ISTUDY
CHAPTER OUTLINE
1.1 Levels of Biology
1.2 Core Concepts of Biology
1.3 Biological Evolution
1.4 Classification of Living Things
1.5 Biology as a Scientific Discipline
1.6 Core Skills of Biology
Summary of Key Concepts
Assessing Your Knowledge and Skills
1
An Introduction
to Biology
B
iology is the study of life. The diverse forms of life
found on Earth provide biologists with an amazing array
of organisms to study. In many cases, the investigation of living
things leads to discoveries that no one would have imagined. For
example, researchers determined that the venom from certain
poisonous snakes contains a chemical that lowers blood pressure
in humans. By analyzing that chemical, scientists developed drugs
to treat high blood pressure (Figure 1.1).
Biologists have discovered that plants can communicate
with each other. For example, the beautiful umbrella thorn acacia
(Vachellia tortillis), shown in Figure 1.2, emits volatile organic molecules when it is attacked by herbivores. These molecules warn
other nearby acacia trees that herbivores are in the area, and
those trees release toxins to protect themselves.
Another interesting example of a biological discovery is a
seemingly bizarre phenomenon known as zombie parasites. As
you may know, zombies are fictional creatures featured in some
horror and fantasy novels and movies, where they appear as dead
creatures that are able to move because of some magical force. A
The red fox, Vulpes vulpes. Russian researchers have bred red
foxes in captivity and selected for those that are more tame than red
foxes in nature. Their temperament is similar to that of friendly dogs.
Paul Reeves Photography/Shutterstock
H
N
N
O
CH2COOH
C
O
OCH2CH3
ACE inhibitor (Lotensin)
Figure 1.1 The Brazilian arrowhead viper and an inhibitor of high
blood pressure. Derivatives of a chemical, called an angiotensinconverting enzyme (ACE) inhibitor, are found in the venom of the
Brazilian arrowhead viper and are commonly used to treat high
blood pressure. Francois Gohier/Science Source
Figure 1.2 Plant communication. If attacked by herbivores, this
acacia tree will emit molecules that will warn other acacia trees in
the area. Mark Snodgrass/Getty Images
ISTUDY
Table 1.1 Examples of Zombie Parasites
Host
Parasite
Description
House cricket
(Acheta domesticus)
Horsehair worm
(Paragordius varius)
A horsehair worm larva infects a cricket and grows inside it. The cricket is terrestrial, but the adult stage of
the horsehair worm is aquatic. When the larva matures into an adult, it alters the behavior of the cricket,
causing it to jump into the nearest body of water! As the cricket drowns, an adult horsehair worm emerges.
Spider (Plesiometa
argyra)
Wasp (Hymenoepimecis
argyraphaga)
A female wasp glues an egg onto a spider’s body. After the egg develops into a larva, the larva pokes
a few holes in the spider’s abdomen, which allows it to suck the spider’s blood and also to transfer
chemicals into the spider, which control its behavior. The spider stops building its normal orb-shaped
web and starts building a web whose geometry is strikingly different: The new web is designed to
suspend the larva’s cocoon in the air, where it will be protected from predators.
Various vertebrates,
including mice and
rats
Protozoan (Toxoplasma
gondii)
Toxoplasma gondii is a parasite whose life cycle involves more than one vertebrate host. The definitive
host is the cat, which is where T. gondii becomes mature and reproduces sexually. An intermediate
host can be any of a variety of vertebrates, including mice and rats, which can ingest the parasite from
cat feces. In the intermediate host, the parasite develops and reproduces asexually. To escape an
intermediate host, such as a mouse or rat, and move to the definitive host, T. gondii dramatically alters
the host’s behavior. The infected animal becomes attracted to the smell of cat urine! This makes it
more likely to be eaten by a cat and thereby allows T. gondii to enter its definitive host and mature.
zombie parasite is a parasite that infects its host and is then able to
control the host’s behavior. A relatively small group of researchers
have begun to investigate this phenomenon, and their work has
spawned a new field called neuroparasitology—the study of how
parasites control the nervous systems of their hosts. During the
past few decades, researchers have discovered many examples of
zombie parasites. A few are described in Table 1.1.
These are but a few of the many discoveries that make biology
an intriguing discipline. The study of life not only reveals the fascinating characteristics of living species but also leads to the development of medicines and research tools that benefit the lives of people.
To make new discoveries, biologists view life from many different perspectives: What is the composition of living things? How is life
organized? How do organisms reproduce? Sometimes the questions
posed by biologists are fundamental and even philosophical in nature:
How did living organisms originate? Can we live forever? What is the
physical basis for memory? Can we save endangered species?
1.1
Levels of Biology
Learning Outcome:
1. Explain how life can be viewed at different levels of biological
complexity.
