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Exploring the
Diversity of Life
Fifth Canadian Edition
Fenton • Maxwell • Haffie • Milsom • Nickle • Ellis • Riskin
• Hertz • McMillan • Benington
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Exploring the
Diversity of Life
Fifth Canadian Edition
M. Brock Fenton
Western University
Bill Milsom
University of British Columbia
Denis Maxwell
Western University
Todd Nickle
Mount Royal University
Tom Haffie
Western University
Shona Ellis
University of British Columbia
Shelby Riskin
University of Toronto
Peter J. Russell
Paul E. Hertz
Beverly McMillan
Joel H. Benington
With contributions by Ivona Mladenovic, Simon Fraser University,
Jonathan Ferrier, Dalhousie University, Jeff Baker, University of Saskatchewan,
Jean Becker, University of Waterloo, and Erin Hodson, Wilfrid Laurier University
Australia • Brazil • Canada • Mexico • Singapore • United Kingdom • United States
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Biology: Exploring the Diversity of Life,
Fifth Canadian Edition
M. Brock Fenton, Denis Maxwell, Tom
Haffie, Bill Milsom, Todd Nickle, Shona
Ellis, Shelby Riskin, Peter J. Russell, Paul
E. Hertz, Beverly McMillan, and Joel H.
Benington
Sr. Director, Product: Jackie Wood
© 2023, 2019 Cengage Learning Canada, Inc. ALL RIGHTS RESERVED.
Adapted from Biology: The Dynamic Science, Fifth Edition, by Peter J. Russell, Paul E. Hertz,
Beverly McMillan, and Joel H. Benington. Copyright © Cengage Learning, Inc., 2021.
No part of this work covered by the copyright herein may be reproduced or distributed in
any form or by any means, except as permitted by Canadian copyright law, without
the prior written permission of the copyright owner.
Cognero and Full-Circle Assessment are registered trademarks of Madeira Station LLC.
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Product Marketing Manager: Scott Brayne
For product information and technology assistance, contact us at
Director, Content and Production:
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Cengage Customer & Sales Support, 1-800-354-9706
or support.cengage.com.
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For permission to use material from this text or product, submit all
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Copy Editor: Frances Robinson
Library and Archives Canada Cataloguing in Publication
Title: Biology : exploring the diversity of life / M. Brock Fenton (Western University), Denis
Maxwell (Western University), Tom Haffie (Western University), Bill Milsom (University
of British Columbia), Todd Nickle (Mount Royal University), Shona Ellis (University of
Compositor: MPS Limited
British Columbia), Shelby Riskin (University of Toronto), Peter J. Russell, Paul E. Hertz,
Art Director: Chris Doughman
Beverly McMillan, Joel H. Benington ; with contributions by Ivona Mladenovic (Simon
Illustrators: Dragonfly Media Group,
MPS Limited
Text Designer: Chris Doughman
Fraser University) [and four others].
Names: Russell, Peter J., author. | Fenton, M. Brock (Melville Brockett), 1943– author. |
Maxwell, Denis, author. | Haffie, Tom, author. | Milsom, Bill, 1947– author. | Nickle,
Cover Designer: Courtney Hellam
Cover Image: Shona Ellis
Todd, 1967–2021 author. | Ellis, Shona, 1962– author. | Riskin, Shelby, author.
Description: Fifth Canadian edition. | Issued also in 3 volumes. | Includes index.
Identifiers: C
anadiana (print) 20210378492 | Canadiana (ebook) 2021037862X | ISBN
9780176911140 (hardcover) | ISBN 9780176911225 (PDF)
Subjects: LCSH: Biology—Textbooks. | LCGFT: Textbooks.
Classification: LCC QH308.2 .R88 2022 | DDC 570—dc23
ISBN: 978-0-17-691114-0
Ebook ISBN: 978-0-17-691122-5
Cengage
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Printed in the United States of America
Print Number: 01
Print Year: 2022
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our generations of students.
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Penny Nickle
In Memoriam: Dr. Todd Nickle
The entire Cengage Canada production team is saddened, yet
honoured, to dedicate this fifth
Canadian edition of Biology:
Exploring the Diversity of Life
to our friend, colleague, and
coauthor Dr. Todd Nickle, as a
celebration of his life.
Before his death in August
of 2021, Todd completed his
revisions for this edition with
characteristic passion, dedication, and enthusiasm. He was
a particularly generous man,
quick with praise and quicker
with helpful support for colleagues and students. A very
early adopter of bleeding-edge educational technologies for learning
and assessment, Todd brought many innovative ideas to the table,
while always keeping student learning at the centre of our discussions.
If there was a new aspect of the project we wanted to explore, like The
Purple Pages videos or the COVID-19 supplement, Todd was always
happy to step up and mock up an example. He once apologized for the
birdsong on the audio track of one of his draft video commentaries
on research figures. He had been working on the piece at his cabin in
the woods.
Always the good-hearted and playful provocateur, Todd had a knack for
engaging the author team in lively debate on important issues of student
experience. While he did not live to see publication of this edition, his legacy and influence on this work will continue for many iterations to come.
Todd received his PhD from Oklahoma State University in 1998 and
taught biology at Mount Royal University, advocating active learning:
students come to class prepared to work with material rather than just
hear about it. Student preparation involves reading the text and applying the concepts to online exercises, the results of which inform what
the next lecture will be about. Class time focuses on exploring connections between concepts and ideas in biology and how they relate to other
disciplines. This inspired Todd to coauthor a handbook for first-year
science students, Science3. A compelling candidate for the 3M National
Fellowship, Todd’s work put him in the first cohort of full professors
at Mount Royal University in 2012. He also garnered the 2015 ACIFA
Innovation in Teaching Award and the 2016 Distinguished Faculty Award
from MRU. Todd’s interest in promoting best teaching practices among
educators beyond his home campus saw him expand and lead the Alberta
Introductory Biology Association (AIBA) to official society status in
Alberta as the Undergraduate Biology Educators of Alberta (UBEA). At
the national level, Todd also leaves many close colleagues in the Open
Consortium of Undergraduate Biology Educators (oCUBE).
iv
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About the Canadian Authors
M. B. Fenton
M. B. (Brock) Fenton received his PhD from the
University of Toronto in 1969. Since then, he has been a
faculty member in biology at Carleton University, then
at York University, and then at Western University. In
addition to teaching parts of first-year biology, he has
also taught Vertebrate Biology, Animal Biology, and
Conservation Biology, as well as field courses in the
biology and behaviour of bats. Brock has received awards
for his teaching (Carleton University Faculty of Science
Teaching Award; Ontario Confederation of University
Faculty Associations Teaching Award; and a 3M Teaching
Fellowship, Society for Teaching and Learning in Higher
Education) in addition to recognition of his work on public
awareness of science (Gordin Kaplan Award from the
Denis Maxwell
Denis Maxwell received his PhD from the University
of Western Ontario in 1995. His thesis focused on
photosynthetic acclimation in green algae. Following
his doctorate, he undertook postdoctoral training at the
Department of Energy Plant Research Laboratory at
Michigan State University, where he studied the function
of the mitochondrial alternative oxidase. After taking up
a faculty position at the University of New Brunswick in
Mitch Zimmer
Tom Haffie is a graduate of the University of Guelph
and the University of Saskatchewan in the study of
microbial genetics. Newly retired, he devoted his 33-year
career at Western University to teaching large biology
classes in lecture, laboratory, and tutorial settings. He
led the development of the innovative core laboratory
course in the Biology program; he was an early adopter
of computer animation in lectures; and, most recently,
he led a deep blended redevelopment of introductory
biology informed by a students-as-partners approach to
collaborative course design. Tom was a founding force
in the Western Biology Undergraduate Society (BUGS),
Bruce Moffat
Bill Milsom received his PhD from the University
of British Columbia and is a professor in UBC’s
Department of Zoology, where he has taught a variety
of courses, including first-year biology, for almost 40
years. His research interests include the evolutionary
origins of respiratory processes and the adaptive
changes in these processes that allow animals to exploit
diverse environments. He examines respiratory and
cardiovascular adaptations in vertebrate animals in
rest, sleep, exercise, altitude, dormancy, hibernation,
diving, and so on. This research contributes to our
understanding of the mechanistic basis of biodiversity
Canadian Federation of Biological Societies; Honorary Life
Membership, Science North, Sudbury, Ontario; Canadian
Council of University Biology Chairs Distinguished
Canadian Biologist Award; The McNeil Medal for the
Public Awareness of Science of the Royal Society of Canada;
and the Sir Sandford Fleming Medal for Public Awareness
of Science, the Royal Canadian Institute). He also received
the C. Hart Merriam Award from the American Society
of Mammalogists for excellence in scientific research. Bats
and their biology, behaviour, evolution, and echolocation
are the topics of his research, which has been funded by
the Natural Sciences and Engineering Research Council of
Canada (NSERC). In November 2014, Brock was inducted
as a Fellow of the Royal Society of Canada.
2000, Denis moved in 2003 to the Department of Biology
at Western University. He served as Associate Chair for
Undergraduate Education for the Department of Biology
from 2009 to 2016. Currently, he is Assistant Dean for
the Faculty of Science, with a portfolio that includes
Recruitment and First-Year Studies and outreach. Denis
has taught first-year Biology to over 15 000 students, most
of the time with coauthor Tom Haffie.
the Open Consortium for Undergraduate Biology
Educators (oCUBE), and the Western Conference on
Science Education (WCSE). Tom’s educational practice
was honoured with several awards, including a Western
University Students’ Council Award for Excellence
in Teaching, a Western University Edward G. Pleva
Award for Excellence in Teaching, a Western University
Fellowship in Teaching Innovation, a Western University
Teaching Fellowship for Science, a Province of Ontario
Award for Leadership in Faculty Teaching (LIFT), and
a 3M National Teaching Fellowship for excellence in
teaching.
and the physiological costs of habitat selection. Bill’s
research has been funded by NSERC, and he has
received several academic awards and distinctions,
including the Fry Medal of the Canadian Society of
Zoologists, the August Krogh Distinguished Lectureship
Award of the American Physiological Society, the
Bidder Lecture of the Society for Experimental Biology,
and the Izaak Walton Killam Award for Excellence
in Mentoring. He has served as President of the
Canadian Society of Zoologists and as President of the
International Congress of Comparative Physiology and
Biochemistry.
v
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Shona Ellis received her MSc from the University
Andy Cotton
of British Columbia and is a professor of teaching in
the Botany Department. She developed a keen interest
in forests and oceans growing up on the central coast
of British Columbia in Heiltsuk Territory. As an
undergraduate, Shona pursued her interests in botany
and entomology. Her MSc research incorporated tissue
culture, phytochemistry, and plant anatomy. She realized
a passion for teaching and joined the faculty at UBC in
1998. Shona teaches botany courses that include vascular
plants, economic botany, bryology, and plant systematics,
as well as Introductory Biology. She also currently teaches
Shelby Riskin received her BA from Grinnell College
Dan Riskin
in Iowa, where she was first exposed to the wonderful
world of biological research. She received her PhD from
Brown University in a joint program with the Marine
Biological Laboratory in Woods Hole, Massachusetts. Her
dissertation focused on ecosystem-level biogeochemical
consequences of conversion to agriculture in the Brazilian
Amazon, the region of the world where deforestation and
conversion to large-scale farming are happening most
rapidly. Shelby then joined the University of Toronto as
vi
a course through the Haida Gwaii Institute that takes
her and her class into the natural environment of Haida
Territory. Shona teaches in a number of settings; in large
and small lecture classes, in laboratories, and on field
trips. While she feels the best classroom is outdoors,
she integrates online technologies into all her courses;
she is an early adopter of online teaching and learning
resources. Shona has received two Killam Teaching
Awards, a Dean of Science Service Award (UBC), UBC’s
Margaret Fulton Award for student development, and
the Charles Edwin Bessey Teaching Award from the
Botanical Society of America.
Assistant Professor in the teaching stream of the Ecology
and Evolutionary Biology Department. She teaches a
variety of undergraduate courses exploring ecosystem
ecology and conservation biology and is Director of the
U of T National Biology Competition, an international
competition for high school students. Shelby is also
passionate about mentoring undergraduates through
independent research projects and about teaching biology
and ecology to students outside the life sciences—
understanding the diversity of life is for everyone.
A B O U T T H E C A N A D I A N AU T H O R S
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About the US Authors
Courtesy of Peter J. Russell
Peter J. Russell received his BSc in biology from the
University of Sussex, England, in 1968 and his PhD in
genetics from Cornell University in 1972. He has been
a member of the Biology faculty of Reed College since
1972 and is currently Professor of Biology, Emeritus.
Peter taught a section of the introductory biology course,
a genetics course, and a research literature course on
molecular virology. In 1987, he received the Burlington
Northern Faculty Achievement Award from Reed
College in recognition of his excellence in teaching. Since
1986, he has been the author of a successful genetics
textbook; the current edition is iGenetics: A Molecular
Approach. Peter’s research was in the area of molecular
genetics, with a specific interest in characterizing the role
of host genes in the replication of the RNA genome of a
pathogenic plant virus and the expression of the genes of
Courtesy of Aaron Kinard
Paul E. Hertz was born and raised in New York City.
He received a BA in biology from Stanford University
in 1972, a master’s degree in biology from Harvard
University in 1973, and a PhD in biology from Harvard
University in 1977. While completing field research for
his doctorate, he served on the Biology faculty of the
University of Puerto Rico at Rio Piedras. After spending
two years as an Isaac Walton Killam Postdoctoral Fellow
at Dalhousie University, Paul accepted a teaching position
at Barnard College, where he has taught since 1979. He
was named Ann Whitney Olin Professor of Biology in
2000 and the Claire Tow Professor of Biology in 2016. He
received The Barnard Award for Excellence in Teaching
in 2007. In addition to serving on numerous college
committees, Paul chaired Barnard’s Biology Department
for eight years and served as Acting Provost and Dean of
the Faculty from 2011 to 2012. He was also the founding
Program Director of the Hughes Science Pipeline Project
at Barnard, an undergraduate curriculum and research
program funded continuously by the Howard Hughes
Courtesy of Beverly McMillan
Beverly McMillan holds undergraduate and graduate
degrees from the University of California, Berkeley. She
has worked extensively in educational and commercial
publishing as an author, science writer, project manager,
and multimedia content developer. In addition to her
contributions to college textbooks, Beverly has written or
coauthored multiple popular books on topics in natural
the virus; yeast was used as the model host. His research
has been funded by agencies such as the National
Institutes of Health, the National Science Foundation, the
American Cancer Society, the Department of Defense,
the Medical Research Foundation of Oregon, and the
Murdoch Foundation. He has published his research
in a variety of journals, including Genetics, Journal of
Bacteriology, Molecular and General Genetics, Nucleic
Acids Research, Plasmid, and Molecular and Cellular
Biology. Peter has a long history of encouraging faculty
research involving undergraduates, including cofounding
the biology division of the Council on Undergraduate
Research in 1985. He was Principal Investigator/Program
Director of a National Science Foundation Award for the
Integration of Research and Education (NSF–AIRE) to
Reed College, 1998 to 2002.
Medical Institute, from 1992 to 2016. The Pipeline Project
included the Intercollegiate Partnership, a program for
local community-college students that facilitated their
transfer to four-year colleges and universities. Since
2016, he has served as Director of the Science Pathways
Scholars Program, which provides support and research
opportunities to first-generation college students and
students of colour at Barnard. He teaches one semester
of the introductory sequence for biology majors and
pre-professional students, lecture and laboratory courses
in vertebrate zoology and ecology, and seminars that
introduce first-year students to scientific research. Paul is
an animal physiological ecologist with a specific research
interest in the thermal biology of lizards. He has conducted
fieldwork in the West Indies since the mid-1970s, most
recently focusing on the lizards of Cuba and Puerto
Rico. His work has been funded by the National Science
Foundation, and he has published his research in such
prestigious journals as The American Naturalist, Ecology,
Nature, Oecologia, and The Proceedings of the Royal Society.
history and human health and biology, as well as field guides
to the flora and fauna of more than 20 US states. She has
also created Web and print content for such clients as the US
National Park Service, the Science Museum of Virginia, The
Mariners’ Museum, the San Francisco Exploratorium, the
University of California system, and the Virginia Institute of
Marine Science/College of William and Mary.
vii
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Joel H. Benington received his BA from St. John’s
Courtesy of Joel H. Benington
College in Annapolis, Maryland, in 1985 and his PhD in
biology from Stanford University in 1992. He performed
postdoctoral research at the University of Los Angeles
and Stanford University until 1996. Since then, he has
been a member of the Biology faculty of St. Bonaventure
University, where he is currently Professor of Biology
and Director of the Bioinformatics and Health and
Society programs. He has twice served as Chair of the
Department of Biology. During his entire time at St.
Bonaventure University, he has taught one or both
semesters of the general biology sequence for firstyear life science majors. He also teaches upper-level
viii
Neurobiology, Genomics, and Evolution courses and
has led a variety of seminar courses in the university’s
Honors Program. He has published his research in
journals such as Progress in Neurobiology, Brain Research,
The American Journal of Physiology, and The Scientist.
In addition to laboratory research, he has published
hypotheses concerning the role of sleep in brain energy
metabolism, the functional relationship between REM
sleep and non-REM sleep, and connections between
sleep and learning. Joel’s research has been funded by
the National Institutes of Health, and he has served as
Principal Investigator of a National Grid grant to support
K–12 STEM education in Cattaraugus County, New York.
A B O U T T H E U S AU T H O R S
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Brief Contents
VOLUME 1: BIOLOGY OF THE CELL
1 Defining Life and Its Origins 5
1
UNIT 1 SYSTEMS AND PROCESSES—THE CELL
2 The Cell: An Overview 31
3 Energy and Enzymes 59
4 Cell Membranes and Signalling 83
5 Cellular Respiration 109
6 Photosynthesis 135
UNIT 2 GENES
7 Cell Cycles 161
8 Genetic Recombination 185
9 The Chromosomal Basis of Inheritance 211
10 Genetic Linkage, Sex Linkage, and Other Extensions
to Basic Inheritance Mechanisms
UNIT 6 ECOLOGY AND BEHAVIOUR
26 Population Ecology 689
27 Species Interactions and Community Ecology
28 Ecosystems 753
29 Conservation of Biodiversity 779
THE CHEMICAL AND PHYSICAL FOUNDATIONS OF
BIOLOGY (THE PURPLE PAGES) F-1
VOLUME 3: SYSTEMS AND PROCESSES
33
34
VOLUME 2: EVOLUTION, ECOLOGY, AND THE
DIVERSITY OF LIFE 403
UNIT 4 EVOLUTION AND CLASSIFICATION
16 Evolution: The Development of the Theory 407
17 Microevolution: Changes within Populations 429
18 Speciation and Macroevolution 451
19 Systematics and Phylogenetics: Revealing the Tree
40
41
42
43
44
471
UNIT 5 THE DIVERSITY OF LIFE
20 Bacteria and Archaea 497
21 Protists 519
22 Fungi 547
23 Plants 571
24 Animals 603
25 Viruses, Viroids, and Prions: Infectious Biological
Particles
Plants 853
Plant Nutrition 875
Plant Signals and Responses to the Environment
895
UNIT 8 SYSTEMS AND PROCESSES—ANIMALS
35 Introduction to Animal Organization and
36
37
38
39
of Life
801
UNIT 7 SYSTEMS AND PROCESSES—PLANTS
30 Organization of the Plant Body 805
31 Transport in Plants 833
32 Reproduction and Development in Flowering
237
UNIT 3 DNA AND GENE EXPRESSION
11 DNA Structure, Replication, and Repair 265
12 Gene Structure, Expression, and Mutation 291
13 Regulation of Gene Expression 321
14 DNA Technologies 347
15 Genomes 375
717
45
Physiology 925
Animal Nutrition 947
Gas Exchange: The Respiratory System 977
Internal Transport: The Circulatory System 1001
Regulation of the Internal Environment: Water, Solutes,
and Temperature 1027
Control of Animal Processes: Endocrine Control 1059
Animal Reproduction and Development 1085
Control of Animal Processes: Neural Control 1123
Muscles, Skeletons, and Body Movements 1179
Animal Behaviour and Responses to the
Environment 1201
Defences against Disease 1237
APPENDIX A: ANSWERS TO SELF-TEST
QUESTIONS A-1
GLOSSARY G-1
INDEX I-1
671
ix
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Contents
4
Cell Membranes and Signalling
4.1
An Overview of the Structure of Membranes 84
83
Figure 4.2 Experimental Research The Frye–Edidin Experiment
Demonstrating That the Phospholipid Bilayer Is Fluid 85
In Memoriam: Dr. Todd Nickle
About the Canadian Authors
About the US Authors
Letter to Students
xvii
New to This Edition
xxi
Figure 4.3 Research Method Freeze Fracture 86
iv
v
vii
Welcome to Biology: Exploring the Diversity
of Life, 5Ce xxiv
Active Learning
4.2
The Lipid Fabric of a Membrane 86
4.3
Membrane Proteins 89
4.4
Passive Membrane Transport 91
4.5
Active Membrane Transport 95
4.6
Exocytosis and Endocytosis 98
4.7
The Role of Membranes in Cell Signalling 100
SUMMARY ILLUSTRATION FOR CHAPTER 4 104
xxvi
Student and Instructor Resources
xxx
Acknowledgments xxxi
VOLUME 1: BIOLOGY OF THE CELL
1
5
Cellular Respiration 109
5.1
The Chemical Basis of Cellular Respiration 110
5.2
Cellular Respiration: An Overview 112
5.3
Glycolysis: The Splitting of Glucose 113
5.4
Pyruvate Oxidation and the Citric Acid Cycle 116
5.5
Oxidative Phosphorylation: Electron Transport
and Chemiosmosis 119
5.6
The Efficiency and Regulation of Cellular Respiration 122
5.7
Oxygen and Cellular Respiration 125
1
Defining Life and Its Origins
1.1
What Is Life? 6
1.2
The Chemical Origins of Life 8
1.3
The Evolution of Information Flow: RNA, DNA, Protein 11
1.4.
