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(ZOO301)Biology of the Invertebrates          Download
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Integrated Principles of Zoology  

Zoology book By Miller & Harley By The Smart Science

  1. 1. Miller−Harley: Zoology, Fifth Edition Front Matter Preface © The McGraw−Hill Companies, 2001 xiii P R E F A C E The planning for the first edition of Zoology began in the late 1980s at a time when instructors and their students had few op- tions in the choice of a general zoology textbook. In the first four editions of Zoology, we have tried to present zoology as an exciting and dynamic scientific field. We have made very deliberate choices in content and style to enhance the readability of the textbook, realizing that authority and detail of content are of lit- tle consequence if students find the book difficult to use. Many of these choices have been challenging, and the labor involved has at times been exhausting. With each edition we have received student and instructor feedback that has confirmed our approach and rewarded our efforts. We believe that the decisions we, and our colleagues at McGraw-Hill, have made have largely been the right decisions. This is why we are privileged to have a fifth edi- tion of Zoology in your hands, while other books have not survived the rigors of “textbook selection.” Our goals in preparing the fifth edition of Zoology were the same as in previous editions. We prepared an introductory general zoology textbook that we believe is manageable in size and adapt- able to a variety of course formats. We have retained the friendly, informative writing style that has attracted instructors and stu- dents through the first four editions. Users of the fourth edition will quickly notice that the fifth edition of Zoology is 200 pages shorter. This change is in response to user requests for a text that is less expensive and more useful in one-semester course formats. Course sequences at many colleges and universities dictate that biological principles are taught in general biology courses rather than general zoology courses. All of these factors were carefully considered in the revision of this latest edition of Zoology. CONTENT AND ORGANIZATION We have retained the evolutionary and ecological focus of Zool- ogy, believing that these perspectives captivate students and are fundamental to understanding the unifying principles of zoology and the remarkable diversity within the animal kingdom. We have enhanced the ecological perspective by expanding the use of “Wildlife Alerts,” which we included in a limited fashion in the fourth edition. Wildlife Alerts are now incorporated into each of the first 22 chapters of the book, and feature some issues related to endangered and threatened species of animals. In most cases, these readings depict the plight of a selected animal species. In other cases, they depict broader ecosystem issues, or questions re- lated to preserving genetic diversity within species. In all cases, the purpose of these Wildlife Alerts is to increase student aware- ness of the need to preserve animal habits and species. Zoology is organized into three parts. Part One covers the common life processes, including cell and tissue structure and function, the genetic basis of evolution, and the evolutionary and ecological principles that unify all life. Part Two is the survey of animals, emphasizing evolutionary and ecological relationships, aspects of animal organization that unite major animal phyla, and animal adaptations. All of the chapters in Part Two have been carefully updated, including new examples and photographs. The coverage of animal classification and organization in Chapter 7 has been expanded from previous editions to include more background on cladistics and enhanced coverage of protostome/deuterostome relationships. As in previ- ous editions, the remaining survey chapters (8–22) include clado- grams to depict evolutionary relationships, full-color artwork and photographs, and lists of phylum characteristics. Part Three covers animal form and function using a com- parative approach. This approach includes descriptions and full- color artwork that depict the evolutionary changes in the struc- ture and function of selected organ systems. Part Three includes an appropriate balance between invertebrate and vertebrate de- scriptions. NEW TO THE FIFTH EDITION • “Wildlife Alert” boxes now appear in all of the survey chap- ters, including many that are new to the 5th edition. Most of these readings feature a particular species, but some feature a larger ecosystem concern. • Chapter 1 has been revised to focus on the evolutionary and ecological emphasis of the book. • Instead of beginning Chapter 3 with classical (Mendelian) ge- netics, we begin with molecular genetics and explain classical genetics in terms of DNA structure and function. The con- cept of dominance is explained in molecular terms. • Chapter 4 now begins with a discussion of evidence of evolu- tion, to help students relate the evidence to the process. • A section on “Higher Animal Taxonomy” is now included in Chapter 7, including a new table of higher taxonomic group- ings, based on the latest information from cladistic analyses of the animal kingdom. • Chapter 18 contains new information from molecular and cladistic studies on the origin of vertebrates and the relation- ship of vertebrates to other chordates. New information is also presented on the evolution of terrestrialism in vertebrates. • Chapter 19 contains a new section covering amphibians in peril, exploring possible reasons that amphibians around the world are declining at an alarming rate. SUPPLEMENTARY MATERIALS Supplementary materials are available to assist instructors with their presentations and general course management, to augment students’ learning opportunities. The usefulness of these supplements is
  2. 2. Miller−Harley: Zoology, Fifth Edition Front Matter Preface © The McGraw−Hill Companies, 2001 xiv Preface • A Zoology Test Item File is also available for instructors. This contains approximately 50 multiple-choice questions for each chapter. • General Zoology Study Guide, prepared by Jane Aloi and Gina Erickson, contains subject-by-subject summaries, ques- tions, and learning activities. • A set of 100 full-color acetate transparencies is available to supplement classroom lectures. • General Zoology Laboratory Manual, fifth edition, by Stephen A. Miller, is an excellent corollary to the text and in- corporates many learning aids. This edition includes new il- lustrations and photographs, plus activities on scientific method, cladistics, ecological and evolutionary principles, and animal structure and function. A Laboratory Resource Guide, available within the Online Learning Center, provides information about materials and procedures, and answers to worksheet questions that accompany the lab exercises. • Digital Zoology is a new and exciting interactive product de- signed to help you to make the most of your zoology classes and laboratory sessions. This program contains interactive cladograms, laboratory modules, video, interactive quizzes, hundreds of photographs, a full glossary, and much detailed information about the diversity and evolution of the animals that we find on the planet. To find out the latest news on this ever-expanding product, log on to www.mhhe.com/ digitalzoology and find out how to get your copy. • The Zoology Visual Resource Library is a dual-platform CD-ROM that allows instructors to search with key words or terms and access 1,000 images to illustrate classroom lectures, with just the click of a mouse. It contains images from four McGraw-Hill textbooks in the zoology field. • Available through the Zoology Online Learning Center, the Zoology Essential Study Partner is a complete, interactive study tool offering animations and learning activities to help students understand complex zoology concepts. This valuable resource also includes self-quizzing to help students review each topic. • BioCourse.com is an electronic meeting place for students and instructors. Its breadth and depth go beyond our Online Learning Center to offer six major areas of up-to-date and rel- evant information: Faculty Club, Student Center, News Brief- ing Room, BioLabs, Lifelong Learning Warehouse, and R & D Center. • PageOut® is the solution for professors who need to build a course website. The following features are now available to professors: • The PageOut Library offers instant access to fully loaded course websites with no work required on the instructor’s part. • Courses can now be password protected. • Professors can now upload, store, and manage up to 10MB of data. • Professors can copy their course and share it with col- leagues or use it as a foundation for next semester. Short on time? Let us do the work. Our McGraw-Hill ser- vice team is ready to build your PageOut website, and now greatly enhanced with the availability of both online and printed resources. As a part of the fifth edition revision, chapters on cell chemistry, energy and enzymes, embryology, and animal behavior—along with numerous boxed readings and pedagogical elements—have been moved to the Online Learning Center. This content-rich website is located at www.mhhe.com/zoology—just click on this book’s title. ONLINE LEARNING CENTER Both instructors and students can take advantage of numerous teaching and learning aids within this book’s Online Learning Center. Instructor Resources • Instructor’s Manual • Laboratory Resource Guide • Zoology Visual Resource Library (VRL), containing 1,000 images for classroom presentation • PowerPoint Lecture Slides Student and Instructor Resources • Interactive Cladistics Laboratory • Chapters on: • Chapter 30: The Chemical Basis of Animal Life • Chapter 31: Energy and Enzymes: Life’s Driving and Con- trolling Forces • Chapter 32: How Animals Harvest Energy Stored in Nutrients • Chapter 33: Embryology • Chapter 34: Animal Behavior • Boxed Readings • Suggested Readings • Readings on Lesser-Known Invertebrates • Quizzing • Key Terms Flashcards • Zoology Essential Study Partner (ESP) • Animations • Free Zoology Screen Saver All of these tools, and even more, are available to you with this text. To access these resources, go to www.mhhe.com/zoology and click on the title of this book. (Also, see pages xvi–xx for more details.) OTHER RESOURCES The following items may accompany Zoology. Please consult your McGraw-Hill representative for policies, prices, and availability as some restrictions may apply. • An Instructor’s Manual, prepared by Jane Aloi Horlings, is available for instructors within the Online Learning Center. It provides examples of lecture/reading schedules for courses with various emphases. In addition, each chapter contains a detailed outline, purpose, objectives, key terms, summary, re- sources for audiovisual materials and computer software.
