The author team is dedicated to producing the most engaging and current text that is available for undergraduate students who are majoring in biology. We want our students to be inspired by the field of biology and become critical thinkers. To this end, we have made the following changes throughout the entire book.

• Each chapter in the second edition begins with an interesting story or set of observations that will capture the students’ interests as they begin to read a chapter.
• To help students test their knowledge and critical thinking skills, we have increased the number of Concept Check questions that are associated with the figure legends and revised many of the questions at the end of each chapter so they are at a higher level in Bloom’s taxonomy. An answer key for the questions is now provided in an appendix at the end of the book.
• To further help students appreciate the scientific process, the Feature Investigation in each chapter now includes three new elements: a Conclusion, the original journal citation for the experiment, and questions that are directly related to the experiment.
• Many photographs and micrographs have been enlarged or replaced with better images.
• The presentation of the material has been refined by dividing some of the chapters into smaller sections and by the editing of complex sentences.

Particularly innovative changes to our second edition are also found at our website: www.brookerbiology.com.

With regard to the scientific content in the textbook, the author team has worked with hundreds of faculty reviewers to refine the first edition and to update the content so that our students are exposed to the most cutting edge material. Some of the key changes that have occurred are summarized below.

Chemistry Unit

• Chapter 2. The Chemical Basis of Life I: Atoms, Molecules, and Water: This stage-setting chapter now introduces the concepts of matter and energy, chemical equilibrium, condensation/hydrolysis reactions, and expands upon the properties of water (e.g., introducing such concepts as specific heat). The nature and importance of radioisotopes in biology and medicine has also been expanded and clarified, along with a new photo of a whole-body PET scan in a person with cancer.
• Chapter 3. The Chemical Basis of Life II: Organic Molecules: Enzymes are now defined in this early chapter. A new figure has been added that reinforces and elaborates upon the mechanism and importance of dehydration and hydrolysis reactions, which were first introduced in Chapter 2. This figure includes the principles of polymer formation and breakdown. Carbohydrates, lipids, proteins and nucleic acids have been reorganized into distinct major headings for sharper focus.

Cell Unit

• Chapter 4. General Features of Cells: You will find improved illustrations of the cytoskeleton and new content regarding the origin of peroxisomes. The chapter has a new section on Protein Sorting to Organelles and ends with a new section called System Biology of Cells: A Summary, which summarizes the content of Chapter 4 from a systems biology perspective.
• Chapter 5. Membrane Structure, Synthesis, and Transport: This chapter has a new section on the Synthesis of Membrane Components in Eukaryotic Cells. In this section, you will find a description of how cells make phospholipids, a critical topic that is often neglected.
• Chapter 6. An Introduction to Energy, Enzymes, and Metabolism: Based on reviewer comments, this newly created chapter splits the material that was originally in Chapter 7 of the first edition. Chapter 6 provides an introduction to energy, enzymes, and metabolism. It includes added material on ribozymes and a novel section at the end of the chapter that describes the important topic of how cells recycle the building blocks of their organic macromolecules.
• Chapter 7. Cellular Respiration, Fermentation, and Secondary Metabolism: In the second edition, Chapter 7 is now divided into three sections called Cellular Respiration in the Presence of Oxygen, Anaerobic Respiration and Fermentation, and Secondary Metabolism.
• Chapter 8. Photosynthesis: The discussion of the light-dependent reactions is now divided into two sections called Reactions that Harness Light Energy and Molecular Features of Photosystems.
• Chapter 9. Cell Communication: Two sections that were in the first edition on Cellular Receptors and Signal Transduction and the Cellular Response have been streamlined and simplified. A new section called Apoptosis: Programmed Cell Death has been added, which includes a pioneering Feature Investigation that describes how apoptosis was originally discovered.
• Chapter 10. Multicellularity: The figures in this chapter have been greatly improved with a greater emphasis on orientation diagrams that help students visualize where an event is occurring in the cell or in a multicellular organism.

