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Concepts of Biology

SENIOR CONTRIBUTING AUTHORS SAMANTHA FOWLER, CLAYTON STATE UNIVERSITY REBECCA ROUSH, SANDHILLS COMMUNITY COLLEGE JAMES WISE, HAMPTON UNIVERSITY

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Table of Contents Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Unit 1. The Cellular Foundation of Life

Chapter 1: Introduction to Biology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.1 Themes and Concepts of Biology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2 The Process of Science . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Chapter 2: Chemistry of Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 2.1 The Building Blocks of Molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.2 Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 2.3 Biological Molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Chapter 3: Cell Structure and Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 3.1 How Cells Are Studied . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 3.2 Comparing Prokaryotic and Eukaryotic Cells . . . . . . . . . . . . . . . . . . . . . . . 59 3.3 Eukaryotic Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 3.4 The Cell Membrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 3.5 Passive Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 3.6 Active Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Chapter 4: How Cells Obtain Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 4.1 Energy and Metabolism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 4.2 Glycolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 4.3 Citric Acid Cycle and Oxidative Phosphorylation . . . . . . . . . . . . . . . . . . . . . 104 4.4 Fermentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 4.5 Connections to Other Metabolic Pathways . . . . . . . . . . . . . . . . . . . . . . . . 111

Chapter 5: Photosynthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 5.1 Overview of Photosynthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 5.2 The Light-Dependent Reactions of Photosynthesis . . . . . . . . . . . . . . . . . . . . 122 5.3 The Calvin Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

Unit 2. Cell Division and Genetics Chapter 6: Reproduction at the Cellular Level . . . . . . . . . . . . . . . . . . . . . . . . . . 135

6.1 The Genome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 6.2 The Cell Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 6.3 Cancer and the Cell Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 6.4 Prokaryotic Cell Division . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

Chapter 7: The Cellular Basis of Inheritance . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 7.1 Sexual Reproduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 7.2 Meiosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 7.3 Errors in Meiosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

Chapter 8: Patterns of Inheritance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 8.1 Mendel’s Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 8.2 Laws of Inheritance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 8.3 Extensions of the Laws of Inheritance . . . . . . . . . . . . . . . . . . . . . . . . . . 185

Unit 3. Molecular Biology and Biotechnology Chapter 9: Molecular Biology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199

9.1 The Structure of DNA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 9.2 DNA Replication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 9.3 Transcription . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210 9.4 Translation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 9.5 How Genes Are Regulated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216

Chapter 10: Biotechnology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 10.1 Cloning and Genetic Engineering . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 10.2 Biotechnology in Medicine and Agriculture . . . . . . . . . . . . . . . . . . . . . . . 232 10.3 Genomics and Proteomics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236

Unit 4. Evolution and the Diversity of Life Chapter 11: Evolution and Its Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249

11.1 Discovering How Populations Change . . . . . . . . . . . . . . . . . . . . . . . . . . 250 11.2 Mechanisms of Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255 11.3 Evidence of Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 11.4 Speciation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261

11.5 Common Misconceptions about Evolution . . . . . . . . . . . . . . . . . . . . . . . . 266 Chapter 12: Diversity of Life . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275

12.1 Organizing Life on Earth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 12.2 Determining Evolutionary Relationships . . . . . . . . . . . . . . . . . . . . . . . . . 280

Chapter 13: Diversity of Microbes, Fungi, and Protists . . . . . . . . . . . . . . . . . . . . . 291 13.1 Prokaryotic Diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292 13.2 Eukaryotic Origins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 13.3 Protists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304 13.4 Fungi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311

Chapter 14: Diversity of Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325 14.1 The Plant Kingdom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326 14.2 Seedless Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332 14.3 Seed Plants: Gymnosperms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338 14.4 Seed Plants: Angiosperms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343

Chapter 15: Diversity of Animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355 15.1 Features of the Animal Kingdom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356 15.2 Sponges and Cnidarians . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361 15.3 Flatworms, Nematodes, and Arthropods . . . . . . . . . . . . . . . . . . . . . . . . . 367 15.4 Mollusks and Annelids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374 15.5 Echinoderms and Chordates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380 15.6 Vertebrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385

Unit 5. Animal Structure and Function Chapter 16: The Body’s Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403

16.1 Homeostasis and Osmoregulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404 16.2 Digestive System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408 16.3 Circulatory and Respiratory Systems . . . . . . . . . . . . . . . . . . . . . . . . . . 414 16.4 Endocrine System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 420 16.5 Musculoskeletal System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 426 16.6 Nervous System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431