  3. 3. Miller−Harley: Zoology, Fifth Edition Front Matter Preface © The McGraw−Hill Companies, 2001 Preface xv provide content and any necessary training. Learn more about PageOut and other McGraw-Hill digital solutions at www.mhhe.com/solutions. ACKNOWLEDGMENTS We wish to thank the reviewers who provided detailed analysis of the text during development. In the midst of their busy teaching and research schedules, they took time to read our manuscript and to offer constructive advice that greatly improved this fifth edition. REVIEWERS Jane Aloi Horlings, Saddleback College; Arthur L. Alt, University of Great Falls; Rodney P. Anderson, Ohio Northern University. Iona Baldridge, Lubbock Christian University; Jerry Beilby, Northwestern College; Barry Boatwright, Gadsden State Commu- nity College; Susan Bornstein-Forst, Marian College; Mimi Bres, Prince George’s Community College; David Brooks, Quachita Bap- tist University; Richard D. Brown, Brunswick Community College; Gary Brusca, Humboldt State University; Frank J. Bulow, Ten- nessee Technological University; Paul J. Bybee, Utah Valley State College. Fernando Cofresi-Sala, Pontifical Catholic University of Puerto Rico; Sarah Cooper, Beaver College; Neil W. Crenshaw, In- dian River Community College; Mary Carla Curran, University of South Carolina at Beaufort. Armando A. de la Cruz, Mississippi State University; James N. DeVries, Lancaster Bible College; Donald Dorfman, Monmouth University; Tom Dudley, Angelina College. Bruce Edinger, Salem-Teikyo University; Adria A. Elskus, State University of New York, Stony Brook; DuWayne C. Englert, Southern Illinois University at Carbondale. Rob Fitch, Wenatchee Valley College. M.J. Galliher, Cochise College; Thaddeus Gish, St. Mary’s College; Jim Goetze, Laredo Community College;Walter M. Godl- berg, Florida International University; Edward J. Greding, Jr., Del Mar College. Paul A. Haefner, Jr., Rochester Institute of Technology; Jim Hampton, Salt Lake Community College; Willard N. Harman, State University of New York, Oneonta; Mary D. Healey, Springfield College; Gary A. Heidt, University of Arkansas, Little Rock; Karen Hickman, University of Mary Hardin-Baylor; Nan Ho, Las Positas College; Jeff Holmquist, University of Puerto Rico-Mayaquez. Dan F. Ippolito, Anderson University. Kathryn Kavanagh, Boston University; Sekender K. Khan, Elizabeth City State University; Anna Koshy, Houston Community College. Matthew Landau, Richard Stockton College; Stephen C. Landers, Troy State University; Larry N. Latson, Lipscomb Univer- sity; Standley E. Lewis, St. Cloud State University; Eddie Lunsford, North Carolina Community College. Paul C. Makarewicz, Three Rivers Community Technical Col- lege; Sarantos John Manos, Massasoit Community College; Robert C. Maris, Mansfield University of Pennsylvania; Vicki J. Martin, University of Notre Dame; Joel M. McKinney, South Plains College; Dwayne Meadows, Weber State University; Tina Miller-Way, Uni- versity of Mobile; Ronald S. Mollick, Christopher Newport Univer- sity; Thomas Moon, California University of Pennsylvania; John F. Morrissey, Hofstra University; Tim R. Mullican, Dakota Wesleyan University; G. Steven Murphree, Belmont University. Maha Nagarajan, Wilberforce University. John F. Pilger, Agnes Scott College; Kathryn Stanley Pod- wall, Nassau Community College. Mohammad A Rana, St. Josephs’s College; Lois Galgay Reckitt, University of Southern Maine; John Rickett, University of Arkansas, Little Rock; Richard G. Rose, West Valley College; Vaughn M. Rundquist, Montana State University-Northern. Neil Sabine, Indiana University East; Neil B. Schanker, College of The Siskiyous; Fred H. Schindler, Indian Hills Commu- nity College; Michelle Schoon, Cowley County Community Col- lege; Erik P. Scully, Towson University; Richard H. Shippee, Vin- cennes University; Sandra E. Schumway, Long Island University Southampton College; Doug Sizemore, Bevill State Community Col- lege; Alan F. Smith, Mercer University; Gregory B. Smith, Edison Community College; Susan E. Smith, Massasoit Community Col- lege; Scott C. Swanson, Ohio Northern University. John Tibbs, University of Montana; S. Gregory Tolley, Florida Gulf Coast University; Richard E. Trout, Oklahoma City Community College; Geraldine W. Twitty, Howard University. Dwina W. Willis, Freed-Hardeman University; Jeffrey Scott Wooters, Pensacola Junior College. Robert W. Yost, Indiana University-Purdue University. David D. Zeigler, University of North Carolina, Pembroke. The publication of a text requires the efforts of many people. We are grateful for the work of our colleagues at McGraw-Hill, who have shown extraordinary patience, skill, and commitment to this text. Marge Kemp, Sponsoring Editor, has helped shape Zoology from its earliest planning stages. Our Development Editor, Donna Nemmers, helped make the production of the fifth edition re- markably smooth. Donna kept us on schedule and the production moving in the plethora of directions that are nearly unimaginable to us. Kay Brimeyer served as our project manager. We are grateful for her skilled coordination of the many tasks involved with the publishing of this edition of Zoology. Finally, but most importantly, we wish to extend apprecia- tion to our families for their patience and encouragement. Janice A. Miller lived with this text through many months of planning and writing. She died suddenly 2 months before the first edition was released. Our wives, Carol A. Miller and Jane R. Harley, have been supportive throughout the revision process. We appreciate the sacrifices that our families have made during the writing and revision of this text. We dedicate this book to the memory of Jan, and to our families. STEPHEN A. MILLER JOHN P. HARLEY
  4. 4. Miller−Harley: Zoology, Fifth Edition Front Matter Guided Tour © The McGraw−Hill Companies, 2001 G U I D E D T O U R This chapter contains evolutionary concepts, which are set off in this font. 369 Outline Neurons: The Basic Functional Units of the Nervous System Neuron Structure: The Key to Function Neuron Communication Resting Membrane Potential Mechanism of Neuron Action Transmission of the Action Potential Invertebrate Nervous Systems Vertebrate Nervous Systems The Spinal Cord Spinal Nerves The Brain Cranial Nerves The Autonomic Nervous System Sensory Reception Invertebrate Sensory Receptors Baroreceptors Chemoreceptors Georeceptors Hygroreceptors Phonoreceptors Photoreceptors Proprioceptors Tactile Receptors Thermoreceptors Vertebrate Sensory Receptors Lateral-Line System and Electrical Sensing Lateral-Line System and Mechanoreception Hearing and Equilibrium in Air Hearing and Equilibrium in Water Skin Sensors of Damaging Stimuli Skin Sensors of Heat and Cold Skin Sensors of Mechanical Stimuli Sonar Smell Taste Vision Concepts 1. The nervous system helps to communicate, integrate, and coordinate the functions of the various organs and organ systems in the animal body. 2. Information flow through the nervous system has three main steps: (1) the collection of information from outside and inside the body (sensory activities), (2) the processing of this information in the nervous system, and (3) the initiation of appropriate responses. 3. Information is transmitted between neurons directly (electrically) or by means of chemi- cals called neurotransmitters. 4. The evolution of the nervous system in invertebrates has led to the elaboration of orga- nized nerve cords and the centralization of responses in the anterior portion of the animal. 5. The vertebrate nervous system consists of the central nervous system, made up of the brain and spinal cord, and the peripheral nervous system, composed of the nerves in the rest of the body. 6. Nervous systems evolved through the gradual layering of additional nervous tissue over reflex pathways of more ancient origin. 7. Sensory receptors or organs permit an animal to detect changes in its body, as well as in objects and events in the world around it. Sensory receptors collect information that is then passed to the nervous system, which determines, evaluates, and initiates an appro- priate response. 8. Sensory receptors initiate nerve impulses by opening channels in sensory neuron plasma membranes, depolarizing the membranes, and causing a generator potential. Receptors differ in the nature of the environmental stimulus that triggers an eventual nerve impulse. 9. Many kinds of receptors have evolved among invertebrates and vertebrates, and each re- ceptor is sensitive to a specific type of stimulus. 10. The nature of its sensory receptors gives each animal species a unique perception of its body and environment. The two forms of communication in an animal that integrate body functions to maintain homeostasis are: (1) neurons, which transmit electrical signals that report information or initiate a quick response in a specific tissue; and (2) hormones, which are slower, chemical signals that initiate a widespread, prolonged response, often in a variety of tissues. This chapter focuses on the function of the neuron, the anatomical organization of the nervous system in animals, and the ways in which the senses collect information and transmit it C H A P T E R 2 4 COMMUNICATION I: N E R V O U S A N D S E N S O R Y S Y S T E M S CHAPTER CONCEPTS The concepts most important to the under- standing of each chapter are highlighted on the first page of each chapter. PART REVIEW The three Parts of the text present an overview of the chapters within them, and also highlight important concepts and events within the chapters. The organization and features of this book have been planned with students’ learning and comprehension in mind. PA RT O N E BIOLOGICAL PRINCIPLES Animals are united with all other forms of life by the biological processes that they share with other organisms. Understanding these processes helps us to know how animals func- tion and why animals are united with other forms of life from the evolutionary and eco- logical perspectives. Chapter 1 examines some of these unifying themes and sets the stage for the evolutionary and ecological perspectives that are developed throughout this book. An understanding of the cell as the fundamental unit of life is key to understand- ing life on this planet. As you learn more about cell structure and function, you will find that many cellular components and processes are very similar in cells from a vari- ety of organisms. One of the common func- tions of all cells is reproduction. Reproduc- tion may involve individual cells within a multicellular organism, a single-celled organ- ism, or the formation of single reproductive cells in multicelluar organisms. The processes involved in cellular reproduction, and the processes involved in determining the char- acteristics of the new cells and organisms that are produced, are based on common biologi- cal themes. Chapters 2 and 3 present cell structure and inheritance as an important, unifying framework within which biologists approach the diversity of organisms. Principles of inheritance explain not only why offspring resemble their parents, but also why variation exists within populations. This variation is a key to understanding evo- lution. All organisms have an evolutionary history, and evolution helps us to understand the life-shaping experiences that all organisms share. Chapter 4 explores the work of pioneers of evolutionary theory, Charles Darwin and Alfred Russell Wallace, and how their work forms the nucleus for modern evolutionary theory. Chapter 5 examines the influence of modern genetics on evolutionary theory. This coverage of evolution will provide core knowledge for understanding the diversity of animal life presented in Part Two and how evolution has influenced the animal structure and function described in Part Three. A fundamental unity of life also oc- curs at the environmental level. All animals are partners in the use of the earth’s re- sources. Only by studying the interactions of organisms with one another and with their environment can we appreciate the need for preserving resources for all organisms. Chapter 6 presents basic ecological princi- Chapter 1 ZOOLOGY: AN EVOLUTIONARY AND ECOLOGICAL PERSPECTIVE Chapter 2 CELLS, TISSUES, ORGANS, AND ORGAN SYSTEMS OF ANIMALS Chapter 3 CELL DIVISION AND INHERITANCE Chapter 4 EVOLUTION: A HISTORICAL PERSPECTIVE Chapter 5 EVOLUTION AND GENE FREQUENCIES Chapter 6 ECOLOGY: PRESERVING THE ANIMAL KINGDOM ples that everyone must understand if we are to preserve the animal kingdom. Photo (top): Examples of evolutionary adaptation and ecological interdependence abound in the animal king- dom. This cleaning shrimp (Periclimenes yucatani- cus) seeks refuge within the cnidocyte (stinging cells) laden tentacles of the giant anemone (Condylactis gigantea). While receiving protection from the anemone, the cleaning shrimp provides a service to fish that visit the shrimp’s home—cleaning the fish’s mouth, gills, and skin of parasites and debris. 1 xvi
