SECOND EDITION Concepts of TM Sylvia S. Mader mad03482_FM_i-xxvi, 1.indd i 02/08/10 1:32 PM TM CONCEPTS OF BIOLOGY, SECOND EDITION Published by McGraw-Hill, a business unit of The McGraw-Hill Companies, Inc., 1221 Avenue of the Americas, New York, NY 10020. Copyright © 2011 by The McGraw-Hill Companies, Inc. All rights reserved. Previous edition © 2009. No part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written consent of The McGraw-Hill Companies, Inc., including, but not limited to, in any network or other electronic storage or transmission, or broadcast for distance learning. Some ancillaries, including electronic and print components, may not be available to customers outside the United States. This book is printed on acid-free paper 1 2 3 4 5 6 7 8 9 0 DOW/DOW 1 0 9 8 7 6 5 4 3 2 1 0 ISBN 978–0–07–340348–9 MHID 0–07–340348–2 Vice President, Editor-in-Chief: Marty Lange Vice President, EDP: Kimberly Meriwether David Vice-President New Product Launches: Michael Lange Publisher: Janice Roerig-Blong Executive Editor: Michael S. Hackett Senior Developmental Editor: Rose M. Koos Senior Marketing Manager: Tamara Maury Senior Project Manager: Jayne L. Klein Senior Buyer: Sandy Ludovissy Senior Media Project Manager: Jodi K. Banowetz Senior Designer: Laurie B. Janssen Cover Image: Bronzy Hermit (Glaucis aenea) hummingbird, feeding and pollinating a Perfumed Passion Flower (Passifl ora vitifolia) fl ower, rainforest, Costa Rica. © Michael & Patricia Fogden, Minden Pictures Senior Photo Research Coordinator: Lori Hancock Photo Research: Evelyn Jo Johnson Compositor: Electronic Publishing Services Inc., NYC Typeface: 9.5/12 Slimbach Printer: R. R. Donnelley All credits appearing on page or at the end of the book are considered to be an extension of the copyright page. Library of Congress Cataloging-in-Publication Data Mader, Sylvia S. Concepts of biology / Sylvia S. Mader. — 2nd ed. p. cm. Includes index. ISBN 978-0-07-340348-9 — ISBN 0-07-340348-2 (hard copy : alk. paper) 1. Biology—Textbooks. I. Title. QH308.2.M234 2011 570—dc22 2010017189 www.mhhe.com mad03482_FM_i-xxvi, 1.indd ii 02/08/10 1:33 PM Brief Contents Preface iv Applications xxvii 1 Biology, the Study of Life 2 PART I Organisms Are Composed of Cells 22 2 Basic Chemistry and Cells 24 3 Organic Molecules and Cells 42 4 Structure and Function of Cells 62 5 Dynamic Activities of Cells 84 6 Pathways of Photosynthesis 104 7 Pathways of Cellular Respiration 122 PART II Genes Control the Traits of Organisms 140 8 Cell Division and Reproduction 142 9 Patterns of Genetic Inheritance 168 10 Molecular Biology of Inheritance 190 11 Regulation of Gene Activity 210 12 Biotechnology and Genomics 228 PART III Organisms Are Related and Adapted to Their Environment 246 13 Darwin and Evolution 248 14 Speciation and Evolution 270 15 The Evolutionary History of Life on Earth 290 16 Evolution of Microbial Life 308 17 Evolution of Protists 332 18 Evolution of Plants and Fungi 350 19 Evolution of Animals 378 20 Evolution of Humans 410 PART IV Plants Are Homeostatic 429 21 Plant Organization and Homeostasis 430 22 Transport and Nutrition in Plants 450 23 Control of Growth and Responses in Plants 468 24 Reproduction in Plants 488 PART V Animals Are Homeostatic 505 25 Animal Organization and Homeostasis 506 26 Coordination by Neural Signaling 524 27 Sense Organs 548 28 Locomotion and Support Systems 568 29 Circulation and Cardiovascular Systems 588 30 Lymph Transport and Immunity 608 31 Digestive Systems and Nutrition 626 32 Gas Exchange and Transport in Animals 648 33 Osmoregulation and Excretion 664 34 Coordination by Hormone Signaling 680 35 Reproduction and Development 698 PART VI Organisms Live in Ecosystems 724 36 Population Ecology 726 37 Behavioral Ecology 742 38 Community and Ecosystem Ecology 758 39 Major Ecosystems of the Biosphere 780 40 Conservation Biology 798 iii mad03482_FM_i-xxvi, 1.indd iii 02/08/10 1:33 PM Focus on Key Biological Concepts Biology—like no other discipline—uses concepts as a way to understand ourselves and the world we live in, and an understanding of biological principles should be within the grasp of all those who decide to study biology. Sylvia Mader is motivated by the desire to help science-shy students gain a conceptual understanding of biology. Concepts of Biology was written not only to present the major concepts of biology clearly and concisely but also to show the relationships between the concepts at various levels of complexity. Emphasis on biological concepts begins in the introductory chapter. In this edition, the fi rst chapter discusses the scientifi c process and then proceeds to an overview of the fi ve major concepts of biology. These key concepts have become the part titles for the book: Part I: Organisms Are Composed of Cells Part II: Genes Control the Traits of Organisms Part III: Organisms Are Related and Adapted to Their Environment Part IV: Plants Are Homeostatic Part V: Animals Are Homeostatic Part VI: Organisms Live in Ecosystems Mader Writing Style Well-known for its clarity and simplicity, the Mader writing style makes the content accessible to students. Mader’s writing appeals to students because it meets them where they are and helps them understand the concepts with its clear “take-home messages” and relevant examples. iv About the Author Dr. Sylvia S. Mader has authored several nationally recognized biology texts published by McGraw-Hill. Educated at Bryn Mawr College, Harvard University, Tufts University, and Nova Southeastern University, she holds degrees in both Biology and Education. Over the years she has taught at University of Massachusetts, Lowell, Massachusetts Bay Community College, Suffolk University, and Nathan Mathew Seminars. Her ability to reach out to science-shy students led to the writing of her fi rst text, Inquiry into Life, that is now in its thirteenth edition. Highly acclaimed for her crisp and entertaining writing style, her books have become models for others who write in the fi eld of biology. Although