Chapter 17: The Immune System and Disease . . . . . . . . . . . . . . . . . . . . . . . . . 449 17.1 Viruses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450 17.2 Innate Immunity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456 17.3 Adaptive Immunity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459 17.4 Disruptions in the Immune System . . . . . . . . . . . . . . . . . . . . . . . . . . . 468

Chapter 18: Animal Reproduction and Development . . . . . . . . . . . . . . . . . . . . . . 477 18.1 How Animals Reproduce . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478 18.2 Development and Organogenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 482 18.3 Human Reproduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484

Unit 6. Ecology Chapter 19: Population and Community Ecology . . . . . . . . . . . . . . . . . . . . . . . . 499

19.1 Population Demographics and Dynamics . . . . . . . . . . . . . . . . . . . . . . . . 500 19.2 Population Growth and Regulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 504 19.3 The Human Population . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 510 19.4 Community Ecology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514

Chapter 20: Ecosystems and the Biosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . 529 20.1 Energy Flow through Ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . 530 20.2 Biogeochemical Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537 20.3 Terrestrial Biomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 547 20.4 Aquatic and Marine Biomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 554

Chapter 21: Conservation and Biodiversity . . . . . . . . . . . . . . . . . . . . . . . . . . . 567 21.1 Importance of Biodiversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 568 21.2 Threats to Biodiversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575 21.3 Preserving Biodiversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 582

Appendix A: The Periodic Table of Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593 Appendix B: Geological Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 595 Appendix C: Measurements and the Metric System . . . . . . . . . . . . . . . . . . . . . . . . . 597 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 605

This OpenStax book is available for free at http://cnx.org/content/col11487/1.9

PREFACE Welcome to Concepts of Biology, an OpenStax resource. This textbook has been created with several goals in mind: accessibility, customization, and student engagement—all while encouraging students toward high levels of academic scholarship. Instructors and students alike will find that this textbook offers a strong introduction to biology in an accessible format.

About OpenStax OpenStax is a non-profit organization committed to improving student access to quality learning materials. Our free textbooks are developed and peer-reviewed by educators to ensure they are readable, accurate, and meet the scope and sequence requirements of today’s college courses. Unlike traditional textbooks, OpenStax resources live online and are owned by the community of educators using them. Through our partnerships with companies and foundations committed to reducing costs for students, OpenStax is working to improve access to higher education for all. OpenStax is an initiative of Rice University and is made possible through the generous support of several philanthropic foundations.

About OpenStax's Resources OpenStax resources provide quality academic instruction. Three key features set our materials apart from others: they can be customized by instructors for each class, they are a “living” resource that grows online through contributions from science educators, and they are available free or for minimal cost.

Customization OpenStax learning resources are designed to be customized for each course. Our textbooks provide a solid foundation on which instructors can build, and our resources are conceived and written with flexibility in mind. Instructors can select the sections most relevant to their curricula and create a textbook that speaks directly to the needs of their classes and student body. Teachers are encouraged to expand on existing examples by adding unique context via geographically localized applications and topical connections.

Concepts of Biology can be easily customized using our online platform. Simply select the content most relevant to your syllabus and create a textbook that speaks directly to the needs of your class. Concepts of Biology is organized as a collection of sections that can be rearranged, modified, and enhanced through localized examples or to incorporate a specific theme of your course. This customization feature will help bring biology to life for your students and will ensure that your textbook truly reflects the goals of your course.

Curation To broaden access and encourage community curation, Concepts of Biology is “open source” licensed under a Creative Commons Attribution (CC-BY) license. The scientific community is invited to submit examples, emerging research, and other feedback to enhance and strengthen the material and keep it current and relevant for today’s students. You can submit your suggestions to info@openstaxcollege.org.

Cost Our textbooks are available for free online, and in low-cost print and e-book editions.

About Concepts of Biology Concepts of Biology is designed for the single-semester introduction to biology course for non-science majors, which for many students is their only college-level science course. As such, this course represents an important opportunity for students to develop the necessary knowledge, tools, and skills to make informed decisions as they continue with their lives. Rather than being mired down with facts and vocabulary, the typical non-science major student needs information presented in a way that is easy to read and understand. Even more importantly, the content should be meaningful. Students do much better when they understand why biology is relevant to their everyday lives. For these reasons, Concepts of Biology is grounded on an evolutionary basis and includes exciting features that highlight careers in the biological sciences and everyday applications of the concepts at hand. We also strive to show the interconnectedness of topics within this extremely broad discipline. In order to meet the needs of today’s instructors and students, we maintain the overall organization and coverage found in most syllabi for this course. A strength of Concepts of Biology is that instructors can customize the book,

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adapting it to the approach that works best in their classroom. Concepts of Biology also includes an innovative art program that incorporates critical thinking and clicker questions to help students understand—and apply—key concepts.