The Development of Metabolism and the First Cells 13
1.5
The Tree of Life 16
1.6
Eukaryotes and the Rise of Multicellularity 19
6
Photosynthesis
1.7
The Fossil Record 24
6.1
The Physical Nature of Light 136
6.2
Photosynthesis: An Overview 138
5
UNIT 1 SYSTEMS AND PROCESSES—THE CELL
SUMMARY ILLUSTRATION FOR CHAPTER 6 130
135
6.3
The Photosynthetic Apparatus 140
6.4
The Light Reactions 144
Basic Features of Cell Structure and Function 32
6.5
The Calvin Cycle 146
2.2
Prokaryotic Cells 36
6.6
Photorespiration and CO2-Concentrating Mechanisms 149
2.3
Eukaryotic Cells 37
6.7
Photosynthesis and Cellular Respiration Compared 154
2
The Cell: An Overview
2.1
31
Figure 2.8 Research Method Cell Fractionation 38
SUMMARY ILLUSTRATION FOR CHAPTER 5 156
2.4
Specialized Structures of Plant Cells 49
2.5
The Animal Cell Surface 51
UNIT 2 GENES
SUMMARY ILLUSTRATION FOR CHAPTER 2 54
3
Energy and Enzymes
3.1
Energy and the Laws of Thermodynamics 60
3.2
Free Energy and Spontaneous Processes 63
3.3
Thermodynamics and Life 66
3.4
Overview of Metabolism 67
3.5
The Role of Enzymes in Biological Reactions 70
3.6
Factors That Affect Enzyme Activity 74
59
SUMMARY ILLUSTRATION FOR CHAPTER 3 78
7
Cell Cycles
7.1
The Cycle of Cell Growth and Division: An Overview 162
7.2
The Cell Cycle in Prokaryotic Organisms 163
7.3
Mitosis and the Eukaryotic Cell Cycle 164
7.4
Formation and Action of the Mitotic Spindle 172
7.5
Cell Cycle Regulation 174
161
Figure 7.19 Experimental Research Movement of Chromosomes
during Anaphase of Mitosis 176
SUMMARY ILLUSTRATION FOR CHAPTER 7 180
x
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8
Genetic Recombination
8.1
Mechanism of Genetic Recombination 186
Figure 11.2 Experimental Research The Hershey and Chase
Experiment Demonstrating That DNA Is the Hereditary Molecule 268
8.2
Genetic Recombination in Bacteria 187
11.2
DNA Structure 269
Figure 8.2 Research Method Replica Plating 188
11.3
DNA Replication 272
Figure 8.3 Experimental Research Genetic Recombination in
Bacteria 189
Figure 11.9 Experimental Research The Meselson and Stahl
Experiment Demonstrating the Semiconservative Model for DNA
Replication to Be Correct 274
8.3
185
Genetic Recombination Occurs in Eukaryotes during
Meiosis 195
9.1
The Chromosomal Basis of Inheritance
Repair of Damage in DNA 283
SUMMARY ILLUSTRATION FOR CHAPTER 11 286
SUMMARY ILLUSTRATION FOR CHAPTER 8 206
9
11.4
211
Mendel’s Experiments with Garden Peas 212
12
Gene Structure, Expression, and Mutation
12.1
The Connection between DNA, RNA, and Protein 292
291
Figure 9.2 Research Method Making a Genetic Cross between Two
Pea Plants 213
Figure 12.2 Experimental Research The Gene–Enzyme
Relationship 294
Figure 9.4 Experimental Research The Principle of Segregation:
Inheritance of Flower Colour in Garden Peas 216
12.2
Transcription: DNA-Directed RNA Synthesis 297
12.3
Processing of mRNAs in Eukaryotes 299
12.4
Translation: mRNA-Directed Polypeptide Synthesis 303
12.5
Mutations Can Affect Protein Structure and Function 313
Figure 9.7 Experimental Research Testing the Predicted Outcomes
of Genetic Crosses 220
Figure 9.8 Experimental Research The Principle of Independent
Assortment 221
9.2
Later Modifications and Additions to Mendel’s Hypotheses 224
Figure 9.12 Experimental Research Experiment Showing
Incomplete Dominance of a Trait 225
SUMMARY ILLUSTRATION FOR CHAPTER 9 232
10
Genetic Linkage, Sex Linkage, and Other Extensions
to Basic Inheritance Mechanisms 237
10.1
Genetic Linkage and Recombination 238
Figure 10.2 Experimental Research Evidence for Gene Linkage 240
10.2
Sex-Linked Genes 243
SUMMARY ILLUSTRATION FOR CHAPTER 12 316
13
Regulation of Gene Expression
13.1
Regulation of Gene Expression in Prokaryotic Cells 322
13.2
Regulation of Transcription in Eukaryotes 328
13.3
Posttranscriptional, Translational, and Posttranslational
Regulation 335
13.4
The Loss of Regulatory Controls in Cancer 339
321
SUMMARY ILLUSTRATION FOR CHAPTER 13 342
14
DNA Technologies
14.1
DNA Cloning 348
347
Figure 14.3 Research Method Identifying a Recombinant Plasmid
Containing a Gene of Interest 351
Figure 10.8 Experimental Research Evidence for Sex-Linked
Genes 246
Figure 14.4 Research Method Synthesis of DNA from mRNA Using
Reverse Transcriptase 352
10.3
Chromosomal Mutations That Affect Inheritance 248
10.4
Human Genetic Traits, Pedigree Analysis, and
Genetic Counselling 252
Figure 14.5 Research Method The Polymerase Chain Reaction
(PCR) 353
10.5
Additional Patterns of Inheritance 256
Figure 14.6 Research Method Separation of DNA Fragments by
Agarose Gel Electrophoresis 354
SUMMARY ILLUSTRATION FOR CHAPTER 10 260
14.2
Applications of DNA Technologies 355
Figure 14.8 Research Method Southern Blot Analysis 357
UNIT 3 DNA AND GENE EXPRESSION
Figure 14.11 Research Method Making a Knockout Mouse 361
11
DNA Structure, Replication, and Repair
11.1
Establishing DNA as the Hereditary Molecule 266
265
Figure 11.1 Experimental Research Griffith’s Experiment with
Virulent and Nonvirulent Strains of Streptococcus pneumoniae 267
Figure 14.14 Experimental Research The First Cloning of a
Mammal 364
Figure 14.16 Research Method Using the Ti Plasmid of Rhizobium
radiobacter to Produce Transgenic Plants 366
CONTENTS
xi
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SUMMARY ILLUSTRATION FOR CHAPTER 14 370
18.4
15
Genomes
15.1
Genomics: An Overview 376
Figure 18.16 Observational Research Chromosomal Similarities and
Differences among Humans and the Great Apes 465
15.2
Genome Sequencing 377
375
SUMMARY ILLUSTRATION FOR CHAPTER 18 466
Figure 15.1 Research Method Sanger Sequencing 378
Figure 15.2 Research Method Pyrosequencing 382
15.3
Genetic Mechanisms of Speciation 461
Annotation Identifies Genes 385
19
Systematics and Phylogenetics: Revealing the
Tree of Life 471
19.1
Nomenclature and Classification 472
19.2
Phylogenetic Trees 474
Figure 15.8 Research Method Analysis of Gene Expression Levels
using RNA-seq 390
19.3
Sources of Data for Phylogenetic Analyses 477
19.4
Traditional Classification and Paraphyletic Groups 480
15.4
19.5
The Cladistic Revolution 481
Comparative Genomics Can Reveal How Genes and
Genomes Evolved 391
Figure 19.11 Research Method Using Cladistics to Construct a
Phylogenetic Tree 483
SUMMARY ILLUSTRATION FOR CHAPTER 15 400
19.6
Phylogenetic Trees as Research Tools 486
VOLUME 2: EVOLUTION, ECOLOGY, AND
THE DIVERSITY OF LIFE 403
UNIT 4 EVOLUTION AND CLASSIFICATION
Figure 19.13 Research Method Using Genetic Distances to
Construct a Phylogenetic Tree 487
16
Evolution: The Development of the Theory
SUMMARY ILLUSTRATION FOR CHAPTER 19 490
16.1
What Is Evolution through Natural Selection? 408
16.2
Evidence for Evolution through Natural Selection 411
16.3
Development of the Theory of Evolution 414
19.7
407
UNIT 5 THE DIVERSITY OF LIFE
Figure 16.9 Experimental Research Adaptation of E. coli to a Change
in Temperature 415
16.4
Molecular Phylogenetic Analyses 489
Evolutionary Theory since Darwin 421
20
Bacteria and Archaea
20.1
The Full Extent of the Diversity of Bacteria and Archaea
Is Unknown 498
20.2
Prokaryotic Structure and Function 498
497
Figure 20.5 Experimental Research Genetic Recombination in
Bacteria 501
SUMMARY ILLUSTRATION FOR CHAPTER 16 424
17
Microevolution: Changes within Populations
17.1
Variation in Natural Populations 430
20.4 The Domain Archaea 510
17.2
Population Genetics 432
SUMMARY ILLUSTRATION FOR CHAPTER 20 514
17.3
The Agents of Microevolution 434
429
Figure 17.8 Research Method Using the Hardy–Weinberg
Principle 435
Figure 17.13 Experimental Research Do Humans Experience
Stabilizing Selection? 440
17.4
Non-random Mating 441
Figure 17.16 Experimental Research Sexual Selection in
Action 443
17.5
Maintaining Genetic and Phenotypic Variation 444
SUMMARY ILLUSTRATION FOR CHAPTER 17 446
20.3
The Domain Bacteria 508
21
Protists
21.1
The Vast Majority of Eukaryotes Are Protists 520
21.2
Characteristics of Protists 521
21.3
Protists’ Diversity Is Reflected in Their Habitats, Structure,
Metabolism, and Reproduction 522
21.4
Eukaryotic Supergroups and Key Protist Lineages 523
519
Figure 21.8 Observational Research Isolation and Identification
of Marine Diplonemids, Potentially the Most Abundant Marine
Organism 525
21.5
Some Protist Lineages Arose from Primary Endosymbiosis
and Others from Secondary Endosymbiosis 539
18
Speciation and Macroevolution
18.1
What Is a Species? 452
18.2
Maintaining Reproductive Isolation 455
22
Fungi
18.3
The Geography of Speciation 458
22.1
General Characteristics of Fungi 548
xii
451
SUMMARY ILLUSTRATION FOR CHAPTER 21 542
547
CONTENTS
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22.2
Evolution and Diversity of Fungi 550
26.5
Models of Population Growth 697
22.3
Fungal Life Styles 561
26.6 Population Regulation 702
Figure 22.20 Experimental Research Hidden Third Partner in Lichen
Symbiosis 562
Figure 26.16 Experimental Research Evaluating Density-Dependent
Interactions between Species 704
SUMMARY ILLUSTRATION FOR CHAPTER 22 566
26.7
Human Population Growth 707
SUMMARY ILLUSTRATION FOR CHAPTER 26 712
23
Plants
23.1
Defining Characteristics of Land Plants 572
27
Species Interactions and Community Ecology
23.2
The Transition to Life on Land 573
27.1
Population Interactions Shape Communities 718
571
23.3
Bryophytes: Nonvascular Land Plants 579
27.2
Symbioses: Close Associations 719
23.4
Seedless Vascular Plants 583
27.3
Energy Intake and Exchange 721
23.5
Gymnosperms: The First Seed Plants 588
27.4
Defence 723
23.6
Angiosperms: Flowering Plants 593
27.5
Competition 727
Figure 23.30 Experimental Research Exploring a Possible Early
Angiosperm Adaptation for Efficient Photosynthesis in Dim
Environments 595
SUMMARY ILLUSTRATION FOR CHAPTER 23 598
Figure 27.15 Experimental Research Gause’s Experiments on
Interspecific Competition in Paramecium 728
Figure 27.18 Experimental Research Demonstration of Competition
between Two Species of Barnacles 730
Figure 27.19 Experimental Research The Complex Effects of a
Herbivorous Snail on Algal Species Richness 731
24
Animals
24.1
What Are Animals? 604
24.2
Animal Origins: Animals Probably Arose from a Colonial
Flagellate 605
24.3
Key Features Used to Classify Animals 606
24.4
Basal Phyla 611
24.5
The Protostomes 619
24.6
The Deuterostomes 638
603
SUMMARY ILLUSTRATION FOR CHAPTER 24 666
25
Viruses, Viroids, and Prions: Infectious Biological
Particles 671
25.1
What Is a Virus? Characteristics of Viruses 672
25.2
Viruses Infect Bacterial, Animal, and Plant Cells by Similar
Pathways 675
27.6
The Nature of Ecological Communities 732
27.7
Community Characteristics 734
27.8
Effects of Population Interactions on Community
Structure 738
27.9
Succession 740
27.10 Variations in Species Richness among Communities 743
SUMMARY ILLUSTRATION FOR CHAPTER 27 748
28
Ecosystems
28.1
Ecosystems and Energy 754
753
Figure 28.12 Experimental Research A Trophic Cascade in Salt
Marshes 763
28.2
Nutrient Cycling in Ecosystems 764
Anthropogenic Global Change 771
25.3
Treating and Preventing Viral Infections 680
28.3
25.4
Virotherapy: Using Viruses to Cure Disease 681
SUMMARY ILLUSTRATION FOR CHAPTER 28 774
25.5
Viruses May Have Evolved from Fragments of Cellular
DNA or RNA 681
29
Conservation of Biodiversity
29.1
The Anthropocene 780
29.2
Threats to Biodiversity 781
25.6
717
Viroids and Prions Are Infective Agents Even Simpler in
Structure than Viruses 682
SUMMARY ILLUSTRATION FOR CHAPTER 25 684
UNIT 6 ECOLOGY AND BEHAVIOUR
Figure 29.3 Observational Research Near-Complete Extinction of
Small Mammals in Tropical Forest Fragments 783
29.3
26
Population Ecology
26.1
Introduction 690
26.2
Population Characteristics 690
26.3
Demography 693
689
26.4 Evolution of Life Histories 695
779
Ecosystem Services Highlight the Benefits of Ecosystems 787
29.4 Conservation Biology: Principles and Theory 789
Figure 29.16 Experimental Research Effect of Landscape Corridors
on Plant Species Richness in Habitat Fragments 793
29.5
Assessing Threatened Species and Prioritizing Efforts 793
CONTENTS
xiii
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29.6 Protecting Biodiversity Requires a Diversity of Solutions 794
34
Plant Signals and Responses to the Environment
SUMMARY ILLUSTRATION FOR CHAPTER 29 798
34.1
Plant Hormones 896
THE CHEMICAL AND PHYSICAL FOUNDATIONS OF
BIOLOGY (THE PURPLE PAGES) F-1
VOLUME 3: SYSTEMS AND PROCESSES 801
UNIT 7 SYSTEMS AND PROCESSES—PLANTS
30
Organization of the Plant Body
30.1
Plant Structure and Growth: An Overview 806
30.2
The Three Plant Tissue Systems 810
805
Figure 34.3 Experimental Research The Darwins’ Experiments on
Phototropism 899
Figure 34.4 Experimental Research Two Experiments by Frits
Went Demonstrating the Effect of Indoleacetic Acid (IAA) on an Oat
Coleoptile 900
34.2
Plant Chemical Defences 907
34.3
Plant Movements 911
34.4
Plant Biological Clocks 915
34.5
Learned Behaviour in Plants 919
SUMMARY ILLUSTRATION FOR CHAPTER 34 920
Figure 30.9 Experimental Research Networking the Secondary
Cell Wall 813
UNIT 8 SYSTEMS AND PROCESSES—ANIMALS
30.3
35
Introduction to Animal Organization and
Physiology 925
35.1
Organization of the Animal Body 926
Primary Shoot Structure 815
30.4 Primary Root Structure 820
30.5
Secondary Growth 823
SUMMARY ILLUSTRATION FOR CHAPTER 30 828
895
35.2 Animal Tissues 928
35.3 Coordination of Tissues in Organs and Organ Systems 935
31
Transport in Plants
31.1
Principles of Water and Solute Movement in Plants 834
31.2
Uptake and Transport of Water and Solutes by Roots 837
Figure 35.12 Experimental Research Demonstration of the Use of
the Bill for Thermoregulation in Birds 939
31.3
Long-Distance Transport of Water and Minerals
in the Xylem 839
SUMMARY ILLUSTRATION FOR CHAPTER 35 942
31.4
Transport of Organic Substances in the Phloem 844
36
Animal Nutrition
Figure 31.12 Experimental Research Translocation Pressure 845
36.1
Nutrients Are Essential Components of Any Diet 948
SUMMARY ILLUSTRATION FOR CHAPTER 31 848
36.2
Feeding to Obtain Nutrients 952
36.3
Digestive Processes 954
833
32
Reproduction and Development in Flowering
Plants 853
32.1
Overview of Flowering Plant Reproduction 854
32.2
Flower Structure and Formation of Gametes 856
32.3
Pollination, Fertilization, and Germination 860
32.4
Asexual Reproduction in Flowering Plants 866
Figure 32.16 Research Method Plant Tissue Culture
Protocol 868
35.4 Homeostasis 935
947
36.4 Structure and Function of the Mammalian Digestive
System 957
36.5
Regulation of Digestive Processes 967
Figure 36.20 Experimental Research Association of Bacterial
Populations in the Gut Microbiome with Obesity in Humans 969
36.6 Reflections on the Chapter 971
SUMMARY ILLUSTRATION FOR CHAPTER 36 972
37
Gas Exchange: The Respiratory System
37.1
General Principles 979
37.2
Ventilation of the Gas-Exchange Organs 983
37.3
The Mammalian Respiratory System 987
37.4
Exchange of Gas with Blood 989
Figure 33.2 Research Method Hydroponic Culture 877
37.5
Transport of Gases in Blood 990
33.2
Soil 880
37.6
Reflections on the Chapter 994
33.3
Root Adaptations for Obtaining and Absorbing Nutrients 883
Figure 37.21 Experimental Research Demonstration of a Molecular
Basis for High-Altitude Adaptation in Deer Mice 995
32.5
Early Development of Plant Form and Function 868
SUMMARY ILLUSTRATION FOR CHAPTER 32 870
33
Plant Nutrition
33.1
Plant Nutritional Requirements 876
875
SUMMARY ILLUSTRATION FOR CHAPTER 33 890
977
SUMMARY ILLUSTRATION FOR CHAPTER 37 996
xiv
CONTENTS
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38
Internal Transport: The Circulatory System
38.1
Animal Circulatory Systems: An Introduction 1003
Figure 41.12 Experimental Research Vocal Cues to Ovulation in
Human Females 1097
38.2
Blood and Its Components 1006
41.5
38.3
The Heart 1009
SUMMARY ILLUSTRATION FOR CHAPTER 41 1118
1001
Development 1104
38.4 Blood Vessels of the Circulatory System 1013
38.5
Maintaining Blood Flow and Pressure 1017
Figure 38.19 Experimental Research Demonstration of a
Vasodilatory Signalling Molecule 1019
Reflections on the Chapter 1021
39
Regulation of the Internal Environment: Water, Solutes,
and Temperature 1027
39.1
Introduction to Osmoregulation and Excretion 1028
39.2
Osmoregulation and Excretion in Invertebrates 1032
39.3
Osmoregulation and Excretion in Non-mammalian
Vertebrates 1034
39.4 Osmoregulation and Excretion in Mammals 1036
The Basis of Information Flow in Nervous Systems:
An Overview 1124
1123
Sensory Inputs: Reception 1137
Figure 42.25 Experimental Research How Do Sea Urchins Detect
Light? 1147
Figure 42.42 Experimental Research Magnetic Sense in Sea
Turtles 1158
42.3
The Central Nervous System: Integration 1159
42.4
The Peripheral Nervous System: Transmission and
Response 1171
SUMMARY ILLUSTRATION FOR CHAPTER 42 1174
Figure 39.15 Experimental Research ADH-Stimulated Water
Reabsorption in the Kidney Collecting Duct 1042
Introduction to Thermoregulation 1043
43
Muscles, Skeletons, and Body Movements
43.1
Vertebrate Skeletal Muscle: Structure and Function 1180
1179
Figure 43.5 Experimental Research The Sliding Filament Model of
Muscle Contraction 1183
39.6 Ectothermy 1045
39.7
42.1
42.2
SUMMARY ILLUSTRATION FOR CHAPTER 38 1022
39.5
Control of Animal Processes: Neural Control
Figure 42.13 Experimental Research Demonstration of Chemical
Transmission of Nerve Impulses at Synapses 1136
38.6 The Lymphatic System 1019
38.7
42
Endothermy 1048
39.8 Reflections on the Chapter 1053
43.2
Skeletal Systems 1189
SUMMARY ILLUSTRATION FOR CHAPTER 39 1054
43.3
Vertebrate Movement: The Interactions between Muscles and
Bones 1193
40
Control of Animal Processes: Endocrine Control
40.1
Hormones and Their Secretion 1060
1059
40.2 Mechanisms of Hormone Action 1063
Figure 40.6 Experimental Research Demonstration That
Epinephrine Acts by Binding to a Plasma Membrane
Receptor 1066
40.3 The Hypothalamus and Pituitary 1068
40.4 Other Major Endocrine Glands of Vertebrates 1071
40.5 Endocrine Systems in Invertebrates 1076
Figure 40.16 Experimental Research Demonstration That Growth
and Moulting in Insects Is Hormonally Controlled 1078
SUMMARY ILLUSTRATION FOR CHAPTER 43 1196
44
Animal Behaviour and Responses to the
Environment 1201
44.1
Introduction 1203
Figure 44.3 Experimental Research The Role of Sign Stimuli in
Parent–Offspring Interactions 1204
44.2
Genes and Behaviour: Nature or Instinct 1204
44.3
Environment and Behaviour: Learning or Nurture 1206
44.4 Hormones and Behaviour 1207
44.5 Neurophysiology and Behaviour 1209
44.6 Finding Food/Defences against Predation 1211
40.6 Reflections on the Chapter 1079
44.7
SUMMARY ILLUSTRATION FOR CHAPTER 40 1080
Communication 1212
44.8 Choice of Habitat 1216
41.1
The Drive to Reproduce 1086
Figure 44.28 Experimental Research Experimental Analysis of the
Indigo Bunting’s Star Compass 1221
41.2
Asexual and Sexual Reproduction 1086
44.9 Mating 1224
41.3
Mechanisms of Sexual Reproduction 1088
44.10 Social Behaviour 1226
41.4
Sexual Reproduction in Mammals 1095
SUMMARY ILLUSTRATION FOR CHAPTER 44 1232
41
Animal Reproduction and Development
1085
CONTENTS
xv
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45
Defences against Disease
45.1
Three Lines of Defence against Invasion 1238
45.5
45.2
Innate Immunity: Nonspecific Defence 1239
SUMMARY ILLUSTRATION FOR CHAPTER 45 1256
45.3
Adaptive Immunity: Specific Defences 1242
1237
Figure 45.10 Research Method Production of Monoclonal
Antibodies 1248
xvi
45.4 Impairment and Peculiarities of the Immune System 1251
Immune Systems in Other Organisms 1254
Appendix A: Answers to Self-Test Questions
Glossary G-1
Index I-1
A-1
CONTENTS
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Letter to Students
As you take another step toward increasing your understanding
of the biological world, we welcome you to this exploration of
the diversity of life. The main goal of this textbook is to guide
you on a journey of discovery about life’s diversity across interconnected levels of organization, ranging from molecules to
genes, from cells to organs, and from species to ecosystems.
Along the way, we will explore many questions about the mechanisms underlying diversity as well as the importance of maintaining diversity for all species, including our own.
Diverse perspectives…
With this edition of Biology: Exploring the Diversity of Life, we have
been deliberate in beginning an ongoing process of opening this
resource to a wider range of sources, voices, and perspectives
devoted to a more fulsome understanding of the interconnected
biological world. In particular, we offer this edition as a first step in
responding to the Truth and Reconciliation Commission of
Canada’s (TRC) Calls to Action and to the United Nations Declaration on the Rights of Indigenous Peoples (UNDRIP). The
truth of the relationship between science and Indigenous Peoples in Canada has often, unfortunately, been one of oppression
and exploitation. The racism that fuelled the colonization of the
land that is now Canada influenced all aspects of social life,
including the delivery of education and the conduct of science.
The residential school system used education as a tool of cultural assimilation, with tragic effects on Indigenous communities that continue to play out today. Science education was rarely
provided in these schools, thus limiting the capacity for Indigenous peoples to effectively interact with scientists representing
government, industry, or academia. A significant underrepresentation of Indigenous peoples in Canadian science- and technology-related careers continues to this day.
In many Indigenous communities, science and research
have been viewed fearfully as tools of oppression. Some scientists have engaged in unethical practices in Indigenous communities that have resulted in deliberate harm to people and/or
their environment. Indigenous Traditional Knowledge and
technologies have been taken, and sometimes commercialized,
without consent from or benefit to the original KnowledgeKeeping Elders and their communities.
Part of the work of reconciliation in this edition is a contribution to the ongoing shift in perspectives of science from
those of Eurocentrism (i.e., science as emanating from, and
largely exclusive to, European nations and their current or
former colonies) to a more open, decolonized, “multi-science”
perspective that acknowledges all Indigenous Peoples as having
scientific knowledge of the natural world, albeit through their
own cultural lenses. One such perspective is Indigenous
Science, the accumulated empirical knowledge that has been
generated by thriving and prosperous Indigenous peoples
through their observations of and relationships with natural
phenomena over millennia.
This book is one result of deepening relationships among
the primary authors and their professional colleagues, the editorial and production teams at Cengage Canada, students of
biology, Indigenous Elders and scholars, as well as members of
our Indigenous Advisory Board. The author team participated
in Ceremony with Indigenous advisors, experiencing firsthand Indigenous cultural practices to acknowledge the collective desire for the success of this project as an example of and
inspiration for reconciliatory learning. With open minds and
hearts, we are committed to creating a meeting place where scientists of all backgrounds can tell their stories.
As an author, advisory, and production team including
both settlers and Indigenous People of Turtle Island, we want
our work to contribute to reconciliation and improved relations
among settlers and First Nations, Inuit, and Métis Peoples. As
educators, we want our classes to be widely accessible. We
understand that this means making efforts to increase the level
of safety felt by Indigenous students and others who have been
excluded in our science education system. As authors of educational resources, we want to promote innovative, wholistic,
effective andragogy that supports teaching and learning by all
students and instructors. As global citizens, we want to promote collaboration in harnessing the creative power of a wide
variety of perspectives in the face of global challenges.
An emphasis on the diversity of life…
At first glance, the riot of life that animates the biosphere overwhelms our minds. One way to begin to make sense of this
diversity in a textbook is to divide it into manageable sections
on the basis of either similarities or differences. We examine
how different organisms solve the common problems of finding
nutrients, energy, and mates on the third rock from our Sun.
Evolution provides a powerful conceptual lens for viewing
and understanding the roots and history of the diversity of
living things. What basic evolutionary principles inform the
relationships among life forms regardless of their different
body plans, habitats, or life histories?
We will demonstrate how knowledge of evolution helps us
appreciate the changes we observe in organisms. Whether the
focus is the conversion of free-living prokaryotic organisms
into mitochondria and chloroplasts or the loss of eyes in cave
fish, selection for particular traits over time can explain the
current observations.
Examining how biological systems work is another theme
pervading this text and underlying the idea of diversity. We have
intentionally tried to include examples that will tax your imaginaxvii
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tion, from sea slugs that steal chloroplasts for use as solar panels, to
the molecular basis of high-altitude adaptations in deer mice, to
adaptive radiation of viruses. In each situation, we examine how
biologists have explored and assessed the inner workings of organisms, from gene regulation to the challenges of digesting cellulose.
Solving problems is another theme that runs throughout
the book. Whether the topic is gene therapy to treat a disease in
people, preventing harmful algal blooms, or reducing the incidence of human cancer, both the problem and the solution lie
in biology. We will explore large problems facing planet Earth
and the social implications that arise from them.