Let’s begin our journey through the wonderful world of biology by
considering how life is organized. The term organism can be applied
to all forms of life. Organisms maintain an internal order that is separated from the environment. The complexity of living organisms can
be analyzed at different levels, starting with the smallest level of organization and progressing to levels that are physically much larger and
more complex. Figure 1.3 depicts a biologist’s view of the levels of
biological organization.
1. Atoms. An atom is the smallest unit of an element that has the
chemical properties of the element. All matter is composed of atoms.
Future biologists will continue to make important advances.
Biologists are scientific explorers looking for answers to some of
life’s most enduring mysteries. Unraveling these mysteries presents
exciting challenges to the best and brightest minds. The rewards of
a career in biology include the excitement of forging into uncharted
territory, the thrill of making discoveries that can improve the health
and lives of people, and the satisfaction of trying to preserve the
environment and protect endangered species. For these and
many other compelling reasons, students seeking challenging and
rewarding careers may wish to choose biology as a lifelong pursuit.
In this chapter, we will begin by examining the levels of biology
and the core concepts that are common to all forms of life. One of
those core concepts is evolution, which is discussed in greater depth
in Section 1.3. We then explore the general approaches that scientists
follow when making new discoveries. Finally, we will consider the skills
that students need to develop as they pursue careers in this exciting
discipline and the ways in which this textbook fosters those skills.
2. Molecules and macromolecules. As discussed in Unit I, atoms bond
with each other to form molecules. A polymer such as a polypeptide
is formed of many molecules bonded together and is called a
macromolecule. Carbohydrates, proteins, and nucleic acids (DNA
and RNA) are important macromolecules found in living organisms.
3. Cells. The simplest unit of life is the cell, which we will
examine in Unit II. A cell is surrounded by a membrane and
contains a variety of molecules and macromolecules. Unicellular
organisms are composed of one cell, whereas multicellular
organisms, such as plants and animals, contain many cells.
4. Tissues. In multicellular organisms, many cells of the same
type associate with each other to form tissues. An example is
muscle tissue.
5. Organs. In complex multicellular organisms, an organ is
composed of two or more types of tissue. For example, the
heart is composed of several types of tissues, including muscle,
nervous, and connective tissue.
ISTUDY
AN INTRODUCTION TO BIOLOGY
1
Atoms
2
Molecules and
macromolecules
3
5
6
4
Organs
Cells
Tissues
Organism
10
7
3
Biosphere
Population
9
8
Ecosystem
Community
Figure 1.3 The levels of biological organization.
Concept Check:
At which level of biological organization would you place a herd of buffalo?
6. Organism. All living things can be called organisms.
Biologists classify organisms as belonging to a particular
species, which is a related group of organisms that share a
distinctive form and set of attributes in nature. The members of
the same species are closely related genetically. In Units VI and
VII, we will examine plants and animals at the levels of cells,
tissues, organs, and complete organisms.
7. Population. A group of organisms of the same species that
occupy the same environment is called a population.
8. Community. A biological community is an assemblage of
populations of different species. The types of species found in
a community are determined by the environment and by the
interactions of the species with each other.
9. Ecosystem. Researchers may extend their work beyond living
organisms and also study the physical environment. Ecologists
analyze ecosystems, which are formed by the interactions of
a community of organisms with their physical environment.
Unit VIII considers biological organization from populations to
ecosystems.
10. Biosphere. The biosphere includes all of the places on the
Earth where living organisms exist. Life is found in the air, in
bodies of water, on the land, and in the soil.
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4
CHAPTER 1
1.2
Core Concepts of Biology
Learning Outcome:
1. Describe the core concepts of biology as advocated by Vision
and Change.
In 2007, the American Association for the Advancement of Science
initiated a series of regional conversations with more than 200 biology faculty to discuss how to improve undergraduate biology education. In 2009, using the findings of these regional conversations,
the organization held a conference called Vision and Change in
Undergraduate Biology Education. More than 500 biology faculty,
college and university administrators, representatives of professional
societies, and students and postdoctoral scholars from around the
country attended the conference. The proceedings led to various recommendations that can be found at http://visionandchange.org.
A key outcome of Vision and Change was the identification of
five core concepts of biology (Figure 1.4):
1. Evolution: The diversity of life evolved over time by processes
of mutation, natural selection, and genetic exchange.
2. Structure and function: Basic units of structure define the
function of all living things.
(a) Evolution:
Biological evolution, or simply evolution, refers to a heritable change in a population
of organisms from generation to generation. As a result of evolution, populations
become better adapted to the environment in which they live. For example, the long
snout of an anteater is an adaptation that enhances its ability to obtain food, namely
ants, from hard-to-reach places. Over the course of many generations, the fossil
record indicates that the long snout occurred via biological evolution in which modern anteaters evolved from populations of organisms with shorter snouts.