her writing schedule is always quite demanding, Dr. Mader enjoys taking time to visit and explore the various ecosystems of the biosphere. Her several trips to the Florida Everglades and Caribbean coral reefs resulted in talks she has given to various groups around the country. She has visited the tundra in Alaska, the taiga in the Canadian Rockies, the Sonoran Desert in Arizona, and tropical rain forests in South America and Australia. A photo safari to the Serengeti in Kenya resulted in a number of photographs for her texts. She was thrilled to think of walking in Darwin’s steps when she journeyed to the Galápagos Islands with a group of biology educators. Dr. Mader was also a member of a group of biology educators who traveled to China to meet with their Chinese counterparts and exchange ideas about the teaching of modern-day biology. For My Children —Sylvia Mader Preface: What Sets Mader Apart? “ This book uses everyday language to immerse the student into the world of science.” —Michael P. Mahan, Armstrong Atlantic State University iv mad03482_FM_i-xxvi, 1.indd iv 02/08/10 1:33 PM Applications Applications are used throughout Concepts of Biology to show how biological concepts relate to students’ lives. • NEW How Life Changes applications emphasize evolution as the unifying theme of biology and how it pertains to students’ lives. • How Biology Impacts Our Lives applications examine issues that affect our health and environment. • How Science Progresses applications discuss scientifi c research and advances that have helped us gain valuable biological knowledge. All applications end with several Form Your Opinion questions that can serve as a basis for class discussion. See page xxvii for a complete listing of application topics. In the second edition, the “Connecting the Concepts” feature appears at the end of each chapter. This feature includes narrative and several questions to help students understand how the concepts in the present chapter are related to one another and to those in other chapters. PREFACE v CONNECTING THE CONCEPTS Energy from the sun flows through all liv- ing things with the participation of chlo- roplasts and mitochondria. Through the process of photosynthesis, chloroplasts in plants and algae capture solar energy and use it to produce carbo- hydrates, which are broken down to carbon dioxide and water in the mitochondria of nearly all organisms. The energy released when carbohydrates (and other organic molecules) are oxidized is used to produce ATP molecules. When the cell uses ATP to do cellular work, all the captured energy dissipates as heat. During cellular respiration, oxidation by removal of hydrogen atoms (e– + H+) from glucose or glucose prod- ucts occurs during glycolysis, the prep reaction, and the Krebs cycle. The prep reaction and Krebs cycle release CO2. The elec- trons are carried by NADH and FADH2 to the electron transport chain (ETC) in the cristae of mitochondria. Oxygen serves as the final acceptor of electrons, and H2O is produced. The pumping of hydrogen ions by the ETC into the intermembrane space leads to ATP production. PUT THE PIECES TOGETHER 1. Tell how the pre-eukaryotic cell must have produced ATP. What event in the history of life would have allowed cellular respira- tion to evolve? Explain. sun heat heat carbohydrate CO2+H2O ATP mitochondrion chloroplast O2 Photosynthesis Cellular respiration 2. Explain the statement, “if chloroplasts and mitochondria are descended from a free-living common ancestor it would explain their structural similarities.” What are some structural similarities? A Curculigo plant The fruits develop at base of leaves. HOW LIFE CHANGES Application 13B Sometimes Mutations Are Benefi cial Imagine trying to redesign a vital mechanical part of an airplane, while still keeping that plane in fl ight. Sounds nearly impossible, doesn’t it? This was one of the puzzles facing early evolutionary biologists. After all, mutations are the main way in which new traits and features arise during evolution, and yet most mutations cause damage. If a feature is important, how can it be altered while still allowing an organism and its offspring to survive? Geneticists have shown one possible way mutations can accumulate without impairing present function: gene duplication (Fig. 13B.1). An extra (and possibly unused) copy of a gene may result from errors during cell division, efforts to repair breakage to DNA, or other mechanisms. The surprising idea here is that these seeming accidents actually can provide raw material for natural selection. Particularly in plants, many examples of gene duplication have been found—for example, the wild mustard plant has undergone at least two duplications of all its chromo- somes in the past, as well as duplication of several individual genes at various times in history. An intriguing example of gene duplication involves the sweet-tasting proteins. Of the thousands of proteins studied so far, most have no noticeable fl avor—but about half a dozen have an intensely sweet taste. These rare, sweet-tasting proteins are found in plants and plant products from several different conti- nents: The protein “curculin” is found in the fruit of a Malaysian herb (Fig. 13B.2); “mabinlin” can be extracted from a traditional Chinese herb; “thaumatin” is found in the fruit of a West African rain forest shrub; and “brazzein” comes from a fruit that grows wild in Gabon, Cameron, and Zaire. Each of these proteins tastes sweet only to humans and certain monkeys. From the plant’s point of view, the proteins likely provided an advantage: Sweeter fruits would be eaten more often and their seeds distributed more widely, ensuring the growth of more plants with genes for making sweet proteins. A question still remains: How did these unusual proteins come about? No one yet knows exactly how these proteins originated, but gene duplication is a likely answer. The proteins look nothing alike, are found in unrelated plants, and clearly did not come from some ancient