Emphasizing the big picture…
While many biology textbooks use the first few chapters to review
fundamentals of chemistry and biochemistry as well as information on the scientific method, this book immediately engages in
some of the excitement, mystery and controversy that is modern
biology right up front in Chapter 1. Important background information appears in the centre of the book as a distinct reference
section entitled The Chemical and Physical Foundations of
Biology. With their purple borders, these pages are distinct and
easy to find, and have become affectionately known as The Purple
Pages. These pages enable information to be readily identifiable
and accessible to you as you move through the textbook rather
than it being tied to a particular chapter. The concepts of atoms,
molecules, and macromolecules are connected through the
theme of “emergent properties.” By considering how the “stuff of
life” interrelates as a function of increasing complexity rather
than just memorizing the attributes of individual items, you can
better grasp why biology works the way it does rather than be
awed by how much information we know about it.
Throughout this book, we have highlighted the work of
Indigenous and non-Indigenous scientists in Canada and elsewhere, and we present many examples and biological concepts
in Canadian contexts. We hope that you, as a student studying
in Canada, will find this context accessible and engaging.
Focusing on research to engage the living
world through a scientific lens…
A primary goal of this book is to evoke and sustain your curiosity
about biology, rather than dulling it with a mountain of disconnected facts. We can help you develop the mental habits of scientists and a fascination with the living world by conveying our
passion for biological research. We want to excite you not only
with what biologists know about the living world but also with how
they know it and what they still need to learn. In doing so, we can
encourage some of you to accept the challenge and become biologists, posing and answering important new questions through
your own innovative research. For those of you who pursue other
careers, we hope that you will leave your introductory—and
perhaps only—biology course armed with intellectual skills that
will enable you to evaluate future knowledge with a critical eye.
xviii
In this book, we introduce you to a biologist’s “way of
learning.” Research biologists constantly integrate new observations, hypotheses, questions, experiments, and insights with
existing knowledge and ideas. To help you engage the world as
biologists do, we must not simply introduce you to the current
state of knowledge, we must also foster an appreciation of the
historical context within which those ideas developed and identify the future directions that biological research is likely to take.
Because advances in science occur against a background of
research, we also give you a feel for how biologists of the past
formulated basic knowledge in the field. By fostering an appreciation of such discoveries, given the information and theories
available to scientists in their own time, we can help you understand the successes and limitations of what we consider cutting-edge today. This historical perspective also encourages
you to view biology as a dynamic intellectual enterprise, not
just a collection of facts and generalities to be memorized.
We have endeavoured to make the science of biology come
alive by describing how biologists formulate hypotheses and
evaluate them using hard-won data, how data sometimes tell
only part of a story, and how the results of studies often end up
posing more questions than they answer. Our exploration of
the Tully Monster in Chapter 23 is a case in point. Since its
fossil discovery and description, this mainly soft-bodied animal
has been tentatively classified with species in five different
groups of animals. Through this example and throughout
Chapter 23, we explore the current recognition that the historical and traditional grouping of animals into protostomes and
deuterostomes is more artificial than real.
Although you might prefer simply to learn the right answer
to a question, we encourage you to embrace the unknown—
those gaps in knowledge that create opportunities for further
research. An appreciation of what biologists do not yet know
may draw you into the field. And by defining why scientists do
not understand interesting phenomena, we encourage you to
think critically about possible solutions and to follow paths dictated by your own curiosity. We hope that this approach will
encourage you to make biology a part of your daily life by
having informal discussions and debates about new scientific
discoveries with members of your personal and academic
communities.
This textbook is a toolbox…
You may see your professor as primarily a teacher, but as practicing scientists, professors are always learning from colleagues,
from the scientific literature, from their research programs, and
from their students. You may see yourself as primarily a learner,
but as a member of a social network, you are very likely to find
yourself explaining biological concepts to your friends, family
members, and the general public. Recognizing that we are all
lifelong learners and teachers may help you to see how each part
of your learning, both in and out of class, fits into the continuously developing picture of your life.
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Although it’s usual to think of this resource as merely a
book, it may be more helpful to imagine it as a toolbox containing various interrelated components carefully designed to
inspire, inform, structure, connect, and confirm your learning.
Modern science courses are often blended and/or flipped.
That is, you will likely be assigned an online learning component
to complement subsequent face-to-face classroom interaction.
Professors will often assign textbook readings in advance of class.
If, for example, you are assigned to read Sections 14.2 to 14.4 of the
text, be aware that educational research has identified specific
strategies for approaching this reading that are more likely to
result in durable learning. The least-effective strategy is to go
directly to the assigned material and simply read it as you would
read a novel or social media post. Learning is more durable if new
concepts can be connected to ideas that are already known or relevant to you. This means that the structure and context for new
learning is important. Assume that you are responsible for reading
certain sections of a chapter. Begin with the brief Why It Matters
section at the opening of the chapter. This will help you to see the
relevance of the material and, hopefully, allow you to make some
personal connection to the concepts. Check the chapter-opening
Roadmap to see how the assigned topics are related to other ideas
within the chapter and also to material in other chapters. Then
look over the Summary Illustration at the end of the chapter to
get a broad visual sense of the scope of the material. What do you
recognize from previous learning? What looks new? What looks
especially interesting? Then, go to the assigned sections of the
chapter with the awareness of how they fit into the bigger picture
of the chapter and to the concepts that are already known or interesting to you. Even then, don’t just start reading at the first word.
Instead, continue the exercise of noting the structure of the material by just noticing the main headings and perusing the figures.
Once you begin to read, create your own organization of
the material by making your own notes, highlights, etc.
Learning science requires that you understand new vocabulary; consult the Glossary to confirm the meaning of unfamiliar terms (or look up elsewhere terms not included in the
Glossary—get comfortable with all of the vocabulary). Use
the embedded Study Break questions as an opportunity to
pause and help confirm that you have identified and understood
the major ideas. If you don’t know the answer to a Study Break
question, this is a sign that you should go back and read more
carefully and/or seek additional help. Pay particular attention to
the Concept Fix feature as well. These brief sections identify
and clarify many misconceptions that biology students are
prone to experience as they are learning. As your notes develop,
notice any connections that arise to what you have already
learned in previous classes and other courses. Highlighting such
relationships will help you to retain your new knowledge.
As you read, use the complementary photos and illustrations to supplement and confirm your understanding. Notice
that graphs and anatomical drawings are annotated with interpretive explanations that lead you step by step through the
major points they convey.
Science is a progressive enterprise in which answers open
new questions for consideration. As you read a chapter, watch
for the underlying thread of the research process that gave rise
to the information you are learning. Notice the three types of
specially designed research figures providing more detailed
information about how biologists formulate specific hypotheses and test them by gathering and interpreting data. Experimental Research figures describe specific studies in which
researchers used both experimental and control treatments,
either in the laboratory or in the field, to test hypotheses or
Why It Matters will help
you see the relevance of the
material and allow you to
make some personal
connections to the concepts.
Study Break Questions
provide an opportunity to
pause and help confirm that
you have identified and
understood the major ideas.
Assigned Readings
The Summary Illustration
will give you a broad, visual
sense of the scope of the material.
• What do you recognize from
previous learning?
• What looks new?
• What looks especially
interesting?
The Chapter Roadmap will
show you how each of the
chapters’ topics are related to
other ideas within the chapter
and to the material in other
chapters.
L E T T E R TO S T U D E N T S
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answer research questions by manipulating the system they
studied. Observational Research figures describe specific
studies in which biologists have tested hypotheses by comparing systems under varying natural circumstances. Research
Method figures provide examples of important techniques,
such as light and electron microscopy, the polymerase chain
reaction, making a knockout mouse, DNA microarray analysis,
plant cell culture, producing monoclonal antibodies, radiometric dating, and cladistic analysis. Each Research Method
figure leads you through the purpose of the technique and protocol and describes how scientists interpret the data it
generates.
To complement the textbook material relating to research,
we encourage you to take any opportunity to participate in
hands-on laboratory or field investigations. Such first-hand
experiences can help you to see how the theoretical knowledge
in the book relates to your life and the aspects of biology that
interest you most.
As a final check of your learning, you might address selected
Self-Test Questions at the end of the chapter. These chapterreview questions are organized according to Bloom’s Taxonomy
into three sections: Recall/Understand, Apply/Analyze, and
Create/Evaluate. This structure allows you to review the material in a sequence that moves from the basic knowledge of factual material to more challenging and sophisticated applications
of that knowledge to novel situations. Although answers to the
xx
Self-Test Questions are found in an appendix at the back of the
book, looking at answers before generating your own can lead to
hindsight bias and misplaced confidence. Working through the
questions before consulting the answers will give you a more
accurate assessment of your understanding of the material
before you are faced with high-stakes exam questions.
In summary, we have applied our collective experience as
teachers, researchers, and writers to create text and complementary visuals that provide accessible explanations of fundamental concepts from an evolutionary perspective that binds
all the biological sciences. We hope that you are as captivated
by the biological world as we are and are drawn from one
chapter to another. But don’t stop there; use MindTap and other
resources to broaden your search for understanding and, most
importantly, observe and enjoy the diversity of life around you.
M. Brock Fenton
Denis Maxwell
Tom Haffie
Bill Milsom
Todd Nickle
Shona Ellis
Shelby Riskin
London, Toronto, Calgary, and Vancouver
January 2022
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New to This Edition
This section highlights the changes we made to enhance the
effectiveness of Biology: Exploring the Diversity of Life, Fifth
Canadian Edition. Every chapter has been updated to ensure
currency of information. We made organizational changes to
more closely link related topics and preferred teaching
sequences. Key chapters have been extensively revised to provide a full treatment of the subject matter that reflects new
developments in these specialized fields.
Organization
We begin the fifth Canadian edition with the question “What is
life?” Chapter 1: Defining Life and Its Origins starts with the recognition that the origin and definition of life are widely considered to be one of the great mysteries and challenges in science.
It explores how we define the characteristics of life, why scientists cannot agree on a universal definition of life, and how the
way a discipline defines life is intimately connected to the questions it explores. This opening chapter situates biology as a
method of inquiry that has at its core curiosity and a sense of awe.
This sense of wonderment is once again brought to the fore
in Unit 5: The Diversity of Life, which features a two-page spread
introducing students to the Tree of Life. The starburst tree presents students with a perspective on the truly astounding organismal diversity on the planet, the relative place of humans within
it, and the equally astounding amount of biological diversity that
remains unknown. This unit has been reorganized so that Bacteria and Archaea (Chapter 20) now precedes Protists (Chapter
21), followed by Fungi (Chapter 22), Plants (Chapter 23), Animals
(Chapter 24), and Viruses, Viroids, and Prions (Chapter 25).
Conservation of Biodiversity (Chapter 29) was moved from this
unit to the end of Unit 6: Ecology and Behaviour.
Plant Signals and Responses to the Environment (Chapter 34)
and Animal Behaviour and Responses to the Environment
(Chapter 44) have been moved to their respective units covering the systems and processes of plants and animals. And
finally, the fifth Canadian edition concludes with a new and
timely Chapter 45: Defences against Disease. Reintroduced into
the book by popular demand, this chapter covers innate and
adaptive immunity, vaccines, convalescent plasma and antibody therapies, malfunction and failures of the immune
system, and defence systems in other organisms.
Indigenous Ways of Knowing and Learning in the Why It Matters
sections. We have included specific examples from First Nations,
Inuit, and Métis communities, using the traditional names of
Indigenous Nations and the traditional languages of Indigenous
groups. We have attempted to cite research from Indigenous
researchers; research where Indigenous communities have partnered with the researchers; and research where Indigenous
knowledge has informed, enhanced, or changed our understanding of a particular phenomenon. To authentically represent
concepts and stories that we have been given permission to share,
we have committed to ensuring that any associated artwork is
created by an Indigenous artist.
Points of Interest in Each Chapter
At the beginning of each chapter are redesigned Chapter Roadmaps. Instead of providing a visual representation of how the
chapter is organized, we revisited this feature with an eye to providing a clear visual overview of how the major topic areas in the
chapter relate to one another. In addition to showing how concepts relate to each other within the chapter, the roadmaps also
show the connections between the topics in the chapter and the
other chapters in the book.
Chapter 1: Defining Life and Its Origins
●
●
●
●
Chapter 5: Cellular Respiration
●
The fifth Canadian edition constitutes a modest first step in our
contribution to the ongoing shift in perspectives of science from
Eurocentrism to a more open, decolonized, “multi-science”
perspective that acknowledges all Indigenous Peoples as having
scientific knowledge of the natural world through their own cultural lenses. Throughout the book, we have made connections to
NEW Why It Matters exploring the role of mitochondria and
cold tolerance in Inuit individuals
Chapter 6: Photosynthesis
●
Diversity in Ways of Knowing and Learning
NEW. While we know so much about life, science struggles
to arrive at a simple definition of what it means to be living.
We discuss this interesting question.
NEW. More robust discussion of the origins of metabolism
and how it may have evolved in close association with alkaline hydrothermal vents.
NEW discussion of how science has moved from a threedomain view of the tree of life to a two-domain view
NEW exploration of the latest evidence showing that eukaryotes are descended from a lineage of the Archaea
●
●
NEW section on the physical nature of light
NEW Concept Fix—Why are there three membranes in
chloroplasts and only two in mitochondria, both of which
evolved through endosymbiosis?
NEW section on electron transport
Chapter 7: Cell Cycles
●
NEW references to the fastest-growing prokaryotic cell,
Bibrino natiegens
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●
●
Expanded relevance to cancer through reference to Peto’s
Paradox as commentary on underlying genetics of low
cancer incidence in large mammals
NEW Summary Illustration
Chapter 8: Genetic Recombination
●
●
Reconstructed chapter to integrate sources of variability
with the description of respective stages of meiosis
NEW Summary Illustration
Chapter 9: The Chromosomal Basis
of Inheritance
●
●
NEW Why It Matters begins the process of decolonization
by acknowledging that people have applied their understanding of inheritance to purposefully increase desirable
characteristics among successive generations of plants and
animals for tens of thousands of years before Mendel
NEW Summary Illustration
Chapter 10: Genetic Linkage, Sex Linkage,
and Other Extensions to Basic Inheritance
Mechanisms
●
●
●
●
NEW reference to Indigenous clan system and ethical,
respectful efforts to address the lack of Indigenous sequences
in DNA databases
NEW discussion of the three-parent baby controversy
NEW connection to epigenetics and the possibility of a role
for epigenetics in multigenerational trauma
NEW Summary Illustration
Chapter 11: DNA Structure, Replication, and
Repair
●
●
Refined and clarified text descriptions of early experiments
NEW Summary Illustration
Chapter 12: Gene Structure, Expression, and
Mutation
●
NEW Summary Illustration
Chapter 13: Regulation of Gene Expression
●
●
●
Substantial update of the paradigm of the mechanism underlying diauxic growth with respect to the lac operon
NEW material on cancer incidence in Canada
NEW Summary Illustration
Chapter 14: DNA Technologies
Chapter 16: Evolution: The Development
of the Theory
●
Chapter 17: Microevolution: Changes within
Populations
●
●
●
●
xxii
NEW Why It Matters discussing how the Golden State Killer
was caught because a relative submitted their DNA to a
public database
NEW Why It Matters describing how Native Papuans and
Ernst Mayr identified a nearly identical number of bird
species using very different methods
Chapter 19: Systematics and Phylogenetics:
Revealing the Tree of Life
●
Revised Summary Illustration
Chapter 20: Bacteria and Archaea
●
●
●
NEW discussion around Pseudomonas aeruginosa as
common co-infecting pathogen in COVID-19 patients
Discussion of how tuberculosis is a leading cause of death
due to infectious disease throughout history and how Indigenous people have been disproportionately affected by this
disease
Revised Summary Illustration
Chapter 21: Protists
●
●
NEW Why It Matters about how the people of Haíl~zaqv,
Heiltsuk Nation, collect, process, and use seaweeds from
intertidal areas
NEW Summary Illustration
Chapter 22: Fungi
●
●
NEW material on the four main invasive fungal co-infections with COVID-19
NEW discussion of Ch’ãłtthi (willow tinder fungus), used by
the Denesuline (Chipewyan) people as tinder and
packaging
Chapter 23: Plants
●
●
Updated discussion of CRISPR
Chapter 15: Genomes
Clarified discussion around the four key aspects of
mutation
Selected figures reviewed and revised for clarity
Chapter 18: Speciation and Macroevolution
●
●
Thoroughly revised and reorganized, bringing the theory of
natural selection itself to the fore
●
●
●
Reorganized for flow and clarity
Updated and revised selected illustrations for clarity
NEW discussion of the story behind the name of Indian pipe
(Monotropa uniflora)
NEW discussion of sk’in (“horsetails” in the Haida language)
and how it was used
NEW discussion of the pitch from species of the pine family,
which has many traditional uses by Indigenous Peoples
Revised Summary Illustration
N E W TO T H I S E D I T I O N
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Chapter 24: Animals
●
●
●
●
Completely reorganized and streamlined to shift the
approach to understanding and recognizing patterns and
variations
Emphasis on key groups rather than a description of all
groups
More emphasis on concepts and less on details
NEW figures providing an overview of the group of animals
discussed in each section
Chapter 25: Viruses, Viroids, and Prions:
Infectious Biological Particles
●
●
●
NEW Why It Matters discussing the impact of smallpox on
Indigenous communities
Thoroughly revised and updated, including material on
SARS-CoV-2
NEW section on virotherapy
Chapter 26: Population Ecology
●
●
●
NEW Why It Matters discussing a collaboration between the
University of Guelph and the Chippewa of Nawash Unceded
First Nation identifying five general principles associated
with Nawash harvesting
Thoroughly revised, streamlined, and updated
NEW definitions and discussion of semelparity and
iteroparity
Chapter 28: Ecosystems
●
●
●
●
●
NEW Why It Matters about the impact of 19th-century colonial development along Lake Erie
NEW discussion of Three Sisters crop complementarity
Thoroughly revised, streamlined, and updated
Updated discussion of climate change and disruption of the
global carbon cycle
NEW Summary Illustration
Chapter 30: Organization of the Plant Body
●
●
NEW Why It Matters featuring a discussion of culturally
modified trees written by researcher and Heiltsuk archeologist Elroy White (Q̌íx̌ itasu) of central coast British Columbia
Revised Summary Illustration
Chapter 31: Transport in Plants
●
Figures revised and updated for clarity
Chapter 34: Plant Signals and Responses
to the Environment
●
●
●
Chapter 36: Animal Nutrition
●
●
●
NEW Why It Matters about the role of the salmon cycle and
plant growth, featuring original artwork by Indigenous artist
Chester Lawson of the Haíłzaqv (Heiltsuk) Territory, Central
Coast, British Columbia.
NEW discussion of Palliser’s Triangle in Alberta/Saskatchewan, a hunting ground for Cree, Sioux, and Blackfoot
NEW Why It Matters about dietary requirements in animals
and across cultures, and how there are no “essential foods,”
only essential nutrients
NEW material on the human gut biome
Chapter 37: Gas Exchange: The Respiratory
System
●
NEW Why It Matters featuring a discussion of the many
roles that breathing plays across different cultures
Chapter 38: Internal Transport: The Circulatory
System
●
●
●
NEW Why It Matters featuring the significance of the notion
of the beating heart across different cultures
NEW section—Heart Attacks and Strokes Arise from Poor
Blood Flow to the Heart Muscle and Brain
Revised Summary Illustration
Chapter 40: Control of Animal Processes:
Endocrine Control
●
Revised Summary Illustration
Chapter 41: Animal Reproduction and
Development
●
●
NEW Why It Matters featuring the reproductive process of
Pacific herring off the coast of British Columbia
Revised Summary Illustration
Chapter 44: Animal Behaviour and Responses
to the Environment
●
Chapter 33: Plant Nutrition
●
NEW Why It Matters about the observation of plant behaviour to predict the timing of other resources, such as the
soapberry harvest of Nlaka’pamux First Nation of Thompson
River, British Columbia, and the link between elderberry
blooms and halibut fishing among the First Nations of Nuuchah-nulth on Vancouver Island
NEW discussion of heliotropism
Revised Summary Illustration
●
NEW Why It Matters featuring a discussion of how Indigenous hunting societies around the globe have relied on
knowledge of the behaviours of their food species for
survival
Thoroughly revised and streamlined
NEW Chapter 45: Defences against Disease
●
●
NEW chapter
Why It Matters featuring a discussion of plagues, epidemics,
and pandemics, including COVID-19
N E W TO T H I S E D I T I O N
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Welcome to Biology:
Exploring the Diversity of Life, 5Ce
Biology: Exploring the Diversity of Life and MindTap engage students so they learn not only WHAT
scientists know, but HOW they know it and what they still need to learn.
◀ Each chapter begins with Why Does ___ Matter to Me?,
an engaging reading that explores a real-life application of
the chapter topic, providing students with context around
the relevance of the material they are learning.
▲ Learn It! The Media Library, with its dynamic animations
and videos, offers a different entry point into the content that
helps students process and understand concepts in a different
way.
▲ Study It! Exam Prep auto-graded questions have been
carefully curated to replicate the type and level of questions
that students will encounter in a testing scenario. Chapter
Flashcards help students remember key term in each chapter.
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◀ Apply It! Think and Engage Like a Scientist by taking
gradable short-answer quizzes:
•
•
•
Apply Evolutionary Thinking questions ask students to
interpret a relevant topic in relation to the principles of
evolutionary biology.
Design an Experiment challenges students’
understanding of the chapter and helps them deepen
their understanding of the scientific method as they
consider how to develop and test hypotheses about a
situation that relates to a main chapter topic.
Interpret the Data questions help students develop
analytical and quantitative skills by asking them to
interpret graphical or tabular results of experimental or
observational research experiments for which the
hypotheses and methods of analysis are presented.
Also available in MindTap for Biology are engaging and
informative videos that accompany The Purple Pages. From
matter to polypeptides, author Todd Nickle of Mount Royal
University (pictured) will walk students through these
foundational concepts, strengthening their understanding
and helping them build a strong base of knowledge and
understanding of biology.
Test students’ mastery of concepts
with Conceptual Learning
Activities that complement the
text and help them learn and
understand key concepts through
focused assignments, an engaging
variety of problem types,
exceptional text/art integration,
and immediate feedback.
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Active Learning
Visually stunning features are provided engage your students in the process of
learning because an engaged student is a successful student.
Chapter Roadmap
Plant Nutrition
33.1
From Chapter 30 to make
connections between root
structure and water/nutrient
absorption
Plant Nutritional Requirements
Plants can make all the macromolecules,
including their subunits. Plants supply
macromolecules to other trophic levels. Nitrogen
acquisition often limits plant growth. Symbiosis
and predation on animals are adaptations to help
plants thrive.
© Chester Lawson
To Chapter 6 for details about
photosynthesis and how some
plants are modified for hot and
dry environments
PT
33.2
Soil
To Chapter 27 make connections
between nutrients and organism
interactions
Plant health depends on soil for both
texture and dissolved nutrients. Humus
provides nutrition and also stores water, both of
which are absorbed by roots. Soil acidity and ion
content also affect availability of dissolved
nutrients to the plant.
Plant Nutrition
33.3
Root Adaptations for
Obtaining and Absorbing Nutrients
Microorganisms such as bacteria and
fungi contribute to nutrient cycling. Symbiotic
associations are important in making nutrients
from the soil more available to the plant. Root
adaptations encourage symbiotic interactions.
Xylem carries dissolved materials to the shoots
from the roots.
To Chapter 31 to consider how nutrients
are taken up and distributed in plants
To Chapter 22 to consider
how nutrients are taken up
and distributed in plants
To Chapter 28 to investigate
how nutrients are cycled
within an ecosystem
Spawning Salmon by Chester Lawson
To Chapter 34 to make
connections between
nutrients and auxin as
well as other plant
hormones
Why it matters. . . Coastal British Columbia is known for its rugged mountains, rivers,
and lush forests. The ocean is connected through the rivers to what have been termed the “salmon
forests.” Salmon has sustained the peoples of these lands for thousands of years; First Nations fisheries were run sustainably, ensuring the returning runs of coho, pink, sockeye, chinook, and chum.
Fishing technologies were designed so that only what was needed was taken. The migration runs
occur at certain times of the year, when enough salmon would be collected and processed to provide food all year round. Drying and smoking were important forms of preservation; more recently,
canning and freezing have become important. These salmon are on their migratory path to their
place of birth in rivers, streams, and lakes, where they spawn and then die.