  5. 5. Miller−Harley: Zoology, Fifth Edition Front Matter Guided Tour © The McGraw−Hill Companies, 2001 Guided Tour xvii CHAPTER 11 The Pseudocoelomate Body Plan: Aschelminths 171 W I L D L I F E A L E RT Indiana Bat (Myotis sodalis) VITAL STATISTICS Classification: Phylum Chordata, class Mammalia, order Chiroptera, family Vespertilionidae Range: Midwest and eastern United States Habitat: Limestone caves are used for winter hibernation; summer habitat data are scarce but include under bridges, in old buildings, under bark, and in hollow trees Number remaining: 500,000 Status: Endangered throughout its range NATURAL HISTORY AND ECOLOGICAL STATUS The Indiana bat (also called the Indiana myotis; myotis refers to the mouse-eared bats) is a medium-sized bat with dull gray to chestnut- colored fur (box figure 1). The bat’s underparts are pinkish to cinnamon-colored. Little is known of the bat’s diet beyond the fact that it consists of insects. Families and juveniles forage in the airspace near the foliage of riverbank and floodplain trees. Males usually forage in densely wooded areas at treetop height. The Indiana bat lives in the Midwest and in the eastern United States, from the western edge of the Ozark region in Arkansas, throughout Kentucky, Tennessee, most of Alabama, and as far south as northern Florida (box figure 2). In summer, it is absent south of Ten- nessee; in winter, it is absent from Michigan, Ohio, and northern Indi- ana, where suitable habitats (caves and mines) are unknown. The Indiana bat’s breeding period is during the first 10 days of October. Mating takes place at night on the ceilings of large rooms near cave entrances. Hibernating colonies disperse in late March, and most of the bats migrate to more northern habitats for the summer. However, some males remain in the hibernating area during this period and wander from cave to cave. Birth occurs in June in widely scattered colonies consisting of about 25 females and their young. Each female bears a single offspring. The young require 25 to 37 days to develop to the flying stage and to feed independently. Migration to the wintering caves usually begins in August. The bats replace depleted fat reserves from the migration during September. Feeding then declines until mid-November, when the population en- ters a state of hibernation. The hibernating bats form large, compact clusters. Each individual hangs by its feet from the ceiling. Every 8 to 10 days, hibernating individuals awaken to spend an hour or more fly- ing about before returning to hibernation. The bats prefer limestone caves with an average temperature of 37° C and a relative humidity around 87% for hibernation. The decline of the Indiana bat is attributed to commercialization of roosting caves, wanton destruction by vandals, disturbances caused by increased numbers of spelunkers and bat banding programs, the use of bats as laboratory animals, and possibly, insecticide poisoning. To date, primary conservation efforts have focused on installing gates across cave entrances to control access. Some gating has already been accomplished on federal and state lands. Gating of all seven of the major wintering habitats would protect about 87% of the Indiana bat population. The National Speleological Society and the American Society of Mammologists are working together to preserve this species of bat. LA MS AR KY TN AL FL GA SC NC BOX FIGURE 1 Indiana Bat (Myotis sodalis). BOX FIGURE 2 Distribution of the Indiana Bat (Myotis sodalis). WILDLIFE ALERT BOXES These boxes feature issues related to endan- gered and threatened species of animals. CRITICAL THINKING QUESTIONS Students can synthesize the chapter information by applying it to the Critical Thinking Questions in each chapter. 172 PART TWO Animal-like Protists and Animalia S U M M A R Y 1. The aschelminths are seven phyla grouped for convenience. Most have a well-defined pseudocoelom, a constant number of body cells or nuclei (eutely), protonephridia, and a complete digestive system with a well-developed pharynx. No organs are developed for gas ex- change or circulation. A cuticle that may be molted covers the body. Only longitudinal muscles are often present in the body wall. 2. The phylogenetic affinities among the seven phyla and with other phyla are uncertain. 3. The majority of rotifers inhabit freshwater. The head of these ani- mals bears a unique ciliated corona used for locomotion and food capture. Males are smaller than females and unknown in some species. Females may develop parthenogenetically. 4. Kinorhynchs are minute worms living in marine habitats. Their bodies are comprised of 13 zonites, which have cuticular scales, plates, and spines. 5. Nematodes live in aquatic and terrestrial environments. Many are parasitic and of medical and agricultural importance. They are all elongate, slender, and circular in cross section. Two sexes are present. 6. Nematomorpha are threadlike and free-living in freshwater. They lack a digestive system. 7. Acanthocephalans are also known as spiny-headed worms because of their spiny proboscis. All are endoparasites in vertebrates. 8. The phylum Loricifera was described in 1983. These microscopic animals have a spiny head and thorax, and they live in gravel in marine environments. 9. The phylum Priapulida contains only 16 known species of cucumber- shaped, wormlike animals that live buried in the bottom sand and mud in marine habitats. SELECTED KEY TERMS amictic eggs (p. 161) aschelminths (p. 157) corona (p. 159) cuticle (p. 159) CRITICAL THINKING QUESTIONS 1. Discuss how the structure of the body wall places limitations on shape changes in nematodes. 2. What characteristics set the Nematomorpha apart from the Nema- toda? What characteristics do the Nematomorpha share with the Nematoda? 3. In what respects are the kinorhynchs like nematodes? How are they like rotifers? 4. How are nematodes related to the rotifers? 5. What environmental factors appear to trigger the production of mictic females in monogonont rotifers? ONLINE LEARNING CENTER Visit our Online Learning Center (OLC) at www.mhhe.com/zoology (click on this book’s title) to find the following chapter-related materials: • CHAPTER QUIZZING • RELATED WEB LINKS Phylum Rotifera Phylum Kinorhyncha Phylum Loricifera Phylum Priapulida Phylum Nematoda Human Diseases Caused by Nematodes Caenorhabditis elegans Phylum Nematomorpha Phylum Acanthocephala • BOXED READINGS ON An Application of Eutely The Ecology of Soil Nematodes • SUGGESTED READINGS • LAB CORRELATIONS Check out the OLC to find specific information on these related lab exercises in the General Zoology Laboratory Manual, 5th edition, by Stephen A. Miller: Exercise 12 The Pseudocoelomate Body Plan: Aschelminths mastax (p. 160) mictic eggs (p. 161) trichinosis (166) zonites (p. 162) ONLINE LEARNING CENTER The Online Learning Center hosts specific study tools for each chapter, which are summarized at the end of each text chapter. KEY TERMS The most important terms from each chapter are linked to their page of definition in the text, for further study.
  6. 6. Miller−Harley: Zoology, Fifth Edition I. Biological Principles Introduction © The McGraw−Hill Companies, 2001 PA RT O N E BIOLOGICAL PRINCIPLES Animals are united with all other forms of life by the biological processes that they share with other organisms. Understanding these processes helps us to know how animals func- tion and why animals are united with other forms of life from the evolutionary and eco- logical perspectives. Chapter 1 examines some of these unifying themes and sets the stage for the evolutionary and ecological perspectives that are developed throughout this book. An understanding of the cell as the fundamental unit of life is key to understand- ing life on this planet. As you learn more about cell structure and function, you will find that many cellular components and processes are very similar in cells from a vari- ety of organisms. One of the common func- tions of all cells is reproduction. Reproduc- tion may involve individual cells within a multicellular organism, a single-celled organ- ism, or the formation of single reproductive cells in multicelluar organisms. The processes involved in cellular reproduction, and the processes involved in determining the char- acteristics of the new cells and organisms that are produced, are based on common biologi- cal themes. Chapters 2 and 3 present cell structure and inheritance as an important, unifying framework within which biologists approach the diversity of organisms. Principles of inheritance explain not only why offspring resemble their parents, but also why variation exists within populations. This variation is a key to understanding evo- lution. All organisms have an evolutionary history, and evolution helps us to understand the life-shaping experiences that all organisms share. Chapter 4 explores the work of pioneers of evolutionary theory, Charles Darwin and Alfred Russell Wallace, and how their work forms the nucleus for modern evolutionary theory. Chapter 5 examines the influence of modern genetics on evolutionary theory. This coverage of evolution will provide core knowledge for understanding the diversity of animal life presented in Part Two and how evolution has influenced the animal structure and function described in Part Three. A fundamental unity of life also oc- curs at the environmental level. All animals are partners in the use of the earth’s re- sources. Only by studying the interactions of organisms with one another and with their environment can we appreciate the need for preserving resources for all organisms. Chapter 6 presents basic ecological princi- Chapter 1 ZOOLOGY: AN EVOLUTIONARY AND ECOLOGICAL PERSPECTIVE Chapter 2 CELLS, TISSUES, ORGANS, AND ORGAN SYSTEMS OF ANIMALS Chapter 3 CELL DIVISION AND INHERITANCE Chapter 4 EVOLUTION: A HISTORICAL PERSPECTIVE Chapter 5 EVOLUTION AND GENE FREQUENCIES Chapter 6 ECOLOGY: PRESERVING THE ANIMAL KINGDOM ples that everyone must understand if we are to preserve the animal kingdom. Photo (top): Examples of evolutionary adaptation and ecological interdependence abound in the animal king- dom. This cleaning shrimp (Periclimenes yucatani- cus) seeks refuge within the cnidocyte (stinging cells) laden tentacles of the giant anemone (Condylactis gigantea). While receiving protection from the anemone, the cleaning shrimp provides a service to fish that visit the shrimp’s home—cleaning the fish’s mouth, gills, and skin of parasites and debris. 1
  7. 7. Miller−Harley: Zoology, Fifth Edition I. Biological Principles 1. Zoology: An Ecological Perspective © The McGraw−Hill Companies, 2001 2 Outline Zoology: An Evolutionary Perspective Evolutionary Processes Animal Classification and Evolutionary Relationships Zoology: An Ecological Perspective World Resources and Endangered Animals Concepts 1. The field of zoology is the study of animals. It is a very broad field with many subdisciplines. 2. An understanding of evolutionary processes is very important in zoology because evolu- tion explains the family relationships among animals and how the great variety of ani- mals arose. 3. An understanding of ecological principles is very important in zoology because it helps zoologists to understand the interrelationships among individual animals and groups of animals. Understanding ecological principles also helps zoologists to understand how human interference threatens animal populations and the human environment. Zoology (Gr. zoon, ϩ logos, to study) is the study of animals. It is one of the broadest fields in all of science because of the immense variety of animals and the complexity of the processes occurring within animals. There are, for example, over 20,000 described species of bony fishes and over 300,000 described (and many more undescribed) species of beetles! It is no wonder that zoologists usually specialize in one or more of the subdisciplines of zoology. They may study particular functional, structural, or ecological aspects of one or more animal groups (table 1.1), or they may choose to specialize in a particular group of animals (table 1.2). Ichthyology, for example, is the study of fishes, and ichthyologists work to understand the structure, function, ecology, and evolution of fishes. These studies have uncovered an amazing diversity of fishes. One large group, the cichlids, is found in Africa (1,000 species), Central and South America (300 species), India (3 species) and North America (1 species). Members of this group have an enormous variety of color patterns (figure 1.1), habitats, and body forms. Ichthyologists have described a wide variety of feeding habits in cichlids. These fish include algae scrapers, like Eretmodus, that nip algae with chisel-like teeth; insect pickers, like Tanganicodus; and scale eaters, like Perissodus. All cichlids have two pairs of jaws. The mouth jaws are used for scraping or nipping food, and the throat jaws are used for crushing or macerating food before it is swallowed. Many cichlids mouth brood their young. A female takes eggs into her mouth after the eggs are spawned. She then inhales sperm released by the male, and fertilization and develop- ment take place within the female’s mouth! Even after the eggs hatch, young are taken back into the mouth of the female if danger threatens (figure 1.2). Hundreds of variations in color pattern, body form, and behavior in this family of fishes illustrate the remarkable diversity present in one relatively small branch of the animal kingdom. Zoologists are working around the world to understand and preserve the enormous diversity. C H A P T E R 1 ZOOLOGY: A N E V O L U T I O N A R Y A N D E C O L O G I C A L P E R S P E C T I V E This chapter contains evolutionary concepts, which are set off in this font.