shared plant gene. Each protein, however, does resemble other proteins normally found in healthy plants. Brazzein and mabinlin, for example, closely resemble “protein- ase inhibitors,” proteins that can help prevent further damage when a plant is injured. Interestingly, however, neither sweet protein has that function. Similar stories are true of most sweet- tasting proteins: They closely resemble other plant proteins with ordinary functions, but the sequences necessary for those other functions seem to be missing or mutated. It’s as though pre- existing genes were recycled to become genes for sweet proteins. Presumably a gene duplication in the distant past resulted in an “extra” gene that could mutate freely, while still leaving a “good” copy of the gene to support the plant’s functions. In time, the extra copy of the gene acquired mutations that happened to pro- vide a sweet taste, and plants with that mutation gained a spe- cial appeal for local diners. FORM YOUR OPINION 1. Humans and perhaps apes and mon- keys like sweet foods. How does this benefi t plants containing sweet proteins? 2. Are humans infl uencing the evolution of plants when they propagate them? When they genetically modify them and then propagate them? 3. In what way is artifi cial selection harmful to the plants and animals selected to reproduce? FIGURE 13B.2 The sweet protein curculin is present in the fruit of a Curculigo plant. single copy of gene mutated copy of gene duplicate copies of gene protein product protein product FIGURE 13B.1 Duplication of a gene followed by a mutation in one of the genes is a way for complexity to arise: The new protein might function diff erently than the original one. 262 PART 3 Organisms Are Related and Adapted to Their Environment fruits would be eaten mo ng the ns. A me ab ws exa a like unrela shared prote in, fo eins t ured. tion. y clos ut th e mis ecycle uplica ld mu suppo e acq nd pla diners FORR 1. H k t p 2. A o W a 3. I h s single copy of gene fruits would be eate n n m w a u s li e u t y b e e u l s e n d g py g Stem cells Different treatments Types of cells Types of tissues embryonic stem cells (ES) pancreatic cell nerve cell cardiac cell pancreatic tissue nervous tissue cardiac tissue induced pluripotent stem cells (iPS) human skin human embryo HOW BIOLOGY IMPACTS OUR LIVES Application 8B Tissues Can Be Grown in the Lab Most people are now aware that stem cells can undergo the cell cycle and generate tissues for the cure of devastating human diseases, such as diabetes, cancer, brain disorders, and heart ailments (Fig. 8B). For many years, scientists have known about two types of stem cells: embryonic stem (ES) cells and adult stem cells. Embryonic stem cells are simply the cells of an early embry- onic stage. These cells can stay alive longer and are better at producing different tissues than adult stem cells, but to acquire them a human embryo must be destroyed. Embryos are some- times “left over” at fertility clinics, but even so many people reject the use of ES cells because it means the destruction of a potential human life. Adult stem cells are diffi cult to glean from the human body, and they do not multiply readily in the labora- tory. Also, their potential to become all different types of tissues is not as great as that of ES cells. One drawback to both ES cells and adult stem cells is the danger of rejection by the recipient. Remember the many different types of proteins that occur in the plasma membrane? Some of those mark the cell as belonging to us, and if a transplanted tissue or organ carries different mark- ers, our body works against them until they die. This is called rejection of the transplant. Breakthrough By now, scientists are experienced at coaxing stem cells to become specialized cells, but research would really benefi t from an unlim- ited source of stem cells in order to achieve the goal of replacing diseased or damaged tissues in the human body. The scientifi c community is now hopeful that such a source has been found, thanks to a little-known Japanese scientist who worked alone for ten years in a tiny laboratory. Through patient research, Shinya Yamanaka was able to discover why ES cells are pluripotent—able to become any type of tissue in the body. He hypothesized that pluripotent cells produce certain proteins that specialized cells do not produce. Yamanaka worked with mouse skin cells until he knew that only four particular genes do the trick of making cells pluripotent. In 2006 he published his results in the journal Cell. Just fi ve months later, United States scientists induced human skin cells to become pluripotent by supplying them with active forms of the four genes. These skin cells are termed iPS (induced pluripo- tent stem) cells. For every cell that became pluripotent, thousands of skin cells are treated. But the ineffi ciency doesn’t matter because scientists have access to millions of skin cells. Such cells can even be obtained by simply swabbing the inside of a person’s mouth! Researchers are still improving their technique and resolving vari- ous safety issues, but they feel confi dent they will be able to make tissues for human transplant. If replacement tissues are produced using the patient’s own skin cells, rejection should not be a prob- lem. However, scientists hope that eventually labs can stockpile so many different types of tissues, a good match will be available for most every person. Because spinal cord injuries should be treated within a few hours, there isn’t time to use the patient’s own skin cells to produce replacement nerve cells. FORM YOUR OPINION 1. Currently, the main safety issue with iPS cells is that they might cause cancer. If you were 75 and had Alzheimer dis- ease, would you be willing to take the chance of cancer in order to correct this condition? 