(b) Structure and function:
Biologists often say “structure determines function.” This core concept pertains to
very tiny biological molecules and to very large biological structures. The feet of different birds provide a striking example. Aquatic birds have webbed feet that function as paddles for swimming. By comparison, the feet of nonaquatic birds are not
webbed and are better adapted for grasping food, perching on branches, and running along the ground. The structure of a bird’s feet, webbed versus nonwebbed, is
a critical feature that affects their function.
(c) Information:
Genetic material composed of DNA (deoxyribonucleic acid) provides a blueprint for the
organization, development, and function of living things. During reproduction, a copy
of this blueprint is transmitted from parents to offspring. DNA is heritable, which means
that offspring inherit DNA from their parents. A key feature of reproduction is that offspring tend to have characteristics that greatly resemble those of their parent(s). As
seen here, this mother dolphin and her offspring have strikingly similar features.
(d) Energy and matter:
All living organisms acquire energy and matter from the environment and use them
to synthesize essential molecules and maintain the organization of their cells and
bodies. These sunflower plants carry out photosynthesis, in which they capture
light energy and acquire carbon dioxide and water, thereby allowing them to make
carbohydrates. This process provides energy and organic molecules, allowing the
plants to grow and produce beautiful flowers.
(e) Systems:
When the parts of an organism interact with each other or with the external environment to create novel structures and functions, the resulting characteristics are called
emergent properties. For example, the human eye is composed of many different
types of cells that are organized to sense incoming light and transmit signals to the
brain. Our ability to see is an emergent property of this complex arrangement of different cell types. Biologists use the term systems biology to describe the study of
how new properties of life emerge due to complex interactions of its individual parts.
Figure 1.4 Core concepts of biology, as advocated by Vision and Change. These core concepts will be emphasized throughout
this textbook. a: Lucas Leuzinger/Shutterstock; b: G.K. & Vikki Hart/Getty Images; c: Image Source/Getty Images; d: Photo by Bruce Fritz/USDA; e: Maria Teijeiro/Getty
Images
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AN INTRODUCTION TO BIOLOGY
3. Information flow, exchange, and storage: The growth and
behavior of organisms are activated through the expression of
genetic information.
4. Pathways and transformations of energy and
matter: Biological systems grow and change via processes
that are based on chemical transformation pathways and are
governed by the laws of thermodynamics.
5. Systems: Living systems are interconnected and interacting.
The interactions of living systems result in emergent
properties, which are properties that manifest themselves as the
result of various system components working together, not as a
property of any individual component.
A key goal of this textbook is to bring to life these five core concepts
of biology. These concepts will be highlighted in each chapter with a
Vision and Change icon,
, which identifies subsections and figures
that focus on one or more of these five core concepts.
1.3 Biological Evolution
Learning Outcomes:
1. Explain two mechanisms by which evolutionary change occurs:
vertical descent with mutation and horizontal gene transfer.
2. Describe how changes in genomes and proteomes underlie
evolutionary changes.
3. Explain how a population can change from generation to
generation via artificial selection.
Unity and diversity are two words often used to describe the living
world. All modern forms of life display a common set of characteristics that distinguish them from nonliving objects. In this section, we
will explore how this unity of common traits is rooted in the phenomenon of biological evolution, or simply evolution, which is a heritable change in a population of organisms from one generation to the
next. Life on Earth is united by an evolutionary past in which modern
organisms have evolved from populations of pre-existing organisms.
This unity is a core concept of biology.
However, evolutionary unity does not mean that organisms are
exactly alike. The Earth has many different types of environments,
ranging from tropical rain forests to salty oceans, hot and dry deserts,
and cold mountaintops. Diverse forms of life have evolved in ways
that help them prosper in the different environments the Earth has to
offer. In this and the following section, we will begin to examine the
unity and diversity that exist within the biological world.
Modern Forms of Life Are Connected by an
Evolutionary History
Life began on Earth as primitive cells about 3.5–4 billion years ago
(bya). Since that time, populations of living organisms have undergone evolutionary changes that ultimately gave rise to the species
we see today. Understanding the evolutionary history of species can
provide key insights into the structure and function of an organism’s
body, because evolutionary change frequently involves modifications
of characteristics in pre-existing populations. Over long periods of
time, populations may change so that structures with a particular
5
Ancestral
limb
Modification over time
Bat wing
Dolphin
flipper
Figure 1.5 An example of a modification that has occurred as a
result of evolution. The wing of a bat and the flipper of a dolphin are
modifications of a limb that was used for walking in a pre-existing
ancestor.
Core Concepts: Evolution, Structure and Function
Via evolution, the different structures of the front limbs
seen here result in functions that are best suited for
these organisms.
function become modified to serve a new function. For example, the
wing of a bat is used for flying, and the flipper of a dolphin is used
for swimming. Evidence from the fossil record indicates that both
structures were modified from a front limb that was used for walking
in a pre-existing ancestor (Figure 1.5).