What does this have to do with plant nutrition? Salmon are not only integral to the health and
nutrition of First Nations, they are crucial to the health of the ecosystems of the coast as well as
further inland as the fish venture up into the interior through the networks of waterways. Imagine
thousands of fish making their way up rivers, with bears, otters, eagles, and ravens depending on
their arrival. The salmon that make it to their spawning grounds lay their eggs, fertilize them, and
then die. Bears in particular drag the fish carcasses up into the forest. They are selective eaters and
often consume only particular portions of the fish, leaving the carcasses to provide food and nesting
sites (e.g., for blowflies), and for decomposers to recycle their nutrient-rich bodies (Figure 33.1). There
is a distinct fragrance that fills the air during these runs, the smell of decomposition, as you find
carcasses along the riverside, the riparian areas, and deep in the forest. The nutrients within the fish,
particularly nitrogen, are made available to other organisms. As we will see in this chapter, nitrogen
is a limiting nutrient in plants, and a number of researchers have followed its path through coastal
ecosystems. Nitrogen does not have a direct route into plants; microorganisms are instrumental in
breaking down the carcasses, and important intermediaries make the nitrogen available for uptake
by plants. Animals that consume the fish release nitrogen in their excrement and urine (urea), which
get broken down by soil enzymes and microbes. Plants absorb nitrogen in the form of nitrate and
ammonium, often facilitated by fungi through mycorrhizal associations or bacterial symbioses.
Within the plants, this nitrogen is incorporated into organic molecules such as proteins and nucleic
33
875
▲ Chapter Roadmaps The Chapter Roadmaps provide a visual overview of how the major topic areas in the chapter
relate to one another and show the connections between the topics in the chapter and other chapters in the book.
Why It Matters Why It Matters draws students in with an engaging vignette that is linked to the concepts discussed in
the chapter.
Concept Fix Concept Fix sections draw on the extensive
research literature dealing with misconceptions commonly
held by biology students. Strategically placed throughout
the text, these short segments help students identify—and
correct—a wide range of misunderstandings. ▼
▲ Study Break The Study Break features fall at the end of
each major section and encourage students to pause and
review what they have learned before going on to the next
topic within the chapter.
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◀ Experimental Research Experimental Research
Experimental Research
FIGURE 10.2
Evidence for Gene Linkage
Question: Do the purple-eye and vestigial-wing genes of Drosophila assort independently?
Experiment: Morgan crossed true-breeding, wild-type flies having red eyes and normal wings with purple-eyed, vestigial-winged flies. The F 1
dihybrids were all wild type in phenotype. Next, he crossed the F1 dihybrid flies with purple-eyed, vestigial-winged flies (this is a testcross) and
analyzed the phenotypes of the progeny.
1. P generation
Wild-type female
(red eyes, wild-type wings)
2. F1 generation
Double mutant male
(purple eyes, vestigial wings)
pr + pr + vg + vg +
pr pr vg vg
F1 dihybrid
(red eyes, wild-type wings)
F1 dihybrid
(red eyes, wild-type wings)
3. Testcross
All F1 flies were wildtype in phenotype and
were heterozygous for
both pairs of alleles:
pr+pr vg+vg.
pr + pr vg + vg
pr + pr vg + vg
F1 dihybrid
(red eyes, wild-type wings)
Double mutant male
(purple eyes, vestigial wings)
Morgan next performed
a testcross of F1 wild-type
phenotype females with
purple-eyed, vestigialwinged males; this is a
testcross.
pr + pr vg + vg
4. Progeny of testcross
Gamete from
male parent
The wild-type parent is
homozygous for the
wild-type allele of each
gene: pr+pr+ vg+vg+. The
purple-eyed,
vestigial-winged parent
is homozygous for the
recessive allele of each
gene: prpr vgvg.
figures describe specific studies in which research used both
experimental and control treatments—either in the
laboratory or in the field—to test hypotheses or answer
research questions by manipulating the system they
studied.
pr pr vg vg
Gametes from female parent
pr+ vg+
pr vg
pr+ vg
pr vg+
Wild type,
wild type
Purple,
vestigial
Red,
vestigial
Purple,
normal
Fusion of the one type
of sperm produced by
the male, and the four
types of eggs produced
by the female,
generates the progeny
of the testcross.
pr vg
pr + pr vg + vg
prpr vg vg
pr + pr vg vg
pr pr vg+ vg
Observed
1339
1195
151
154
Expected,
if assort
independently
Parental phenotypes
Recombinant phenotypes
~710
~710
~710
~710
=
2839 total progeny
(709.75 each) = 2839 total progeny
Results: 2534 of the testcross progeny flies were parental—wild type or purple, vestigial—while 305 of the progeny were recombinant—red,
vestigial or purple, wild type. If the genes assorted independently, the expectation is for a 1:1:1:1 ratio for testcross progeny: approximately 1420
of both parental and recombinant progeny.
Conclusion: The purple-eye and vestigial-wing genes do not assort independently. The simplest alternative is that the two genes are linked on the
same chromosome. The small number of flies with recombinant phenotypes is explained by crossing-over.
240
UNIT 2
Research Method Research Method figures provide
examples of important techniques, lead students through
the purpose of the technique and protocol, and describe
how scientists interpret the data generated. ▼
GENES
FIGURE 14.3
FIGURE 18.16
Research Method
Identifying a Recombinant Plasmid Containing a Gene of Interest
Observational Research
Chromosomal Similarities and Differences among Humans and the Great Apes
Purpose: To identify a recombinant plasmid containing a gene of
Protocol:
Inserted DNA fragment
with gene of interest (red)
Question: Does chromosome structure differ between humans and their closest relatives among the apes?
Hypothesis: Large-scale chromosome rearrangements contributed to the development of reproductive isolation between species within the
Resealed plasmid cloning vector
with no inserted DNA fragment
interest from a ligation reaction mixture containing a bacterial
cloning vector and a DNA fragment containing the gene of
interest, each digested with the same restriction enzyme
evolutionary lineage that includes humans and apes.
1. The ligation reaction produces recombinant plasmids (the only
products that might contain the gene of interest), nonrecombinant
plasmids, and joined pieces of genomic DNA (not shown).
Prediction: Chromosome structure differs markedly between humans and their close relatives among the great apes: chimpanzees, gorillas,
and orangutans.
Method: Jorge J. Yunis and Om Prakash of the University of Minnesota Medical School used Giemsa stain to visualize the banding patterns on
metaphase chromosome preparations from humans, chimpanzees, gorillas, and orangutans. They identified about 1000 bands that are
present in humans and in the 3 ape species. By matching the banding patterns on the chromosomes, the researchers verified that they were
comparing the same segments of the genomes in the four species. They then searched for similarities and differences in the structure of the
chromosomes.
Recombinant plasmid
Nonrecombinant plasmid
Results: Analysis of human chromosome 2 reveals that it was produced by the fusion of two smaller chromosomes that are still present in the
other three species. Although the position of the centromere in human chromosome 2 matches that of the centromere in one of the
chimpanzee chromosomes, in gorillas and orangutans it falls within an inverted segment of the chromosome.
Human
Bacteria transformed with plasmids
Centromere position is similar
in humans and chimpanzees
Chimpanzee
Selection:
Bacteria transformed with plasmids
grow on medium containing ampicillin
because of ampR gene on plasmid.
Untransformed bacteria
or bacteria transformed
with gene fragments
cannot grow on medium
containing ampicillin.
Matching bands
Screening:
Gorilla
Orangutan
Compared to the chromosomes of humans and chimpanzees,
the region that includes the centromere is inverted (its position
is reversed) in both gorillas and orangutans.
Blue colony contains bacteria
with a nonrecombinant
plasmid; that is, the lacZ +
gene is intact.
White colony contains bacteria
with a recombinant plasmid, that is,
the vector with an inserted DNA fragment,
in this case the gene of interest.
Conclusion: Differences in chromosome structure between humans and both gorillas and orangutans are more pronounced than they are
Bacteria not transformed with
a plasmid or transformed
with gene fragments
3. Spread the bacterial cells on a plate of growth medium
containing ampicillin and X-gal, and incubate the plate
until colonies appear.
Plate of growth
medium containing
ampicillin and X-gal
between humans and chimpanzees. Structural differences in the chromosomes of these four species may contribute to their reproductive
isolation.
Source: Based on J. J. Yunis and O. Prakash. 1982. The origin of man: A chromosomal pictorial legacy. Science 215:1525–1530.
▲ Observational
Research STUDY
Observational
Research
chromosome rearrangement becomes established within a
BREAK QUESTIONS
population, that population will diverge more rapidly from
figures
describe
specific
studies
in
which
biologists
have
populations lacking the rearrangement. The genetic divergence eventually causes reproductive isolation.
tested
hypotheses by comparing systems under varying
natural circumstances.
1. How can natural selection promote reproductive isolation in
allopatric populations?
2. How does polyploidy promote speciation in plants?
CHAPTER 18
S P E C i AT i o n A n d M A C R o E v o lu T i o n
2. Transform ampicillin-sensitive, lacZ–
E. coli (which cannot make
β-galactosidase) with a sample of the
ligation reaction. In this step, some
bacteria will take up DNA, whereas
others will not.
KEY
Restriction
site
lacZ+ gene
ampR
gene
Origin of
replication (ori)
Plasmid
cloning
vector
Interpreting the Results: All the colonies on the plate contain plasmids because the bacteria that form the colonies are resistant to the ampicillin
present in the growth medium. Blue–white screening distinguishes bacterial colonies with nonrecombinant plasmids from those with
recombinant plasmids. Bacteria making up blue colonies contain nonrecombinant plasmids. These plasmids have intact lacZ 1 genes and produce
β-galactosidase, which changes X-gal to a blue product. Bacteria that form the white colonies contain recombinant plasmids. Each recombinant
plasmid has a DNA fragment (in this example, the gene of interest) inserted into the lacZ1 gene, so β-galactosidase cannot be produced. As a
result, bacteria with recombinant plasmids cannot convert X-gal to the blue product and the colonies are white. Culturing a white colony produces
large quantities of the recombinant plasmid that can be isolated and purified for analysis and/or manipulation of the gene 5 “gene of interest.”
465
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Summary Illustrations Vivid, engaging, and carefully developed Summary Illustrations appear at the end of each chapter
and help students visualize the main concepts covered in the chapter. ▼
Summary Illustration
Acetyl CoA
C C – CoA
Citric Acid Cycle
CoA
Six-carbon molecule formed
from acetyl CoA + oxaloacetate
Cellular respiration is a collection of reactions that converts the chemical
energy present in carbohydrates, fats, and proteins into an energy currency,
ATP, that is readily used by the cell. The phases of cellular respiration
are (i) glycolysis, (ii) pyruvate oxidation and the citric acid cycle, and
(iii) oxidative phosphorylation. The overall process is represented by the
chemical equation for the oxidation of glucose.
Four-carbon acceptor molecule
(regenerated in each cycle)
C C C C Oxaloacetate
C C C C C C Citrate
NAD+
NADH + CO2
NADH
C C C C C
NAD+
NAD+
Cellular respiration is a redox process.
• The overall change in free energy (ΔG) is
negative.
C6H12O6 + 6O2
Reduced electron carrier
similar to NADH
Low [O2]
FAD
GTP
Second carbon
lost as CO2
i
Energy-carrying molecule
equivalent to ATP
Pyruvate is transported into the mitochondrial matrix and converted to acetyl-CoA,
which enters the citric acid cycle and is oxidized. Notice the products formed.
Glycolysis
Pyruvate
GDP, P
FADH2
• The goal is to couple the energy released
to the synthesis of ATP!
Glucose
Glycolysis occurs in the cytosol and splits
glucose into pyruvate, which yields ATP and
NADH. The fate of pyruvate depends on
the availability of oxygen.
NADH + CO2
C C C C
• Energy released during the formation
of the bonds in CO2 and H2O is greater
than the energy required to break the
bonds in glucose and O2.
6CO2 + 6H2O
One carbon
lost as CO2
Oxidative Phosphorylation
Lactate/ethanol
Cytosol
Fermentation
Outer
mitochondrial
membrane
High [O2]
While prokaryotic cells lack mitochondria,
many bacteria and archaea possess a
complete respiratory pathway that is
similar to eukaryotes.
Citric Acid Cycle
H+
+
H+ H
H+
H+
Intermembrane
compartment
H+
H+
H+
H+
H+
H+
H+
cyt c
e–
Inner
mitochondrial
membrane
NADH ,
FADH2
Complex
I
UQ
e–
Oxidative
Phosphorylation
Complex
e– II
H+
ATP
NADH
H+ NAD+
FADH2
H+
H+
H+
H+
ATP
synthase
FAD
e–
Complex
IV
e–
Complex
III
UQ
H+
H+
H+
e–
H+
2e– + 2 H+ + 1/2 O2
H2O
Mitochondrial
matrix
ADP + P
Electron transport
i
H+
ATP
Chemiosmosis
Electrons from the oxidation of NADH and FADH2 produced by glycolysis and the
citric acid cycle are passed along an electron transport chain. Electron transport
and chemiosmotic synthesis of ATP are coupled by a proton gradient.
130
131
Self-Test Questions These chapter-review questions are organized according to Bloom’s Taxonomy into three sections:
Recall/Understand, Apply/Analyze, and Create/Evaluate. This structure allows students to review the material in a sequence
that moves from the basic knowledge of factual material to more challenging and sophisticated applications of that
knowledge to novel situations. Answers to the Self-Test Questions are found in the appendix at the back of the book. ▼
self - test questions
Recall/Understand
1. Which of these factors is found in organic molecules that are
considered good fuels?
a. many C—H bonds
b. many C=C double bonds
c. an abundance of oxygen
d. a high molecular weight
2. What is one of the places in a cell where cellular respiration
occurs?
a. in plant mitochondria, but not in animal mitochondria
b. in plant chloroplasts
c. in the mitochondria of both animals and plants
d. in animal mitochondria, but not in plant mitochondria
3. Which of these processes occurs during glycolysis?
a. oxidation of pyruvate
b. reduction of glucose
c. oxidative phosphorylation
d. substrate-level phosphorylation
4. Which of these processes feeds glycolysis products into the citric
acid cycle?
a. chemiosmosis
b. formation of G3P
c. reduction of NAD+
d. pyruvate oxidation
Apply/Analyze
5. The breakdown of fats releases fatty acids. In what form do the
carbon molecules enter the respiratory pathway?
a. as NADH
b. as acetyl-CoA
c. a glucose
d. as pyruvate
6. You are reading this text while breathing in oxygen and breathing
out carbon dioxide. Which two processes are the sources of the
carbon dioxide?
a. glycolysis and pyruvate oxidation
b. glycolysis and oxidative phosphorylation
c. pyruvate oxidation and the citric acid cycle
d. the citric acid cycle and oxidative phosphorylation
7. Under conditions of low oxygen, what key role is played by fermentation in overall metabolism?
a. It regenerates the NAD+ required for glycolysis.
b. It synthesizes additional NADH for the citric acid cycle.
c. It allows for pyruvate to be oxidized in mitochondria.
d. By activating oxidative phosphorylation, it allows for the
synthesis of extra ATP.
8. Suppose you are a doctor and your patient complains of feeling
hot all the time, even on the coldest winter days. The young
man perspires constantly and his skin is always flushed. He also
eats a lot but is rather thin. You perform some laboratory tests,
and find that the patient consumes lots of oxygen in his metabolic pathways. What would you suspect this patient suffers
from and why?
Create/Evaluate
9. In cellular respiration, which of the following does the term uncoupled refer to, specifically?
a. The two parts of glycolysis are running independently of
each other.
b. Respiratory electron transport is operating, but chemiosmosis is inhibited.
c. Respiratory electron transport is operating, but proton
pumping is inhibited.
d. Oxidative phosphorylation is occurring, but the protonmotive force remains high.
10. Phosphofructokinase (PFK) is regulated by a number of metabolites. In addition to those mentioned in the text, which one of the
following would also make sense?
a. Pyruvate could function as an activator of PFK.
b. Glucose could function as an inhibitor of PFK.
c. ADP could function as an activator of PFK.
d. Acetyl-CoA could act as an activator of PFK.
11. Which of these statements best describes the “paradox of aerobic
life”?
a. Humans are completely protected from the toxic effects of
oxygen.
b. Hydrogen peroxide is formed when a single electron is
donated to O2.
c. Cytochrome oxidase is a major source of reactive oxygen
species.
d. Strict anaerobes often lack the enzyme(s) superoxide dismutase and/or catalase.
12. Compare direct burning of glucose and cellular respiration with
reference to their progression.
13. Distinguish between reduction and oxidation during redox
reactions.
14. Explain what happens with hydrogen and its bonding electrons
during cellular respiration.
15. Cyanide is a strong toxin that reacts with the final protein in the
electron transport chain (ETC). Explain why it can kill a human
within a few minutes.
Appendix A: Answers to Self-Test
Questions
Chapter 1
1. c 2. b 3. a 4. a 5. d 6. d 7. b 8. c 9. d
10. b 11. b 12. d
13. To determine relative dates, scientists
order fossils found in different strata
in sequence from the lowest (oldest)
to the highest (newest) strata. This
sequencing reveals their relative ages.
By using a technique called radiometric dating, scientists can estimate
the age of a rock by noting how much
of an unstable “parent” isotope has
decayed to another form. By measuring the relative amounts of the
parent radioisotope and its breakdown products, and comparing this
ratio with the isotope’s half-life—the
time it takes for half a given amount of
radioisotope to decay—researchers
can estimate the absolute age of the
rock.
14. LUCA stands for Last Universal
Common Ancestor. We know it existed
because of the core similarities that all
forms of life on Earth today possess.
The likeliest explanation for these
common traits is all organisms today
are descended from a single ancestor
that also possessed all those traits.
15. Bacteria and Archaea have circular
chromosomes; eukaryotes have linear
chromosomes. The location of DNA
in prokaryotes is in the nucleoid
region, and in eukaryotes it is in the
nucleus. Chromosomes segregate by
binary fission in prokaryotes, and by
mitosis/meiosis in eukaryotes. Introns
are rarely present in bacteria, but are
common in archaea and eukaryotes.
Chapter 2
1. d 2. c 3. c 4. a 5. a 6. b 7. b 8. a 9. d
10. a 11. d 12. d 13. c
14. ribosomes, rough ER, transport vesicle, Golgi complex, secretory vesicle,
plasma membrane
15. Anchoring junctions function to reinforce cell-to-cell connections made by
adhesion molecules. Tight junctions
seal the spaces between cells. Gap junctions create direct channels for communicating between adjacent cells.
Chapter 3
1. c 2. d 3. b 4. a 5. b 6. c 7. c 8. d 9. c
10. d
11. As they dissolve, the sugar molecules
raise their entropy. However, the crystals re-form because the water
decreases in its order, changing from
compact liquid to disordered vapour.
12. Although sugar breakdown is an exergonic process, the activation energy
required for the reaction to proceed is
high, which makes sugar unreactive.
The addition of heat or an enzyme can
increase the rate of breakdown.
13. Any substance in an ordered state
(minimum entropy) will contain molecules with maximum free energy. On
the contrary, any substance in a disordered state (maximum entropy) will
contain molecules with minimum
free energy. The relationship is
reversed.
14. In an exergonic reaction, reactants
contain more free energy than the
products; energy is released and the
reaction is spontaneous. In an endergonic reaction, reactants contain less
free energy than the products; energy
is required and the reaction is not
spontaneous.
15. At any time in a cell, there must be
exergonic reactions happening to provide enough energy for endergonic
reactions. In addition, the energy
released by exergonic reactions must
be higher than the energy needed for
endergonic reactions because some
energy is always transferred to heat
(second law of thermodynamics).
Chapter 4
1. a 2. c 3. b 4. c
5. Some proteins perform transport;
others have enzymatic activities; some
are a part of signal transduction process; and others are involved in attachment and/or recognition.
6. b 7. c 8. b 9. c 10. c 11. b 12. a 13. d
14. Passive transport occurs down the
concentration gradient of the solute,
and active transport occurs against
the gradient of the transported solute.
Active transport therefore requires a
protein and energy to perform.
15. They are both a form of passive transport, but facilitated diffusion utilizes
proteins to speed up the transport of
solute across the membrane.
Chapter 5
1. a 2. c 3. d 4. d 5. b 6. c 7. a
8. This patient might have defective
mitochondria in his cells. This condition is common in a number of diseases. The reason why it was suspected
is that, based on his symptoms, probably little ATP is synthesized, in spite
of high oxygen consumption, since his
cells dissipated a lot of heat (the
patient was hot all the time).
9. b 10. c 11. d
12. Direct burning of glucose is an uncontrolled process; cellular respiration
occurs in a series of steps and is therefore a form of controlled combustion.
13. Reduction is the acceptance of electrons during a redox reaction. Oxidation is the loss of electrons during a
redox reaction.
14. Hydrogen and its electrons move from
sugar to oxygen, forming water.
15. The process of oxidative phosphorylation produces the large number of
ATP molecules needed for the endergonic reactions in the cell that we are
so dependent on. One of the major
A-1
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SYSTEMS AND PROCESSES—THE CELL
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◀ The Chemical and Physical Foundations of
Biology (The Purple Pages) While many textbooks use
the first few chapters to introduce and/or review, we believe
that the first chapters should convey the excitement and
interest of biology itself. We therefore placed important
background information about biology and chemistry in a
reference section entitled The Chemical and Physical
Foundations of Biology in the centre of the book. With their
purple borders, these pages are distinct and easy to find
and have become affectionately known as The Purple Pages.
References to material covered in The Purple Pages are set in
purple in the Chapter Roadmaps and in the Index.
The Green Pages—Unit 5: The Diversity of Life opens with the Tree of Life, emphasizing the richness and tremendous
variability among living organisms explored in the chapters of The Green Pages. With their green borders, these pages identify
chapters that introduce and explore the diversity of life. ▼
Staphylococcus
Actinobacteria Armatimonadetes
Zixibacteria
Atribacteria
Cloacimonetes
Aqui cae
Chloro exi
Fibrobacteres
Calescamantes
Gemmatimonadetes
Caldiserica
WOR-3
Dictyoglomi
TA06
Thermotogae
Poribacteria
Deinococcus-Therm.
Latescibacteria
Synergistetes
BRC1
Fusobacteria
Marinimicrobia
Bacteroidetes Ignavibacteria
Caldithrix
Chlorobi
UNIT 5 THE DIVERSITY OF LIFE
(Tenericutes)
Bacteria
Firmicutes
Nomurabacteria
Kaiserbacteria
Adlerbacteria
Campbellbacteria
Cyanobacteria
Cyanobacteria
Giovannonibacteria
Wolfebacteria
Jorgensenbacteria
Melainabacteria
RBX1
WOR1
Azambacteria
PVC
superphylum
Planctomycetes
Chlamydiae,
Lentisphaerae,
Verrucomicrobia
Parcubacteria
Yanofskybacteria
Moranbacteria
Elusimicrobia
Magasanikbacteria
Uhrbacteria
Falkowbacteria
Omnitrophica
Candidate
Phyla Radiation
SM2F11
Aminicentantes Rokubacteria NC10
Acidobacteria
Tectomicrobia, Modulibacteria
Nitrospinae
Nitrospirae
Dadabacteria
Deltaprotebacteria
(Thermodesulfobacteria)
Chrysiogenetes
Deferribacteres
Hydrogenedentes NKB19
Spirochaetes
Peregrinibacteria
Gracilibacteria BD1-5, GN02
Absconditabacteria SR1
Saccharibacteria
Berkelbacteria
Woesebacteria
Shapirobacteria
Amesbacteria
Collierbacteria
Pacebacteria
Beckwithbacteria
Roizmanbacteria
Dojkabacteria WS6
Gottesmanbacteria
CPR1
Levybacteria
CPR3
Daviesbacteria Microgenomates
Katanobacteria Curtissbacteria
WWE3
Wirthbacteria
TM6
Epsilonproteobacteria
Alphaproteobacteria
Zetaproteo.
Acidithiobacillia
Betaproteobacteria
0.4
Major lineages with isolated representative - italics
Major lineage lacking isolated representative -
Gammaproteobacteria
E. coli
Salmonella
Micrarchaeota
Diapherotrites
Nanohaloarchaeota
Aenigmarchaeota
Parvarchaeota
0.4
Eukaryotes
Loki.
Thor.
Tree of Life
Researchers at the University of California, Berkeley, recently generated a Tree of Life
(opposite) comprising 3083 species, representing the major lineages of life on Earth.
The tree was constructed by comparing the DNA sequences of genes that code for specific ribosomal proteins. Organisms with fewer sequence differences were grouped more
closely together than species where the sequences were more dissimilar.
This tree is called a starburst tree. The distant past is at the centre and the outer edge
represents today. This type of representation is called an un-rooted tree because, in the
centre, you will notice there is no clear starting point. The research that produced the
tree was not designed to provide clarity about the origin of life or how early lineages
developed—questions related to the distant past are met with tremendous uncertainty.
Instead, the research team was focused on looking at the relationships among the diversity of life that exists today. And this is the focus of the chapters that make up Unit 5.
Of the 3083 DNA sequences used to build the tree, over 1000 represent different
microbial species that scientists have never actually studied in a laboratory! Their DNA
was discovered in various environmental samples (e.g., soil, water) and is represented
on the tree by red dots. Several research groups are developing methods to try and isolate and grow these microbes in the laboratory, a critical step to linking an actual
organism to the DNA sequences isolated from the environment. This includes members
of a specific group of archaeans called Asgard, which is represented on this tree by Loki.
As discussed in Chapter 1, evidence indicates that the Asgard are the closest prokaryotic relatives of eukaryotes.
