The prokaryotic cells that built stromatolites are classified as _____

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.

Chapter 1 | Introduction to Biology 5

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

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

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.