  8. 8. Miller−Harley: Zoology, Fifth Edition I. Biological Principles 1. Zoology: An Ecological Perspective © The McGraw−Hill Companies, 2001 CHAPTER 1 Zoology: An Evolutionary and Ecological Perspective 3 ZOOLOGY: AN EVOLUTIONARY PERSPECTIVE Animals share a common evolutionary past and evolutionary forces that influenced their history. Evolutionary processes are remarkable for their relative simplicity, yet they have had awe- some effects on life-forms. These processes have resulted in an estimated 4 to 30 million species of organisms living today. (Only 1.4 million species have been described.) Many more ex- isted in the past and have become extinct. Zoologists must un- derstand evolutionary processes if they are to understand what an animal is and how it originated. EVOLUTIONARY PROCESSES Organic evolution (L. evolutus, unroll) is change in populations of organisms over time. It is the source of animal diversity, and it ex- plains family relationships within animal groups. Charles Darwin published convincing evidence of evolution in 1859 and proposed a mechanism that could explain evolutionary change. Since that time, biologists have become convinced that evolution occurs. The mechanism proposed by Darwin has been confirmed and now serves as the nucleus of our broader understanding of evolutionary change (chapters 4 and 5). Understanding how the diversity of animal structure and function arose is one of the many challenges faced by zoologists. For example, the cichlid scale eaters of Africa feed on the scales of other cichlids. They approach a prey cichlid from behind and bite a mouthful of scales from the body. The scales are then stacked TABLE 1.1 EXAMPLES OF SPECIALIZATIONS IN ZOOLOGY SUBDISCIPLINE DESCRIPTION Anatomy Study of the structure of entire organisms and their parts Cytology Study of the structure and function of cells Ecology Study of the interaction of organisms with their environment Embryology Study of the development of an animal from the fertilized egg to birth or hatching Genetics Study of the mechanisms of transmission of traits from parents to offspring Histology Study of tissues Molecular biology Study of subcellular details of animal structure and function Parasitology Study of animals that live in or on other organisms at the expense of the host Physiology Study of the function of organisms and their parts Systematics Study of the classification of, and the evolutionary interrelationships among, animal groups TABLE 1.2 EXAMPLES OF SPECIALIZATIONS IN ZOOLOGY BY TAXONOMIC CATEGORIES Entomology Study of insects Herpetology Study of amphibians and reptiles Ichthyology Study of fishes Mammalogy Study of mammals Omithology Study of birds Protozoology Study of protozoa FIGURE 1.1 Cichlids. Cichlids of Africa exist in an amazing variety of color pat- terns, habitats, and body forms. (a) This dogtooth cichlid (Cynotilapia afra) is native to Lake Malawi in Africa. Females of the species brood developing eggs in her mouth to protect them from predators. (b) The fontosa (Cyphontilapia fontosa) is native to Lake Tanganyika in Africa. (a) (b)
  9. 9. Miller−Harley: Zoology, Fifth Edition I. Biological Principles 1. Zoology: An Ecological Perspective © The McGraw−Hill Companies, 2001 4 PART ONE Biological Principles and crushed by the second set of jaws and sent to the stomach and intestine for protein digestion. Michio Hori of Kyoto University found that there were two body forms within the species Perissodus micolepis. One form had a mouth that was asymmetrically curved to the right and the other form had a mouth that was asymmetri- cally curved to the left. The asymmetry allowed right-jawed fish to approach and bite scales from the left side of their prey and the left-jawed fish to approach and bite scales from the right side of their prey. Both right- and left-jawed fish have been maintained in the population; otherwise the prey would eventually become wary of being attacked from one side. The variety of color patterns within the species Topheus duboisi has also been explained in an evolutionary context. Different color patterns arose as a result of the isolation of populations among sheltering rock piles separated by expanses of sandy bottom. Breeding is more likely to occur within their isolated populations because fish that venture over the sand are exposed to predators. ANIMAL CLASSIFICATION AND EVOLUTIONARY RELATIONSHIPS Evolution not only explains why animals appear and function as they do, but it also explains family relationships within the animal kingdom. Zoologists have worked for many years to understand the evolutionary relationships among the hundreds of cichlid species. Groups of individuals are more closely related if they share more of their genetic material (DNA) with each other than with individuals in other groups. (You are more closely related to your brother or sister than to your cousin for the same reason. Because DNA determines most of your physical traits, you will also more closely resemble your brother or sister.) Genetic studies have found that African cichlids originated in Lake Tanganyika, and from there the fish invaded African rivers and Lakes Malawi and Victoria. Lake Victoria’s four hundred species have been linked to an invasion by ancestral cichlids approximately 200,000 years ago (figure 1.3). That time period is long from the perspec- tive of a human lifetime, but it is a blink of the eye from the per- spective of evolutionary time. Even more remarkably, zoologists now believe that most of these species arose much more recently. Lake Victoria nearly dried out 14,000 years ago, and most of the original Victorian species would have been lost in the process. Like all organisms, animals are named and classified into a hierarchy of relatedness. Although Karl von Linne (1707–1778) is primarily remembered for collecting and classifying plants, his system of naming—binomial nomenclature—has also been adopted for animals. A two-part name describes each kind of or- ganism. The first part indicates the genus, and the second part in- dicates the species to which the organism belongs. Each kind of organism—for example, the cichlid scale-eater Perissodus microlepis—is recognized throughout the world by its two-part name. Above the species and genus levels, organisms are grouped into families, orders, classes, phyla, kingdoms, and domains, based on a hierarchy of relatedness (figure 1.4). Organisms in the same FIGURE 1.2 A Mouth-Brooding Cichlid. Nimbochromis livingstonii is a mouth- brooding species. Eggs develop in the mouth of the female and, after hatching, young return to the female’s mouth when danger threatens. Uganda Kenya Lake Victoria Lake Tanganyika Tanzania Lake Malawi Mozambique Malawi Democratic Republic of the Congo Zambia FIGURE 1.3 Lakes Victoria, Tanganyika, and Malawi. These lakes have cichlid populations that have been traced by zoologists to an ancestry that is ap- proximately 200,000 years old. Cichlid populations originated in Lake Tanganyika and then spread to the other two lakes.
  10. 10. Miller−Harley: Zoology, Fifth Edition I. Biological Principles 1. Zoology: An Ecological Perspective © The McGraw−Hill Companies, 2001 CHAPTER 1 Zoology: An Evolutionary and Ecological Perspective 5 species are more closely related than organisms in the same genus, and organisms in the same genus are more closely related than or- ganisms in the same family, and so on. When zoologists classify an- imals into taxonomic groupings they are making hypotheses about the extent to which groups of animals share DNA, even when they study variations in traits like jaw structure, color patterns, and behavior, because these kinds of traits ultimately are based on the genetic material. Evolutionary theory has affected zoology like no other single theory. It has impressed scientists with the fundamental unity of all of biology. As the cichlids of Africa illustrate, evolutionary concepts hold the key to understanding why animals look and act in their unique ways, live in their particular geographical regions and habitats, and share characteristics with other related animals. ZOOLOGY: AN ECOLOGICAL PERSPECTIVE Just as important to zoology as an evolutionary perspective is an ecological perspective. Ecology (Gr. okios, house ϩ logos, to study) is the study of the relationships between organisms and their en- vironment (chapter 6). Throughout our history, humans have de- pended on animals, and that dependence too often has led to ex- ploitation. We depend on animals for food, medicines, and clothing. We also depend on animals in other, more subtle ways. This dependence may not be noticed until human activities upset the delicate ecological balances that have evolved over hundreds of thousands of years. In the 1950s, the giant Nile perch (Lates niloticus) was introduced into Lake Victoria in an attempt to increase the lake’s fishery. This voracious predator reduced the cichlid population from 99% to less than 1% of the total fish population and has resulted in the extinction of many cichlid species. Because many of the cichlids fed on algae, the algae in the lake grew uncontrolled. When algae died and decayed, much of the lake became depleted of its oxygen. To make matters worse, when Nile perch are caught, their excessively oily flesh must be dried. Fishermen cut local forests for the wood needed to smoke the fish. This practice has resulted in severe deforestation around Lake Victoria. The resulting runoff of soil into the lake has caused further degradation. Ecological problems also threaten Lake Tanganyika’s cichlid populations. The area to the north of the lake has experienced nearly 100% deforestation. One-half of the forests on the Tanzania side of the lake are deforested to maintain a meager agricultural subsistence for human populations. Overfishing, agricultural runoff, and wastes from growing urban populations have led to some cichlid extinctions in the lake. WORLD RESOURCES AND ENDANGERED ANIMALS There is grave concern for the ecology of the entire world, not just Africa’s greatest lakes. The problems, however, are most acute in developing countries, which are striving to attain the same wealth as industrialized nations. Two problems, global overpopulation and the exploitation of world resources, are the focus of our eco- logical concerns. Population Global overpopulation is at the root of virtually all other environ- mental problems. Human population growth is expected to con- tinue in the twenty-first century. Most growth (92%) is in less de- veloped countries, where 5 billion out of a total of 6.1 billion humans now live. Since a high proportion of the population is of childbearing age, the growth rate will increase in the twenty-first Tabanus opacus Homo sapiens Perissodus microlepis Species Tabanidae Family Cichlidae Hominidae Order Diptera Primates Perciformes Musca domestica Muscidae Genus Perissodus Homo Musca Tabanus Osteichthyes Class Hexapoda Mammalia Phylum Chordata Arthropoda Kingdom Animalia Domain Eukarya FIGURE 1.4 Hierarchy of Relatedness. The classification of a housefly, horsefly, cichlid fish, and human illustrates how the classification system depicts degrees of relatedness.
