechnology), the detailed invertebrate sections of Chapter 28 and the behavioural biology section of Chapter 45 can be cut or assigned as extension reading.

For each section, read the learning objectives first and check them against the chapter summary afterwards. Do the Visual Connection questions with the figure in front of you; they test whether you can read a diagram, which exams often require. Use the odd-numbered answers in the student solution manual to check your work. The Link to Learning animations are especially useful for processes that are hard to picture on a page, such as the electron transport chain, meiosis and the action potential.

Edition and Sources

This guide is based on Biology 2e (second edition, original publication 2018; senior contributing authors Mary Ann Clark, Matthew Douglas and Jung Choi), read in the free official PDF linked from the OpenStax book page, https://openstax.org/details/books/biology-2e (PDF last updated July 2025, CC BY-NC-SA 4.0 licence). The guide draws on the preface (scope, second-edition changes, pedagogy and features), the full table of contents, and for all 47 chapters the chapter introductions, every section heading and the section-by-section chapter summaries, with Chapters 1, 13, 18–20 and 45 read in more detail.