Genetics Unit

• Chapter 11. Nucleic Acid Structure, DNA Replication, and Chromosome Structure: The section on Chromosome Structure has been moved from Chapter 15 in the first edition to this chapter, so that the main molecular features of the genetic material are contained within a single chapter. To help students grasp the major concepts, the topic of DNA replication has been split into two sections entitled Overview of DNA replication and Molecular Mechanism of DNA Replication.
• Chapter 12. Gene Expression at the Molecular Level: Several topics in this chapter have been streamlined to make it easier for students to grasp the big picture of gene expression.
• Chapter 13. Gene Regulation: Topics in gene regulation, such as micro RNAs, have been updated.
• Chapter 14. Mutation, DNA Repair, and Cancer: Information regarding the effects of oncogenes has been modified so that students can appreciate how mutations in particular oncogenes and tumor suppressor genes promote cancer.
• Chapter 15. The Eukaryotic Cell Cycle, Mitosis, and Meiosis: This chapter now begins with a section on the eukaryotic cell cycle, which was in Chapter 9 of the first edition. This new organization allows students to connect how the cell cycle is related to mitosis and meiosis. Also, a new Genomes and Proteomes Connection on cytokinesis has also been added which explains new information on how cells divide.
• Chapter 16. Simple Patterns of Inheritance: To make the topics stand out better for students, this chapter has been subdivided into six sections entitled Mendel’s Laws of Inheritance, The Chromosome Theory of Inheritance, Pedigree Analysis of Human Traits, Sex Chromosomes and X-Linked Inheritance Patterns, Variations in Inheritance Patterns and Their Molecular Basis, and Genetics and Probability.
• Chapter 17. Complex Patterns of Inheritance: The coverage of X-inactivation, genomic imprinting, and maternal effect genes has been streamlined to focus on their impacts on phenotypes.
• Chapter 18. Genetics of Viruses and Bacteria: In response to reviewers of the first edition, this chapter now begins with viruses. The topics of viroids and prions are set apart in their own section. Also, the information regarding bacterial genetics comes at the end of the chapter and is divided into two sections on Genetic Properties of Bacteria and on Gene Transfer between Bacteria.
• Chapter 19. Developmental Genetics: Invertebrate development has been streamlined to focus on the major themes of development. The topic of stem cells has been updated with new information regarding their importance in development and their potential uses in medicine.
• Chapter 20. Genetic Technology: New changes to this chapter include an improved figure on polymerase chain reaction (PCR) and new information regarding the engineering of Bt crops in agriculture.
• Chapter 21. Genomes, Proteomes, and Bioinformatics: This chapter has been updated with the newest information regarding genome sequences. Students are introduced to the NCBI website, and a collaborative problem at the end of the chapter asks the students to identify a mystery gene sequence using the BLAST program.

Evolution Unit

• Chapter 22. The Origin and History of Life: The topic of fossils has been separated into its own section. The second edition has some new information regarding ideas about how polymers can be formed abiotically in an aqueous setting. The role of oxygen has been expanded.
• Chapter 23. An Introduction to Evolution: To help the students make connections between genes and traits, newly discovered examples, such as the role of allelic differences in the Igf2 gene among dog breeds, have been added.
• Chapter 24. Population Genetics: To bring the topics into sharper focus, this chapter is now subdivided into five sections entitled Genes in Populations, Natural Selection, Sexual Selection, Genetic Drift, and Migration and Nonrandom Mating. The important topic of single nucleotide polymorphisms is highlighted near the beginning of the chapter along with its connection to personalized medicine.
• Chapter 25. Origin of Species: The topic of species concepts has been updated with an emphasis on the general lineage concept. Sympatric speciation has been divided into three subtopics which are Polyploidy, Adaptation to Local Environments, and Sexual Selection.
• Chapter 26. Taxonomy and Systematics: The chapter begins with a modern description of taxonomy that divides eukaryotes into eight supergroups. To make each topic easier to follow, the chapter is now subdivided into five sections entitled Taxonomy, Phylogenetic Trees, Cladistics, Molecular Clocks, and Horizontal Gene Transfer.

Diversity Unit

• Chapter 27. Bacteria and Archaea: In this chapter featuring bacterial and archeal diversity, several illustrations have been improved. New information has been added to the Feature Investigation highlighting radiation resistance in Deinococcus.
• Chapter 28. Protists: In this exploration of protist diversity, recent research findings have been incorporated into chapter organization and phylogenetic trees. The evolutionary and ecological importance of cryptomonads and haptophytes are emphasized more completely. Life cycle diagrams have been improved for clarity. A new Genomes and Proteomes Connection features genomic studies of the human pathogens Trichomonas and Giardia.
• Chapter 29. Plants and the Conquest of Land: This chapter on seedless plant diversity incorporates new molecular phylogenetic information on relationships. A new Genomes and Proteomes Connection features the model fern genus Ceratopteris. Life cycles have been improved for greater clarity.
• Chapter 30. The Evolution and Diversity of Modern Gymnosperms and Angiosperms: This chapter highlighting seed plant diversity features a new Genomes and Proteomes Connection on the role of whole genome duplication via autopolyploidy and allopolyploidy in the evolution of seed plants.
• Chapter 31. Fungi: The fungal diversity chapter’s position has been changed to emphasize the close relationship of fungi to animals. There is an increased emphasis upon the role of fungi as pathogens and in other biotic associations. For example, a new Genomes and Proteomes Connection explores the genetic basis of beneficial plant associations with ectomycorrhizal fungi, and a new Feature Investigation features experiments that reveal a partnership between a virus and endophytic fungi that increases heat tolerance in plants. Life cycles of higher fungi have been modified to highlight heterokaryotic phases.
• Chapter 32: An Introduction to Animal Diversity: A brief evolutionary history of animal life has been added. A new figure shows the similarity of a sponge to its likely ancestor, a colonial choanoflagellate. The summary characteristics of the major animal phyla have been simplified.
• Chapter 33: The Invertebrates: With the huge number of invertebrate species and the medical importance of many, a new Genomes and Proteomes Connection discusses DNA barcoding, which may allow for rapid classification of species. The taxonomy of the annelids, arthropods and chordates has been updated.
• Chapter 34: The Vertebrates: The organization of the section headings now follows the vertebrate cladogram introduced at the start of the chapter. A more modern approach to the taxonomy of vertebrates has been adopted, particularly in the discussion of primates. In addition, there is an extended treatment of human evolution and a new Genomes and Proteomes Connection comparing the human and chimpanzee genetic codes.