  11. 11. Miller−Harley: Zoology, Fifth Edition I. Biological Principles 1. Zoology: An Ecological Perspective © The McGraw−Hill Companies, 2001 6 PART ONE Biological Principles century. It is estimated that the world population will reach 10.4 billion by the year 2100. As the human population grows, the dis- parity between the wealthiest and poorest nations is likely to increase. World Resources Human overpopulation is stressing world resources. Although new technologies continue to increase food production, most food is produced in industrialized countries that already have a high per-capita food consumption. Maximum oil production is ex- pected to continue in this millennium. Continued use of fossil fu- els adds more carbon dioxide to the atmosphere, contributing to the greenhouse effect and global warming. Deforestation of large areas of the world results from continued demand for forest prod- ucts and fuel. This trend contributes to the greenhouse effect, causes severe regional water shortages, and results in the extinc- tion of many plant and animal species, especially in tropical forests. Forest preservation would result in the identification of new species of plants and animals that could be important human resources: new foods, drugs, building materials, and predators of pests (figure 1.5). Nature also has intrinsic value that is just as im- portant as its provision of human resources. Recognition of this intrinsic worth provides important aesthetic and moral impetus for preservation. Solutions An understanding of basic ecological principles can help prevent ecological disasters like those we have described. Understanding how matter is cycled and recycled in nature, how populations grow, and how organisms in our lakes and forests use energy is fundamental to preserving the environment. There are no easy solutions to our ecological problems. Unless we deal with the problem of human overpopulation, however, solving the other problems will be impossible. We must work as a world community to prevent the spread of disease, famine, and other forms of suffer- ing that accompany over-population. Bold and imaginative steps toward improved social and economic conditions and better re- source management are needed. “Wildlife Alerts’’ that appear at the end of each chapter in the first two parts of this text remind us of the peril that an un- precedented number of species face around the world. Endangered or threatened species from a diverse group of animal phyla are highlighted. FIGURE 1.5 Tropical Rain Forests: A Threatened World Resource. A Brazilian tropical rain forest (a) before and (b) after clear-cutting to make way for agriculture. These soils quickly become depleted and are then aban- doned for the richer soils of adjacent forests. Loss of tropical forests re- sults in the extinction of many valuable forest species. (a) (b)
  12. 12. Miller−Harley: Zoology, Fifth Edition I. Biological Principles 1. Zoology: An Ecological Perspective © The McGraw−Hill Companies, 2001 CHAPTER 1 Zoology: An Evolutionary and Ecological Perspective 7 W I L D L I F E A L E RT An Overview of the Problems Extinction has been the fate of most plant and animal species. It is a natural process that will continue. In recent years, however, the threat to the welfare of wild plants and animals has increased dramatically— mostly as a result of habitat destruction. Tropical rain forests, the most threatened areas on the earth, have been reduced to 44% of their orig- inal extent. In certain areas, such as Ecuador, forest coverage has been reduced by 95%. This decrease in habitat has resulted in tens of thou- sands of extinctions. Accurately estimating the number of extinctions is impossible in areas like rain forests, where taxonomists have not even described most species. We are losing species that we do not know exist, and we are losing resources that could lead to new medicines, foods, and textiles. Other causes of extinction include climate change, pollution, and invasions from foreign species. Habitats other than rain forests—grasslands, marshes, deserts, and coral reefs—are also being seriously threatened. No one knows how many species living today are close to extinc- tion. As of 2001, the U.S. Fish and Wildlife Service lists 1,539 species on its endangered or threatened species lists. An endangered species is in imminent danger of extinction throughout its range (where it lives). A threatened species is likely to become endangered in the near fu- ture. Box figure I shows the number of endangered and threatened species in different regions of the United States. Clearly, much work is needed to improve these alarming statistics. In the chapters that follow, you will learn that saving species requires more than preserving a few remnant individuals. It requires a large diversity of genes within species groups to promote species sur- vival in changing environments. This genetic diversity requires large populations of plants and animals. Preservation of endangered species depends on a multifaceted con- servation plan that includes the following components: 1. A global system of national parks to protect large tracts of land and wildlife corridors that allow movement between natural areas 2. Protected landscapes and multiple-use areas that allow controlled private activity but also retain value as a wildlife habitat 3. Zoos and botanical gardens to save species whose extinction is imminent BOX FIGURE 1 Map Showing Approximate Numbers of Endangered and Threatened Species in the United States. Because the ranges of some organisms overlap two or more regions, the sum of all numbers is greater than the sum of all endangered and threatened species. (a) Northwest region, including Alaska. (b) Southwest region. (c) Great Plains region. (d) Mississippi Valley region. (e) Great Lakes region. (f) Northeast region.(g) Southeast region. (h) Hawaii. The total number of endangered and threatened species in the United States is 1,539. (h) 300 (a) 89 (b) 421 (d) 132 (c) 58 (e) 110 (f) 139 (g) 506
  13. 13. Miller−Harley: Zoology, Fifth Edition I. Biological Principles 1. Zoology: An Ecological Perspective © The McGraw−Hill Companies, 2001 8 PART ONE Biological Principles S U M M A R Y 1. Zoology is the study of animals. It is a broad field that requires zool- ogists to specialize in one or more subdisciplines. 2. Animals share a common evolutionary past and evolutionary forces that influenced their history. 3. Evolution explains how the diversity of animals arose. 4. Evolutionary relationships are the basis for the classification of ani- mals into a hierarchical system. This classification system uses a two-part name for every kind of animal. Higher levels of classifica- tion denote more distant evolutionary relationships. 5. All animals share a common environment, and ecological princi- ples help us to understand how animals interact within that environment. 6. Human overpopulation is at the root of virtually all other environ- mental problems. It stresses world resources and results in pollu- tion, global warming, deforestation, and the extinction of many plant and animal species. SELECTED KEY TERMS binomial nomenclature (p. 4) ecology (p. 5) endangered species (p. 7) CRITICAL THINKING QUESTIONS 1. How is zoology related to biology? What major biological concepts, in addition to evolution and ecology, are unifying principles within the two disciplines? 2. What are some current issues that involve both zoology and ques- tions of ethics or public policy? What should be the role of zoolo- gists in helping to resolve these issues? 3. Some people object to the teaching of evolution in public schools. What would be the effect on science education if evolution were banned from public school curricula? 4. Many of the ecological problems facing our world concern events and practices that occur in less developed countries. Many of these practices are the result of centuries of cultural evolution. What ap- proach should people and institutions of developed countries take in helping to encourage ecologically minded resource use? 5. Why should people in all parts of the world be concerned with the extinction of cichlids in Lake Victoria? organic evolution (p. 3) threatened species (p. 7) zoology (p. 2) ONLINE LEARNING CENTER Visit our Online Learning Center (OLC) at www.mhhe.com/zoology (click on this book’s title) to find the following chapter-related materials: • CHAPTER QUIZZING • RELATED WEB LINKS Introductory Materials Evolution Classification and Phylogeny of Animals Endangered Species Human Population Growth • BOXED READINGS ON Science and Pseudoscience The Origin of Life on Earth—Life from Nonlife Box Continental Drift The Zebra Mussel Jaws from the Past • SUGGESTED READINGS • LAB CORRELATIONS Check out the OLC to find specific information on these related lab exercises in the General Zoology Laboratory Manual, 5th edition, by Stephen A. Miller: Exercise 6 Adaptations of Stream Invertebrates—A Scavenger Hunt Exercise 7 The Classification of Organisms
  14. 14. Miller−Harley: Zoology, Fifth Edition I. Biological Principles 2. Cells, Tissues, Organs, and Organ Systems © The McGraw−Hill Companies, 2001 9 Outline What Are Cells? Why Are Most Cells Small? Cell Membranes Structure of Cell Membranes Functions of Cell Membranes Movement Across Membranes Simple Diffusion Facilitated Diffusion Osmosis Filtration Active Transport Endocytosis Exocytosis Cytoplasm, Organelles, and Cellular Components Cytoplasm Ribosomes: Protein Workbenches Endoplasmic Reticulum Golgi Apparatus Lysosomes: Digestion and Degradation Mitochondria: Power Generators Cytoskeleton (Microtubules, Intermediate Filaments, and Microfilaments) Cilia and Flagella: Movement Centrioles and Microtubule-Organizing Centers Vacuoles: Cell Maintenance The Nucleus: Information Center Nuclear Envelope (Gateway to Nucleus) Chromosomes: Genetic Containers Nucleolus Tissues Epithelial Tissue: Many Forms and Functions Connective Tissue: Connection and Support Muscle Tissue: Movement Nervous Tissue: Communication Organs Organ Systems C H A P T E R 2 CELLS, TISSUES, ORGANS, AND ORGAN SYSTEMS OF ANIMALS Because all animals are made of cells, the cell is as fundamental to an understanding of zoology as the atom is to an understanding of chemistry. In the hierarchy of biological organization, the cell is the simplest organization of matter that exhibits the properties of life (figure 2.1). Some organisms are single celled; others are multicellular. An animal has a body composed of many kinds of specialized cells. A division of labor among cells allows specialization into higher levels of organization (tissues, organs, and organ systems). Yet, everything that an animal does is ultimately happening at the cellular level. WHAT ARE CELLS? Cells are the functional units of life, in which all of the chemical reactions necessary for the maintenance and reproduction of life take place. They are the smallest independent units of life. Structurally speaking, cells are either prokaryotic or eukaryotic. All prokary- otes (“before nucleus”) are independent, single-celled organisms (e.g., bacteria). The word “prokaryote” describes cells in which DNA is localized in a region but is not bound by a mem- brane. Table 2.1 summarizes some of the more salient characteristics of a prokaryotic cell. All eukaryotes (“true nucleus”) have cells with a membrane-bound nucleus con- taining DNA. In addition, eukaryotic cells contain many other structures called organelles (“little organs”) that perform specific functions. Eukaryotic cells also have a network of specialized structures called filaments and tubules organized into the cytoskeleton, which gives shape to the cell and allows intracellular movement. All eukaryotic cells have three basic parts (table 2.1): 1. The plasma membrane is the outer boundary of the cell. It separates the internal metabolic events from the environment and allows them to proceed in organized, controlled ways. The plasma membrane also has specific receptors for external mole- cules that alter the cell’s function. 2. Cytoplasm (Gr. kytos, hollow vessel ϩ plasm, fluid) is the portion of the cell outside the nucleus. The semifluid portion of the cytoplasm is called the cytosol. Suspended within the cytosol are the organelles. Concepts 1. Cells are the basic organizational units of life. 2. Eukaryotic cells exhibit a considerable degree of internal organization, with a dynamic system of membranes forming internal compartments called organelles. 3. The structure and function of a typical cell usually apply to all animals. 4. Different cell types organize into structural and functional units called tissues, organs, and organ systems.