Evolutionary Change Involves Changes
in the Genetic Material
The example shown in Figure 1.5 represents evolution at the macroscopic level. At the molecular level, evolution involves changes in
the genetic material, which is composed of DNA (deoxyribonucleic
acid). DNA provides a blueprint for the organization, development,
and function of living things. During reproduction, a copy of this
blueprint is transmitted from parent to offspring. DNA is heritable,
which means that offspring inherit DNA from their parents.
As discussed in Unit III, genes, which are segments of DNA,
govern the characteristics, or traits, of organisms. Most genes are
transcribed into a type of RNA (ribonucleic acid) molecule called
messenger RNA (mRNA), which is then translated into a polypeptide with a specific amino acid sequence. A protein is composed of
one or more polypeptides. The structures and functions of proteins
play a key role in determining the traits of organisms.
On relatively rare occasions, changes may occur in DNA. A
mutation is a heritable change in the genetic material—one that can
be passed from cell to cell or from parent to offspring. Mutations can
alter the properties of genes and thereby affect the characteristics of
the offspring that inherit them. With regard to survival, mutations can
be beneficial, detrimental, or neutral. As described next, changes in
the genetic material underlie the process of evolution.
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6
CHAPTER 1
Changes to the Genetic Material during Evolution
May Occur in Different Ways
As a given species evolves and as new species are formed, different
types of mechanisms may cause changes in the genetic material. Two
common mechanisms are vertical descent with mutation and horizontal gene transfer. Let’s take a brief look at each one.
Vertical Descent with Mutation The traditional way to study evolution is to examine a progression of changes in a series of related
ancestral species. Such a series is called a lineage. Figure 1.6 shows
a portion of the lineage that gave rise to modern horses. This type of
evolution is called vertical evolution because it occurs in a lineage.
Biologists have traditionally depicted such evolutionary change in a
diagram like the one shown in Figure 1.6. In this mechanism of evolution, new species evolve from pre-existing ones by the accumulation
of mutations. But why would some mutations accumulate in a population and eventually change the characteristics of an entire species?
One reason is that a mutation may alter the traits of organisms in a
way that increases their chances of survival and reproduction. When a
mutation causes such a beneficial change, the frequency of the mutation may increase in a population from one generation to the next, a
process called natural selection. This topic is discussed in Units IV
and V. Evolution also involves the accumulation of neutral changes
that do not benefit or harm a species, and it sometimes involves rare
changes that may be harmful.
With regard to the horses shown in Figure 1.6, the fossil
record has revealed adaptive changes in various traits such as size
and tooth morphology. The first horses were the size of dogs,
whereas modern horses typically weigh more than a half ton. The
teeth of Hyracotherium were relatively small compared with those
of modern horses. Over the course of millions of years, horses’
teeth have increased in size, and a complex pattern of ridges has
developed on the molars.
How do evolutionary biologists explain these changes in horse
characteristics? They can be attributed to natural selection, in which
changing global climates favored the survival and reproduction of
horses with certain types of traits. Over North America, where much
of horse evolution occurred, large areas changed from dense forests
to grasslands. Horses with genetic variation that made them larger
0
Hippidium and
other genera
Equus
5
Nannippus
Styohipparion
Neohipparion
Hipparion
10
Sinohippus
Pliohippus
Megahippus
Calippus
Millions of years ago (mya)
Archaeohippus
20
Anchitherium
Merychippus
Hypohippus
Parahippus
Miohippus
Mesohippus
40
Figure 1.6 An example of vertical evolution: the
Paleotherium
Epihippus
Propalaeotherium
Orohippus
Pachynolophus
55
Hyracotherium
horse lineage. This diagram shows the horse lineage.
The highlighted branch gave rise to the modern horse
(Equus), which evolved from ancestors that were much
smaller. The vertical evolution shown here occurred
due to the accumulation of mutations that altered the
traits of the species.
Concept Check: What is the relationship between
biological evolution and natural selection?
ISTUDY
AN INTRODUCTION TO BIOLOGY
were more likely to escape predators and to be able to travel greater
distances in search of food. The changes seen in horses’ teeth are consistent with a dietary shift from eating tender leaves to eating grasses
and other types of vegetation that are more abrasive and require more
chewing.
Horizontal Gene Transfer The most common way for genes to
be transferred is in a vertical manner. This can involve the transfer of
genetic material from a mother cell to daughter cells, or it can occur
via gametes—sperm and egg—that unite to form a new organism.
However, as discussed in later chapters, genes are sometimes transferred between organisms by other mechanisms. These other mechanisms are collectively known as horizontal gene transfer, which is
the transfer of genetic material from one organism to another organism that is not its offspring. In some cases, horizontal gene transfer can occur between members of different species. For example,
you may have heard in the news media that resistance to antibiotics among bacteria is a growing medical problem. As discussed in
Chapter 19, genes that confer antibiotic resistance are sometimes
transferred between different bacterial species (Figure 1.7).