2. Imagine that you are a scientist who worked all alone for ten years to reach a breakthrough. Should you be allowed to patent your “invention,” or should it be available to everyone? FIGURE 8B ES (embryonic stem) cells and iPS (induced pleuripotent stem) cells both produce many diff erent types of specialized cells and tissues in the lab. Safety issues need to be resolved, but eventually scientists believe that iPS tissues will be available to cure human ills. CHAPTER 8 Cell Division and Reproduction 151 Types of tissues pancreatic cell n l nerve cell cardiac cell pancreatic tissue nervous tissue cardiac tissue tissues for using the p lem. Howe many diffe most every within a fe cells to pro FORRM Y 1. Curren might ease, order 2. Imagin ten ye to pat everyo FIGURE 8B ES (embryonic stem) cells and iPS (induced pleuripotent stem) cells both produce many diff erent types of ff specialized cells and tissues in the lab. Safety issues need to be resolved, but eventually scientists believe that iPS tissues will be available to cure human ills. C HOW SCIENCE PROGRESSES Application 29E Leeches, a Form of Biotherapy Although it may seem more like an episode of a popular TV show than a real-life medical treatment, the U.S. Food and Drug Administration has approved the use of leeches as medical “devices” for treating conditions involving poor blood supply to various tissues. Leeches are blood-sucking, aquatic creatures, whose closest living relatives are earthworms (Fig. 29E). Prior to modern times, medical practitioners fre- quently applied leeches to patients, mainly in an attempt to remove the bad “humors” that they thought were responsible for many diseases. This practice was abandoned, thankfully, in the nineteenth century when peo- ple realized that the “treatment” often harmed the patient. True to their tenacious nature, however, leeches are making a come- back in twenty-fi rst–century medi- cine. By applying leeches to tissues that have been injured by trauma or disease, blood supply can be improved. When reattaching a fi nger, for example, it is easier to suture together the thicker-walled arteries than the thinner- walled veins. Poorly draining blood from veins can pool in the appendage and threaten its survival. Leech saliva contains chemicals that dilate blood vessels and prevent blood from clot- ting by blocking the activity of thrombin. These effects can improve the circulation to the body part. Another substance in leech saliva actually anesthetizes the bite wound. In a natural setting, this allows the leech to feast on the blood supply of its victim undetected, but in a medical setting, it makes the whole experience more tolerable, at least physically. Mentally, how- ever, the application of leeches can still be a rather unsettling experience, and patient acceptance is a major factor limiting their more widespread use. FORM YOUR OPINION 1. Would you be willing to let leeches feast for a few minutes on your hand to improve the changes of recovering from an injury? 2. At one time, leeches were used to remove blood from a patient. How might physicians have gotten the idea that removing blood could help cure illnesses? FIGURE 29E Leeches can attach to the body and suck out blood. CHAPTER 29 Circulation and Cardiovascular Systems 603 v mad03482_FM_i-xxvi, 1.indd v 02/08/10 1:33 PM Instructional Art Outstanding photographs and dimensional illustrations, vibrantly colored, are featured throughout Concepts of Biology. Accuracy and instructional value were primary considerations in the development of each fi gure. “ The illustrations support the text strongly.” —Anju Sharma, Stevens Institute of Technology Multilevel Perspective Illustrations depicting complex structures show macroscopic and microscopic views to help you see the relationships between increasingly detailed drawings. Combination Art Drawings of structures are paired with micrographs to give you the best of both perspectives: the realism of photos and the explanatory clarity of line drawings. vi PREFACE mad03482_FM_i-xxvi, 1.indd vi 02/08/10 1:33 PM “ The art, fi gures, and photos are excellent.” —Larry Szymczak, Chicago State University zygote developing sporophyte sperm egg Archegonia Antheridia Sporophyte Spores stalk Sporangium Gametophytes buds The mature ���� gametophytes: In mosses, the dominant gametophyte shoots bear either antheridia or archegonia, where ���� gametes are produced by mitosis. Fertilization: ����Flagellated sperm produced in antheridia swim in external water to archegonia, each bearing a single egg. Developing sporophyte: ��� The sporophyte embryo is retained within the archegonium, where it develops, becoming a mature sporophyte. The sporophyte: ��� The dependent sporophyte has a foot buried in female gametophyte tissue, a stalk, and an upper capsule (the sporangium), where meiosis occurs and windblown spores are produced. Spore dispersal: ���� Spores are released when they are most ���� likely to be dispersed ���� by air currents. The immature ���� gametophyte: ��� A spore germinates into the first stage of the male and the female gametophytes. FERTILIZATION MEIOSIS Mitosis Mitosis haploid (n) diploid (2n) 1 2 3 4 5 6 onia antheridium archegonium The large ribosomal subunit completes the ribosome. Initiator tRNA occupies the P site. The A site is ready for the next tRNA. An mRNA binds to a small ribosomal subunit. An initiator tRNA with the anticodon UAC pairs with the mRNA start codon AUG. met amino acid methionine mRNA 3ʹ 5ʹ small ribosomal subunit large ribosomal subunit P site A site E site 3ʹ 5ʹ met start codon U A C A U G U A C A U G 10.6 During translation, polypeptide synthesis occurs one amino acid at a time Although we often speak of protein synthesis, some proteins have more than one polypeptide, so it is more accurate to recog- nize that polypeptide synthesis occurs at a ribosome. Polypep- tide synthesis involves three events: initiation, elongation, and termination. Enzymes are needed so that each of the three events will occur, and both initiation and elongation also require an input of energy. Initiation During initiation all translation components come together. Proteins called initiation factors help assemble a