Coverage and Scope Our Concepts of Biology textbook adheres to the scope and sequence of most one-semester non-majors courses nationwide. We also strive to make biology, as a discipline, interesting and accessible to students. In addition to a comprehensive coverage of core concepts and foundational research, we have incorporated features that draw learners into the discipline in meaningful ways. Our scope of content was developed after surveying over a hundred biology professors and listening to their coverage needs. We provide a thorough treatment of biology’s fundamental concepts with a scope that is manageable for instructors and students alike.

Unit 1: The Cellular Foundation of Life. Our opening unit introduces students to the sciences, including the process of science and the underlying concepts from the physical sciences that provide a framework within which learners comprehend biological processes. Additionally, students will gain solid understanding of the structures, functions, and processes of the most basic unit of life: the cell.

Unit 2: Cell Division and Genetics. Our genetics unit takes learners from the foundations of cellular reproduction to the experiments that revealed the basis of genetics and laws of inheritance.

Unit 3: Molecular Biology and Biotechnology. Students will learn the intricacies of DNA, protein synthesis, and gene regulation and current applications of biotechnology and genomics.

Unit 4: Evolution and the Diversity of Life. The core concepts of evolution are discussed in this unit with examples illustrating evolutionary processes. Additionally, the evolutionary basis of biology reappears throughout the textbook in general discussion and is reinforced through special call-out features highlighting specific evolution-based topics. The diversity of life is explored with detailed study of various organisms and discussion of emerging phylogenetic relationships between and among bacteria, protist kingdoms, fungi, plants, and animals.

Unit 5: Animal Structure and Function. An introduction to the form and function of the animal body is followed by chapters on the immune system and animal development. This unit touches on the biology of all organisms while maintaining an engaging focus on human anatomy and physiology that helps students connect to the topics.

Unit 6: Ecology. Ecological concepts are broadly covered in this unit, with features highlighting localized, real-world issues of conservation and biodiversity.

Pedagogical Foundation and Features Because of the impact science has on students and society, an important goal of science education is to achieve a scientifically literate population that consistently makes informed decisions. Scientific literacy transcends a basic understanding of scientific principles and processes to include the ability to make sense of the myriad instances where people encounter science in day-to-day life. Thus, a scientifically literate person is one who uses science content knowledge to make informed decisions, either personally or socially, about topics or issues that have a connection with science. Concepts of Biology is grounded on a solid scientific base and designed to promote scientific literacy. Throughout the text, you will find features that engage the students in scientific inquiry by taking selected topics a step further.

Evolution in Action features uphold the importance of evolution to all biological study through discussions like “Global Decline of Coral Reefs” and “The Red Queen Hypothesis.”

Career in Action features present information on a variety of careers in the biological sciences, introducing students to the educational requirements and day-to-day work life of a variety of professions, such as forensic scientists, registered dietitians, and biogeographers.

Biology in Action features tie biological concepts to emerging issues and discuss science in terms of everyday life. Topics include “Invasive Species” and “Photosynthesis at the Grocery Store.”

Art and Animations that Engage Our art program takes a straightforward approach designed to help students learn the concepts of biology through simple, effective illustrations, photos, and micrographs. Concepts of Biology also incorporates links to relevant animations and interactive exercises that help bring biology to life for students.

Art Connection features call out core figures in each chapter for student attention. Questions about key figures, including clicker questions that can be used in the classroom, engage students’ critical thinking and analytical abilities to ensure their genuine understanding of the concept at hand.

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Concepts in Action features direct students to online interactive exercises and animations to add a fuller context and examples to core content.

About Our Team Concepts of Biology would not be possible if not for the tremendous contributions of the authors and community reviewing team

Senior Contributing Authors

Samantha Fowler Clayton State University

Rebecca Roush Sandhills Community College

James Wise Hampton University

Contributing Authors and Reviewers

Mark Belk Brigham Young University

Lisa Boggs Southwestern Oklahoma State University

Sherryl Broverman Duke University

David Byres Florida State College at Jacksonville

Aaron Cassill The University of Texas at San Antonio

Karen Champ College of Central Florida

Sue Chaplin University of St. Thomas

Diane Day Clayton State University

Jean DeSaix University of North Carolina at Chapel Hill

David Hunnicutt St. Norbert College

Barbara Kuehner Hawaii Community College

Brenda Leady University of Toledo

Bernie Marcus Genesee Community College

Flora Mhlanga Lipscomb University

Madeline Mignone Dominican College

Elizabeth Nash Long Beach City College

Mark Newton San Jose City College

Diana Oliveras University of Colorado Boulder

Ann Paterson Williams Baptist College

Joel Piperberg Millersville University

Nick Reeves Mt. San Jacinto College

Ann Reisenauer San Jose State University

Lynn Rumfelt Gordon College

Michael Rutledge Middle Tennessee State University

Edward Saiff Ramapo College of New Jersey

Brian Shmaefsky Kingwood College

Gary Shultz Marshall University

Donald Slish SUNY Plattsburgh

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Anh-Hue Tu Georgia Southwestern State University