Genes transferred horizontally may be subject to natural selection
and promote changes in an entire species. This has been an important
mechanism of evolutionary change, particularly among bacterial species. In addition, during the early stages of evolution, which occurred
a few billion years ago, horizontal gene transfer was an important part
of the process that gave rise to all modern species.
Traditionally, biologists have described evolution using diagrams
that depict the vertical evolution of species on a long time scale. This
type of evolutionary tree was shown earlier in Figure 1.6. For many
decades, a simplistic view held that all living organisms evolved from
a common ancestor, resulting in a “tree of life” that depicted the vertical evolution that gave rise to all modern species.
Now that we understand the great importance of horizontal
gene transfer in the evolution of life on Earth, biologists have reevaluated the way evolution has occurred over time. Rather than
a tree of life, a more appropriate way to view the unity of living
DNA
Antibioticresistance
gene
Bacterial species such as
Escherichia coli
DNA
Antibioticresistance
gene from
E. coli
Horizontal
gene
transfer to
another
species
Bacterial species such as
Streptococcus pneumoniae
Figure 1.7 An example of horizontal gene transfer: antibiotic
resistance. One bacterial species may transfer a gene, such as a
gene that confers resistance to an antibiotic, to another bacterial
species.
7
organisms is a “web of life,” as shown in Figure 1.8, which accounts
for both vertical descent with mutation and horizontal gene transfer. In a lineage in which the time scale is depicted on a vertical
axis, horizontal gene transfer between different species is shown as
a horizontal line.
Core Concept: Evolution
The Study of Genomes and Proteomes
Provides an Evolutionary Foundation
for Our Understanding of Biology
As we have seen, evolutionary unity is a core concept of biology. We can understand the unity of modern organisms by realizing that all living species evolved from an interrelated group
of ancestors. However, from an experimental perspective, this
realization presents a dilemma—we cannot take a time machine
back over the course of 4 billion years to carefully study the
characteristics of extinct organisms and fully appreciate the
series of changes that have led to modern species. Fortunately,
though, evolution has given biologists some wonderful puzzles
to study, including the fossil record and the genomes of modern
species.
The term genome refers to the complete genetic material of an
organism or species (Figure 1.9a). The genomes of bacteria and
archaea usually contain a few thousand genes, whereas those of
eukaryotes may contain tens of thousands. A genome is critical to
life because it performs these functions:
∙∙ Stores information in a stable form. The genome of every
organism stores information that provides a blueprint for
producing that organism’s characteristics.
∙∙ Provides continuity from generation to generation. The
genome is copied and transmitted from generation to
generation.
∙∙ Acts as an instrument of evolutionary change. Every now
and then, an organism's genome undergoes a mutation that
may alter the characteristics of the organism. In addition, a
genome may acquire new genes by horizontal gene transfer.
The accumulation of genome changes from generation to
generation produces the evolutionary changes that alter
species and produce new species.
An exciting advance in biology over the past couple of
decades has been the ability to analyze the DNA sequence
of genomes, a technology called genomics. For example, a
researcher can compare the genomes of a frog, a giraffe, and
a petunia and discover intriguing similarities and differences.
These comparisons help us to understand how new traits
evolved. All three types of organisms have the same kinds of
genes needed for the breakdown of nutrients such as sugars. In
contrast, only the petunia has genes that allow it to carry out
photosynthesis.
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8
CHAPTER 1
Bacteria
Archaea
Eukarya
Fungi
Animals
Plants
Protists
KEY
Vertical evolution
Horizontal gene transfer
Common ancestral community of primitive cells
Figure 1.8 The web of life, showing both vertical evolution and horizontal gene transfer. This diagram includes both of these important
mechanisms in the evolution of life on Earth. Note: Archaea are unicellular species that are similar in cell structure to bacteria.
Concept Check:
How does the concept of a tree of life differ from that of a web of life?
An extension of genome analysis is the study of the proteome,
which refers to all of the proteins that a cell or an organism makes.
The function of most genes is to encode polypeptides that become
units in proteins. As shown in Figure 1.9b, these include proteins
that form a cytoskeleton and proteins that function in cell organization and as enzymes, transport proteins, cell-signaling proteins,
and extracellular proteins. The genome of each species carries the
information to make its proteome—the hundreds or thousands of
proteins that each cell of that species makes. Proteins are largely
responsible for the structures and functions of cells and organisms.
The set of techniques known as proteomics allows researchers to analyze the proteome of a single species and compare the
proteomes of different species. Proteomics helps us understand
how the various levels of biology are related to one another, from
the molecular level—at the level of protein molecules—to higher
levels, such as how the functioning of proteins produces the characteristics of cells and organisms and affects the ability of populations of organisms to survive in their natural environments.