small ribosomal subunit, mRNA, initiator tRNA, and a large ribosomal subunit for the start of a polypeptide synthesis. Initiation is shown in Figure 10.6A. In prokaryotes, an mRNA binds to a small ribosomal subunit at the mRNA bind- ing site. The start codon AUG is at the P site. The fi rst, or initia- tor, tRNA pairs with this codon because its anticodon is UAC. As you can see by examining Figure 10.4B, AUG is the codon for methionine. Methionine is always the fi rst amino acid of a polypeptide. After the small ribosomal unit has attached, a large ribosomal subunit joins to the small subunit. Although similar in many ways, initiation in eukaryotes is much more complex. FIGURE 10.6A Participants in the initiation event assemble as shown. The fi rst amino acid is typically methionine. Initiation is shown in Figure 10.6A. In prokaryotes, an mRNA binds to a small ribosomal subunit at the mRNA bind- ing site. The start codon AUG is at the P site. The first, or initia- fi tor, tRNA pairs with this codon because its anticodon is UAC. As you can see by examining Figure 10.4B, AUG is the codon for methionine. Methionine is always the first amino acid of a fi polypeptide. After the small ribosomal unit has attached, a large ribosomal subunit joins to the small subunit. Although similar in many ways, initiation in eukaryotes is much more complex. 5′ 5′ 3′ mature mRNA primary mRNA DNA introns During elongation, polypeptide synthesis takes place one amino acid at a time. Ribosome attaches to rough ER. Polypeptide enters the ER interior, where it folds and is modified. mRNA moves into cytoplasm and becomes associated with ribosomes. tRNAs with anticodons carry amino acids to mRNA. TRANSLATION TRANSCRIPTION nuclear pore mRNA large and small ribosomal subunits amino acids anticodon tRNA polypeptide codon anticodon ribosome 5′ 3′ 3′ C C G G G C G C G C C C C G U A C U A U A U A U U A U A A U C G A DNA in nucleus serves as a template for mRNA. mRNA is processed before leaving the nucleus. During initiation, anticodon-codon complementary base pairing begins as the ribosomal subunits come together at a start codon. During termination, a ribosome reaches a stop codon; mRNA and ribosomal subunits disband. 1 2 3 4 5 6 7 8 Process Figures Complex processes are broken down into a series of smaller steps that are easy to follow. Numbers guide you through the process. In process fi gures, numbered steps are coordinated with the narrative for an integrated approach to learning. Color Consistency Consistent use of color organizes information and clarifi es concepts. PREFACE vii mad03482_FM_i-xxvi, 1.indd vii 02/08/10 1:34 PM The Mader Learning System Each chapter features numerous learning aids that were carefully developed to help students grasp challenging concepts. Cancer cell dividing Colon cancer cell surface blebs Cancer Is a Genetic Disorder W e often think of diseases in terms of organs, and therefore it is customary to refer to colon cancer, or lung cancer, or pan- creatic cancer. But actually cancer is a cellular disease. Cancer is present, when abnormal cells have formed a tumor. Exceptions are cancers of the blood, in which abnormal cells are coursing through the bloodstream. The cells of a tumor share a common ancestor—the fi rst cell to become cancerous. Uncontrolled growth leading to a tumor is characteristic of multicellular organisms, not unicellular ones. The very mechanism that allows our bodies to grow and repair tissues is the one that turns on us and allows cancer to begin. Cancer is uncontrolled cell division. Usually, cell division is confi ned to just certain cells of the body, called adult stem cells. For example, skin can replenish itself because stem cells below the surface have the ability to divide. In embryos all cells can divide. How else could a new- born arise from a single fertilized egg? But something happens as development progresses: The cells undergo specialization and become part of a particular organ. A mature multicellular organism contains many kinds of specialized cells in many 8 Cell Division and Reproduction CHAPTER OUTLINE Chromosomes Become Visible During Cell Division 8.1 A karyotype displays the chromosomes 144 8.2 The eukaryotic cell cycle has a set series of stages 145 Mitosis Maintains the Chromosome Number 8.3 Following mitosis, daughter cells have the same chromosome count as the parent cell 146 8.4 Mitosis has a set series of phases 148 8.5 Cytokinesis divides the cytoplasm 150 Cancer Is Uncontrolled Cell Division 8.6 Cell cycle control is lacking in cancer cells 152 Meiosis Reduces the Chromosome Number 8.7 Homologous chromosomes separate during meiosis 155 8.8 Synapsis and crossing-over occur during meiosis I 156 8.9 Sexual reproduction increases genetic variation 156 8.10 Meiosis requires meiosis I and meiosis II 158 8.11 Life cycles are varied 160 8.12 Meiosis can be compared to mitosis 161 Chromosome Anomalies Can Be Inherited 8.13 Nondisjunction causes chromosome number anomalies 162 8.14 Chromosome number anomalies can be observed 163 8.15 Chromosome structure anomalies can also be observed 164 APPLICATIONS HOW LIFE CHANGES Evolution of the Spindle Apparatus 147 HOW BIOLOGY IMPACTS OUR LIVES Tissues Can Be Grown in the Lab 151 HOW BIOLOGY IMPACTS OUR LIVES Protective Behaviors and Diet Help Prevent Cancer 154 142 MEIOSIS I Duplicated homologous pairs synapse and then separate. centrioles homologous chromosomes homologous chromosomes sister chromatids synapsis nucleolus centromere CHROMOSOME DUPLICATION MEIOSIS II Sister chromatids separate, becoming daughter chromosomes. n = 2 n = 2 2n = 4 2n = 4 8.7 Homologous chromosomes separate during meiosis Meiosis is reduction division. Because meiosis involves two divisions, four daughter cells result. Each of these daughter cells has one of each kind of chromosome and, therefore, half as many chromosomes as the parent cell. In Figure 8.7, the diploid (2n) number of chromosomes is four, and there are two pairs of chromosomes. The short chromosomes are one