Elena Zoubina Bridgewater State University

Learning Resources Wiley Plus for Biology-Fall 2013 Pilot

WileyPLUS provides an engaging online environment for effective teaching and learning. WileyPLUS builds students’ confidence because it takes the guesswork out of studying by providing a clear roadmap; what to do, how to do it, and if they did it right. With WileyPLUS, students take more initiative. Therefore, the course has a greater impact on their learning experience. Adaptive tools provide students with a personal, adaptive learning experience so they can build their proficiency on topics and use their study time most effectively. Please let us know if you would like to participate in a Fall 2013 Pilot.

Concepts of Biology Powerpoint Slides (faculty only)

The PowerPoint slides are based on the extensive illustrations from College Physics. They can be edited, incorporated into lecture notes, and you are free to share with anyone in the community. This is a restricted item requiring faculty registration. NOTE: This file is very large and may take some time to download.

SimBio (Laboratory)

SimBio’s interactive modules (virtual labs and interactive tutorials and chapters) provide engaging, discovery-based learning tools that complement many of the chapters of Concepts of Biology. SimBio is best known for their EcoBeaker® and EvoBeaker® suites of simulated ecology and evolution laboratories that guide students through the “discovery” of important concepts via a mix of structured and open-ended experimentation on simulated systems. In response to popular demand, SimBio has begun applying the same powerful approaches to topics in cell biology, genetics, and neurobiology. All of SimBio’s modules include instant-feedback questions that enhance student comprehension and auto-graded questions that facilitate implementation.

4 Preface

This OpenStax book is available for free at http://cnx.org/content/col11487/1.9

1 | INTRODUCTION TO BIOLOGY

Figure 1.1 This NASA image is a composite of several satellite-based views of Earth. To make the whole-Earth image, NASA scientists combine observations of different parts of the planet. (credit: modification of work by NASA)

Chapter Outline 1.1: Themes and Concepts of Biology

1.2: The Process of Science

Introduction Viewed from space, Earth (Figure 1.1) offers few clues about the diversity of life forms that reside there. The first forms of life on Earth are thought to have been microorganisms that existed for billions of years before plants and animals appeared. The mammals, birds, and flowers so familiar to us are all relatively recent, originating 130 to 200 million years ago. Humans have inhabited this planet for only the last 2.5 million years, and only in the last 200,000 years have humans started looking like we do today.

1.1 | Themes and Concepts of Biology

By the end of this section, you will be able to:

• Identify and describe the properties of life

• Describe the levels of organization among living things

• List examples of different sub disciplines in biology

Biology is the science that studies life. What exactly is life? This may sound like a silly question with an obvious answer, but it is not easy to define life. For example, a branch of biology called virology studies viruses, which exhibit some of the characteristics of living entities but lack others. It turns out that although viruses can attack living organisms, cause diseases, and even reproduce, they do not meet the criteria that biologists use to define life.

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From its earliest beginnings, biology has wrestled with four questions: What are the shared properties that make something “alive”? How do those various living things function? When faced with the remarkable diversity of life, how do we organize the different kinds of organisms so that we can better understand them? And, finally—what biologists ultimately seek to understand—how did this diversity arise and how is it continuing? As new organisms are discovered every day, biologists continue to seek answers to these and other questions.

Properties of Life All groups of living organisms share several key characteristics or functions: order, sensitivity or response to stimuli, reproduction, adaptation, growth and development, regulation, homeostasis, and energy processing. When viewed together, these eight characteristics serve to define life.

Order

Organisms are highly organized structures that consist of one or more cells. Even very simple, single-celled organisms are remarkably complex. Inside each cell, atoms make up molecules. These in turn make up cell components or organelles. Multicellular organisms, which may consist of millions of individual cells, have an advantage over single-celled organisms in that their cells can be specialized to perform specific functions, and even sacrificed in certain situations for the good of the organism as a whole. How these specialized cells come together to form organs such as the heart, lung, or skin in organisms like the toad shown in Figure 1.2 will be discussed later.