Humans Have Changed the Characteristics of
Populations via Artificial Selection
The term artificial selection refers to programs and procedures
designed to modify traits in domesticated species. This practice is
similar to natural selection except that, in artificial selection, humans
select for traits that they deem desirable, rather than nature selecting
for traits that confer greater reproductive success. Both artificial and
natural selection alter the properties of a population from one generation to the next.
The red fox, Vulpes vulpes, shown on the cover of this textbook,
provides an example in which researchers applied artificial selection
to modify behavior (Figure 1.10). The work began in the late 1950s
by a Russian geneticist, Dmitry Belyaev. He was trying to replicate
the process that produced domesti­cated dogs from wolves, a process
that began 15,000 years ago.
First, Belyaev and colleagues traveled to various fur farms
and chose foxes for their study. They selected foxes based on how
they responded when their cage was opened. When approached by
humans, about 10% of the foxes displayed a weak “wild-response,”
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AN INTRODUCTION TO BIOLOGY
9
In eukaryotes, most of the genome is
contained within chromosomes that are
located in the cell nucleus.
Gene
(a) The genome
Cytoplasm
Chromosome
Most genes encode mRNAs
that contain the information to
make proteins.
DNA
Cell signaling:
Proteins are needed
for cell signaling with
other cells and with the
environment.
Sets of
chromosomes
Nucleus
Cytoskeleton:
Proteins are involved in
cell shape and
movement.
Cell organization:
Proteins organize the
components within
cells.
Enzymes:
Proteins function as
enzymes to synthesize
and break down cellular
molecules and
macromolecules.
(b) The proteome
Transport proteins:
Proteins facilitate the
uptake and export of
substances.
Extracellular
proteins:
Proteins hold cells
together in tissues.
Extracellular fluid
Figure 1.9 Genomes and proteomes. (a) The genome, which is composed of DNA, is all the genetic material an organism possesses. Most
of the genetic material in eukaryotic cells is found in the cell nucleus. The primary function of the genome is to encode the proteome (b), which
is the entire protein complement of a cell or organism. Six general categories of proteins are illustrated. Proteins are largely responsible for the
structure and function of cells and organisms.
Concept Check: Biologists sometimes say that the genome is the storage unit of life, whereas the proteome is largely the functional unit of life. Explain this statement.
meaning that they were more docile compared to other foxes. Of
those friendly foxes, 100 females and 30 males were chosen as the
first generation of parents.
During the course of this study, foxes were categorized based on
their eagerness to interact with humans:
∙∙ Class I animals were friendly to humans, wagging their tails
and whining. These foxes were eager to establish contact with
humans, whimpering to attract attention and sniffing and licking
experimenters.
∙∙ Class II foxes allowed themselves to be petted and handled.
∙∙ Class III foxes bit humans when stroked or handled.
Figure 1.10 The red fox, Vulpes vulpes. In captivity, this species
has been subjected to artificial selection experiments that resulted
in a population of foxes that are much more tame than wild foxes.
Soru Epotok/Shutterstock
After 40 years of selection for positive behavior toward humans,
70–80% of the population was composed of class I animals! These foxes
were described as playful, friendly and behaving like domestic dogs. The
vocalizations they made were different from those of wild foxes.
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CHAPTER 1
How did this result happen? The original fox population exhibited genetic variation that affected the animals' behavior. Some
genetic variation promoted aggressive behavior, whereas other variation resulted in tame behavior. The process of artificial selection
increased the relative amount of genetic variation that promoted tame
behavior and decreased the amount that favored aggressive behavior.
Note that the foxes in this study were not trained to become tame.
Rather, the tame behavior was the result of genetic variation that the
tame foxes carried.
In addition to the tame line of foxes, the researchers also maintained two other lines:
∙∙ a line of the least tamable foxes—those that avoided human
contact, as do most wild foxes;
∙∙ and a nonselected line.
In 2018, Anna Kukekova and colleagues sequenced the
genomes of 10 individuals from each of the three populations—
tame foxes, aggressive foxes, and foxes from the nonselected line—
and compared them with each other. They found 103 chromosomal
regions that differed among the populations, including regions containing genes that are known to con­fer tameness in dogs, genes that
play a role in certain human neurological disorders, and genes that
affect mouse behavior.
1.4 Classification of Living Things
Learning Outcome:
1. Outline how organisms are classified.
As biologists study species and discover new species, they try to
place them into groups based on their evolutionary history. This is a
difficult task because researchers estimate that the Earth has between
5 and 50 million different species! The rationale for classification is
based on vertical descent. Species with a recent common ancestor
are grouped together, whereas species whose common ancestor was
in the very distant past are placed into different groups. The field of
biology that is concerned with the grouping and classification of species is termed taxonomy.