You will notice that some branches of the tree are longer than others. Branch length
is related to the amount of evolutionary change. Along longer branches, more sequence
change has occurred than along shorter branches. For example, the branch leading to
eukaryotes is particularly long, meaning there are many genetic differences between the
organisms in that group compared to other organisms on the tree. To figure out exactly
how much genetic change has occurred you need to use the scale bar. The 0.4 on the
scale means that, for that length on any branch of the tree, there have been 0.4 changes
at each nucleotide position in the RNA genes used to produce the tree.
Korarch.
Crenarch.
Bathyarc.
Pacearchaeota
YNPFFA
Nanoarchaeota
Aigarch.
Opisthokonta
Woesearchaeota
Altiarchaeales Halobacteria
Z7ME43
Methanopyri
TACK
Methanococci
Excavata
Hadesarchaea
Animals
Thaumarchaeota Archaeplastida
Thermococci
Methanobacteria
and
Thermoplasmata
Chromalveolata
fungi
Archaeoglobi
Methanomicrobia
Amoebozoa
DPANN
Archaea
Plants, red and
green algae
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Student and Instructor Resources
Student Resources
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Modern students require modern solutions. MindTap is a flexible all-in-one teaching and learning platform that includes the
full ebook, a customizable learning path, and various coursespecific activities that drive student engagement and critical
thinking.
Download the Cengage Mobile App
Get access to a full, interactive ebook, readable online or off;
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TurningPoint®
Another valuable resource for instructors is TurningPoint® classroom response software customized for Biology: Exploring the
Diversity of Life, Fifth Canadian Edition. Now instructors can
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instructors true PowerPoint integration. With JoinIn, instructors are no longer tied to their computers. Instructors can walk
about the classroom as they lecture, showing slides and collecting and displaying responses with ease. There is simply no
easier or more effective way to turn a lecture hall into a personal, fully interactive experience for students. If an instructor
can use PowerPoint, they can use JoinIn on TurningPoint! It
contains poll slides and pre- and post-test slides for each chapter
in the text.
Image Library
Instructor Resources
This resource consists of digital copies of figures, tables, and
photographs used in the book. Instructors may use these JPEGs
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The Instructor Guide is organized according to the textbook
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stumbling blocks student face and how to address them.
PowerPoint
Microsoft PowerPoint® lectures have an average of 80 slides per
chapter, many featuring key figures, tables, and photographs
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selected illustrations with labels from the book that have been
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MindTap
MindTap is the digital learning solution that powers students from
memorization to mastery. It gives instructors complete control of
their course—to provide engaging content, challenge every individual, and build student confidence. Instructors can customize
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Acknowledgments
We would like to begin by expressing our gratitude for the contribution of Jonathan Ferrier. Jonathan has been an important
member of this team from the very beginning, and his passion,
insight, and guidance have informed and grounded our ongoing
journey to a more open, “multi-science” perspective that
acknowledges all Indigenous Peoples as having scientific knowledge of the natural world that enriches more Eurocentric views.
We are very grateful for the quiet wisdom of Jean Becker, the
patient guidance and expertise of Jeff Baker, and the warmth and
insight of Erin Hodson. The three of you have been a source of
inspiration, guidance, and encouragement.
With great appreciation we acknowledge the contributions
of Chester Lawson and Elroy White of the Haíłzaqv (Heiltsuk)
Territory, Central Coast, British Columbia. Chester (Q'vúmkviá)
is Yím'ás (Haíɫzaqv hereditary chief). He is a community artist
and retired teacher. Chester has been creating art for over
70 years in several traditional and western art forms. Elroy
(Q'íxitasu) is Yím'ás, a potlatch historian, and an archaeologist
(Central Coast Archeology). We are grateful for the cultural
knowledge he generously shared about seaweed harvest and
processing and his work on assessing culturally modified trees
(CMTs). As an archeologist, Elroy approaches his research in a
way that combines academia and oral history; he calls this
approach Mnuxvit (to unite/become one).
We are deeply appreciative of the willingness of Elders Dan
Smoke and Mary Lou Smoke, Cliff Summers, John Brown, and
others to facilitate the Pipe Ceremony expressing our collective
desire for a positive and productive impact of this project through
strengthened relationships and respectful collaborations.
We are also grateful to the members of the fifth Canadian
edition Editorial Advisory Board and Student Advisory Board,
who provided us with valuable feedback and alternative perspectives (special acknowledgments to these individuals are
listed below).
We also thank Richard Walker at the University of Calgary
and Ken Davey at York University, who began this journey with
us but were unable to continue. We are very grateful to Heather
Addy of the University of Calgary for her significant contributions to the first three editions.
The authors are all indebted to Ivona Mladenovic of Simon
Fraser University for her excellent work on the Self-Test Questions
and to Johnston Miller, whose extensive background research
anchored our Concept Fix feature in the education literature.
We are profoundly grateful to Toni Chahley, Content
Development Manager, who was an insightful and reliably
cheerful constant on this project. We appreciate the warm professionalism of Carmen Yu, Portfolio Manager, and Imoinda
Romain, Senior Content Production Manager. We thank
Christine Myaskovsky, Senior Intellectual Property Analyst,
and Betsy Hathaway, Senior Intellectual Property Project Manager, for their hard work with the numerous visuals in the book
and Frances Robinson for her careful and thoughtful copyediting. Finally, we thank Scott Brayne, Marketing Manager,
for making us look good.
Paul Fam was a warm friend and a truly fearless leader
through the previous four editions of this text. The direction
and emphasis of this fifth Canadian edition was sparked by his
energy and enthusiasm and carries his vision forward.
It is never easy to be the family of an academic scientist.
We are especially grateful to our families for their sustained
support over the course of our careers, particularly during
those times when our attentions were fully captivated by bacteria, algae, fungi, parasites, snakes, geese, or bats. Saying “yes”
to a textbook project means saying “no” to a variety of other
pursuits. We appreciate the patience and understanding of
those closest to us that enabled the temporary reallocation of
considerable time from other endeavours and relationships.
Many of our colleagues have contributed to our development as teachers and scholars by acting as mentors, collaborators, and, on occasion, “worthy opponents.” Like all teachers,
we owe particular gratitude to our students. They have gathered with us around the discipline of biology, sharing their
potent blend of enthusiasm and curiosity, and leaving us energized and optimistic for the future.
Indigenous Advisory Board
Jonathan Ferrier, Assistant Professor, Department of Biology,
Dalhousie University
Jeff Baker, Assistant Professor and Chair in Indigenous
Education, University of Saskatchewan
Jean Becker, Associate Vice-President, Indigenous Relations,
University of Waterloo
Erin Hodson, Educational Developer, Wilfrid Laurier University
Editorial and Student Advisory Boards
We were very fortunate to have the assistance of some extraordinary students and instructors of biology across Canada who
provided us with feedback that helped shape this textbook into
what you see before you. As such, we would like to say a very
special thank you to the following people:
Editorial Advisory Board
Dora Cavallo-Medved, University of Windsor
Emma Despland, Concordia University
Heidi Engelhardt, University of Waterloo
Mark Fitzpatrick, University of Toronto
William Huddleston, University of Calgary
Sobia Iqbal, Wilfrid Laurier University
Amy Jeon, Kwantlen Polytechnic University
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Ivona Mladenovic, Simon Fraser University
Ken Otter, University of Northern British Columbia
Melissa Perrault, University of Guelph
Alexandra Pettit, University of Ottawa
Roy Rea, University of Northern British Columbia
Ross Shaw, MacEwan University
Student Advisory Boards
University of Calgary
Brooklyn Mattila
Korbin Nunez
Gurleen Randhawa
Yvaine Stelmack
Rayyan Zuberi
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Catherine Andary
Deepshikha
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Muhammad Hussain Jan
Helen Jiang
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Sofia Varon
Jonathan Wei
Michelle Yu
ACKNOWLEDGMENTS
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BIOLOGY OF THE CELL
Volvox is a genus of green algae. As a photosynthetic eukaryote, Volvox is a simple multicellular
organism that exists as spheres of two distinct cell types. Small non-reproductive cells surround
an interior that contains six to eight much larger reproductive cells.
VOLUME 1
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What is life? We can make a list of the characteristics of living things, but why is it difficult to
simply define life? In the introductory chapter of this opening volume, we tackle this question
before exploring hypotheses around how life evolved some 4 billion years ago. Today, Earth is
teaming with life; some estimates peg the total number of species at over 1 billion (with most yet
to be described!). Yet, what this volume of the textbook should covey to you is that underlying that
diversity is a remarkable level of similarity. From monkeys to mycoplasma to monocots, everything that is alive on Earth employs a variation on that remarkable innovation: the cell. No matter
whether that cell is communicating with other cells in the brain of a fruit fly, or capturing sunlight in a spruce needle, or driving the muscles of a sprinting cheetah, or thriving in the mineralrich water of deep-sea vents; no matter what their role or activity, all cells share a remarkably long
list of common features. Volume 1 explores these common features in detail.
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The invention of the microscope allowed scientists to
finally understand how living organisms were built from cells,
which to early scientists were astonishingly small. Further work
clearly delineated two major divisions in cell types: those
without a nucleus (prokaryotic) and those with a nucleus
(eukaryotic). And within both these groups there are clear subdivisions: for example, plants, fungi, and animal cells, in
eukaryotes.
The chapters of Unit 1 talk a lot about energy because
without it living cells would die. Like the non-living world, all
forms of life abide by the foundational laws of thermodynamics
and need to bring in energy and matter from the environment
to maintain their highly ordered state. In part, energy is
required to build complex things (e.g., proteins) out of simpler
things (e.g., amino acids). In addition to energy, the evolution
of life is tied to the development of a remarkable group of proteins called enzymes, which when they get tied to a biochemical
reaction can increase its rate by 1010 times!
Another remarkable feature of cells that we dedicate a
chapter to in Unit 1 is membranes. These self-forming lipid
bilayers act as the gatekeepers of the cell: they allow certain
things in but keep other things out. How they do this is by
acting in concert with membrane-specific proteins that shuttle
molecules from one side to another. Membrane proteins also
play a remarkable role in transducing signals from outside the
cells and compartments to the inside. As we will see, the transduction of signals associated with hormones, for example, can
profoundly affect cell function.
What you may not realize is that virtually all the energy
used by living systems comes ultimately from sunlight being
harvested and converted into a useable chemical form through
photosynthesis. This process evolved perhaps as early as 3.5
billion years ago and used photons of light energy to extract
electrons from water, releasing oxygen as a by-product. The rise
in oxygen in an atmosphere that previously had none led to an
explosion of life as the mechanism of cellular respiration
evolved that could use that oxygen and enabled cells to produce
huge amounts of energy.
The chapters of Units 2 and 3 are dedicated to molecular
biology and genetics, the central player being the gene. All cells
possess genes that are coded by the molecule DNA that,
2
V O LU M E 1
through the process of transcription, get copied into RNA. All
cells contain ribosomes where some kinds of RNAs get
translated into proteins, the fundamental structural, functional, and regulatory molecule of the cell.
Genes are stretches of DNA sequence in an organism that
collectively comprise a kind of library of information about
how a cell functions. Recent advances in technology have made
it relatively easy to determine the entire DNA sequence of an
organism, including individual humans. As a result, modern
biology is awash in the As, Ts, Gs, and Cs of DNA sequences
revealed by thousands of sequencing projects. New insights
into evolutionary history as well as gene structure and function are arising from bioinformatic analysis of such extensive
data sets.
The elegant double-strandedness of DNA, whereby two
long strands of nucleotides are held together by hydrogen bonds
formed between complementary base pairs, affords a straightforward mechanism for replication that was recognized early
on by Watson and Crick. Although conceptually simple, the
mechanism for unwinding the DNA double helix and polymerizing new complementary bases is rather complicated and
managed by a suite of interacting enzymes. Again, we see that
all DNA on the planet is replicated using variations on one
underlying strategy.
DNA genes provide the cell with needed RNA by transcription. One remarkable feature of all protein-coding genes is
that, with minor exceptions, the information they carry is
specified by a universal code. That is, a gene from one organism
can be “understood” by any other organism, even if only distantly related: a gene from a spider can be expressed by a goat;
a gene from a jellyfish can be expressed in a flower. The field of
genetic engineering is devoted to developing the tools and
applications of this technology for moving genes from one
organism to another.
In a story that is about to come full circle, synthetic biologists have extensively customized naturally occurring cells and
have made important advances toward their ultimate goal of
creating novel life forms artificially in the lab. As students of
biology in the early 21st century, you can well expect to witness
a momentous event in Earth’s history, the creation of one life
form by another.
B I O LO G Y O F T H E C E L L
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Chapter Roadmap
Defining Life and Its Origins
What is life, and what do we know about how it may have begun about 4 billion years ago?
1.1
1.2
What Is Life?
The Chemical Origins of Life
Biology is the study of life, but a
simple definition of life is not easy to
come up with.
The conditions on early
Earth allowed for the synthesis
of key molecules essential for life.
The Purple Pages provides
an overview of the key
molecules of life.
1.3
The Evolution of Information
Flow: DNA, RNA, Protein
RNA was likely the first of these three molecules to
evolve. It could carry information and
act as a catalyst.
1.4
The Development of Metabolism
and the First Cells
Life may have evolved in alkaline hydrothermal vents,
an environment with a constant source of geothermal
energy and mineral catalysts.
The chapters of Unit 3 introduce
major concepts related to DNA
and gene expression.
Chapter 4 provides more
details on energy
and metabolism.
1.5
The Tree of Life
Recent research indicates that there are two
primary domains of life: Bacteria and Archaea.
Eukaryotes evolved from a lineage of Archaea.
In Chapter 19, we discuss the tree
of life and the discipline of
phylogenetics in more detail.
1.6
Eukaryotes and the
Rise of Multicellularity
1.7
The Fossil Record
Much of our understanding of the
history of life comes from the fossil record.
However, the fossil record has a lot
of gaps and does not provide a
record of the earliest forms of life.
Eukaryotic cells have structural and
functional complexity not found in prokaryotic
cells. In addition to the nucleus, this
includes mitochondria and chloroplasts
that are descended from bacteria.
In Chapter 2, we
provide an overview
of both prokaryotic and
eukaryotic cells.
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Perseverance landed on Mars on February 18, 2021, to search for signs of life.
Defining Life and Its Origins
Why it matters… Finding evidence of life somewhere else would be the most profound dis-
covery in human history. On February 18, 2021, the NASA rover Perseverance landed on Mars and,
along with characterizing the Martian climate and geology, it is looking for signs of life. The landing
site of Perseverance is the 45-kilometre–wide Jezero Crater that a few billion years ago was the site of a
large lake. As the rover slowly roams over the Jezero lakebed, it employs an instrument with the
acronym SHERLOC that uses laser light to detect within the sediments the presence of organic molecules that, on Earth, we know are produced through biological activity. Detailed analysis of samples
that Perseverance collects will have to wait until they are sent back to Earth as part of a later mission.
A hope of many astrobiologists is that Perseverance comes across a surface feature that can’t
be attributed to anything other than ancient microbial life. On Earth, a good example of that is
stromatolites, which are sediment formations generated by the action of photosynthetic bacteria.
But therein lies one of the problems with searching for life elsewhere: we only know about life on
Earth, and maybe life on other planets is very different. And then, of course, what is life anyway?
It is actually really hard to come up with even a simple definition. While we continue to search
for life elsewhere, our understanding of life and how it may have developed is limited to
understanding how life may have developed on Earth.
The events we are going to discuss in this chapter may seem improbable: the synthesis of
organic molecules; the development of the first cells; the evolution of DNA, RNA, and proteins; the
building of metabolic pathways; and all the way to the evolution of multicellular eukaryotes.
Improbable? Perhaps. But we must keep in mind that these events took place over hundreds of
millions of years. As scientist and author George Wald of Harvard University put it, given so much
time, “the impossible becomes possible, the possible probable, and the probable virtually certain.”
1
5
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1.1 What Is Life?
Picture a frog sitting in a pond, slowly shifting its head to follow
the movements of an insect flying nearby (Figure 1.1). Most of us
instinctively know that the frog is alive and the water is not. Or
is water alive? The atoms found in living and non-living entities
are the same. The oxygen and hydrogen atoms, for example,
aren’t any different within cells than they are in a pool of water
or a rock. As well, living cells may be extraordinary things but
they abide by the same fundamental laws of chemistry and
physics as the abiotic (non-living) world. Before we embark on a
discussion of how life may have developed billions of years ago
and the characteristics that early forms of life must have possessed it would be helpful if we had a clear notion of what distinguishes something that is living from something that is not
living.
1.1a Why It’s Hard to Define Life
Alexander Sviridov/Shutterstock.com
Biology is the study of life, and the purpose of Biology: Exploring
the Diversity of Life is to provide you with an introduction to
many aspects of living things: from the unique features of biological molecules, reaching outward to cells, organisms, and the
interconnectedness that defines ecosystems.
It may surprise you that, while we can describe in considerable detail the features that one organism has compared to
another, and certainly we can think about the things that living
things can do that non-living things can’t do, we struggle to
come up with a clear definition of what life actually is. Doesn’t
that seem a little odd? If you think about the other core disciplines often taught in first year, chemistry and physics, most of
the concepts in those disciplines are pretty easy to define, even
if they may not necessarily be easy to learn.
A major hurdle in coming up with a definition for life is the
pursuit of something that is universal. Ideally, the definition of
life should be acceptable to scientists and non-scientists alike,
and be useful and applicable across disciplines. As you will see,
the way a discipline defines life is intimately connected to the
questions that it explores. Let’s consider at three disciplines
FIGURE 1.1 Northern leopard frog resting in a pond
6
CHAPTER 1
where defining life seems to be of fundamental importance.
First, let’s think about evolutionary biology, the study of how
life on Earth changes over time through processes such as natural selection and speciation. Second, there is the growing science of astrobiology, which considers questions related to the
possibility of life beyond Earth and the factors necessary to
support life on other planets. Any definition of life that we can
come up with would need to apply to entities we may discover
(or meet) on other worlds. Third, there is the field of artificial
life, which uses computer simulations, robotics, and synthetic
biochemistry to simulate many of the attributes of life.
As shown in Figure 1.2, part of the problem with defining
life is that each of these groups of researchers approach life
from a slightly different perspective, and what one group thinks
is an essential aspect of life, another group may not.
One of the first people to take a crack at defining life was
Aristotle, who mentioned that it is something that “grows, is selfsustaining and reproduces.” This seems like a pretty solid start;
the ability to make more of itself seems a central feature of all
forms of life. Another central feature seems to be the cell. Peering
into the primitive light microscopes in the 17th century, it soon
became obvious that all living things were formed of cells. As we
will discuss in detail in the next chapter, this became part of cell
theory: The cell was defined as the smallest unit of life and new
cells were derived only when old cells divided. So, for a long time,
if we couldn’t strictly define life, at least everyone could agree on
one universally accepted characteristic: the cell. We will see later
in this section how the discovery of viruses has muddled this
cell-centric view of life.
An entity is alive for
evolutionary biologists only
if it has properties A, B, and C.
An entity is alive for
astrobiologists only if it
has properties B, D, and F.
An entity is alive for artificial-life
researchers only if it has
properties A, D, and E.
FIGURE 1.2 One of the issues with defining life is that, depending
upon the branch of biology where it is important, the properties of
life don’t completely match. For example, does life have to be composed
of cells, evolve, contain DNA, undergo metabolism, reproduce? Some of
these properties are important to some researchers and not important to
others. We have yet to arrive at a definition of life that is universally accepted.
DEFInInG LIFE AnD ITs ORIGIns
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1.1b Viruses Complicate Our Idea of Life
Whether or not viruses should be considered life has been an
argument that goes back to when they were first visualized
early in the 20th century, after the advent of the electron
microscope. Viruses, which we will discuss in detail in
Chapter 25, don’t have their own metabolism; they don’t respire
or carry out photosynthesis. But, like traditional forms of cellular life, they do contain nucleic acid and replicate, and they
can evolve rapidly by natural selection. But they can’t complete
their lifecycle without invading living cells, whether that be a
bacterium or a human (Figure 1.3). Taking up residence within
living cells is required for a virus because it does not have its
own protein-making factories—ribosomes and key enzymes
required for it to replicate. Because of this last fact, many put
viruses clearly in the “not life” camp. But if viruses are not considered life because they are parasitic, what about Rickettsia?
This bacterium is considered to be alive despite its inability to
live outside a host cell.
Things became more complicated on the virus front in
1992 with the discovery of a virus initially thought to be a bacterium. Named mimivirus for “mimicking microbe,” no one
had ever observed a virus that was so large you could visualize
it using conventional light microscopy. Its genome, at 1.2 million base pairs, far exceeds the size of any other known virus
Image courtesy of John Wertz, Yale University
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In 1992, the NASA exobiology advisory board put forward
a working definition of life as being “a self-sustaining system
capable of Darwinian evolution.” As we will see in Chapter 16,
“Darwinian evolution” means the system can undergo the process of natural selection. While this definition was not formally
adopted by NASA, it did help to define what types of chemistry
would constitute life on another planet. The problem with the
NASA definition is that there are many exceptions to it. There
are many clearly living entities that are unable to reproduce.
Think of a mule, which is the sterile hybrid offspring of a horse
and a donkey.
There are also entities that science deems “non-living” that
possess qualities of life such as reproduction, evolution, or
something else. For example, fire can certainly make more of
itself (reproduce) and it can grow and consume matter. For
decades, it has been known that mineral crystals can grow and
maintain a highly ordered structure not unlike an organism. It
was the physicist Erwin Schrödinger in 1945 who saw the
maintenance of order as one key defining property of life. As
we will see in Chapter 3, maintaining order (or low entropy) is
a central reason for why life undergoes energy-requiring
metabolism. Yet, within the past few years, researchers have
shown that energy from light can be used to drive lifelike, selforganizing behaviours (think schooling fish or flocking birds)
in particles. Published in the prestigious journal Science, the
authors made reference to these as “living crystals.” As well,
many computer viruses can reproduce and change over time
(e.g., evolve), which, as we will see, are two key attribues.
FIGURE 1.3 Bacteriophage infecting a bacterium. Notice the
bacteriophages on the cell surface as well as inside the bacterium. A
bacteriophage is a type of virus, and most scientists do not consider viruses
to be alive.
and is larger than many bacteria. Its genome has been predicted
to encode over 900 proteins, many of them associated with
functions never before seen in a virus. This includes proteins
central to protein synthesis and metabolism, two hallmarks of
life. However, like other viruses, mimivirus is still dependent
upon host cell ribosome for protein synthesis. Clearly, if mimivirus is not allowed to be a member of the life “club,” it stands
right outside the door.
1.1c
Seven Characteristics Shared
by All Cellular Life Forms
From the above discussion it is pretty clear that we don’t have a
universally accepted definition of life. In fact, a growing number
of researchers reject the need for a common definition. Many
want a “theory of living systems” that can fully describe life (its
origins and characteristics) without forcing a strict definition.
Others argue that, since we are constantly discovering new species and have yet to detect evidence of life on another planet,
trying to strictly define it is silly because we simply don’t understand enough about it.
For now, we need to make a compromise. While we can
use the word entity to include a wide range of self-replicating
and evolving systems, we are going to reserve the word organism
for forms of life that are made of cells. It is cellular life that is
going to hold our attention through the next 44 chapters of this
textbook.
Without a strict definition of life, organisms on Earth all
possess a key list of attributes. As detailed in Figure 1.4, all life
displays order, harnesses and utilizes energy, reproduces,
responds to stimuli, exhibits homeostasis, grows and develops,
and evolves.
STUDY BREAK QUESTIONS
1. Why is it difficult to arrive at a definition for life?
2. Why is a virus often considered not to be alive?
CHAPTER 1
DEFInInG LIFE AnD ITs ORIGIns
7
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SCIMAT/Science Source
f. Grow and develop
g. Evolve
Stanislav Duben/Shutterstock.com
Uwe Krejci/Stone/Getty Images
Dr. Jeremy Burgess/Science Source
e. Exhibit homeostasis
Karin Duthie/Alamy Stock Photo
d. Respond to stimuli
c. Reproduce
Steve Byland/Shutterstock.com
b. Harness and utilize energy
harmeet/StockXchng
a. Display order
FIGURE 1.4 Although it is hard to strictly define life, all cellular forms of life on Earth display these seven characteristics. (a) Display order.
All forms of life, including this flower, are arranged in a highly ordered manner, with the cell being the fundamental unit that exhibits all properties of life.
(b) Harness and utilize energy. Like this hummingbird, all forms of life acquire energy from the environment and use it to maintain their highly ordered state.
(c) Reproduce. All organisms have the ability to make more of their own kind. Here, some of the bacteria have just divided into two daughter cells.
(d) Respond to stimuli. Organisms can make adjustments to their structure, function, and behaviour in response to changes to the external environment.