Figure 1.2 A toad represents a highly organized structure consisting of cells, tissues, organs, and organ systems. (credit: "Ivengo(RUS)"/Wikimedia Commons)

Sensitivity or Response to Stimuli

Organisms respond to diverse stimuli. For example, plants can bend toward a source of light or respond to touch (Figure 1.3). Even tiny bacteria can move toward or away from chemicals (a process called chemotaxis) or light (phototaxis). Movement toward a stimulus is considered a positive response, while movement away from a stimulus is considered a negative response.

6 Chapter 1 | Introduction to Biology

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Figure 1.3 The leaves of this sensitive plant (Mimosa pudica) will instantly droop and fold when touched. After a few minutes, the plant returns to its normal state. (credit: Alex Lomas)

Watch this video (http://openstaxcollege.org/l/thigmonasty) to see how the sensitive plant responds to a touch stimulus.

Reproduction

Single-celled organisms reproduce by first duplicating their DNA, which is the genetic material, and then dividing it equally as the cell prepares to divide to form two new cells. Many multicellular organisms (those made up of more than one cell) produce specialized reproductive cells that will form new individuals. When reproduction occurs, DNA containing genes is passed along to an organism’s offspring. These genes are the reason that the offspring will belong to the same species and will have characteristics similar to the parent, such as fur color and blood type.

Adaptation

All living organisms exhibit a “fit” to their environment. Biologists refer to this fit as adaptation and it is a consequence of evolution by natural selection, which operates in every lineage of reproducing organisms. Examples of adaptations are diverse and unique, from heat-resistant Archaea that live in boiling hot springs to the tongue length of a nectar-feeding moth that matches the size of the flower from which it feeds. All adaptations enhance the reproductive potential of the individual exhibiting them, including their ability to survive to reproduce. Adaptations are not constant. As an environment changes, natural selection causes the characteristics of the individuals in a population to track those changes.

Growth and Development

Organisms grow and develop according to specific instructions coded for by their genes. These genes provide instructions that will direct cellular growth and development, ensuring that a species’ young (Figure 1.4) will grow up to exhibit many of the same characteristics as its parents.

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http://openstaxcollege.org/l/thigmonasty
Figure 1.4 Although no two look alike, these kittens have inherited genes from both parents and share many of the same characteristics. (credit: Pieter & Renée Lanser)

Regulation

Even the smallest organisms are complex and require multiple regulatory mechanisms to coordinate internal functions, such as the transport of nutrients, response to stimuli, and coping with environmental stresses. For example, organ systems such as the digestive or circulatory systems perform specific functions like carrying oxygen throughout the body, removing wastes, delivering nutrients to every cell, and cooling the body.

Homeostasis

To function properly, cells require appropriate conditions such as proper temperature, pH, and concentrations of diverse chemicals. These conditions may, however, change from one moment to the next. Organisms are able to maintain internal conditions within a narrow range almost constantly, despite environmental changes, through a process called homeostasis or “steady state”—the ability of an organism to maintain constant internal conditions. For example, many organisms regulate their body temperature in a process known as thermoregulation. Organisms that live in cold climates, such as the polar bear (Figure 1.5), have body structures that help them withstand low temperatures and conserve body heat. In hot climates, organisms have methods (such as perspiration in humans or panting in dogs) that help them to shed excess body heat.

Figure 1.5 Polar bears and other mammals living in ice-covered regions maintain their body temperature by generating heat and reducing heat loss through thick fur and a dense layer of fat under their skin. (credit: "longhorndave"/Flickr)

Energy Processing

All organisms (such as the California condor shown in Figure 1.6) use a source of energy for their metabolic activities. Some organisms capture energy from the Sun and convert it into chemical energy in food; others use chemical energy from molecules they take in.

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Figure 1.6 A lot of energy is required for a California condor to fly. Chemical energy derived from food is used to power flight. California condors are an endangered species; scientists have strived to place a wing tag on each bird to help them identify and locate each individual bird. (credit: Pacific Southwest Region U.S. Fish and Wildlife)

Levels of Organization of Living Things Living things are highly organized and structured, following a hierarchy on a scale from small to large. The atom is the smallest and most fundamental unit of matter. It consists of a nucleus surrounded by electrons. Atoms form molecules. A molecule is a chemical structure consisting of at least two atoms held together by a chemical bond. Many molecules that are biologically important are macromolecules, large molecules that are typically formed by combining smaller units called monomers. An example of a macromolecule is deoxyribonucleic acid (DNA) (Figure 1.7), which contains the instructions for the functioning of the organism that contains it.

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Figure 1.7 A molecule, like this large DNA molecule, is composed of atoms. (credit: "Brian0918"/Wikimedia Commons)

To see an animation of this DNA molecule, click here (http://openstaxcollege.org/l/rotating_DNA2) .