  15. 15. Miller−Harley: Zoology, Fifth Edition I. Biological Principles 2. Cells, Tissues, Organs, and Organ Systems © The McGraw−Hill Companies, 2001 10 PART ONE Biological Principles 3. The nucleus (pl., nuclei) is the cell control center. It con- tains the chromosomes and is separated from the cytoplasm by its own nuclear envelope. The nucleoplasm is the semi- fluid material in the nucleus. Because cells vary so much in form and function, no “typi- cal” cell exists. However, to help you learn as much as possible about cells, figure 2.2 shows an idealized version of a eukaryotic cell and most of its component parts. WHY ARE MOST CELLS SMALL? Most cells are small and can be seen only with the aid of a micro- scope. (Exceptions include the eggs of most vertebrates [fishes, amphibians, reptiles, and birds] and some long nerve cells.) One reason for the smallness of cells is that the ratio of the volume of the cell’s nucleus to the volume of its cytoplasm must not be so small that the nucleus, the cell’s major control center, cannot con- trol the cytoplasm. Another aspect of cell volume works to limit cell size. As the radius of a cell lengthens, cell volume increases more rapidly than cell surface area (figure 2.3). The need for nutrients and the rate of waste production are proportional to cell volume. The cell takes up nutrients and eliminates wastes through its surface plasma membrane. If cell volume becomes too large, the surface- area-to-volume ratio is too small for an adequate exchange of nu- trients and wastes. CELL MEMBRANES The plasma membrane surrounds the cell. Other membranes in- side the cell enclose some organelles and have properties similar to the plasma membrane. Animal Organ systems Organs Tissues Cells Organelles Membranes Macromolecules Simple molecules Atoms Living Nonliving IncreasingcomplexityDecreasingcomplexity FIGURE 2.1 Structural Hierarchy in a Multicellular Animal. At each level, func- tion depends on the structural organization of that level and those below it. TABLE 2.1 COMPARISON OF PROKARYOTIC AND EUKARYOTIC CELLS COMPONENT PROKARYOTE EUKARYOTE Cell wall Present Absent in animals (present in plants) Centrioles and Absent Present in animals microtubule (absent in plants) organizing center Chloroplasts Present in some Present in some cells cells Genetic material Single circular Arranged in multiple chromosome chromosomes; of DNA DNA associated with protein Cilia (9 + 2) Absent Present in some cells Cytoskeleton Absent Present Endoplasmic Absent Present reticulum Flagellum Often present Present in some cells Glycocalyx Absent Present Golgi apparatus Absent Present Lysosomes Absent Present Mitochondria Absent Present Nucleus Absent Present Plasma membrane Present Present Ribosomes Present Present Vacuoles Present Present Vesicles Present Present
  16. 16. Miller−Harley: Zoology, Fifth Edition I. Biological Principles 2. Cells, Tissues, Organs, and Organ Systems © The McGraw−Hill Companies, 2001 CHAPTER 2 Cells, Tissues, Organs, and Organ Systems of Animals 11 STRUCTURE OF CELL MEMBRANES In 1972, S. Jonathan Singer and Garth Nicolson developed the fluid-mosaic model of membrane structure. According to this model, a membrane is a double layer (bilayer) of proteins and phospholipids, and is fluid rather than solid. The phospholipid bi- layer forms a fluid “sea” in which specific proteins float like ice- bergs (figure 2.4). Being fluid, the membrane is in a constant state of flux—shifting and changing, while retaining its uniform struc- ture. The word mosaic refers to the many different kinds of pro- teins dispersed in the phospholipid bilayer. The following are important points of the fluid-mosaic model: 1. The phospholipids have one polar end and one nonpolar end. The polar ends are oriented on one side toward the out- side of the cell and into the fluid cytoplasm on the other side, and the nonpolar ends face each other in the middle of the bilayer. The “tails” of both layers of phospholipid mole- cules attract each other and are repelled by water (they are hydrophobic, “water dreading”). As a result, the polar spher- ical “heads” (the phosphate portion) are located over the cell surfaces (outer and inner) and are “water attracting” (they are hydrophilic). 2. Cholesterol is present in the plasma membrane and or- ganelle membranes of eukaryotic cells. The cholesterol mol- ecules are embedded in the interior of the membrane and help to make the membrane less permeable to water-soluble substances. In addition, the relatively rigid structure of the cholesterol molecules helps to stabilize the membrane (figure 2.5). 3. The membrane proteins are individual molecules attached to the inner or outer membrane surface (peripheral proteins) or embedded in it (intrinsic proteins) (see figure 2.4). Some intrinsic proteins are links to sugar-protein markers on the cell surface. Other intrinsic proteins help to move ions or molecules across the membrane, and still others attach the membrane to the cell’s inner scaffolding (the cytoskeleton) or to various molecules outside the cell. 4. When carbohydrates unite with proteins, they form glyco- proteins, and when they unite with lipids, they form glyco- lipids on the surface of a plasma membrane. Surface carbohydrates and portions of the proteins and lipids make up the glycocalyx (“cell coat”) (figure 2.6). The complexly arranged and distinctively shaped groups of sugar molecules of the glycocalyx act as a molecular “fingerprint” for each cell type. The glycocalyx is necessary for cell-to-cell recogni- tion and the behavior of certain cells, and is a key compo- nent in coordinating cell behavior in animals. FUNCTIONS OF CELL MEMBRANES Cell membranes (1) regulate material moving into and out of the cell, and from one part of the cell to another; (2) separate the in- side of the cell from the outside; (3) separate various organelles within the cell; (4) provide a large surface area on which specific Microtubule-organizing centers (with centriole pairs) Lysosome Microtubules Mitochondrion Plasma membrane Nuclear envelope Nucleus Nucleolus Chromatin Golgi apparatus Polyribosome (polysome) Vesicle Free ribosomes Smooth endoplasmic reticulum Rough endoplasmic reticulum FIGURE 2.2 A Generalized Animal Cell. Understanding of the structures in this cell is based mainly on electron microscopy. The sizes of some organelles and structures are exaggerated to show detail. Radius (r ) Surface area (SA) Volume (V ) SA/V Surface area of a sphere = 4 π r 2 Volume of sphere = 4/3 π r 3 4 cm 201.06 cm2 268.08 cm3 0.75 2 cm 50.26 cm2 33.51 cm3 1.50 1 cm 12.57 cm2 4.19 cm3 3.0 FIGURE 2.3 The Relationship Between Surface Area and Volume. As the radius of a sphere increases, its volume increases more rapidly than its surface area. (SA/V ϭ surface area to volume ratio.)
  17. 17. Miller−Harley: Zoology, Fifth Edition I. Biological Principles 2. Cells, Tissues, Organs, and Organ Systems © The McGraw−Hill Companies, 2001 12 PART ONE Biological Principles chemical reactions can occur; (5) separate cells from one another; and (6) are a site for receptors containing specific cell identifica- tion markers that differentiate one cell type from another. The ability of the plasma membrane to let some substances in and keep others out is called selective permeability (L. per- meare or per, through ϩ meare, pass) and is essential for main- taining cellular homeostasis. Homeostasis (Gr. homeo, always the same ϩ stasis, standing) is the maintenance of a relatively constant internal environment despite fluctuations in the exter- nal environment. However, before you can fully understand how substances pass into and out of cells and organelles, you must know how the molecules of those substances move from one place to another. Carbohydrate Outside cell Glycolipid Fibrous proteins Double layer of phospholipid molecules Phospholipid "head" Phospholipid "tail" Globular proteinCholesterol molecules Cytoplasmic side of membrane FIGURE 2.4 Fluid-Mosaic Model of Membrane Structure. Intrinsic globular proteins may protrude above or below the lipid bilayer and may move about in the membrane. Peripheral proteins attach to either the inner or outer surfaces. Phospholipid Phospholipid Cholesterol More fluid region Region stiffened by cholesterolHydrophobic (nonpolar) tail Hydrophilic (polar) head Water FIGURE 2.5 The Arrangement of Cholesterol Between Lipid Molecules of a Lipid Bilayer. Cholesterol stiffens the outer lipid bilayer and causes the inner region of the bilayer to become slightly more fluid. Only half the lipid bilayer is shown; the other half is a mirror image. Protein fibers Glycolipid Sugar molecules Proteins Glyco- protein Glyco- calyx Lipid bilayer Cytoplasm Extracellular fluid (outside of cell) FIGURE 2.6 The Glycocalyx, Showing the Glycoproteins and Glycolipids. Note that all of the attached carbohydrates are on the outside of the plasma membrane.
  18. 18. Miller−Harley: Zoology, Fifth Edition I. Biological Principles 2. Cells, Tissues, Organs, and Organ Systems © The McGraw−Hill Companies, 2001 CHAPTER 2 Cells, Tissues, Organs, and Organ Systems of Animals 13 MOVEMENT ACROSS MEMBRANES Molecules can cross membranes in a number of ways, both by using their own energy and by relying on an outside energy source. Table 2.2 summarizes the various kinds of transmembrane move- ment, and the sections that follow discuss them in more detail. SIMPLE DIFFUSION Molecules move randomly (due to spontaneous molecular motion) from areas where they are highly concentrated to areas of lower concentration, until they are evenly distributed in a state of dy- namic equilibrium. This process is simple diffusion (L. diffundere, to spread). Simple diffusion accounts for most of the short- distance transport of substances moving into and out of cells. Figure 2.7 shows the diffusion of sugar particles away from a sugar cube placed in water. FACILITATED DIFFUSION Polar molecules (not soluble in lipids) may diffuse through protein channels (pores) in the lipid bilayer (figure 2.8). The protein chan- nels offer a continuous pathway for specific molecules to move across the plasma membrane so that they never come into contact with the hydrophobic layer or the membrane’s polar surface. Large molecules and some of those not soluble in lipids re- quire assistance in passing across the plasma membrane. These TABLE 2.2 DIFFERENT TYPES OF MOVEMENT ACROSS PLASMA MEMBRANES TYPE OF MOVEMENT DESCRIPTION EXAMPLE IN THE BODY OF A FROG Simple diffusion No cell energy is needed. Molecules move “down’’ A frog inhales air containing oxygen, which moves a concentration gradient. Molecules spread out into the lungs and then diffuses into the randomly from areas of higher concentration to bloodstream. areas of lower concentration until they are dis- tributed evenly in a state of dynamic equilibrium. Facilitated diffusion Carrier (transport) proteins in a plasma Glucose in the gut of a frog combines with carrier membrane temporarily bind with molecules proteins to pass through the gut cells into the and help them pass across the membrane. bloodstream. Other proteins form channels through which molecules move across the membrane. Osmosis Water molecules diffuse across selectively Water molecules move into a frog’s red blood cell permeable membranes from areas of higher when the concentration of water molecules outside concentration to areas of lower concentration. the blood cell is greater than it is inside. Filtration Hydrostatic pressure forces small molecules A frog’s blood pressure forces water and dissolved across selectively permeable membranes from wastes into the kidney tubules during urine areas of higher pressure to areas of lower pressure. formation. Active transport Specific carrier proteins in the plasma membrane Sodium ions move from inside the neurons of the bind with molecules or ions to help them cross sciatic nerve of a frog (the sodium-potassium pump) the membrane against a concentration gradient. to the outside of the neurons. Energy is required. Endocytosis The bulk movement of material into a cell by formation of a vesicle. Pinocytosis The plasma membrane encloses small amounts of The kidney cells of a frog take in fluid to maintain fluid droplets (in a vesicle) and takes them into fluid balance. the cell. Phagocytosis The plasma membrane forms a vesicle around a The white blood cells of a frog engulf and digest solid particle or other cell and draws it into the harmful bacteria. phagocytic cell. Receptor-mediated endocytosis Extracellular molecules bind with specific receptor The intestinal cells of a frog take up large molecules proteins on a plasma membrane, causing the from the inside of the gut. membrane to invaginate and draw molecules into the cell. Exocytosis The movement of material out of a cell. A vesicle The sciatic nerve of a frog releases a chemical (with particles) fuses with the plasma membrane (neurotransmitter). and expels particles or fluids from the cell across the plasma membrane.