Plant Unit

• Chapter 35. An Introduction to Flowering Plant Form and Function: This overview of flowering plant structure and function has been revised to better serve as an introduction to Chapters 36-39. A new Genomes and Proteomes Connection features the genetic control of stomatal development, and emphases the role of asymmetric division in the formation of specialized plant cells. A new Feature Investigation reveals how recent experiments have demonstrated the adaptive value of palmate venation in leaves.
• Chapter 36. Flowering Plants: Behavior: In this chapter on plant behavior, the general function of plant hormones in reducing gene repression, thereby allowing gene expression, provides a new unifying theme. As an example, new findings on the step-wise evolution of the interaction between gibberellin and DELLA proteins are highlighted. The Feature Investigation, highlighting classic discoveries concerning auxin’s role in phototropism, has been condensed to achieve greater impact.
• Chapter 37. Flowering Plants: Nutrition: In this chapter on plant nutrition, a new Genomes and Proteomes Connection features the development of legume-Rhizobium symbioses.
• Chapter 38. Flowering Plants: Transport: In this chapter on plant transport, the recent use of synthetic tree models has been added to further highlight experimental approaches toward understanding plant structure-function relationships.
• Chapter 39. Flowering Plants: Reproduction: In this chapter on flowering plant reproduction, greater attention is paid to the tradeoffs of sexual versus asexual reproduction, explaining why both commonly occur and are important in nature and agricultural applications. A new Genomes and Proteomes Connection describes a study of the evolution of plants that reproduce via only asexual means from sexually reproducing ancestral species.

Animal Unit

Key changes to the Animal Unit include reorganization of the chapters such that animal nervous systems are presented first, an expanded emphasis on comparative features of invertebrate and vertebrate animal biology, and updates to each of the “Impact on Public Health” sections.