Why is taxonomy useful? First, taxonomy allows us to appreciate the amazing diversity of life on Earth. Also, because taxonomy is
based on evolution, it provides a view of the evolutionary relationships among living species and the relationships between living and
extinct species.
The Classification of Living Organisms
Allows Biologists to Appreciate the Unity
and Diversity of Life
Let’s first consider taxonomy on a broad scale. You may have
noticed that Figure 1.8 showed three main groups of organisms.
From an evolutionary perspective, all forms of life can be placed
into those three large categories, or domains, called Bacteria,
Archaea, and Eukarya (Figure 1.11). Bacteria and archaea are
microorganisms that are also termed prokaryotic because their cell
structure is relatively simple. At the molecular level, bacterial and
archaeal cells show significant differences in their compositions. By
comparison, organisms in the domain Eukarya are eukaryotic and
have cells with internal compartments that serve various functions.
A defining distinction between prokaryotic and eukaryotic cells is
that eukaryotic cells have a cell nucleus in which the genetic material is surrounded by a membrane.
The organisms in domain Eukarya were once subdivided into
four major categories, or kingdoms, called Protista (protists), Plantae (plants), Fungi, and Animalia (animals). However, as discussed in
Chapter 25 and Unit V, this traditional view became invalid as biologists gathered new information regarding the evolutionary relationships of these organisms. We now know that the protists do not form
a single kingdom but instead are divided into several broad categories
called supergroups.
Each Species Is Placed into a
Taxonomic Hierarchy
Taxonomy involves multiple levels in which particular species are
placed into progressively smaller and smaller groups whose members are more closely related to each other evolutionarily. Such an
approach emphasizes the unity and diversity of different species.
As an example, let’s consider the clownfish, a popular saltwater
aquarium fish (Figure 1.12). Several species of clownfish have been
identified.
One species of clownfish, which is orange with white stripes,
has several common names, including ocellaris clownfish. The
broadest grouping for this clownfish is the domain, namely, Eukarya,
followed by progressively smaller divisions, from supergroup (Opisthokonta), to kingdom (Animalia), and eventually to species. In the
animal kingdom, clownfish are part of a phylum, Chordata, the
chordates, which is subdivided into classes. Clownfish are in a class
called Actinopterygii, which includes all ray-finned fishes. The
common ancestor that gave rise to ray-finned fishes arose about 420
million years ago (mya). Actinopterygii is subdivided into several
smaller orders. The clownfish are in the order Perciformes (bony
fish). The order is, in turn, divided into families; the clownfish
belong to the family of marine fish called Pomacentridae, which are
often brightly colored. Families are divided into genera (singular,
genus). The genus Amphiprion is composed of 28 different species;
these are various types of clownfish. Therefore, the genus contains
species that are very similar to each other in form and have evolved
from a common (extinct) ancestor that lived relatively recently on
an evolutionary time scale.
Biologists use a two-part description, called binomial
nomenclature, to provide each species with a unique scientific
name. The scientific name of the ocellaris clownfish is Amphiprion ocellaris. The first word is the genus, and the second
word is the specific epithet, or species descriptor. By convention, the genus name is capitalized, whereas the specific epithet
is not. Both names are italicized. Scientific names are usually
Latinized, which means they are made similar in appearance to
Latin words. The origins of scientific names are typically Latin
or Greek, but they can come from a variety of sources, including
a person’s name.
ISTUDY
AN INTRODUCTION TO BIOLOGY
6.2 μm
(a) Domain Bacteria: Mostly unicellular prokaryotes that inhabit
many diverse environments on Earth.
3.2 μm
(b) Domain Archaea: Unicellular prokaryotes that often live in extreme
environments, such as hot springs.
375.2 μm
Protists: Unicellular and small multicellular organisms
that are now subdivided into seven broad groups based
on their evolutionary relationships.
Plants: Multicellular organisms that can carry out
photosynthesis.
Fungi: Unicellular and multicellular organisms that have a cell
wall but cannot carry out photosynthesis. Fungi usually survive
on decaying organic material.
Animals: Multicellular organisms that usually have a nervous
system and are capable of locomotion. They must eat other
organisms or the products of other organisms to live.
(c) Domain Eukarya: Unicellular and multicellular organisms having cells with internal compartments that serve various functions.
Figure 1.11 The three domains of life. Two of these domains, (a) Bacteria and (b) Archaea, consist of species with prokaryotic cells. The third
domain, (c) Eukarya, comprises species that are eukaryotes. a: BSIP/agefotostock; b: Eye of Science/Science Source; c (protists): Jan Hinsch/Getty Images; c (plants):
Kent Foster/Science Source; c (fungi): Carl Schmidt-Luchs/Science Source; c (animals): Ingram Publishing/age fotostock
Core Skill: Connections Look ahead to Figure 25.1. Are fungi more closely related to plants or animals?