  19. 19. Miller−Harley: Zoology, Fifth Edition I. Biological Principles 2. Cells, Tissues, Organs, and Organ Systems © The McGraw−Hill Companies, 2001 14 PART ONE Biological Principles molecules use facilitated diffusion, which, like simple diffusion, requires no energy input. To pass across the membrane, a molecule temporarily binds with a carrier (transport) protein in the plasma membrane and is transported from an area of higher concentra- tion to one of lower concentration (figure 2.9). OSMOSIS The diffusion of water across a selectively permeable membrane from an area of higher concentration to an area of lower concen- tration is osmosis (Gr. osmos, pushing). Osmosis is just a special type of diffusion, not a different method (figure 2.10). The term tonicity (Gr. tonus, tension) refers to the rela- tive concentration of solutes in the water inside and outside the cell. For example, in an isotonic (Gr. isos, equal ϩ tonus, ten- sion) solution, the solute concentration is the same inside and outside a red blood cell (figure 2.11a). The concentration of wa- ter molecules is also the same inside and outside the cell. Thus, water molecules move across the plasma membrane at the same (d)(c)(b)(a) FIGURE 2.7 Simple Diffusion. When a sugar cube is placed in water (a), it slowly dissolves (b) and disappears. As this happens, the sugar molecules diffuse from a region where they are more concentrated to a region (c) where they are less concentrated. Even distribution of the sugar molecules throughout the wa- ter is diffusion equilibrium (d). FIGURE 2.8 Transport Proteins. Molecules can move into and out of cells through integrated protein channels (pores) in the plasma membrane without using energy. FIGURE 2.9 Facilitated Diffusion and Carrier (Transport) Proteins. Some mole- cules move across the plasma membrane with the assistance of carrier proteins that transport the molecules down their concentration gradi- ent, from a region of higher concentration to one of lower concentra- tion. A carrier protein alternates between two configurations, moving a molecule across a membrane as the shape of the protein changes. The rate of facilitated diffusion depends on how many carrier proteins are available in the membrane and how fast they can move their specific molecule.
  20. 20. Miller−Harley: Zoology, Fifth Edition I. Biological Principles 2. Cells, Tissues, Organs, and Organ Systems © The McGraw−Hill Companies, 2001 CHAPTER 2 Cells, Tissues, Organs, and Organ Systems of Animals 15 rate in both directions, and there is no net movement of water in either direction. In a hypertonic (Gr. hyper, above) solution, the solute con- centration is higher outside the red blood cell than inside. Because the concentration of water molecules inside the cell is higher than outside, water moves out of the cell, which shrinks (figure 2.11b). This condition is called crenation in red blood cells. In a hypotonic (Gr. hypo, under) solution, the solute con- centration is lower outside the red blood cell than inside. Con- versely, the concentration of water molecules is higher outside the cell than inside. As a result, water moves into the cell, which swells and may burst (figure 2.11c). FILTRATION Filtration is a process that forces small molecules across selectively permeable membranes with the aid of hydrostatic (water) pressure (or some other externally applied force, such as blood pressure). For example, in the body of an animal such as a frog, filtration is evident when blood pressure forces water and dissolved molecules through the permeable walls of small blood vessels called capillar- ies (figure 2.12). In filtration, large molecules, such as proteins, do not pass through the smaller membrane pores. Filtration also takes place in the kidneys when blood pressure forces water and dis- solved wastes out of the blood vessels and into the kidney tubules in the first step in urine formation. ACTIVE TRANSPORT Active-transport processes move molecules and other substances across a selectively permeable membrane against a concentration gradient—that is, from an area of lower concentration to one of higher concentration. This movement against the concentration gradient requires ATP energy. The active-transport process is similar to facilitated diffu- sion, except that the carrier protein in the plasma membrane must use energy to move the molecules against their concentration gra- dient (figure 2.13). One active-transport mechanism, the sodium-potassium pump, helps maintain the high concentrations of potassium ions and low concentrations of sodium ions inside nerve cells that are necessary for the transmission of electrical impulses. An- other active-transport mechanism, the calcium pump, keeps the 21 21 (a) (b) Selectively permeable membrane Water molecule Sugar molecule Time FIGURE 2.10 Osmosis. (a) A selectively permeable membrane separates the beaker into two compartments. Initially, compartment 1 contains sugar and wa- ter molecules, and compartment 2 contains only water molecules. Due to molecular motion, water moves down the concentration gradient (from compartment 2 to compartment 1) by osmosis. The sugar mole- cules remain in compartment 1 because they are too large to pass across the membrane. (b) At osmotic equilibrium, the number of water mole- cules in compartment 1 does not increase. FIGURE 2.11 Effect of Salt Concentration on Cell Volumes. (a) An isotonic solu- tion with the same salt concentration inside and outside the cell has no effect on the size of the red blood cell. (b) A hypertonic (high salt) solu- tion causes water to leave the red blood cell, which shrinks. (c) A hypo- tonic (low salt) solution results in an inflow of water, causing the red blood cell to swell. Arrows indicate direction of water movement.
  21. 21. Miller−Harley: Zoology, Fifth Edition I. Biological Principles 2. Cells, Tissues, Organs, and Organ Systems © The McGraw−Hill Companies, 2001 16 PART ONE Biological Principles calcium concentration hundreds of times lower inside the cell than outside. ENDOCYTOSIS Another process by which substances move across the plasma mem- brane is endocytosis. Endocytosis (Gr. endon, within) involves bulk movement of materials across the plasma membrane, rather than movement of individual molecules. The three forms of endocytosis are pinocytosis, phagocytosis, and receptor-mediated endocytosis. Pinocytosis (“cell drinking,” from Gr. pinein, to drink ϩ cyto, cell) is nonspecific uptake of small droplets of extracellular fluid. Any small solid dissolved in the fluid is also taken into the cell. Pinocytosis occurs when a small portion of the plasma membrane indents (invaginates). The open end of the invagina- tion seals itself off, forming a small vesicle. This tiny vesicle de- taches from the plasma membrane and moves into the cytoplasm (figure 2.14a). Phagocytosis (“cell eating,” from Gr. phagein, to eat ϩ cyto, cell) is similar to pinocytosis, except that the cell takes in solid material rather than liquid. Commonly, an organelle called a lyso- some combines with the vesicle to form a phagolysosome (“diges- tion vacuole”), and lysosomal digestive enzymes break down the vesicle’s contents (figure 2.14b). Receptor-mediated endocytosis involves a specific receptor protein on the plasma membrane that “recognizes” an extracellu- lar molecule and binds with it (figure 2.14c). This reaction some- how stimulates the membrane to indent and create a vesicle containing the selected molecule. A variety of important mole- cules (such as cholesterol) are brought into cells in this manner. EXOCYTOSIS An organelle known as the Golgi apparatus (described in a later section) packages proteins and other molecules that the cell pro- duces into vesicles for secretion. In the process of exocytosis (Gr. exo, outside), these secretory vesicles fuse with the plasma membrane and release their contents into the extracellular environment (figure 2.14b). This process adds new membrane ma- terial, which replaces the plasma membrane lost during endocytosis. CYTOPLASM, ORGANELLES, AND CELLULAR COMPONENTS Many cell functions that are performed in the cytoplasmic com- partment result from the activity of specific structures called organelles. Table 2.3 summarizes the structure and function of these organelles, and the sections that follow discuss them in more detail. CYTOPLASM The cytoplasm of a cell has two distinct parts: (1) The cytomem- brane system consists of well-defined structures, such as the endo- plasmic reticulum, Golgi apparatus, vacuoles, and vesicles. (2) The fluid cytosol suspends the structures of the cytomembrane system and contains various dissolved molecules. RIBOSOMES: PROTEIN WORKBENCHES Ribosomes are non-membrane-bound structures that are the sites for protein synthesis. They contain almost equal amounts of pro- tein and a special kind of ribonucleic acid called ribosomal RNA FIGURE 2.12 Filtration. The high blood pressure in the capillary forces small mole- cules through the capillary membrane. Larger molecules cannot pass through the small openings in the capillary membrane and remain in the capillary. Arrows indicate the direction of small molecule movement. FIGURE 2.13 Active Transport. During active transport, a molecule combines with a carrier protein whose shape is altered as a result of the combination. This change in configuration, along with energy, helps move the mole- cule across the plasma membrane against a concentration gradient.
  22. 22. Miller−Harley: Zoology, Fifth Edition I. Biological Principles 2. Cells, Tissues, Organs, and Organ Systems © The McGraw−Hill Companies, 2001 CHAPTER 2 Cells, Tissues, Organs, and Organ Systems of Animals 17 (rRNA). Some ribosomes attach to the endoplasmic reticulum (see next section), and some float freely in the cytoplasm. Whether ribosomes are free or attached, they usually cluster in groups connected by a strand of another kind of ribonucleic acid called messenger RNA (mRNA). These clusters are called polyri- bosomes or polysomes (see figure 2.2). ENDOPLASMIC RETICULUM: PRODUCTION AND TRANSPORT The endoplasmic reticulum (ER) is a complex, membrane-bound labyrinth of flattened sheets, sacs, and tubules that branches and spreads throughout the cytoplasm. The ER is continuous from the (a) Pinocytosis (b) Phagocytosis (c) Receptor-mediated endocytosis Nucleus Receptor site protein Molecules outside cell Phagolysosome Nucleus Lysosome Particle Nucleus Fluid particles Plasma membrane Vesicle Vesicle Residue being expelled by exocytosis Vesicle FIGURE 2.14 Endocytosis and Exocytosis. (a) Pinocytosis. A cell takes in small fluid particles and forms a vesicle. (b) Phagocytosis. A cell takes in a solid particle and forms a vesicle. A lysosome combines with a vesicle, forming a phagolysosome. Lysosomal enzymes digest the particle. The vesicle can also fuse with the plasma membrane and release its contents by exocytosis. (c) In receptor-mediated endocytosis, a specific molecule binds to a receptor protein, inducing the formation of a vesicle.