Some cells contain aggregates of macromolecules surrounded by membranes; these are called organelles. Organelles are small structures that exist within cells and perform specialized functions. All living things are made of cells; the cell itself is the smallest fundamental unit of structure and function in living organisms. (This requirement is why viruses are not considered living: they are not made of cells. To make new viruses, they have to invade and hijack a living cell; only then can they obtain the materials they need to reproduce.) Some organisms consist of a single cell and others are multicellular. Cells are classified as prokaryotic or eukaryotic. Prokaryotes are single-celled organisms that lack organelles surrounded by a membrane and do not have nuclei surrounded by nuclear membranes; in contrast, the cells of eukaryotes do have membrane-bound organelles and nuclei.

In most multicellular organisms, cells combine to make tissues, which are groups of similar cells carrying out the same function. Organs are collections of tissues grouped together based on a common function. Organs are present not only in animals but also in plants. An organ system is a higher level of organization that consists of functionally related organs. For example vertebrate animals have many organ systems, such as the circulatory system that transports blood throughout the body and to and from the lungs; it includes organs such as the heart and blood vessels. Organisms are individual living entities. For example, each tree in a forest is an organism. Single-celled prokaryotes and single-celled eukaryotes are also considered organisms and are typically referred to as microorganisms.

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http://openstaxcollege.org/l/rotating_DNA2
Figure 1.8 From an atom to the entire Earth, biology examines all aspects of life. (credit "molecule": modification of work by Jane Whitney; credit "organelles": modification of work by Louisa Howard; credit "cells": modification of work by Bruce Wetzel, Harry Schaefer, National Cancer Institute; credit "tissue": modification of work by "Kilbad"/Wikimedia Commons; credit "organs": modification of work by Mariana Ruiz Villareal, Joaquim Alves Gaspar; credit "organisms": modification of work by Peter Dutton; credit "ecosystem": modification of work by "gigi4791"/Flickr; credit "biosphere": modification of work by NASA)

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Which of the following statements is false?

a. Tissues exist within organs which exist within organ systems.

b. Communities exist within populations which exist within ecosystems.

c. Organelles exist within cells which exist within tissues.

d. Communities exist within ecosystems which exist in the biosphere.

All the individuals of a species living within a specific area are collectively called a population. For example, a forest may include many white pine trees. All of these pine trees represent the population of white pine trees in this forest. Different populations may live in the same specific area. For example, the forest with the pine trees includes populations of flowering plants and also insects and microbial populations. A community is the set of populations inhabiting a particular area. For instance, all of the trees, flowers, insects, and other populations in a forest form the forest’s community. The forest itself is an ecosystem. An ecosystem consists of all the living things in a particular area together with the abiotic, or non-living, parts of that environment such as nitrogen in the soil or rainwater. At the highest level of organization (Figure 1.8), the biosphere is the collection of all ecosystems, and it represents the zones of life on Earth. It includes land, water, and portions of the atmosphere.

The Diversity of Life The science of biology is very broad in scope because there is a tremendous diversity of life on Earth. The source of this diversity is evolution, the process of gradual change during which new species arise from older species. Evolutionary biologists study the evolution of living things in everything from the microscopic world to ecosystems.

In the 18th century, a scientist named Carl Linnaeus first proposed organizing the known species of organisms into a hierarchical taxonomy. In this system, species that are most similar to each other are put together within a grouping known as a genus. Furthermore, similar genera (the plural of genus) are put together within a family. This grouping continues until all organisms are collected together into groups at the highest level. The current taxonomic system now has eight levels in its hierarchy, from lowest to highest, they are: species, genus, family, order, class, phylum, kingdom, domain. Thus species are grouped within genera, genera are grouped within families, families are grouped within orders, and so on (Figure 1.9).

Figure 1.9 This diagram shows the levels of taxonomic hierarchy for a dog, from the broadest category—domain—to the most specific—species.

The highest level, domain, is a relatively new addition to the system since the 1990s. Scientists now recognize three domains of life, the Eukarya, the Archaea, and the Bacteria. The domain Eukarya contains organisms that have cells with nuclei. It includes the kingdoms of fungi, plants, animals, and several kingdoms of protists. The Archaea, are single-celled organisms without nuclei and include many extremophiles that live in harsh environments like hot springs. The Bacteria are another quite different group of single-celled organisms without nuclei (Figure 1.10). Both the Archaea and the Bacteria are prokaryotes, an informal name for cells without nuclei. The recognition in the 1990s that certain “bacteria,” now known as the Archaea, were as different genetically and biochemically from other bacterial cells as they were from eukaryotes, motivated the recommendation to divide life into three domains. This dramatic change in our knowledge of the tree of life demonstrates that classifications are not permanent and will change when new information becomes available.