A plant can adjust the size of the pores (stomata) on the surface of its leaves to regulate gas exchange. (e) Exhibit homeostasis. Organisms are able to regulate
their internal environment such that conditions remain relatively constant. Sweating is one way in which the human body attempts to remove heat and
thereby maintain a constant temperature. (f) Grow and develop. All organisms increase their size and/or number of cells. Many organisms also change over
time. (g) Evolve. Populations of living organisms change over the course of generations to become better adapted to their environment. The snowy owl
illustrates this perfectly.
1.2 The Chemical Origins of Life
One of the tenets of cell theory states that cells arise only from
the growth and division of preexisting cells. This tenet, which
we will discuss in detail in the next chapter, has probably been
true for a few billion years, yet there must have been a time
when this was not the case. There must have been a time when
no cells existed, when there was no life. It is thought that, over
the course of millions of years, cells with the characteristics of
Oxygen produced
by photosynthetic
bacteria
January 1
Earth
forms
Earliest
life
First
eukaryotes
January
February
March
April
Ma
y
First
animals
Jun
e
July
Aug
ust
Septemb
er
FIGURE 1.5 The history of Earth condensed into one year
8
CHAPTER 1
life arose out of a mixture of molecules that existed on early
Earth. In this section, we present hypotheses for how biologically important molecules could have been synthesized on early
Earth in the absence of life.
1.2a Earth Is 4 600 000 000 Years Old
Earth was formed about 4.6 billion years ago, at the same time
as the rest of the planets in the solar system. The age of our
planet has been arrived at using the technique of radiometric
dating, which looks at specific isotopic ratios in rocks and
knowledge of their rate of decay.
December 31,
The decay of uranium to lead, in
11:43 p.m.
particular, has been used to age
Modern
Earth. To give us some sense of
humans
just how long 4.6 billion years is,
appear
Earliest
as well as the relative timing of
land
some major events in the hisplants
tory of life on Earth, Figure 1.5
condenses the entire history of
Earth into a unit of time that we
er
b
are more familiar with: 1 year.
em
Dec
r
With 4.6 billion years cone
b
m
Nove
densed into a single year, each
October
day represents an interval of
12.6 million years!
DEFInInG LIFE AnD ITs ORIGIns
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Using our condensed version of the history of Earth, we
set the date of the formation of Earth as January 1 at 12:00 a.m.
We will discuss this in detail later but, based on chemical evidence, life may have started as early as 4 billion years ago. This
translates to mid-March in our one-year calendar. The first
clear fossil evidence of prokaryotic cells occurs in late March,
or about 3.5 billion years ago. Fossil evidence of eukaryotes
has been dated to about 2 billion years ago, which is not until
early July using our 1-year analogy. Perhaps surprisingly, animals do not make an appearance until mid-October (about
525 million years ago) and land plants until the following
month. The extinction of dinosaurs, which was completed by
about 65 million years ago, does not occur until late December.
What about humans? We may think humans, Homo sapiens,
have been around a long time but, relative to other forms of
life, the roughly 150 000 years that modern humans have
existed is a very short period of time—a blip on our time scale.
Using our year analogy, modern humans have existed only
since December 31; more precisely, since December 31 at
11:43 p.m.!
1.2b Biologically Important Molecules Can
Be Synthesized outside Living Cells
In comparison to the proposed reducing atmosphere of
early Earth, today’s atmosphere is classified as an oxidizing
atmosphere. The presence of high levels of oxygen prevents
complex, electron-rich molecules from being formed because
oxygen is a particularly strong oxidizing molecule and would
itself accept the electrons from organic molecules and be
reduced to water. Apart from allowing for the buildup of
electron-rich molecules, the lack of oxygen in the young atmosphere also meant that there was no ozone (O3) layer, which
only developed after oxygen levels in the atmosphere began to
increase. Both Oparin and Haldane hypothesized that, without
the ozone layer, energetic ultraviolet light was able to reach the
lower atmosphere and, along with abundant lightning, provided the energy needed to drive the formation of biologically
important molecules.
Experimental evidence in support of the Oparin–Haldane
hypothesis came in 1953, when Stanley Miller, a graduate
student in the lab of Harold Urey at the University of Chicago,
created a laboratory simulation of a reducing atmosphere.
Miller mixed the gasses hydrogen, methane, and ammonia in a
closed apparatus and exposed the gases to an energy source in
the form of continuously sparking electrodes (Figure 1.6). Water
vapour was added to the “atmosphere” in one part of the apparatus and subsequently condensed back into water by cooling
in another part. After running the experiment for one week,
Miller found a large assortment of organic compounds,
including urea; amino acids; and lactic, formic, and acetic acids
in the condensed water. In fact, as much as 15% of the carbon
that was originally in the methane at the start of the experiment ended up in molecules that are common in living
organisms.
All organisms are composed of four classes of essential macromolecules: nucleic acids, proteins, lipids, and polysaccharides
(see The Purple Pages for an overview of these molecules). These
molecules are constantly being synthesized within cells by various biochemical pathways and metabolic processes. If at least
some of these molecules are an absolute requirement for life,
then simple forms of them must have come before the first cells;
they must have been produced in the absence of life, what is
referred to as abiotic synthesis.
When the earliest forms of life developed about
∼4.5 billion years ago
4 billion years ago, Earth was vastly different from
Electrodes
what it is today. The atmosphere probably conSpark
tained an abundance of water vapour from the
Simulated early
discharge
Earth’s atmosphere
evaporation of water at the hot surface, as well as
Inorganic
molecules
large quantities of hydrogen (H2), carbon dioxide
CH4
simulating
NH3
(CO2), ammonia (NH3), and methane (CH4). You
early Earth’s
Gases
H 2O
might be surprised to know there was an almost
atmosphere
H2
complete absence of oxygen (O2) in the early atmoWater out
sphere. In the 1920s, two scientists, Aleksandr
Condenser
Oparin and John Haldane, independently proposed
Boiling water to produce
Water in
that organic molecules, essential to the formation of
water vapour, and using a
Water
life, could have formed in the atmosphere of early
condenser to form water
droplets
droplets, simulates the
Earth. A critical aspect of what is known as the
Water containing
water cycle on early Earth.
Oparin–Haldane hypothesis is that the early atmoorganic compounds
sphere was a reducing atmosphere because of the
Liquid water in trap
presence of large concentrations of molecules such
Boiling water
as hydrogen, methane, and ammonia. These moleFIGURE 1.6 The Miller–Urey experiment. Using this apparatus, Stanley Miller, a
cules possess chemical bonds that allow them to graduate student, demonstrated that organic molecules can be synthesized under
enter into reactions with one another that would conditions simulating primordial Earth.
Source: Based on S. L. Miller, 1955
yield larger and more complex organic molecules.
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Andrew Swift
Other chemicals have been tested in the
Miller–Urey apparatus, including hydrogen cyanide (HCN) and formaldehyde (CH 2O), which
are also considered to have been among the substances formed in the primitive atmosphere.
Microscopic
When cyanide and formaldehyde were added to
layers of clay
the simulated atmosphere in the apparatus, all
the building blocks of complex biological molecules were produced: amino acids; fatty acids; the
purine and pyrimidine components of nucleic
acids; sugars such as glyceraldehyde, ribose, glucose, and fructose; and phospholipids, which
form the lipid bilayers of biological membranes.
In the decades since the first Miller–Urey
Nucleotides undergoing
experiment, considerable debate has developed in
polymerization
the scientific community over whether Earth’s
atmosphere held enough methane and ammonia
FIGURE 1.7 Clay surfaces catalyze polymerization. The charged, microscopic,
for it to be considered a reducing atmosphere. layered structure of clay allows for the formation of relatively short polymers of proteins
Some geologists have suggested that, based on and nucleic acids.
analysis of volcanic activity, primitive Earth contained other gases that made it probably someA working hypothesis to address this question needs to be
what less reactive. And as we will see that, later in this
built from the notion that the very earliest forms of life must
chapter, many scientists have looked to the oceans as the
have been very simple, far simpler than a modern bacterium,
most likely place where abiotic synthesis took place and life
for example. Scientists hypothesize that a polymer that conmost likely started. Regardless of these lingering debates,
sists of even 10 to 50 monomers may have been of sufficient
the significance of the Miller–Urey experiment cannot be
length to impart a specific function (like a protein) or store
overstated. It was the first experiment to demonstrate the
sufficient information (like a nucleic acid) to make their forabiotic formation of molecules critical to life, such as amino
mation advantageous to an organism. It is, however, doubtful
acids, nucleotides, and simple sugars, and it showed that
that polymerization could have occurred in the aqueous envithey could be produced relatively easily. This remarkable
ronment of early Earth, as it would be very rare for monofinding laid the groundwork for further research into the
mers to interact precisely enough with one another to
origins of life.
polymerize. It is more likely that solid surfaces, especially
clays, could have provided the type of environment necessary
1.2c Life Requires Polymers
for polymerization to occur (Figure 1.7). Clays consist of very
Primordial Earth contained very little oxygen and, because of
thin layers of minerals separated by layers of water only a few
this, complex organic molecules could have existed for much
nanometres thick. The layered structure of clay is also
longer than would be possible in today’s oxidizing world. Even if
charged, allowing for molecular adhesion forces to bring
they did accumulate on early Earth, molecules such as amino
monomers together in precise orientations that could more
acids and nucleotides are monomers, which are simpler and
readily lead to polymer formation. Clays can also store the
easier to synthesize than the key chemical components of life,
potential energy that may have been used for energy-requiring
such as nucleic acids and proteins, which are polymers—macropolymerization reactions. This clay hypothesis is supported
molecules formed from the bonding together of individual
by laboratory experiments that demonstrate that the formamonomers. Nucleic acids are polymers of nucleotides, proteins
tion of short nucleic acid chains and polypeptides can be synare polymers of amino acids, and polysaccharides (starch, celthesized on a clay surface.
lulose) are polymers of simple sugars. Polymers are synthesized
by dehydration synthesis, which is discussed in The Purple
Pages.
STUDY BREAK QUESTIONS
Today, the synthesis of proteins and nucleic acids requires
1. For understanding the origins of life, what was the significance
protein-based catalysts called enzymes and results in macroof the Miller–Urey experiment?
molecules that often consist of hundreds to many thousands
2. What is the difference between a reducing atmosphere and an
of monomers linked together. So, how do you make the polyoxidizing atmosphere?
mers that are required for life without sophisticated enzymes?
10
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1.3 The Evolution of
Information Flow:
RNA, DNA, Protein
DNA
RNA
Protein
In the previous section, we discussed how
processes present on early Earth could have
generated macromolecules crucial to the
development of life. However, if we are to
develop a comprehensive model for the
origin of life, we need to explain the evolution of three key properties of a cell that go
well beyond the synthesis of macromolecules. First, a mechanism to store information that can be replicated and passed on to
daughter cells must have developed. Second, Information is
The information
The information in
energy-transforming chemical reactions stored in DNA.
in DNA is copied
RNA guides the
into RNA.
production of proteins.
must have evolved that would have enabled
primitive cells to capture energy from their FIGURE 1.8 The central dogma. Information in DNA is used to synthesize proteins through an
surroundings and use it to do work. Third, RNA intermediate. How did such a system evolve when the product, proteins, is required in
these processes would need to take place modern-day cells to catalyze each step?
within defined compartments (e.g., cells)
that are distinct and separate from the
our understanding of how such a system may have evolved
environment.
came in the early 1980s when Thomas Cech and Sidney Altman,
In this section, we discuss the first of these: the developworking independently, discovered a group of RNA molecules
ment of a genetics system that would allow the passing of inforthat could themselves act as catalysts. This group of RNA catamation to new cells following cell division.
lysts, called ribozymes, are found in all types of cells. They are
not as common as enzymes, but they carry out critical reactions related to the control of gene expression. One type of ribo1.3a RNA Can Carry Information
zyme, for example, catalyzes the removal of introns from newly
and Catalyze Reactions
synthesized RNA molecules; other ribozymes can cleave speAs we will discuss in detail in Chapter 11, DNA (deoxyribose
cific messenger RNA (mRNA) molecules, causing their degranucleic acid) is the molecule that provides every cell with the
dation. The precise catalytic property of a ribozyme is
instructions necessary to function. The information contained
determined by its shape, which is based on the hydrogen
in a sequence of nucleotides in DNA, called a gene, is copied
bonding between specific nucleotides of the RNA molecule.
into a unique molecule of RNA. Some of these RNA molecules
The link between nucleotide sequence, shape, and thus funcprovide information for the synthesis of specific proteins. Even
tion is analogous to an enzyme. The specific reaction catalyzed
the simplest bacterium today contains thousands of genes, RNA
by an enzyme is dependent on its precise three-dimensional
molecules, and proteins. The flow of information from DNA to
shape, which is the result of its unique amino acid sequence. All
RNA to protein is common to all forms of life and is referred to
ribozymes recognize their target by specific base pairing
as the central dogma (Figure 1.8). Each step of the information
between the ribozyme nucleotide sequence and the nucleotide
flow requires the involvement of enzymes that catalyze the
sequence of the target molecule (Figure 1.9).
transcription of DNA into
Ribozyme
RNA, and the translation of
the RNA into protein.
A fundamental question
about the flow of information
from DNA to RNA to protein
is How did such a system
evolve when the final prodMessenger RNA
Ribozyme-mediated cut
Cut (cleaved) messenger
introduced into RNA message
RNA molecules
ucts, proteins, are required to
catalyze each step (e.g., tran- FIGURE 1.9 Ribozyme. An example of a ribozyme binding to an RNA molecule and catalyzing its breakage. Within
scription, translation) of the a modern-day cell, such reactions help control gene expression by altering the abundance of functional messenger
process? A breakthrough in RNA (mRNA) molecules.
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The discovery of ribozymes revolutionized our thinking
about the origin of life. Instead of the contemporary system
that requires all three molecules—DNA, RNA, and protein—
early life may have existed in an “RNA world.” RNA could
have served both as a carrier of information, by virtue of its
nucleotide sequence, and as a structural/catalytic molecule
due to its ability to fold on itself and form unique threedimensional shapes. Before the discovery of ribozymes,
enzymes were the only known biological catalysts. For their
remarkable discovery of RNA catalysts, Sidney Altman and
Thomas Cech shared the Nobel Prize in Chemistry
in 1989.
1.3b RNA Is Replaced by DNA for Information
Storage and Proteins for Catalysis
If life developed in an environment where RNA served as both
an information carrier and a catalyst, why is it that, in all
modern organisms, genetic information is stored in DNA, and
why do a class of proteins (e.g., enzymes) catalyze the vast
majority of biological reactions? The simple answer is that they
do the respective jobs of information storage (DNA) and catalysis (protein) far better than RNA does by itself. The evolution
of these other molecules would have given organisms that
developed them a distinct advantage over others that relied
solely on RNA.
A possible scenario for the development of today’s system
of information transfer is shown in Figure 1.10. The first cells
may have contained only RNA, which could make copies of
itself (self-replicating) and could catalyze a small number of
reactions critical for survival. It is hypothesized that a small
population of RNA molecules then evolved that could catalyze
the formation of very short proteins before the development of
ribosomes. Recall that, in modern cells, the ribosome is the site
RNA
of protein synthesis: it binds mRNA molecules and uses the
information in the nucleotide sequence to generate a protein
built from a pool of amino acids. It is interesting to note that
the catalytic component of the ribosome that joins individual
amino acids is itself an RNA molecule. So, in fact, the ribosome
is a type of ribozyme.
Cells that evolved the ability to use the information
present in RNA to direct the synthesis of even small proteins
would be at a tremendous advantage because proteins are far
more versatile than RNA molecules for three reasons. First,
the catalytic power of most enzymes is much greater than
that of a ribozyme. A typical enzyme can catalyze the same
reaction using a pool of substrate molecules many thousands
of times a second. By comparison, the rate of catalysis of
most ribozymes is one-tenth to one-hundredth that of
enzymes. Second, while the number of ribozymes is very
small, a typical cell synthesizes a huge array of different proteins. Twenty different kinds of amino acids, in different
arrangements, can be incorporated into a protein, whereas an
RNA molecule is composed of different combinations of only
four nucleotides. Third, amino acids can interact chemically
with each other in more complex and varied bonding
arrangements not possible between nucleotides. For these
reasons, proteins are the dominant structural and functional
molecule of a modern cell.
Continuing with the possible scenario shown in Figure 1.10,
the evolution of DNA would have followed that of proteins.
Compared with RNA, molecules of DNA are more structurally
complex. Not only is DNA double stranded, but it also contains
the sugar deoxyribose, which is more difficult to synthesize
than the ribose found in molecules of RNA. A possible sequence
begins with DNA nucleotides being produced by random
removal of an oxygen atom from the ribose subunits of RNA
nucleotides. At some point, the DNA nucleotides paired with
the RNA informational molecules and were assembled into
complementary copies of the RNA sequences. Some modernday viruses carry out this RNA-to-DNA reaction using enzyme
reverse transcriptase (see Chapter 25). Once the DNA copies
were made, selection may have favoured DNA, as it is a much
better way to store information than RNA, for three main
reasons:
●
RNA
Protein
●
●
DNA
RNA
Protein
FIGURE 1.10 Possible scenario for the evolution of the flow of
information from DNA to RNA to protein
12
CHAPTER 1
●
Each strand of DNA is chemically more stable, and less likely
to degrade, than a strand of RNA.
The base uracil found in RNA is not found in DNA; it has
been replaced by thymine. This may be because the conversion of cytosine to uracil is a common mutation in DNA. By
utilizing thymine in DNA, any uracil is easily recognized as
a damaged cytosine that needs to be repaired.
DNA is double stranded, so in the case of a mutation to one
of the strands, the information contained on the complementary strand can be used to correctly repair the damaged
strand.
The stability of DNA is illustrated by the fact that intact DNA
can be successfully extracted from tissues that are many
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thousands of years old. The well-known novel and
movie Jurassic Park are based on this demonstrated ability.
By comparison, RNA needs to be isolated quickly, even from
freshly isolated cells, using a strict protocol to prevent its
degradation.
STUDY BREAK QUESTIONS
1. In what ways are ribozymes similar and different from enzymes?
2. RNA may have been the first information-carrying molecule,
but it was replaced by DNA. Why?
1.4. The Development of Metabolism
and the First Cells
One of the seven characteristics of life as outlined in Figure 1.4 is
the ability to harness and utilize energy. All life can bring in
energy from its surroundings and use it to transform simple molecules into a range of complex compounds and structures that
make up cells. To do this required the evolution of ordered chemical reactions and, while these must have started out very simple,
they evolved into interlocked networks of metabolism that
increased in sophistication over time. While simple chemical
reactions important to life could have developed outside cells,
even basic metabolic pathways would have had to be restricted to
compartments (e.g., cells) where concentrations of molecules and
conditions could be distinct from the external environment.
While there remain a lot more questions than answers about how
this all came about, what has been found is a habitat with a unique
combination of characteristics that could have nurtured the earliest forms of life.
Acidic
ocean water
H2S
Fe2+
FeS
Alkaline
vent water
Ni
CO2
1.4a Alkaline Hydrothermal Vents
May Have Led to the First Cells
Over the past few decades, many scientists testing hypotheses
related to the origin of life have come to agree that complex
molecules necessary for life as well as life itself may have originated on the ocean floor at the sites of hydrothermal vents.
These cracks are found around the globe near sites of volcanic
or tectonic activity. Most hydrothermal vents release superheated, nutrient-rich water at temperatures in excess of 3008C.
It’s because of these high temperatures that hydrothermal vents
were largely dismissed as the site of where early life developed.
More recently, however, researchers have discovered a different
type of vent called an alkaline hydrothermal vent. Not only do
these release water that is much cooler (1008C–1508C), the
water is strongly alkaline (pH 9–11) and rich in a range of molecules, including H2, H2S, and NH3 (Figure 1.11).
Chemical reactions that take place where the vent water
encounters ocean water cause calcium carbonate to precipitate
out of the water, forming chimneys that are honeycombed with
microscopic pores that the water percolates through. Within
these porous chimneys, the two different chemical environments of the vent water and the ocean water encounter each
other. Because a fresh supply of alkaline water is constantly
released from the vent, the interface between vent water and
ocean water never reaches thermodynamic equilibrium, which,
as we will see in Chapter 3, is a key feature of life.
H2, H2S, NH3
100°C, pH 9–11
FIGURE 1.11 Alkaline hydrothermal vent. When water is released from
a vent in the ocean floor and encounters ocean water, calcium carbonate
precipitates out of the water, forming chimneys. The vent water is alkaline
and carries hydrogen, hydrogen sulfide, and ammonia to the surface. The
surrounding ocean water is cool and contains CO2 and a wide range of trace
metals. Reactions among these various molecules could have produced the
first metabolic reactions within cells.
1.4b Evolution of Metabolism
To think about how life started, it’s helpful to consider the
fundamentals of metabolism that we find in organisms today.
The foundation of the biosphere includes microbes and
plants that synthesize organic compounds (e.g., carbohydrates) by combining hydrogen (H2) with carbon dioxide
(CO2) like this:
2H2 1 CO2
(CH2O)n 1 H2O
where (CH2O)n is the general formula for a sugar.
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The most common process that drives this reaction today is
photosynthesis, which uses light energy to extract hydrogen atoms
and electrons from molecules of water and use them to convert
carbon dioxide into organic compounds (carbon fixation). Because
photosynthesis is quite sophisticated, it likely did not evolve for
some time after life had become well established. But, there is a
much simpler set of reactions that can fix carbon dioxide that is
related to a metabolic process you’ve probably heard of: the citric
acid cycle (or Krebs cycle).
As we will discuss in Chapter 5, the citric acid cycle is a key
component of cellular respiration and serves to oxidize organic
molecules (e.g., acetate), releasing CO2 and water. The electrons
released by the oxidation are in turn used further along in the
respiratory pathway to generate ATP. In addition to its role in
synthesis ATP, a second critical function of the citric acid cycle
is that it synthesizes important precursor molecules, including
those needed for the synthesis of amino acids and fatty acids.
What is really interesting about the citric acid cycle is that,
in addition to working in what is called the “oxidative mode,” as
described above, in some bacteria it can actually run in reverse,
in a “reductive mode” (Figure 1.12). It can take in energy in the
form of high energy electrons from, for example, hydrogen gas
(H2), and use those electrons to reduce carbon dioxide into
more complex organic molecules, including the important metabolic intermediates pyruvate and acetate. So, in the oxidative
mode, the input is complex organic molecules and the output is
chemical energy; in the reductive mode, the input is chemical
energy and carbon dioxide and the output is larger, more complex molecules. By operating the reverse citric acid cycle and
harnessing the energy in the H2 released from the alkaline
vents, the earliest forms of life would have been able to generate
complex organic molecules, the sugars, amino acids, nucleotides, and fatty acids that are the building blocks of cells.
FIGURE 1.13 FeS protein consists of an FeS cluster bound precisely to
a peptide chain. The FeS cluster shown here consists of four Fe atoms and
four S atoms (Fe4S4) that form a cube. FeS proteins play key roles in enzyme
catalysis as well as in transferring electrons in electron transport chains.
Like all metabolic pathways, the reverse citric acid cycle
found in bacteria today requires enzymes to catalyze the
conversion of one intermediate of the cycle into the next. Could
the pathway have operated in very primitive cells in the absence
of enzymes? Laboratory experiments have shown that the rate
of these chemical reactions can be sped up without enzymes by
the presence of certain metal-mineral complexes. One particular complex that could have served as a catalyst before
enzymes is iron–sulfur (Fe–S) clusters that are produced by
alkaline hydrothermal vents in a reaction between hydrogen
sulfide (H2S) and iron (Fe) (look back at Figure 1.11). What is
really exciting about this hypothesis is Fe–S clusters are essential to life today. They are key cofactors in what are referred to
as FeS proteins (Figure 1.13), which play critical roles in enzyme
a. Forward citric acid cycle: oxidative
Acetate
b. Reverse citric acid cycle: reductive
KEY
H2O
CO2
H2
Carbon
Oxygen
Hydrogen
Transfer of highenergy electrons to
energy-harvesting
pathways
CO2 waste
product
Geologically
produced, highenergy electrons
surrender energy
to reductive cycle
Acetate product enters
biosynthetic pathways
FIGURE 1.12 Forward and reverse citric acid cycle. (a) The reactions and molecules of the citric acid cycle are found in all modern organisms. (b) In
some microbes, the cycle runs in reverse. Instead of oxidizing a fuel molecule (e.g., acetate) and releasing CO2 as waste, the reverse cycle incorporates CO2 in
organic molecules by using geologically produced molecules such as H2, which represent a rich source of usable electrons. The reverse citric acid cycle may
have been the mechanism that early organisms used to generate complex molecules.
Source: https://www.slideserve.com/isanne/origins-and-early-evolution-of-life
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catalysis, as well as in electron transfer, as components of both
photosynthetic and respiratory electron transport chains.
In addition to iron, many other metals (zinc, copper, nickel,
molybdenum, etc.) are required in trace amounts for the function of many proteins, and thus are essential for life. The reliance of all organisms on these metals may reflect how modern
biochemistry is linked to the geochemistry of the hydrothermal
vents where life may have started.