pair, and the long chromosomes are another. They are homologous chromosomes (also called homologues) because they look alike and carry genes for the same traits, such as fi nger length. However, one homologue could call for short fi ngers and the other for long fi ngers. Prior to the fi rst division, called meiosis I, DNA replication has occurred, and the chromosomes are duplicated. During meiosis I, the homologous chromosomes come together and line up side by side. This so-called synapsis results in an association of four chro- matids that stay in close proximity during the fi rst two phases of meiosis I. Also, because of synapsis, there are pairs of homologous chromosomes at the equator during meiosis I. (Keep in mind that only during meiosis I is it possible to observe paired chromosomes at the equator.) Synapsis leads to a reduction in the chromosome number because it permits orderly separation of homologous chro- mosomes. The daughter nuclei are haploid because they receive only one member of each pair. The haploid (n) nature of each daughter cell can be verifi ed by counting its centromeres. Each chromosome, however, is still duplicated, and no replication of DNA occurs between meiosis I and meiosis II. The period of time between meiosis I and meiosis II is called interkinesis. During meiosis II, the sister chromatids of each chromo- some separate, becoming daughter chromosomes that are dis- tributed to daughter nuclei. In the end, each of four daughter cells has the n, or haploid, number of chromosomes, and each chromosome consists of one chromatid. In humans, the daughter cells mature into gametes (sex cells—sperm and egg) that fuse during fertilization. Fertiliza- tion restores the diploid number of chromosomes in the zygote, the fi rst cell of the new individual. If the gametes carried the diploid instead of the haploid number of chromosomes, the chromosome number would double with each fertilization. After several generations, the zygote would be nothing but chromosomes. 8.7 Check Your Progress At the completion of meiosis I, are the cells diploid (2n) or haploid (n)? Explain. Meiosis Reduces the Chromosome Number Learning Outcomes ▶ Describe three ways genetic variation is ensured in the next generation. (8.7–8.9) ▶ Describe the phases of meiosis, and compare the occurrence of meiosis in the life cycle of various organisms. (8.10–8.11) ▶ Compare the process and the result of meiosis to those of mitosis. (8.12) Meiosis is necessary to sexual reproduction, the type of reproduction that requires two parents. In animals, the two parents are called a male and a female. The results of meiosis cause the off spring to be diff erent from each other and from either parent. Exactly where meiosis occurs in the life cycle of organisms determines the adult chromosome number. Even though meiosis is diff erent from mitosis, the two processes bear certain similarities. FIGURE 8.7 Meiosis produces daughter cells that are genetically diff erent from the parent cell. Four daughter cells result because meiosis includes two divisions: During meiosis I, the homologous chromosomes separate, and during meiosis II the chromatids separate, becoming daughter chromosomes. CHAPTER 8 Cell Division and Reproduction 155 A Chapter Outline lists the chapter concepts and the topics (numbered) that will be discussed in the chapter. Applications are also listed. Learning Outcomes are listed at the start of each major section to provide students with an overview of what they are to know. Section Introductions orient students to concepts in a short, easy-to-understand manner. Figure Legends have been expanded in this edition to reinforce the discussion and to improve student learning. Check Your Progress questions at the end of each section help students assess and/or apply their understanding of a concept. “ The organization of the text around the major theories of Biology is a wise path to follow; it integrates the chapters into themes and points out the development of a theory. . . . —Paul E. Wanda, Southern Illinois University, Edwardsville viii PREFACE mad03482_FM_i-xxvi, 1.indd viii 02/08/10 1:35 PM SUMMARY Chromosomes Become Visible During Cell Division 8.1 A karyotype displays the chromosomes • A karyotype shows that eukaryotes have homologous pairs of chromosomes. • Humans have 22 pairs of autosomes and one pair of sex chromosomes. A Y chromosome is shorter than an X chromosome. Males are XY and females are XX. • Following DNA replication, each chromosome has two sister chromatids held together at a centromere. Kinetochores which develop at centromeres function during cell division. • Homologus chromosomes have genes for the same trait—e.g., type of hairline. Sister chromatids have exact genes—e.g., widow’s peak. 8.2 The eukaryotic cell cycle has a set series of stages • In the cell cycle, interphase (G1, S, G2 stages) precedes the M stage, which includes mitosis and cytokinesis. M Cytokinesis M i t o s i s G1 (growth) G0 G2 (growth) S (DNA synthesis) In te rp h a s e • In G1 cells can make a commitment to divide; in S DNA replication results in duplicated chromosomes; and in G2 proteins are made to form microtubules. • Embryonic cells and adult stem cells divide all the time; cells in the G0 stage have dropped out of the cell cycle and do not divide until stimulated to do so. Mitosis Maintains the Chromosome Number 8.3 Following mitosis, daughter cells have the same chromosome count as the parent cell • Mitosis is duplication division; the parent cell and the daughter cells all have the same number and kinds of chromosomes because the identical chromatids of each duplicated chromosome separate and become daughter chromosomes. • The parent cell can be diploid (2n) or haploid (n), depending on the species. • The number of centromeres equals the number of chromosomes a cell has. • Centrosomes form the spindle apparatus, which helps ensure orderly separation of chromatids. THE CHAPTER IN REVIEW 8.4 Mitosis has a set series of phases • The spindle poles of animal cells have centrioles and an aster. Plant cells have poles but no centrioles or asters. • Nuclear envelope fragments and chromosomes attach to spindle fi bers by kinetochores (prophase) and align at the equator (metaphase); sister chromatids separate and become chromosomes (anaphase), and daughter nuclei re-form (telophase). • In plants and animals, mitosis allows growth and repair. In humans, adult stem cells undergo mitosis to replace worn-out cells. 