  23. 23. Miller−Harley: Zoology, Fifth Edition I. Biological Principles 2. Cells, Tissues, Organs, and Organ Systems © The McGraw−Hill Companies, 2001 18 PART ONE Biological Principles nuclear envelope to the plasma membrane (see figure 2.2) and is a series of channels that helps various materials to circulate throughout the cytoplasm. It also is a storage unit for enzymes and other proteins and a point of attachment for ribosomes. ER with attached ribosomes is rough ER (figure 2.15a), and ER without attached ribosomes is smooth ER (figure 2.15b). Smooth ER is the site for lipid production, detoxification of a wide variety of organic molecules, and storage of calcium ions in muscle cells. Most cells contain both types of ER, although the relative proportion varies among cells. TABLE 2.3 STRUCTURE AND FUNCTION OF CELLULAR COMPONENTS COMPONENT STRUCTURE/DESCRIPTION FUNCTION Centriole Located within microtuble-organizing center; Forms basal body of cilia and flagella; functions in contains nine triple microtubules mitotic spindle formation Chloroplast Organelle that contains chlorophyll and is Traps, transforms, and uses light energy to convert involved in photosynthesis carbon dioxide and water into glucose and oxygen Chromosome Made up of nucleic acid (DNA) and protein Controls heredity and cellular activities Cilia, flagella Threadlike processes Cilia and flagella move small particles past fixed cells and are a major form of locomotion in some cells Cytomembrane system The endoplasmic reticulum, Golgi apparatus, Organelles, functioning as a system, to modify, vacuoles, vesicles package, and distribute newly formed proteins and lipids Cytoplasm Semifluid enclosed within plasma membrane; Dissolves substances; houses organelles and vesicles consists of fluid cytosol, organelles, and other structures Cytoskeleton Interconnecting microfilaments and micro- Assists in cell movement; provides support; site for tubules; flexible cellular framework binding of specific enzymes Cytosol Fluid part of cytoplasm; enclosed within plasma Houses organelles; serves as fluid medium for meta- membrane; surrounds nucleus bolic reactions Endoplasmic reticulum (ER) Extensive membrane system extending throughout Storage and internal transport; rough ER is a site the cytoplasm from the plasma membrane to the for attachment of ribosomes; smooth ER makes nuclear envelope lipids Golgi apparatus Stacks of disklike membranes Sorts, packages, and routes cell’s synthesized products Lysosome Membrane-bound sphere Digests materials Microfilament Rodlike structure containing the protein actin Gives structural support and assists in cell movement Microtubule Hollow, cylindrical structure Assists in movement of cilia, flagella, and chromosomes; transport system Microtubule-organizing center Cloud of cytoplasmic material that contains Dense site in the cytoplasm that gives rise to large centrioles numbers of microtubules with different functions in the cytoskeleton Mitochondrion Organelle with double, folded membranes Converts energy into a form the cell can use Nucleolus Rounded mass within nucleus; contains RNA Preassembly point for ribosomes and protein Nucleus Spherical structure surrounded by a nuclear Contains DNA that controls cell’s genetic program envelope; contains nucleolus and DNA and metabolic activities Plasma membrane The outer bilayered boundary of the cell; composed Protection; regulation of material movement; of protein, cholesterol, and phospholipid cell-to-cell recognition Ribosome Contains RNA and protein; some are Site of protein synthesis free, and some attach to ER Vacuole Membrane-surrounded, often large, sac in the Storage site of food and other compounds; also pumps cytoplasm water out of a cell (e.g., contractile vacuole) Vesicle Small, membrane-surrounded sac; contains Site of intracellular digestion, storage, or transport enzymes or secretory products
  24. 24. Miller−Harley: Zoology, Fifth Edition I. Biological Principles 2. Cells, Tissues, Organs, and Organ Systems © The McGraw−Hill Companies, 2001 CHAPTER 2 Cells, Tissues, Organs, and Organ Systems of Animals 19 GOLGI APPARATUS: PACKAGING, SORTING, AND EXPORT The Golgi apparatus or complex (named for Camillo Golgi, who discovered it in 1898) is a collection of membranes associated physically and functionally with the ER in the cytoplasm (figure 2.16a; see also figure 2.2). It is composed of flattened stacks of membrane-bound cisternae (sing., cisterna; closed spaces serving as fluid reservoirs). The Golgi apparatus sorts, packages, and se- cretes proteins and lipids. Proteins that ribosomes synthesize are sealed off in little pack- ets called transfer vesicles. Transfer vesicles pass from the ER to the Golgi apparatus and fuse with it (figure 2.16b). In the Golgi appara- tus, the proteins are concentrated and chemically modified. One function of this chemical modification seems to be to mark and sort the proteins into different batches for different destinations. Even- tually, the proteins are packaged into secretory vesicles, which are released into the cytoplasm close to the plasma membrane. When the vesicles reach the plasma membrane, they fuse with it and release their contents to the outside of the cell by exocytosis. Golgi apparatuses are most abundant in cells that secrete chemical sub- stances (e.g., pancreatic cells secreting digestive enzymes and nerve cells secreting neurotransmitters). As noted in the next section, the Golgi apparatus also produces lysosomes. LYSOSOMES: DIGESTION AND DEGRADATION Lysosomes (Gr. lyso, dissolving ϩ soma, body) are membrane- bound spherical organelles that contain enzymes called acid hydrolases, which are capable of digesting organic molecules (lipids, proteins, nucleic acids, and polysaccharides) under acidic conditions. The enzymes are synthesized in the ER, transported to the Golgi apparatus for processing, and then secreted by the Golgi apparatus in the form of lysosomes or as vesicles that fuse with lysosomes (figure 2.17). Lysosomes fuse with phagocytic vesicles, thus exposing the vesicle’s contents to lysosomal enzymes. FIGURE 2.15 Endoplasmic Reticulum (ER). (a) Ribosomes coat rough ER. Notice the double membrane and the lumen (space) between each membrane. (b) Smooth ER lacks ribosomes. (a) (b) Cisternae Transfer vesicle from ER Exocytosis Outside of Cell Cytoplasm Plasma membrane Budding vesicle Secretory vesicles FIGURE 2.16 Golgi Apparatus. (a) The Golgi apparatus consists of a stack of cister- nae. Notice the curved nature of the cisternae. (b) The Golgi apparatus stores, sorts, packages, and secretes cell products. Secretory vesicles move from the Golgi apparatus to the plasma membrane and fuse with it, releasing their contents to the outside of the cell via exocytosis.
  25. 25. Miller−Harley: Zoology, Fifth Edition I. Biological Principles 2. Cells, Tissues, Organs, and Organ Systems © The McGraw−Hill Companies, 2001 20 PART ONE Biological Principles MITOCHONDRIA: POWER GENERATORS Mitochondria (sing., mitochondrion) are double-membrane-bound organelles that are spherical to elongate in shape. A small space separates the outer membrane from the inner membrane. The in- ner membrane folds and doubles in on itself to form incomplete partitions called cristae (sing., crista; figure 2.18). The cristae in- crease the surface area available for the chemical reactions that trap usable energy for the cell. The space between the cristae is the ma- trix. The matrix contains ribosomes, circular DNA, and other ma- terial. Because they convert energy to a usable form, mitochondria are frequently called the “power generators” of the cell. Mitochon- dria usually multiply when a cell needs to produce more energy. CYTOSKELETON: MICROTUBULES, INTERMEDIATE FILAMENTS, AND MICROFILAMENTS In most cells, the microtubules, intermediate filaments, and mi- crofilaments form the flexible cellular framework called the cy- toskeleton (“cell skeleton”) (figure 2.19). This latticed framework extends throughout the cytoplasm, connecting the various or- ganelles and cellular components. Microtubules are hollow, slender, cylindrical structures in animal cells. Each microtubule is made of spiraling subunits of globular proteins called tubulin subunits (figure 2.20a). Micro- tubules function in the movement of organelles, such as secretory vesicles, and in chromosome movement during division of the cell nucleus. They are also part of a transport system within the cell. For example, in nerve cells, they help move materials through the long nerve processes. Microtubules are an important part of the cy- toskeleton in the cytoplasm, and they are involved in the overall shape changes that cells undergo during periods of specialization. Intermediate filaments are a chemically heterogeneous group of protein fibers, the specific proteins of which can vary with cell type (figure 2.20b). These filaments help to maintain cell shape and the spatial organization of organelles, as well as pro- mote mechanical activities within the cytoplasm. Microfilaments are solid strings of protein (actin) molecules (figure 2.20c). Actin microfilaments are most highly developed in muscle cells as myofibrils, which help muscle cells to shorten or contract. Actin microfilaments in nonmuscle cells provide me- chanical support for various cellular structures and help form con- tractile systems responsible for some cellular movements (e.g., amoeboid movement in some protozoa). CILIA AND FLAGELLA: MOVEMENT Cilia (sing., cilium; L. “eyelashes”) and flagella (sing., flagellum; L. “small whips”) are elongated appendages on the surface of some cells by which the cells, including many unicellular organisms, Plasma membrane Lysosome Phagolysosome Food vacuole Phagocytosis of food particle Food particleSmooth ER Transport vesicle with enzymes Rough ER Golgi apparatus Lysosome engulfing damaged organelle Lysosomes digesting phagocytized material FIGURE 2.17 Lysosome Formation and Function. Lysosomes arise from the Golgi apparatus and fuse with vesicles that have engulfed foreign material to form digestive vesicles (phagolysosomes). These vesicles function in the normal recycling of cell constituents. Outer mitochondrial membrane Matrix Crista Inner mitochondrial membrane FIGURE 2.18 Mitochondrion. Mitochondrial membranes, cristae, and matrix. The matrix contains DNA, ribosomes, and enzymes.
  26. 26. Miller−Harley: Zoology, Fifth Edition I. Biological Principles 2. Cells, Tissues, Organs, and Organ Systems © The McGraw−Hill Companies, 2001 CHAPTER 2 Cells, Tissues, Organs, and Organ Systems of Animals 21 propel themselves. In stationary cells, cilia or flagella move mate- rial over the cell’s surface. Although flagella are 5 to 20 times as long as cilia and move somewhat differently, cilia and flagella have a similar structure. Both are membrane-bound cylinders that enclose a matrix. In this matrix is an axoneme or axial filament, which consists of nine pairs of microtubules arranged in a circle around two central tubules (figure 2.21). This is called a 9 ϩ 2 pattern of micro- tubules. Each microtubule pair (a doublet) also has pairs of dynein (protein) arms projecting toward a neighboring doublet and spokes extending toward the central pair of microtubules. Cilia and flagella move as a result of the microtubule doublets sliding along one another. In the cytoplasm at the base of each cilium or flagellum lies a short, cylindrical basal body, also made up of microtubules and structurally identical to the centriole. The basal body controls the growth of microtubules in cilia or flagella. The microtubules in the basal body form a 9 ϩ 0 pattern: nine sets of three with none in the middle. FIGURE 2.19 The Cytoskeleton. Model of the cytoskeleton, showing the three- dimensional arrangement of the microtubules, intermediate filaments, and microfilaments. Microtubule Intermediate filament Microfilament (a) (b) (c) Tubulin subunit Actin subunit 25 nm 10 nm 7 nm FIGURE 2.20 Three Major Classes of Protein Fibers Making Up the Cytoskeleton of Eukaryotic Cells. (a) Microtubules consist of globular protein sub- units (tubulins) linked in parallel rows. (b) Intermediate filaments in different cell types are composed of different protein subunits. (c) The protein actin is the key subunit in microfilaments. FIGURE 2.21 Internal Structure of Cilia and Flagella. In cross section, the arms ex- tend from each microtubule doublet toward a neighboring doublet, and spokes extend toward the central paired microtubules. The dynein arms push against the adjacent microtubule doublet to bring about movement.

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