STUDY BREAK QUESTIONS
1. What are the characteristics of an alkaline hydrothermal vent?
2. Explain the difference between the forward citric acid cycle and
the reverse citric acid cycle.
1.4c
First Cells
One of the key features that makes alkaline vents a promising
site for the development of life is that the calcium carbonate
chimneys (Figure 1.11) are honeycombed with microscopic
pores that water can move through. These pores are only
micrometres in diameter, which makes them comparable in size
to a modern cell and provide a promising model for how the
earliest cells could have evolved. One hypothesis suggests that
the very first cells were not bound by lipid membranes but
rather an inorganic casing composed of metal sulfides (NiS,
FeS). Laboratory experiments have shown that these metal sulfides produce bubbles when they precipitate that could have
served as the first cell membranes. Such a primitive membrane
would have allowed an important attribute of life to develop—
compartmentalization. These early inorganic membranes would
have trapped and concentrated organic molecules, allowing for
more complex chemical reactions to take place, driven at first by
a mineral catalyst that would have produced products that could
have accumulated to high concentrations. Such an environment
would have been conducive to the evolution of the early metabolic processes (e.g., reverse citric acid cycle) as well as the synthesis of the first replicating molecules (RNA) (Figure 1.14).
One common source of energy that relies on a cell membrane is chemiosmosis: using the difference in proton (H1)
concentration across a membrane to do work. Since membranes
are impermeable to protons, having more protons on one side
than the other produces an electrochemical gradient that can
be harnessed to do energy-requiring processes, including generating ATP from ADP and phosphate (PO432, abbreviated Pi).
In organisms today, cells need to expend energy to pump protons out of the cell and generate proton gradients, but if the
earliest cells evolved in the environment of alkaline hydrothermal vents, the gradient would be generated by geological
processes. Recall that the water coming out of these vents has a
low concentration of protons (they are alkaline). By comparison, the surrounding ocean water has a proton concentration
that is estimated to be about 1000-fold greater (Figure 1.14).
Today, the chemiosmotic synthesis of ATP from ADP and
Pi is a reaction that is catalyzed by a sophisticated membranelocalized enzyme system ATP synthase that harnesses the
energy present in the proton gradient. Being a key component
of both photosynthesis and cellular respiration, ATP synthase
is found across all life today, suggesting that ATP synthase
evolved very early in the development of life. It’s hard to
explain how such an elaborate enzyme complex could have
evolved so early but it is worth reminding ourselves that even
the earliest forms of life must have been quite sophisticated.
It’s not just ATP synthase, the ribosome is another key feature
of all cells that is very complex. The evolution of these cellular
machines must have relied on two key features: easy access to
a supply of usable energy and an environment where molecules could have been synthesized in a confined space. The
alkaline vent system of 4 billion years ago may very well have
supplied both of those features.
At some point the inorganic nature of the first membrane
would have been replaced by one dominated by lipid molecules
produced by reaction pathways within the cell. The earliest
lipid membranes could have been similar to a liposome, which
is a lipid vesicle in which the lipid molecules form a bilayer very
similar to a cell membrane (Figure 1.15). Given a mixture of lipid
Microscopic
compartments
Acidic
ocean
water
H+
ATP
H+
H+
ADP + Pi
H+
H+
David Mccarthy/Science Source
Alkaline
vent
water
High H+
H+
Low H+
a.
FIGURE 1.14 The earliest cells may have been formed within the
microscopic pores of the vent system. They would have had a cell
membrane composed of geologically produced minerals.
b.
FIGURE 1.15 Liposome. (a) An artist’s rendition of a liposome, which is
composed of a lipid bilayer. Liposomes can assemble spontaneously under
simulated primordial conditions. (b) SEM image of lipid vesicles assembled
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molecules, liposomes can form spontaneously (without the
need for energy) and would be selectively permeable—allowing
only some molecules to move in and out. As well, liposomes
have been shown to swell and contract depending on the
osmotic conditions of their environment.
The key attributes of life including rudimentary metabolism and genetics could have developed relatively rapidly within
the safe confines of the alkaline vent system and its constant
supply of usable energy. The development of more varied
metabolic pathways must have been essential to early life forms
being able to leave the vent system, as was the development of a
lipid membrane.
STUDY BREAK QUESTIONS
1. Define chemiosmosis.
2. How was the proton gradient within the earliest cells produced?
3. Why was a cell membrane essential to the development of life?
As we saw in the previous section, the alkaline hydrothermal
vent system is a very promising geological feature where early
life may have developed. Along with looking at the physical features present on Earth, insights into early life can come from
studying the huge diversity of life that we find on Earth today
and developing hypotheses around how different organisms
may be related. To trace the evolutionary history of organisms,
what is referred to as phylogeny, researchers build branching
diagrams called trees that show the relationship among different
groups of species. The construction of evolutionary (also called
phylogenetic) trees has been a central feature of evolutionary
biology since the time of Charles Darwin. In fact, Darwin
sketched an early phylogenetic tree (Figure 1.16) in his notebook
in 1837, 20 years before the publication of On the Origin of
Species.
Considering that life has existed for about 4 billion years
and species change over time, building a reasonably accurate
evolutionary tree that includes all major groups of organisms, a
so-called tree of life, seems like a daunting task. And it shouldn’t
surprise you that, as the research tools and techniques used to
assess relatedness among organisms have improved, so have
the evolutionary trees that are built as a result of that research.
We will see in this section that through the use of modern
molecular techniques we are able to infer a great deal about
what our most ancient ancestors might have been like.
1.5a Analyses of Gene Sequences Have
Revealed the Branching Pattern
of the Entire Tree of Life
When it comes to looking at the relationships among the major
groups of organisms, the way we understood things about
50 years ago made everything seem so simple. All life could be
divided into two clear camps: eukaryotes and prokaryotes. The
eukaryotes were the organisms that we were most familiar
with—the animals, plants, and fungi—each defined their own
kingdom but were united into a single larger group by having
cells that contained membrane-bound organelles, most importantly, the nucleus. Fifty years ago, prokaryotes meant only one
thing—bacteria. Single-celled, structurally and metabolically
simple, bacteria were largely hidden from our everyday world
16
CHAPTER 1
Charles Darwin's First Notebook on Transmutation of Species (1837)
1.5 The Tree of Life
FIGURE 1.16 Darwin’s evolutionary tree. This entry from his notebook
on the “transmutation of species” demonstrates that Charles Darwin first
thought about the branching pattern of evolution in 1837, more than 20 years
before he published On the Origin of Species.
because they were so small. But everything changed when
researchers started to apply the tools and techniques of molecular biology to the study of phylogenetics.
For centuries, biologists had built phylogenetic trees based
on how organisms looked: organisms that have similar structures and features (what we call morphology) were grouped
more closely together than organisms that looked less similar.
But, two organisms that look similar may in fact not share a
similar evolutionary history, and by the 1970s, researchers realized that a more objective and powerful approach to building
trees was to use differences in DNA sequence (the AGC and T
nucleotides that make up DNA). The basis for this approach is
quite simple: As one species splits into two and these two species diverge over time, their DNA sequences will accumulate
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changes and become less and less similar to each other. If there
aren’t very many differences in DNA sequence between two
species, then they’re probably closely related and diverged from
each other quite recently. If there are a lot of differences, they
are likely to be more distantly related.
If you want to use DNA to build a tree of life, this is the first
question you need to consider: What is the sequence that you want
to compare? You could determine the sequence of the entire
genomes of species you want to include in your tree, but even
today that can get expensive, and looking for similarities and differences between the millions of bases that make up whole
genomes can take a long time. Instead, scientists have focused on
looking at differences in the sequence of just one gene. But which
one should they pick? There are two major criteria you need to
consider: First, the specific gene you choose needs to be present in
all organisms. It would make little sense to use a gene required for
eye development to build a tree of life since 99% of species on
Earth don’t have eyes. Second, the gene has to be relatively long (at
least a thousand bases would be good). The longer the DNA
sequence, the more information it contains to make comparisons
among species. For example, having a gene made up of only six
nucleotides (say, GAGCCT) isn’t very useful because many unrelated species would have that sequence simply by chance.
One of the first researchers to use a DNA sequence to build
phylogenetic trees was Carl Woese, a microbiologist at the University of Illinois. He focused his attention on a cell component
that is common to all life: the ribosome, the organelle at the
centre of protein synthesis that uses the information in messenger RNA (mRNA) molecules to synthesize its corresponding
protein. The structure of a ribosome is built by a combination
of protein and a specific kind of RNA called ribosomal RNA
(rRNA), and these components are remarkably similar across
all organisms (Figure 1.17). Woese settled on the specific gene
that codes for the rRNA molecule that makes up the small
subunit of the ribosome. The DNA sequence for this gene is
about 1500 nucleotides in length, so it provides lots of information with which to compare species and build the tree. A small
portion of this sequence is seen in Figure 1.17.
In 1990, Woese and his colleagues published the first tree of
life based on rRNA sequence data. It surprised many in the scientific community because, instead of showing 5 or 7 or maybe
10 distinct kingdoms of life, it clearly showed that all life could
actually be grouped into 3 “superkingdoms” called domains:
Bacteria, Archaea, and Eukarya (Figure 1.18a). The most surprising finding of what has become known as the three-domain
tree of life is that it showed not one but two major groups of
organisms that have prokaryotic cell structure: the Bacteria and
Archaea. The Bacteria include many well-known microbes,
including Escherichia coli (E. coli), and the domain Archaea
includes microorganisms that are far less common and are
often found in harsh environments, such as hot springs and salt
marshes. The domain Eukarya includes the familiar animals,
plants, and fungi and protists. The major distinguishing features of the Bacteria, Archaea, and Eukarya are shown in
Table 1.1. We will discuss the organisms that comprise these
domains in Unit 5 of this textbook.
Bacteria
Archaea
Eukarya
LUCA
a. Three-domain tree
Eukarya
Protein
Large
subunit
Bacteria
Archaea
Ribosomal
RNA (rRNA)
Small
subunit
Species 1 … ATCCGCTAGGCTGACGGCT TAGCCCATATCGA C…
Species 2 … ATCCGGTAGGCTGACGGCT T TGCCCATATCGAC…
Species 3 … ATCCGCTACGCAGATGGCT TAGCCGATA ACGAC…
FIGURE 1.17 The ribosome is made of two subunits, each
composed of protein and ribosomal RNA (rRNA). The sequence of the
rRNA gene of the small subunit is widely used to infer evolutionary
relationships among species. In the example shown here of a small portion
of the sequence, Species 3 has more differences (shown in red) than Species
1 or 2. Based on these data, we can conclude that Species 3 is more distantly
related to Species 1 than Species 2.
LUCA
b. Two-domain tree
FIGURE 1.18 Trees of life with domains. (a) Three-domain tree of life.
rRNA sequence comparisons suggest that Bacteria, Archaea, and Eukarya
are three domains of living organisms, and that Eukarya are more closely
related to Archaea than Bacteria. (b) Two-domain tree of life. The discovery
of the Asgard group of archaeans that have key eukaryotic traits suggests
that eukaryotes evolved from within the Archaea. LUCA stands for Last
Universal Common Ancestor and is discussed in the text.
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TABLE 1.1 Some Differences among the Three Domains
Character
Bacteria
Archaea
Eukarya
Chromosome
structure
Circular
Circular
Linear
DNA location
Nucleoid
Nucleoid
Nucleus
Chromosome
segregation
Binary fission
Binary fission Meiosis/
mitosis
Introns in genes
Rare
Common
Common
Operons
Present
Present
Absent
Initiator tRNA
Formylmethionine
Methionine
Methionine
Ribosomes
70S
70S
80S
Membraneenclosed
organelles
Absent
Absent
Present
Membrane lipids Ester-linked
Ether-linked
Ester-linked
Peptidoglycan in
cell wall
Present
Absent
Absent
Methanogenesis
Absent
Present
Absent
Temperature
tolerance
Up to 90°C
Up to 120°C
Up to 70°C
Before moving on, it’s worth mentioning the scientific
impact of the three-domain tree of life. First, it illustrated the
power of using molecular data to produce evolutionary trees; data
that unlike morphology, could be more accurately interpreted.
Second, the use of molecular data such as gene sequences allowed
for the classification of microbes that are difficult to describe in
other ways, not only because they are microscopic but also
because some are very difficult to grow and study in the lab.
Third, and perhaps most surprisingly, it showed that archaeans
are more closely related to eukaryotes than they are to bacteria!
Since it was first published, the three-domain tree of life has
been well supported by additional gene sequencing projects, as
well as detailed analyses showing how distinct the cell structure
and physiology of archaeans are compared to bacteria. But
microbiologists had long suspected that the bacteria and archaea
that had been studied so far represented only a tiny fraction of
the total microbial diversity on Earth. Many microbes live in
extreme habitats, making them particularly difficult to study.
Sediment cores taken in 2010 near a hydrothermal vent in
the Arctic Ocean contained previously uncharacterized samples of archaeans that have since been assigned to a new group
called Asgard. DNA sequencing of these samples showed something shocking. While the DNA of the Asgard samples contain
key sequences that are found only in the Archaea, they also
18
CHAPTER 1
have genes that were previously thought to be present only in
eukaryotes. These included genes for proteins involved in
building the cytoskeleton, the process of phagocytosis, and certain core genes involved in fundamental cellular processes (e.g.,
transcription, translation).
The analysis of the Asgard genes suggested that archaeans
and eukaryotes are in fact more closely related than previously
thought. That provided evidence that the three-domain tree of
life is probably incorrect. What the most recent findings indicate is that there are only two primary domains of life: Bacteria
and Archaea, and that Eukarya evolved from within the
Archaea (Figure 1.18b). The current two-domain tree of life will
be scrutinized and tested against a range of hypotheses, as it
should. It is remarkable that, in comparing the Asgard samples
with eukaryotic DNA, we are trying to reconstruct an ancient
relationship by looking for DNA sequences that these two
shared at the time they split into distinct lineages. This is estimated to have occurred more than 2 billion years ago.
The Asgard samples used for the DNA sequencing project
that showed they are closely related to eukaryotes came from
sediment samples isolated from the environment, not from
living cells. It was only in 2020 that a group of researchers in
Japan was successfully able to isolate intact cells of Asgard and
get them to grow successfully in a laboratory. This was a
remarkable accomplishment and has already led to the start of
a number of research projects aimed at not only better understanding the structure and physiology of the Asgard but also
more direct testing of a range of hypotheses related to the evolution of eukaryotes.
1.5b All Present-Day Organisms Are
Descended from a Common
Ancestor, LUCA
There are clear distinctions in structure and function between
Bacteria, Archaea, and Eukarya that we will discuss in detail in
Unit 5. Apart from all their differences, it is remarkable that all
forms of life on Earth share a common set of features. This
includes (1) cells defined by a membrane composed of a bilayer of
lipid molecules; (2) a genetic system based on DNA; (3) a system
of information transfer: DNA to RNA to protein; (4) ribosomes as
the central feature of a protein assembly machinery that uses the
information in messenger RNA (mRNA) and transfer RNA
(tRNA) to produce peptide chains from a pool of amino acids;
(5) reliance on proteins as the major structural and catalytic
molecule; (6) use of ATP as the currency of chemical energy; and
(7) common pathways of energy transformation (e.g., glycolysis,
substrate-level phosphorylation, chemiosmosis). Given that all
organisms share these seven characteristics, what is the likelihood
that these traits arose independently in the three major groups of
life? It is far more likely that the reason for these shared traits is
that all organisms today are the descendants of one organism that
possessed all these traits. This shared ancestor probably lived
more than 3 billion years ago.
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Origin
of life
LUCA
Eukarya
Archaea
FIGURE 1.19 Life before LUCA. It is likely that many forms of simple life
predated the evolution of LUCA. As indicated by the light-green part of the
figure, all of these are now extinct, as well as others that have become
extinct more recently.
Looking back at Figure 1.18, whether we consider a twodomain or a three-domain tree of life, both phylogenies show
that all organisms today come from a common ancestor that has
become known as LUCA, which stands for Last Universal
Common Ancestor. In an amazing piece of research, scientists
have pieced together a view of what LUCA was actually like. To
reconstruct the structure, biochemistry, and ecology of LUCA, a
research team looked at the common protein families found
among 1800 sequenced bacterial genomes and 134 archaeal
genomes. This research identified 355 proteins that were common
to all the genomes. That these proteins were so highly conserved
across many different species suggests that these proteins may
have been present in LUCA. The analysis of these proteins and
their possible function provides a remarkable glimpse into how
LUCA lived (Figure 1.19). The research suggests that LUCA lived
without O2 (was anaerobic), fixed CO2 into organic molecules,
possessed a set of reactions similar to the reverse citric acid cycle,
1.6 Eukaryotes and the Rise
of Multicellularity
Compared to the prokaryotic cell structure of Archaea and
Bacteria, present-day eukaryotic cells are much more complex
in both structure and function. There are two major characteristics that distinguish eukaryotic cells from prokaryotic cells:
(1) the separation of DNA and cytoplasm by a nuclear envelope
and (2) the presence in the cytoplasm of membrane-bound
organelles with specialized functions: mitochondria, chloroplasts, the endoplasmic reticulum (ER), and the Golgi complex,
among others. In this section, we discuss how eukaryotes most
probably evolved from associations of prokaryotic cells, and we
end with a discussion of the rise of multicellular eukaryotes.
STUDY BREAK QUESTIONS
1. What is the advantage of using DNA sequence over
morphology as the data used to build an evolutionary tree?
2. We have moved recently from a three-domain tree of life to a
two-domain tree of life. What caused the shift in thinking?
3. LUCA wasn’t the first form of life to develop, so why is it so
important to our understanding of the evolution of life?
began increasing. Evidence for this comes from dating a type of
sedimentary rock called banded iron (Figure 1.20).
An obvious question to ask is, Where did the oxygen come
from? Surprisingly, this oxygen did not have a geological origin;
instead, its source was a group of photosynthetic bacteria called
cyanobacteria. At the time, photosynthetic organisms used light
© Commonwealth of Australia
Bacteria
was dependent upon H2 as a source of hydrogen atoms and electrons, was able to convert N2 into ammonia, and lived in a hot
environment (thermophilic). Its biochemistry was dependent on
FeS clusters and a range of other metals. This research further
supports the notion that LUCA developed in a vent-like setting
and took advantage of the abundance of molecules produced by
a range of geochemical processes.
You may think that LUCA was the first form of
life to exist on early Earth, but that is not the case. Calling something the last common ancestor is like saying the last team to
win the Super Bowl; what we mean is the most recent. LUCA is
the most recent ancestor that gave rise to all the organisms we
see on Earth today. Given that LUCA was quite complex in both
structure and function, it was undoubtedly preceded by other
simpler forms of life, as depicted in Figure 1.19. It is quite possible that life arose many times on early Earth, each form perhaps having only some of the seven attributes listed above. For
example, perhaps some forms of early life did not use ATP as a
common source of chemical energy or developed DNA as the
repository of genetic information. The similarities across all
domains of life present today indicate, however, that only one of
these primitive life forms has descendants that survive today.
1.6a The Rise of Eukaryotes Is Linked
to Increasing Oxygen Levels
When life began, there was no oxygen (O2) in the atmosphere. But,
starting about 2.5 billion years ago, oxygen levels in the atmosphere
FIGURE 1.20 Banded iron. The rust layers in banded iron formations
provide evidence for the rise of atmospheric oxygen.
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energy to extract hydrogen atoms and electrons from compounds
such as hydrogen sulfide. In turn, these hydrogen atoms and electrons were used to fix carbon dioxide into carbohydrates. Instead
of using hydrogen sulfide, cyanobacteria developed the remarkable
ability to oxidize a molecule that was much more abundant: water
(Figure 1.21). This gave cyanobacteria a huge ecological advantage
over other photosynthetic organisms that relied on hydrogen sulfide because it meant they could thrive almost anywhere on the
surface of Earth. After all, when was the last time you walked outside and stepped in a puddle of hydrogen sulfide? The ability to use
water resulted in an explosion of cyanobacterial growth; the planet
turned green. Although it evolved perhaps 2.5 billion years ago, the
water-splitting form of photosynthesis developed by cyanobacteria
is virtually identical to photosynthesis used today by plants and
algae, as well as present-day cyanobacteria.
The photosynthetic oxidation of water not only released valuable electrons, it also released as a by-product molecular oxygen
(O2) (Figure 5.1). After the O2 began to accumulate in the atmosphere, it led to another amazing development in the evolution of
early life: aerobic respiration. As we will discuss in Chapter 5,
compared to anaerobic respiration (e.g., fermentation), aerobic
respiration results in a huge increase in the amount of ATP that
can be generated from the breakdown of food molecules (e.g., glucose). Those prokaryotic cells that developed the pathway of aerobic respiration (e.g., oxidative phosphorylation) had a huge
advantage in terms of energy production. This in turn set the
stage for the next huge step, the evolution of the eukaryotic cell.
1.6b The Theory of Endosymbiosis Suggests
That Mitochondria and Chloroplasts
Evolved from Ingested Prokaryotic Cells
Bacteria and archaea outnumber eukaryotes on the planet by a
massive margin. Compared to eukaryotes, archaea and bacteria
show remarkable biochemical flexibility and thrive in harsh
environments uninhabitable to eukaryotes. That said, prokaryotic cells are simple: they lack the complexity of eukaryotes,
Biophoto Associates/Science Source
a.
b.
2H2O +
light
energy
4H+ + 4e– + O2
FIGURE 1.21 Cyanobacteria. (a) Micrograph of a filamentous
cyanobacterium of the genus Nostoc. (b) Ancient cyanobacteria, like
modern photosynthetic organisms, were able to use water as an electron
donor for photosynthesis. A consequence was the formation of oxygen (O2),
which accumulated in the atmosphere.
20
CHAPTER 1
which evolved into a tremendous diversity of forms, including
plants, fungi, and animals. Within each of these groups are cells
with remarkable specialization in form and function (think of
the flowers of a plant or the brain cells of animals). Contrast this
to archaea and bacteria, which have remained remarkably
simple even though they evolved as early as 4 billion years ago.
A compelling hypothesis for why bacteria and archaea have
remained simple is that increased complexity requires increased
energy production, and eukaryotic cells can generate huge
amounts of it and prokaryotic cells cannot. How can eukaryotes
generate so much more energy? Because they contain energytransducing organelles: mitochondria and chloroplasts. But
how did these organelles develop? Where did they come from?
A wealth of evidence indicates that mitochondria and
chloroplasts are actually descended from free-living prokaryotic cells (Figure 1.22): mitochondria are descended from aerobic bacteria, and chloroplasts are descended from
cyanobacteria. The established model of endosymbiosis states
that the prokaryotic ancestors of modern mitochondria and
chloroplasts were engulfed by larger prokaryotic cells, forming
a mutually advantageous relationship called a symbiosis.
Slowly, over time, the host cell and the endosymbionts became
inseparable parts of the same single-celled organism.
If the theory of endosymbiosis is correct, and both mitochondria and chloroplasts are indeed descendants of bacteria,
then these organelles should share some clear structural and
biochemical features with the forms of life that they evolved
from. Six lines of evidence suggest that both chloroplasts and
mitochondria have distinctly prokaryotic characteristics that
are not found in other eukaryotic organelles:
Morphology. The shape and size of both mitochondria
and chloroplasts are similar to those of prokaryotic cells.
Reproduction. A cell cannot synthesize a mitochondrion or a chloroplast. Just like free-living prokaryotic
cells, where daughter cells arise by cell division, new
mitochondria and chloroplasts are derived from the
division of preexisting organelles. Both chloroplasts
and mitochondria divide by binary fission, which is
how prokaryotic cells divide (see Chapter 20).
Genetic information. If the ancestors of mitochondria and chloroplasts were free-living cells, then these
organelles should contain their own DNA. Both mitochondria and chloroplasts contain their own DNA,
which contains both protein-coding and non-coding
genes (see Chapter 12) that are essential for organelle
function. As with prokaryotic cells, the DNA molecule
in most mitochondria and chloroplasts is circular; the
DNA molecules in the nucleus are linear.
Transcription and translation. Both chloroplasts
and mitochondria contain a complete transcription and
translational machinery. They contain ribosomes
and tRNAs that are necessary to translate organelle
mRNAs into proteins.
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∼1.5 billion years ago
0
Original
prokaryotic
host cell
Billions of years ago
1
2
DNA
Unicellular
eukaryotes
Aerobic bacteria
Multiple
invaginations
of the plasma
membrane
3
4
5
The bacteria
become
mitochondria.
Endoplasmic reticulum
and nuclear envelope
form from the plasma
membrane invaginations
(not part of
endosymbiotic theory).
Photosynthetic
bacteria…
…become
chloroplasts.
Eukaryotic cells:
plants, some
protists
Eukaryotic cells:
animals, fungi,
some protists
FIGURE 1.22 The theory of endosymbiosis. The mitochondrion is thought to have originated
from an aerobic prokaryote that lived as an endosymbiont within an anaerobic prokaryote. The
chloroplast is thought to have originated from a photosynthetic prokaryote that became an
endosymbiont within an aerobic cell that had mitochondria.