8.5 Cytokinesis divides the cytoplasm • In animal cells, cytokinesis involves a cleavage furrow. • In plant cells, cytokinesis involves the formation of a new plasma membrane and cell wall at a cell plate. Cancer Is Uncontrolled Cell Division 8.6 Cell cycle control is lacking in cancer cells • Checkpoint G1 involves cell cycle control; checkpoint G2 ensures that DNA replicated properly; checkpoint M ensures that chromosomes are distributed accurately to daughter cells. • In general, if the cell cycle is unable to continue, apoptosis occurs. Apoptosis initiated by p53 is programmed cell death orchestrated by unleashed enzymes. • Due to mutations, carcinogenesis occurs and cancer is present when cells divide uncontrollably and a tumor develops. Cell cycle control and apoptosis are lacking. • Cancer cells have abnormal characteristics: lack differentiation, have abnormal nuclei, form tumors, undergo metastasis (formation of tumors distant from primary tumor), and promote angiogenesis (formation of new blood vessels). Meiosis Reduces the Chromosome Number 8.7 Homologous chromosomes separate during meiosis • Meiosis is reduction division. Each of four daughter cells has only one of each kind of chromosome. • Meiosis requires one DNA replication and two cell divisions, called meiosis I and meiosis II. The period of time between meiosis I and meiosis II is called interkinesis. • Homologous chromosomes come together during synapsis and then separate during meiosis I; sister chromatids separate during meiosis II. The daughter cells are haploid. • In humans, the daughter cells become gametes (egg and sperm) with the haploid number of chromosomes. The diploid number is restored with fertilization. 8.8 Synapsis and crossing-over occur during meiosis I • During meiosis I, synapsis (pairing of homologues to form a tetrad) and crossing-over (exchange of genetic material) between nonsister chromatids occurs. 8.9 Sexual reproduction increases genetic variation • Crossing-over recombines genetic information and increases the variability of genetic inheritance on the chromosomes. • The gametes contain all possible combinations of chromosomes because of independent assortment. CHAPTER 8 Cell Division and Reproduction 165 1 replication results in duplicated chromosomes; an e all th cycle mbeerr he sam cell an nd kin atids of me dau loid (n mber of which replication results in duplicated chromosom e m h c a a m l m w • Independent assortment occurs because the paired homologous chromosomes align during meiosis I with either homologue facing either pole. • Fertilization brings together genetically different gametes that fuse to form a zygote. 8.10 Meiosis requires meiosis I and meiosis II • Meiosis I: prophase I—homologues pair and crossing-over occurs; metaphase I—homologue pairs align at equator independently; anaphase I—homologues separate; telophase I—daughter cells are haploid. • Interkinesis is the time period between meiosis I and meiosis II. No DNA replication occurs. • Meiosis II: During stages designated by the Roman numeral II, the chromatids of duplicated chromosomes from meiosis I separate, producing a total of four daughter cells for meiosis. 8.11 Life cycles are varied • Asexual reproduction results in offspring that are genetically identical to the single parent. • In the haploid life cycle, asexual reproduction occurs when a haploid parent produces offspring by mitosis that are also haploid. In sexual reproduction, only the zygote is diploid and undergoes meiosis to produce haploid offspring. Algae and fungi often have the haploid life cycle. • In the alternation of generations life cycle, which usually occurs in plants, the diploid sporophyte produces spores by meiosis. A spore undergoes mitosis to become a gametophyte, which produces gametes. When the gametes fuse, the diploid zygote becomes a sporophyte. • In the diploid life cycle, which usually takes place in animals, the diploid adult produces gametes by meiosis, which are the only haploid part of the life cycle. Mitosis is involved in growth. 8.12 Meiosis can be compared to mitosis • See Figure 8.12 and note that homologous chromosomes only pair during metaphase I of meiosis and that four haploid daughter cells result from meiosis but not mitosis. Chromosome Anomalies Can Be Inherited 8.13 Nondisjunction causes chromosome number anomalies • A polyploid has a multiple of the haploid number of chromosomes; an aneuploid is a monosomy (2n–1) or a trisomy (2n+1). • Aneuploidy is due to nondisjunction when homologues do not separate during meiosis I or when chromatids do not separate during meiosis II. 8.14 Chromosome number anomalies can be observed • A syndrome is due to the inheritance of a set of physical characteristics that can be overcome with proper medical care and support. • Down syndrome is an autosomal trisomy. Turner syndrome and Klinefelter syndrome result from sex chromosome anomalies. 8.15 Chromosome structure anomalies can also be observed • Deletion: A segment of a chromosome is missing. • Duplication: A segment occurs twice on the same chromosome. • Inversion: A segment has turned 180 degrees. • Translocation: Segments have moved between nonhomologous chromosomes. TESTING YOURSELF Chromosomes Become Visible During Cell Division 1. Which of these statements is incorrect? Just before mitosis in a eukaryotic cell, a. homologous pairs of chromosomes can be seen. b. each chromosome has two sister chromatids. c. one chromatid came from the father and one came from the mother. d. each sister chromatid carries the same genes. 