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In addition to the hierarchical taxonomic system, Linnaeus was the first to name organisms using two unique names, now called the binomial naming system. Before Linnaeus, the use of common names to refer to organisms caused confusion because there were regional differences in these common names. Binomial names consist of the genus name (which is capitalized) and the species name (all lower-case). Both names are set in italics when they are printed. Every species is given a unique binomial which is recognized the world over, so that a scientist in any location can know which organism is being referred to. For example, the North American blue jay is known uniquely as Cyanocitta cristata. Our own species is Homo sapiens.

Figure 1.10 These images represent different domains. The scanning electron micrograph shows (a) bacterial cells belong to the domain Bacteria, while the (b) extremophiles, seen all together as colored mats in this hot spring, belong to domain Archaea. Both the (c) sunflower and (d) lion are part of domain Eukarya. (credit a: modification of work by Rocky Mountain Laboratories, NIAID, NIH; credit b: modification of work by Steve Jurvetson; credit c: modification of work by Michael Arrighi; credit d: modification of work by Frank Vassen)

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Carl Woese and the Phylogenetic Tree The evolutionary relationships of various life forms on Earth can be summarized in a phylogenetic tree. A phylogenetic tree is a diagram showing the evolutionary relationships among biological species based on similarities and differences in genetic or physical traits or both. A phylogenetic tree is composed of branch points, or nodes, and branches. The internal nodes represent ancestors and are points in evolution when, based on scientific evidence, an ancestor is thought to have diverged to form two new species. The length of each branch can be considered as estimates of relative time.

In the past, biologists grouped living organisms into five kingdoms: animals, plants, fungi, protists, and bacteria. The pioneering work of American microbiologist Carl Woese in the early 1970s has shown, however, that life on Earth has evolved along three lineages, now called domains—Bacteria, Archaea, and Eukarya. Woese proposed the domain as a new taxonomic level and Archaea as a new domain, to reflect the new phylogenetic tree (Figure 1.11). Many organisms belonging to the Archaea domain live under extreme conditions and are called extremophiles. To construct his tree, Woese used genetic relationships rather than similarities based on morphology (shape). Various genes were used in phylogenetic studies. Woese’s tree was constructed from comparative sequencing of the genes that are universally distributed, found in some slightly altered form in every organism, conserved (meaning that these genes have remained only slightly changed throughout evolution), and of an appropriate length.

Figure 1.11 This phylogenetic tree was constructed by microbiologist Carl Woese using genetic relationships. The tree shows the separation of living organisms into three domains: Bacteria, Archaea, and Eukarya. Bacteria and Archaea are organisms without a nucleus or other organelles surrounded by a membrane and, therefore, are prokaryotes. (credit: modification of work by Eric Gaba)

Branches of Biological Study The scope of biology is broad and therefore contains many branches and sub disciplines. Biologists may pursue one of those sub disciplines and work in a more focused field. For instance, molecular biology studies biological processes at the molecular level, including interactions among molecules such as DNA, RNA, and proteins, as well as the way they are regulated. Microbiology is the study of the structure and function of microorganisms. It is quite a broad branch itself, and depending on the subject of study, there are also microbial physiologists, ecologists, and geneticists, among others.

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Another field of biological study, neurobiology, studies the biology of the nervous system, and although it is considered a branch of biology, it is also recognized as an interdisciplinary field of study known as neuroscience. Because of its interdisciplinary nature, this sub discipline studies different functions of the nervous system using molecular, cellular, developmental, medical, and computational approaches.

Figure 1.12 Researchers work on excavating dinosaur fossils at a site in Castellón, Spain. (credit: Mario Modesto)

Paleontology, another branch of biology, uses fossils to study life’s history (Figure 1.12). Zoology and botany are the study of animals and plants, respectively. Biologists can also specialize as biotechnologists, ecologists, or physiologists, to name just a few areas. Biotechnologists apply the knowledge of biology to create useful products. Ecologists study the interactions of organisms in their environments. Physiologists study the workings of cells, tissues and organs. This is just a small sample of the many fields that biologists can pursue. From our own bodies to the world we live in, discoveries in biology can affect us in very direct and important ways. We depend on these discoveries for our health, our food sources, and the benefits provided by our ecosystem. Because of this, knowledge of biology can benefit us in making decisions in our day-to-day lives.