Electron transport. Similar to free-living prokaryotic cells, both mitochondria and chloroplasts have
electron transport chains and the enzyme ATP synthase, which together are used to generate chemical
energy. The electron transport chains of bacteria and
archaea are found associated with the plasma
membrane.
Sequence analysis. Sequencing of the genes that
encode the RNA component of the ribosome (ribosomal RNA or rRNA) firmly establishes that these
organelles belong on the bacterial branch of the tree of
life (we will discuss this later in the chapter). The
sequence of chloroplast rRNA most closely matches
that of cyanobacteria, and the sequence of mitochondrial rRNA is most similar to that of heterotrophic
bacteria.
Whereas virtually all eukaryotic cells
contain mitochondria, only plants and algae
contain both mitochondria and chloroplasts. This fact suggests that endosymbiosis
occurred in stages (see Figure 1.22), with the
event leading to the evolution of mitochondria occurring first. Once eukaryotic cells
with the ability for aerobic respiration developed, some became photosynthetic after
taking up cyanobacteria, evolving into the
plants and algae of today.
Endosymbiosis resulted in eukaryotic
cells gaining the ability to generate large
amounts of energy. And this in turn led to
remarkable changes. More energy meant
that cells could become larger, as now there
was enough energy to support more proteins,
carbohydrates, and lipids that make up the
greater cell volume. And cells could become
more complex. This complexity comes about
by having the energy to support a larger
genome that codes for a greater number of
proteins. By overcoming an energy production barrier, eukaryotes could support a
wider variety of genes, which led to what we
know today to be eukaryotic-specific traits
such as the cell cycle, sexual reproduction,
phagocytosis, endomembrane trafficking,
the nucleus, and multicellularity.
1.6c The Endomembrane
System May Be Derived
from the Plasma
Membrane
As detailed in the next chapter, in addition to energy-transforming organelles (mitochondria and
chloroplasts), eukaryotic cells are characterized by an endomembrane system: a collection of internal membranes that
divide the cell into structural and functional regions. These
include the nuclear envelope, the ER, and the Golgi complex.
As we have just seen, there is very strong evidence in support
of the endosymbiotic origin of chloroplasts and mitochondria; however, the origin of the endomembrane system
remains less clear. The most widely held hypothesis is that it
is derived from the infolding of the plasma membrane
(Figure 1.23). Researchers hypothesize that, in cell lines
leading from prokaryotic cells to eukaryotes, pockets of the
plasma membrane may have extended inward and surrounded the nuclear region. Some of these membranes fused
around the DNA, forming the nuclear envelope, which
defines the nucleus. The remaining membranes formed vesicles in the cytoplasm that gave rise to the ER and the Golgi
complex.
CHAPTER 1
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Cytoplasm
Endoplasmic
reticulum
Nuclear region
Nuclear
envelope
FIGURE 1.23 A hypothetical route for the formation of the nuclear
envelope and ER through segments of the plasma membrane that
were brought into the cytoplasm by endocytosis
1.6d Horizontal Gene Transfer
Two major processes led to the integration of function
between the proto-mitochondrion, proto-chloroplast, and
the parent cell. First, some of the genes that were within the
proto-mitochondrion or proto-chloroplast were lost. Most
of these lost genes would have been redundant as the nucleus
would already have genes that encode proteins with the
same function. Second, many of the genes within the protomitochondrion and proto-chloroplast were relocated to the
nucleus through horizontal gene transfer. It is understood
that gene transfer to the nucleus was evolutionarily advantageous, as it would have centralized genetic information and
its control in one place, the nucleus. It’s important to realize
that the outcome of this horizontal gene transfer was not a
change in gene function, only a change in its location.
In a typical eukaryotic cell today, over 90% of the thousands of proteins required for mitochondrial or chloroplast
function are encoded by genes that are found in the nucleus. To
go along with this change of location, a large protein-trafficking and sorting machinery had to evolve (Figure 1.24). Following transcription in the nucleus and translation on cytosolic
ribosomes, proteins destined for the chloroplast or mitochondrion need to be correctly sorted and imported into these
energy-transducing organelles, where they are trafficked to the
correct location.
Our ideas about the movement of genes between the various domains of life are supported by a wealth of genome
sequence analysis. This has led to the conclusion that an even
more accurate tree of life is shown in Figure 1.25. The next unit
Inheritance from one generation to the next can be referred
to as vertical gene transfer, and it explains why the next
generation of a particular species is similar to the current
generation in any given population. It is what has given rise
to the distinct species we see today. What you may not realize
is it’s possible for genetic information (DNA) to move
between unrelated organisms in what is referred to as horizontal gene transfer. Only recently has horizontal
gene transfer been recognized as making an important contribution to evolution. Horizontal gene
Chloroplast
transfer is known to be quite common in bacteria
where genes from one species become integrated
into the genome of another. As a consequence of
Gene transfer
Integration of gene
Chloroplastendosymbiosis, horizontal gene transfer has also
into nuclear genome
encoded proteins
shaped the evolution of eukaryotic cells with bacterial genes ending up in the nucleus.
Following the initial endosymbiosis event, the
Chloroplast
genome
early eukaryotic cell would have contained two disNuclear
genome
tinct compartments, each with its own genome: the
nucleus and the early mitochondrion (protomitochondrion). The ancestor to modern plants and
Protein synthesis
Nuclear-encoded
algae would have also had a proto-chloroplast. These
and import
proteins
Nucleus
compartments (and their genomes) would have continued to function as the independent organisms they
were before the endosymbiotic event. Each contained
DNA instructions for molecules (RNAs and proteins)
required for their own structure and function. But that
FIGURE 1.24 Horizontal gene transfer. Over evolutionary time, some proteinis a very different situation compared to a modern coding genes that were once part of the chloroplast or mitochondrial genome have
eukaryotic cell, where the metabolism of the been relocated to the nuclear genome. Following transcription of these genes,
mitochondria and chloroplast is well integrated into translation occurs in the cytosol before protein import into the organelle
(mitochondrion or chloroplast).
the overall function of the cell.
22
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all cells are structurally and functionally autonomous (independent). This gave way to a key trait of more advanced multicellular organisms: division of labour. Over time, cells became
structurally and functionally distinct. For example, some cells
may have specialized in harvesting energy, whereas others
developed a role related to the motility of the organism. In a
multicellular system, the cells cooperate with one another for
the benefit of the entire organism. Over evolutionary time, this
specialization of cell function led to the development of the specialized tissues and organs that are so clearly evident in larger
eukaryotes.
Like the earliest forms of life, there is little, if any, evidence
in the fossil record of the earliest multicellular organisms. How
they arose and developed is still an area of intense research. It
is thought, however, that multicellularity arose more than once,
most probably independently along each of the lineages leading
to fungi, plants, and animals. A very useful model for the study
of multicellularity is found in a group of green algae called the
volvocine. All the members of this group are evolutionarily
closely related and span the full range of size and complexity,
from the unicellular Chlamydomonas through various colonial
genera to the multicellular Volvox (Figure 1.26). Unlike a true
multicellular organism, a cell colony is a group of cells that are
all of one type; there is no specialization in cell structure or
function. Volvox consists of a sphere of 2000 to 3000 small,
flagellated Chlamydomonas-like cells that provide the individual Volvox with the ability to move. In addition, within the
sphere lie about 16 large nonmotile cells that serve a specialized
role in reproduction.
Eukarya
Bacteria
Archaea
n
LUCA
FIGURE 1.25 A tree of life incorporating the endosymbiotic events
from Bacteria to Eukarya. While the host eukaryotic cell and the nuclear
genome are directly descended from the Archaea, the energy-transducing
organelles, the mitochondria and chloroplast, are descended from freeliving bacteria.
of this book is devoted to detailed analyses of the biology and
evolutionary relationships between and within the three
domains: Bacteria, Archaea, and Eukarya.
1.6e The Evolution of Multicellular
Eukaryotes Led to Increased
Specialization
STUDY BREAK QUESTIONS
1. The Earth’s atmosphere contains 21% O2. Where did that
oxygen come from?
2. What are the major lines of evidence in support of the theory
that mitochondria and chloroplasts are descendants of
prokaryotic cells?
Cristian A. Solari, University of Arizona
Cristian A. Solari, University of Arizona
One of the most profound transitions in the history of life was
the evolution of multicellular eukaryotes. Clear evidence of
multicellularity, in the form of species of algae, appears in the
fossil record starting about 1.2 billion years ago. The actual
events that led to the development of multicellularity are a mystery, but it is easy to envision how it may have occurred. Perhaps
a group of individual cells of a particular species came together
to form a colony, or a single cell divided and the resulting two
cells did not separate. In the simplest of multicellular organisms,
Chlamydomonas reinhardtii,
a unicellular alga
Gonium pectorale, a group
of eight undifferentiated
cells
Eudorina elegans, a
spherical colony of
undifferentiated cells
Cristian A. Solari, University of Arizona
ho
toc
Mi
a
dri
Cristian A. Solari, University of Arizona
ts
las
rop
lo
Ch
Volvox aureu, smaller
somatic cells and a few
reproductive cells
FIGURE 1.26 Differences in degree of multicellularity among volvocine algae
CHAPTER 1
DEFInInG LIFE AnD ITs ORIGIns
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In all our previous discussions on the origins of life and LUCA,
we need to remind ourselves that there is no direct evidence for
the earliest forms of life. This section provides an overview of
what we actually do know about the history of life on Earth as
reflected by the remains of organisms that have been preserved
in the fossil record.
1.7a The Fossil Record Is Invaluable
but Incomplete
The fossil record provides the only direct evidence about what
life was like millions of years ago. Fossilized skeletons, shells,
stems, leaves, and flowers tell us about the size and appearance of ancient animals and plants. The fossil record has also
allowed scientists to see how species have changed over time
as it chronicles the proliferation and extinction of evolutionary lineages, and it provides data on the geographical distribution of extinct species. As discussed in Chapter 16,
Darwin’s ability to compare fossil specimens with living relatives was very influential in his development of the notion of
natural selection.
Obviously, the fossil record is an invaluable resource to
understand the past, but it is important to note that it represents only a small fraction of the organisms that once lived on
Earth, and thus it vastly underrepresents the diversity of life.
The fossil record only really represents a record of the most
successful of organisms; those that were very abundant, had
wide distributions, and possessed hard parts that could be fossilized. Soft-bodied organisms with small geographic distributions that lived in environments where erosion was a dominant
process are underrepresented in the fossil record—if they are
in it at all.
a. Sedimentation
1.7b Fossils Form When Organisms
Are Buried by Sediments or Preserved
in Oxygen-Poor Environments
Most fossils form in sedimentary rocks. Rain and runoff constantly erode the land, carrying fine particles of rock and soil
downstream to a swamp, a lake, or the sea. Particles settle to the
bottom as sediments, forming successive layers, called strata,
over millions of years (Figure 1.27). The weight of newer sediments compresses the older layers beneath them into a solid
matrix: sand into sandstone and silt, or mud into shale. Fossils
form within the layers when the remains of organisms are buried
in the accumulating sediments. Because sedimentation superimposes new layers over old ones, the lowest strata in a sedimentary rock formation are usually the oldest, and the highest
layers are the newest.
The process of fossilization is a race against time because
the soft remains of organisms are quickly consumed by scavengers or decomposed by microorganisms. Thus, fossils usually
preserve the details of hard structures, such as the bones, teeth,
and shells of animals and the wood, leaves, and pollen of plants.
During fossilization, dissolved minerals replace some parts
molecule by molecule, leaving a fossil made of stone
(Figure 1.28a); other fossils form as moulds, casts, or impressions in material that is later transformed into solid rock
(Figure 1.28b).
In some environments, the near absence of oxygen prevents decomposition, and even soft-bodied organisms are preserved. Some plants, insects, and tiny lizards and frogs are
embedded in amber, the fossilized resin of coniferous trees
(Figure 1.28c). Other organisms are preserved in glacial ice,
deeply frozen soil, coal, tar pits, or the highly acidic water of
peat bogs (Figure 1.28d). Sometimes organisms are so well preserved that researchers can examine their internal anatomy,
cell structure, food in their digestive tracts, and even their
DNA sequences.
Highest strata
contain the most
recent fossils.
b. Geological strata in the Painted Desert, Arizona
Lowest strata
contain the
oldest fossils.
iStock.com/Habesen
1.7 The Fossil Record
FIGURE 1.27 Sedimentation and geological strata. (a) Sedimentation deposits successive layers at the bottom of a lake or sea. (b) Over millions of
years, the upper layers compress those below them into rock. When the rocks are later exposed by uplifting or erosion, the different layers are evident as
geological strata.
24
CHAPTER 1
DEFInInG LIFE AnD ITs ORIGIns
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Newman Mark/Age Fotostock
a. Petrified wood (Araucariaceae)
b. Sphenopteris
a. Stromatolites date to
∼3.4 billion years ago
Tobkatrina/Shutterstock.com
David Lyons/AGE Fotostock
c. Flying insects in amber
cussion of isotopes). Researchers have discovered sedimentary
rocks originating from the ocean floor that contain deposits
that have lower levels of the 13C isotope than expected. The
most likely explanation is that the deposits are actually the
remains of carbon molecules of ancient microbes. These sediments have been dated to approximately 3.9 billion years ago. If
correct, this would push the origins of life to perhaps as early as
4 billion years ago, approximately 600 million years after Earth
was formed.
The earliest conclusive evidence of life is found in the fossilized remains of structures called stromatolites, the oldest
being formed about 3.5 billion years ago. A stromatolite is a
type of layered rock formed when microorganisms bind particles of sediment together, forming thin sheets (Figure 1.29).
b. Cyanobacteria
Dr. Tony Brain/Science Source
Monica Johansen/Shutterstock.com
South China Morning Post/Getty Images
d. Mammoth (Mammonteus)
c. Possible microfossils date to ∼3.4 billion years ago
1.7c
The Earliest Fossils
The earliest indirect evidence of life, which predates any actual
fossil evidence, comes from research looking at the carbon
composition of ancient rocks. Early photosynthetic organisms
would have had the ability to take CO2 from the atmosphere
and use it to synthesize various organic molecules (see Chapter
6 for details). During this process, organisms would have preferentially incorporated the carbon-12 isotope (12C) over other
isotopes such as carbon-13 (13C) (see The Purple Pages for a dis-
© J. William Schopf
FIGURE 1.28 Fossils. (a) Petrified wood in Arizona formed when minerals
replaced the wood of dead trees, molecule by molecule. These forests lived
during the late Triassic period, about 225 million years ago. (b) The remains
of a fern (Sphenopteris) from the Carboniferous period, 300 million years
ago, were preserved in coal. (c) These 10-million-year-old mosquitoes were
trapped in the oozing resin of a coniferous tree and are now encased in
amber. (d) A frozen baby mammoth that lived about 40 000 years ago was
discovered embedded in Siberian permafrost in 1977.
FIGURE 1.29 Early fossil evidence of life. (a) Stromatolites exposed
at low tide in Western Australia’s Shark Bay. These mounds, which consist
of mineral deposits made by cyanobacteria, are about 2000 years old; they
are highly similar in structure to fossil stromatolites that formed more
than 3 billion years ago. (b) Modern cyanobacteria filaments. These
photosynthetic bacteria use water as an electron donor for
photosynthesis and, as a by-product, release oxygen. (c) Microfossils. The
left panel shows a cross-section through rock from Western Australia that
has been dated to 3.4 billion years ago. On the right are further
magnifications of three microfossils that have been interpreted as
filamentous, possibly cyanobacteria.
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The sediments found in any one place form recognizable strata
(layers) that differ in colour, mineral composition, particle size,
and thickness (see Figure 1.27b). If they have not been disturbed, the strata are arranged in the order in which they
formed, with the youngest layers on top.
Geologists of the early 19th century deduced that the fossils discovered in a particular sedimentary stratum, no matter
where on Earth it is found, represent organisms that lived and
died at roughly the same time in the past. Because each stratum
formed at a specific time, the sequence of fossils in the lowest
(oldest) to the highest (newest) strata reveals their relative ages.
Geologists originally used the sequence of strata and their distinctive fossil assemblages to establish the geological time scale
(Table 1.2).
Although the geological time scale provides a relative
dating system for sedimentary strata, it does not tell us how old
the rocks and fossils actually are. But many rocks contain
unstable radioisotopes, which, from the moment they form,
begin to break down into other, more stable elements. The
breakdown proceeds at a steady rate that is unaffected by
chemical reactions or environmental conditions such as temperature or pressure. Using a technique called radiometric
dating, scientists can estimate the age of a rock by noting how
much of an unstable “parent” isotope has decayed to another
form. By measuring the relative amounts of the parent radioisotope and its breakdown products, and comparing this ratio
with the isotope’s half-life (the time it takes for half a given
amount of radioisotope to decay), researchers can estimate the
absolute age of the rock. Table 1.2 presents these age estimates
along with the major geological and evolutionary events of
each period.
Phanerozoic
Eon
Era
Period
Epoch
Cenozoic
Quaternary
Holocene
Pleistocene
Pliocene
Mesozoic
Neogene
Miocene
Paleozoic
Oligocene
Paleogene
Eocene
Paleocene
Proterozoic
1.7d Scientists Assign Relative and Absolute
Dates to Geological Strata and the
Fossils They Contain
TABLE 1.2 The Geological Time Scale and Major Evolutionary Events
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Archean
Modern stromatolites are found in habitats characterized by
warm shallow water and are most common in Australia.
Modern-day stromatolites are formed by the action of a specific
group of photosynthetic bacteria called cyanobacteria. Because
they were able to undertake oxygenic photosynthesis, cyanobacteria (see Figure 1.21) were not the earliest forms of life but,
rather, must have been preceded by much simpler organisms.
STUDY BREAK QUESTIONS
Silurian
Ordovician
Cambrian
Hadean
1. What biological materials are the most likely to fossilize?
2. Why does the fossil record provide an incomplete portrait of
life in the past?
3. What sorts of information can paleobiologists discern from the
fossil record?
26
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Millions of
Years Ago Major Evolutionary Events
0.01
2.6
5.3
Mass Extinctions
RIP
Origin of modern humans; major glaciations
Origin of bipedal human ancestors
Angiosperms and mammals further diversify and dominate terrestrial habitats
23.0
Primates diversify; origin of apes
33.9
Angiosperms and insects diversify; modern orders of mammals differentiate
55.8
65.5
Grasslands and deciduous woodlands spread; modern birds, mammals, snakes, pollinating
insects diversify; continents approach current positions
First angiosperms; insects, marine invertebrates, fishes, dinosaurs diversify; asteroid impact
causes mass extinction at end of period, eliminating most dinosaurs and many other groups
145.5
201.6
251.0
299.0
Gymnosperms abundant in terrestrial habitats; modern fishes diversify; dinosaurs diversify
and dominate terrestrial habitats; frogs, salamanders, lizards, birds, and placental mammals
appear; continents continue to separate
Predatory fishes and reptiles dominate oceans; gymnosperms dominate terrestrial habitats;
diversification of dinosaurs; early mammals; Pangaea starts to break up; mass extinction at
end of period
Insects and amniotes abundant and diverse in swamp forests; some amniotes colonize oceans;
fishes colonize freshwater habitats; continents coalesce into Pangaea, causing glaciation and
decline in sea level; huge volcanic eruptions cause mass extinction at end of period, eliminating
85% of species worldwide
RIP
Cretaceous
RIP
Triassic
RIP
Permian
Vascular plants form large swamp forests; first flying insects; amphibians diversify; first
amniotes appear
359.0
RIP
Terrestrial vascular plants diversify; fungi, invertebrates, tetrapod vertebrates colonize land; first
insects and seed plants; major glaciation at end of period; mass extinction, mostly of marine life
Devonian
416.0
Jawless fishes diversify; first jawed fishes, first terrestrial arthropods and vascular plants
RIP
444.0
Major radiations of marine invertebrates and jawless fishes; first terrestrial plants, fungi,
and animals; major glaciation at end of period causes mass extinction of marine life
Ordovician
Appearance of modern animal phyla, including vertebrates (Cambrian explosion); simple
marine communities; mass extinctions eliminate many groups at end of period
Cambrian
488.0
RIP
542.0
High concentration of oxygen in atmosphere; origin of eukaryotic cells; evolution and
diversification of protists, fungi, soft-bodied animals
2500
Origin of life; evolution of prokaryotes, including anaerobic and photosynthetic bacteria;
oxygen starts to accumulate in atmosphere; origin of aerobic respiration
3850
Formation of Earth, including crust, atmosphere, and oceans
4600
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self - test questions
Recall/Understand
1. Why are viruses NOT considered a form of life?
a. They do not have a nucleus.
b. They are not made of protein.
c. They lack ribosomes.
d. They lack nucleic acid.
2. According to the Oparin–Haldane hypothesis, what was the
composition of the primordial atmosphere?
a. water, molecular nitrogen (N2), and carbon dioxide
b. molecular hydrogen (H2), water, ammonia, and methane
c. water, molecular oxygen (O2), and ammonia
d. molecular hydrogen (H2), water, argon, and neon
3. Clay may have played an important role in what aspect of the
development of life?
a. formation of monomers, such as amino acids, and
membrane-bound compartments, such as liposomes
b. formation of polymers such as short proteins or nucleic
acids
c. formation of multicellular organisms with membranebound compartments, such as liposomes
d. formation of multicellular organisms using polymers such
as short proteins or nucleic acids
4. Which of these statements best describes ribozymes?
a. They are composed of only RNA.
b. They are able to catalyze reactions faster than enzymes.
c. They are found only in ancient cells.
d. They are polymers of amino acids.
5. Which of these statements is the reason why DNA is thought to
have replaced RNA as the means to store genetic information?
a. The sugar ribose, which is present in DNA but not RNA, is
less prone to breakdown.
b. DNA contains uracil, which is more stable than the thymine
present in RNA.
c. Unlike RNA, DNA can exist in very complex threedimensional shapes, which are very stable.
d. The presence of complementary strands in DNA means that
single-base mutations can be easily repaired.
6. As part of the evolution of eukaryotic cells, infolding of the
plasma membrane is thought to have led to the formation of
which of these structures?
a. ribosomes
b. microtubules
c. mitochondria
d. endoplasmic reticulum
Apply/Analyze
7. Which of these statements supports the theory of
endosymbiosis?
a. The plasma membrane is a made of phospholipid bilayer.
b. Both mitochondria and chloroplasts possess their own
genomes.
c. Both mitochondria and chloroplasts are surrounded by a
membrane.
d. The nuclear envelope is derived from infolding of the
plasma membrane.
28
CHAPTER 1
8. Which of these lists of events is in the correct order by first
appearance?
a. O2 in the atmosphere, anoxygenic photosynthesis, aerobic
respiration, oxygenic photosynthesis
b. O2 in the atmosphere, aerobic respiration, oxygenic photosynthesis, anoxygenic photosynthesis
c. anoxygenic photosynthesis, oxygenic photosynthesis, O2 in
the atmosphere, aerobic respiration
d. anoxygenic photosynthesis, aerobic respiration, O2 in the
atmosphere, oxygenic photosynthesis
9. The Asgard is a group of archaeans that evidence suggests is
closely related to eukaryotes. What is the evidence to support this
claim?
a. Like eukaryotes, Asgard cells have been shown to contain
structures similar to nuclei.
b. Asgard cells have been shown to contain mitochondria.
c. Asgard DNA contains genes that are similar to ones found
only in eukaryotes.
d. Similar to eukaryotes, Asgard DNA contains genes that code
from ribozymes.
10. Suppose that the Miller–Urey experiment contained oxygen in its
chamber. How would the results of the experiment change?
a. The presence of oxygen would not affect the synthesis of
organic compounds, but it would prevent the accumulation
of their precursors.
b. The presence of oxygen would prevent the accumulation of
organic compounds by quickly oxidizing them or their
precursors.
c. The presence of oxygen would speed up the accumulation of
organic compounds.
d. The presence of oxygen would speed up the accumulation of
inorganic precursors.
Create/Evaluate
11. Thinking about the origin of life on Earth was transformed by
the discovery that RNA molecules act as catalysts in living cells.
Why is this discovery revolutionary?
a. RNA may have been able to carry genes on it.
b. RNA may have been capable of self-replication and catalysis
of simple reactions, before DNA and enzymes arose.
c. RNA may have been a precursor in the evolution of DNA.
d. RNA viruses might have been involved in the evolution of life.
12. The Miller–Urey experiment was a huge breakthrough in our
understanding of the origins of life. What was its major conclusion?
a. Abiotic synthesis of molecules requires oxygen (O2).
b. Biological molecules could be formed without energy.
c. Proteins could be synthesized without ribosomes.
d. Abiotic synthesis of amino acids was possible.
13. Explain how scientists determine relative and absolutes dates of
geological strata and the fossils they contain.
14. We have no physical evidence that LUCA existed, but we are quite
certain that it did. Why are we so certain that LUCA existed?
15. Compare the three domains regarding their chromosome
structure, DNA location, chromosome segregation, and the
presence of introns in their genes.
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