• Chapter 40. Introduction to Animal Form and Function: This opening chapter has numerous new and improved photos and illustrations, such as those associated with an expanded discussion of different types of connective and epithelial tissue. The utility of the Fick diffusion equation has now been explained, and the very important relationship between surface area and volume in animals has been more thoroughly developed.
• Chapter 41. Neuroscience I: Cells of the Nervous System: Discussion of animal nervous systems has been moved to the beginning chapters of the animal unit, rather than appearing midway through the unit. This was done to better set the stage for all subsequent chapters. In this way, students will gain an appreciation for how the nervous system regulates the functions of all other organ systems. This concept will be continually reinforced as the student progress through the unit. Specific changes to Chapter 41 include an expanded treatment of equilibrium potential, a new discussion and figure on spatial and temporal summation in neurons, and a false-color SEM image of a synapse.
• Chapter 42. Neuroscience II: Evolution and Function of the Brain and Nervous Systems: In this second chapter devoted to nervous systems, the many functions of individual regions of animals’ brains have been more extensively described, and summarized for easy reference in a new table. The epithalamus is now included in this discussion, and the structure and function of the autonomic nervous system has received expanded coverage.
• Chapter 43. Neuroscience III: Sensory Systems: An expanded, detailed and step-by-step treatment of visual and auditory signaling mechanisms has been added to this third and concluding chapter on animal nervous systems. A fascinating comparison of the visual fields of predator and prey animals has been added along with a figure illustrating the differences. A new figure illustrating how people see the world through eyes that are diseased due to glaucoma, macular degeneration, or cataracts is now included.
• Chapter 44. The Muscular-Skeletal System and Locomotion: The events occurring during cross-bridge cycling in muscle have been newly illustrated and detailed. A new figure showing the histologic appearance of healthy versus osteoporotic bones, and the skeleton of a child with rickets has been added.
• Chapter 45. Nutrition, Digestion, and Absorption: An overview figure illustrating the four basic features of energy assimiliation in animals has been added to the beginning of the chapter to set the stage for the later discussions of ingestion, digestion, absorption, and elimination. A more developed comparative emphasis on ingestive and digestive processes in animals has been added, with expanded treatment of adaptations that occur in animals that live in freshwater or marine environments. This is accompanied by newly added photographs of different animals’ teeth being used to chew, tear, grasp, and nip food in their native environments.
• Chapter 46. Control of Energy Balance, Metabolic Rate, and Body Temperature: The text and artwork in this chapter have been considerably streamlined to emphasize major principles of fat digestion and absorption in animals.
• Chapter 47. Circulatory Systems: The local and systemic relationships between pressure, blood flow and resistance are now distinguished more clearly from each other and described in separate sections to emphasize the differences between them. The organization of major topics has been adjusted to better reflect general principles of circulatory systems that apply across taxa, as well as comparative features of vertebrate circulatory systems.
• Chapter 48. Respiratory Systems: This chapter has benefitted from a general upgrade in artwork, but particularly that of the human respiratory system, including the addition of a cross-section through alveoli to illustrate their cellular structures and associations with capillaries.
• Chapter 49. Excretory Systems and Salt and Water Balance: A new photo of proximal tubule cells that reveals their extensive microvilli has been added to reinforce the general principle of surface area adaptations described in earlier chapters. A major reorganization of the manner in which the anatomy and function of nephrons is described has been introduced; each part of the nephron has now been separated into multiple figures for easier understanding.
• Chapter 50. Endocrine Systems: The layout of many figures has been adjusted to improve readability and flow; this has also been facilitated with new orientation illustrations that reveal where within the body a given endocrine organ is located. Along with the new layouts, several figures have been simplified to better illustrate major concepts of hormone synthesis, action, and function. As part of a unit-wide attempt to increase quantitative descriptions of animal biology, additional data have been added in the form of a bar graph to this chapter’s Feature Investigation.
• Chapter 51. Animal Reproduction: The major concepts of asexual and sexual reproduction have been pieced together from various sections of the text into a newly organized single section immediately at the start of the chapter. This reorganization and consolidation of material has eliminated some redundancy, but more importantly allows for a direct, integrated comparison of the two major reproductive processes found in animals. In keeping with a unit-wide effort to improve the flow of major illustrations, certain complex, multi-part figures have been broken into multiple figures linked with the text.
• Chapter 52. Animal Development: To better allow this chapter to be understood on its own, a new introductory section has been added that reinforces basic concepts of cellular and molecular control of animal development that were first introduced in Chapter 19 (Developmental Genetics). The complex processes occurring during gastrulation have been rendered in a newly simplified and clarified series of illustrations. The treatment of Frzb and Wnt proteins in the Genomes and Proteomes Connection has been removed and replaced with a discussion of Spemann’s organizer to better reflect the genetic basis of development across taxa in animals. An amazing series of photographs depicting cleft lip/palette and its surgical reconstruction has also been added to the Impact on Public Health section.
• Chapter 53. Immune Systems: A key change in this chapter is the effective use of additional or re-formatted text boxes in illustrations of multi-step processes. The layout of nearly every figure has been modified for clarity and ease of understanding. The topic of specific immunity has been reorganized such that the cellular and humoral aspects of immunity are clearly defined and distinguished. A new figure illustrating clonal selection has been added.

Ecology Unit

• Chapter 54: An Introduction to Ecology and Biomes: A new table summarizes the various abiotic factors and their effects on organisms. New information on greenhouse gases is provided including their contributions to global warming.
• Chapter 55: Behavioral Ecology: Portions of the section on mating systems have been rewritten in this updated chapter on behavior.
• Chapter 56: Population Ecology: Additional information on population growth models has been provided by discussing the finite rate of increase, , and by discussing growth of black-footed ferret populations in Wyoming, which are recovering after being pushed to the brink of extinction.
• Chapter 57: Species Interactions: This new treatment of species interactions has been streamlined, but at the same time new information is provided on how shark fishing along the eastern seaboard of the United States has disrupted marine food webs.
• Chapter 58: Community Ecology: The content of this chapter has been updated and rewritten and historical information regarding community recovery following volcanic eruption on the island of Krakatau, Indonesia, has been added. The section of species richness has also been reorganized.
• Chapter 59: Ecosystems Ecology: New art and text on the pyramid of numbers has been provided in the first section. The carbon cycle has been rewritten and information on net primary production in different biomes has been updated.
• Chapter 60: Biodiversity and Conservation Biology: The link between biodiversity and ecosystem function has been underscored by better explaining Tilman’s field experiments. The chapter also provides a new section on climate change as a cause of species extinction and loss of biodiversity. A new discussion of bioremediation has been provided in the restoration ecology section.