2. Which is a correct contrast between autosomes and sex chromosomes in humans? a. 22 pairs—one pair b. control gender—control enzymes c. are always duplicated—are always single d. are always visible—are never visible 3. In the cell cycle, a. mitosis cannot occur without interphase. b. the single event during interphase is chromosome duplication. c. cells are metabolically inactive during interphase. d. a DNA double helix divides in two. Mitosis Maintains the Chromosome Number 4. The two identical halves of a duplicated chromosome a. always stay together. c. become daughter chromosomes. b. are different sizes. d. are called homologues. For questions 5–8, match each description to a phase of mitosis in the key. KEY: a. prophase c. anaphase b. metaphase d. telophase 5. The nucleolus disappears, and the nuclear envelope breaks down. 6. The spindle disappears, and the nuclear envelopes form. 7. Sister chromatids separate. 8. Chromosomes are aligned on the spindle equator. 9. Mitosis in animal cells but not plant cells a. maintains the chromosome number. b. uses a spindle apparatus. c. has centrioles at the poles. d. produces two unequal daughter cells. 10. Label this diagram of a cell in early prophase of mitosis: b. a. c. d. Cancer Is Uncontrolled Cell Division 11. Which of these is an incorrect statement? a. Checkpoints allow the cell cycle to continue if all is normal. b. A DNA abnormality can cause apoptosis to occur. 166 PART 2 Genes Control the Traits of Organisms up cat o : seg e t occu s t ce o t e sa chromosome ees. ween of Orga chromosome e w c. The cell cycle stages take place in the order dictated by external signals. d. Mutations can cause the cell cycle to occur repeatedly. 12. Which of the following is typical of normal cells, but not typical of cancer cells? a. Cell cycle control is always present. b. The cells have enlarged nuclei. c. The cells stimulate the formation of new blood vessels. d. The cells are capable of traveling through blood and lymph. Meiosis Reduces the Chromosome Number 13. Which are ways that meiosis increases genetic variation? a. Homologues align independently at the equator. b. Daughter cells always have the same combination of father and mother chromosomes. c. Following crossing-over, sister chromatids carry different genes. e. Both a and c are correct. 14. At the equator during metaphase II of meiosis, there are a. single chromosomes. b. unpaired duplicated chromosomes. c. homologous pairs. d. always 23 chromosomes. 15. During which phase of meiosis do homologous chromosomes separate? a. prophase II d. anaphase I b. telophase I e. anaphase II c. metaphase I 16. THINKING CONCEPTUALLY Use the events of meiosis to briefl y explain why you and a sibling with the same parents have different characteristics. 17. When a haploid alga reproduces asexually by mitosis, the a. offspring are genetically identical to the parent. b. offspring undergo meiosis and become diploid. c. offspring number more than four. d. Both a and c are correct. 18. Which is an incorrect comparison between meiosis and mitosis? a. four daughter cells—two daughter cells b. crossing-over occurs—crossing-over does not occur c. homologues separate—chromatids separate d. daughter cells are diploid—daughter cells are haploid Chromosome Anomalies Can Be Inherited 19. An individual can have too many or too few chromosomes as a result of a. nondisjunction. d. amniocentesis. b. Barr bodies. e. cell cycle control. c. mitosis. 20. Which of the following could cause a chromosome anomaly? a. inheritance of an extra chromosome 21 b. deletion in chromosome 7 c. the inheritance of 23 pairs of chromosomes d. translocation between chromosomes 2 and 20 e. All but c are correct. 21. Turner syndrome (X0) can only result if nondisjunction occurred during a. mitosis. c. meiosis II. b. meiosis I. d. All of these are correct. THINKING SCIENTIFICALLY 1. Genetic testing shows that Mary has only 46 chromosomes, but both members of one homologous pair came from her father. In which parent did nondisjunction occur? Explain. 2. Criticize the hypothesis that it would be possible to clone an individual by using an egg and a sperm with the exact genetic makeup as those that produced the individual. ONLINE RESOURCE www.mhhe.com/maderconcepts2 Enhance your study with animations that bring concepts to life and practice tests to assess your understanding. Your instructor may also recommend the interactive eBook, individualized learning tools, and more. CONNECTING THE CONCEPTS All cells receive DNA from preexisting cells through the process of cell division. Cell division ensures that DNA is passed on to the next generation of cells and to the next generation of organisms. The end product of ordinary cell division (i.e., mitosis) is two new cells, each with the same number and kinds of chromosomes as the parent cell. Mitosis is part of the cell cycle, and negative con- sequences result if the cell cycle becomes unsynchronized. Knowing how the cell cycle is regulated has contributed greatly to our knowl- edge of cancer and other disorders. In contrast to mitosis, meiosis is part of the production of gam- etes, which have half the number of chromosomes as the parent cell. Through the mechanics of meiosis, which involves synapsis, sexually reproducing species have a greater likelihood of genetic variations among offspring than otherwise. However, meiosis brings with it the risk of chromosome anomalies. Genetic variations are essential to the process of evolution, which is discussed in Part III. In the meantime, Chapter 9 reviews the fundamental laws of genetics established by Gregor Mendel. Although Mendel had no knowledge of chromosome behavior, modern students have the advantage of being able to apply their knowledge of meiosis to their understanding of Mendel’s laws. Mendel’s laws are fundamental to understanding the inheritance of particular alleles on the chromosomes. PUT THE PIECES TOGETHER 1. Synapsis during meiosis is necessary to crossing-ov...