The development of technology in the twentieth century that continues today, particularly the technology to describe and manipulate the genetic material, DNA, has transformed biology. This transformation will allow biologists to continue to understand the history of life in greater detail, how the human body works, our human origins, and how humans can survive as a species on this planet despite the stresses caused by our increasing numbers. Biologists continue to decipher huge mysteries about life suggesting that we have only begun to understand life on the planet, its history, and our relationship to it. For this and other reasons, the knowledge of biology gained through this textbook and other printed and electronic media should be a benefit in whichever field you enter.

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Forensic Scientist Forensic science is the application of science to answer questions related to the law. Biologists as well as chemists and biochemists can be forensic scientists. Forensic scientists provide scientific evidence for use in courts, and their job involves examining trace material associated with crimes. Interest in forensic science has increased in the last few years, possibly because of popular television shows that feature forensic scientists on the job. Also, the development of molecular techniques and the establishment of DNA databases have updated the types of work that forensic scientists can do. Their job activities are primarily related to crimes against people such as murder, rape, and assault. Their work involves analyzing samples such as hair, blood, and other body fluids and also processing DNA (Figure 1.13) found in many different environments and materials. Forensic scientists also analyze other biological evidence left at crime scenes, such as insect parts or pollen grains. Students who want to pursue careers in forensic science will most likely be required to take chemistry and biology courses as well as some intensive math courses.

Figure 1.13 This forensic scientist works in a DNA extraction room at the U.S. Army Criminal Investigation Laboratory. (credit: U.S. Army CID Command Public Affairs)

1.2 | The Process of Science

By the end of this section, you will be able to:

• Identify the shared characteristics of the natural sciences

• Understand the process of scientific inquiry

• Compare inductive reasoning with deductive reasoning

• Describe the goals of basic science and applied science

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Figure 1.14 Formerly called blue-green algae, the (a) cyanobacteria seen through a light microscope are some of Earth’s oldest life forms. These (b) stromatolites along the shores of Lake Thetis in Western Australia are ancient structures formed by the layering of cyanobacteria in shallow waters. (credit a: modification of work by NASA; scale- bar data from Matt Russell; credit b: modification of work by Ruth Ellison)

Like geology, physics, and chemistry, biology is a science that gathers knowledge about the natural world. Specifically, biology is the study of life. The discoveries of biology are made by a community of researchers who work individually and together using agreed-on methods. In this sense, biology, like all sciences is a social enterprise like politics or the arts. The methods of science include careful observation, record keeping, logical and mathematical reasoning, experimentation, and submitting conclusions to the scrutiny of others. Science also requires considerable imagination and creativity; a well-designed experiment is commonly described as elegant, or beautiful. Like politics, science has considerable practical implications and some science is dedicated to practical applications, such as the prevention of disease (see Figure 1.15). Other science proceeds largely motivated by curiosity. Whatever its goal, there is no doubt that science, including biology, has transformed human existence and will continue to do so.

Figure 1.15 Biologists may choose to study Escherichia coli (E. coli), a bacterium that is a normal resident of our digestive tracts but which is also sometimes responsible for disease outbreaks. In this micrograph, the bacterium is visualized using a scanning electron microscope and digital colorization. (credit: Eric Erbe; digital colorization by Christopher Pooley, USDA-ARS)

The Nature of Science Biology is a science, but what exactly is science? What does the study of biology share with other scientific disciplines? Science (from the Latin scientia, meaning "knowledge") can be defined as knowledge about the natural world.

Science is a very specific way of learning, or knowing, about the world. The history of the past 500 years demonstrates that science is a very powerful way of knowing about the world; it is largely responsible for the technological revolutions

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that have taken place during this time. There are however, areas of knowledge and human experience that the methods of science cannot be applied to. These include such things as answering purely moral questions, aesthetic questions, or what can be generally categorized as spiritual questions. Science has cannot investigate these areas because they are outside the realm of material phenomena, the phenomena of matter and energy, and cannot be observed and measured.

The scientific method is a method of research with defined steps that include experiments and careful observation. The steps of the scientific method will be examined in detail later, but one of the most important aspects of this method is the testing of hypotheses. A hypothesis is a suggested explanation for an event, which can be tested. Hypotheses, or tentative explanations, are generally produced within the context of a scientific theory. A scientific theory is a generally accepted, thoroughly tested and confirmed explanation for a set of observations or phenomena. Scientific theory is the foundation of scientific knowledge. In addition, in many scientific disciplines (less so in biology) there are scientific laws, often expressed in mathematical formulas, which describe how elements of nature will behave under certain specific conditions. There is not an evolution of hypotheses through theories to laws as if they represented some increase in certainty about the world. Hypotheses are the day-to-day material that scientists work with and they are developed within the context of theories. Laws are concise descriptions of parts of the world that are amenable to formulaic or mathematical description.