11
ISTUDY
12
CHAPTER 1
Taxonomic
group
The ocellaris
clownfish
is found in
Approximate time
when the common
ancestor for this
group arose
Approximate
number of
modern species
in this group
Domain
Eukarya
2,000 mya
> 5,000,000
Supergroup
Opisthokonta
2,000 mya
> 1,000,000
Kingdom
Animalia
600 mya
> 1,000,000
Phylum
Chordata
525 mya
50,000
Class
Actinopterygii
420 mya
30,000
Order
Perciformes
80 mya
7,000
Family
Pomacentridae
~ 40 mya
360
Genus
Amphiprion
~ 9 mya
28
Species
ocellaris
< 3 mya
1
Examples
Figure 1.12 Taxonomic classification of the ocellaris clownfish.
Concept Check:
Why is it useful to place organisms into taxonomic groupings?
1.5 Biology as a Scientific Discipline
Learning Outcomes:
1. Explain how researchers study biology at different levels, ranging
from molecules to ecosystems.
2. CoreSKILL » Distinguish between discovery-based science and
hypothesis testing, and describe the steps of the scientific method.
What is science? Surprisingly, the definition of science is not easy to
state. Most people have an idea of what science is, but actually articulating that idea proves difficult. In biology, we can define science as
the observation, identification, experimental investigation, and theoretical explanation of natural phenomena.
Science is conducted in different ways and at different levels.
Some biologists study the molecules that compose life, and others
try to understand how organisms survive in their natural environments. Experimentally, researchers often focus their efforts on model
organisms—organisms studied by many different researchers so they
can compare their results and determine scientific principles that
apply more broadly to other species. Examples of model organisms
include Escherichia coli (a bacterium), Saccharomyces cerevisiae
(a yeast), Drosophila melanogaster (fruit fly), Caenorhabditis elegans (a nematode worm), Mus musculus (mouse), and Arabidopsis
thaliana (a flowering plant). Model organisms offer experimental
advantages over other species. For example, E. coli is a very simple
organism that can be easily grown in the laboratory. By limiting their
ISTUDY
AN INTRODUCTION TO BIOLOGY
work to a few model organisms, researchers can gain a deeper understanding of these species, and their results may apply more broadly to
other species, including humans.
In this section, we will examine how biologists follow a standard approach, called the scientific method, to test their ideas. We
will explore how scientific knowledge makes predictions that can be
experimentally tested. However, not all discoveries are the result of
researchers following the scientific method. Some discoveries are
made simply by gathering new information. As illustrated earlier, in
Figure 1.1 the characterization of many living organisms has led to
the development of important medicines. In this section, we will also
consider how researchers often set out on fact-finding missions aimed
at uncovering new information that may eventually lead to important
discoveries in biology.
Biologists Investigate Life at Different
Levels of Organization
In Figure 1.3, we examined the various levels of biological organization. The study of these different levels depends not only on the scientific interests of biologists but also on the tools available to them.
Ecologists study species in
their native environments.
Anatomists and physiologists
study how the structures of
organisms are related to their
functions.
(a) Ecology—population/
community/ecosystem
levels
(b) Anatomy and physiology—
tissue/organ/organism levels
∙∙ The study of organisms in their natural environments is a
branch of biology called ecology, which considers populations,
communities, and ecosystems (Figure 1.13a).
∙∙ Some researchers examine the structures and functions of plants
and animals; these subjects form the disciplines called anatomy
and physiology (Figure 1.13b).
∙∙ With the advent of microscopy, cell biology, which is the study
of cells and their interactions, became an important branch of
biology in the early 1900s and remains so today (Figure 1.13c).
∙∙ In the 1970s, genetic tools became available for studying single
genes and the proteins they encode. This genetic technology
enabled researchers to study individual molecules, such as
proteins, in living cells and thereby gave rise to the field of
molecular biology. Together with biochemists and biophysicists, molecular biologists focus their efforts on the structure and
function of the molecules of life (Figure 1.13d). Such researchers want to understand how biology works at the molecular and
even atomic levels. Overall, the 20th century saw a progressive
increase in the number of biologists who used an approach to
understanding biology called reductionism—reducing complex
systems to simpler components as a way to understand how the
system works. In biology, reductionists study the parts of a cell
or organism as individual units.
∙∙ In the 1990s, the pendulum began to swing in the other direction. Scientists have invented new tools that allow them to study
groups of genes (genomic techniques) and groups of proteins
(proteomic techniques). Biologists now use the term systems
biology to describe research aimed at understanding how emergent properties arise. This term is often applied to the study of
cells. In this context, systems biology may involve the investigation of groups of genes that encode proteins with a common
purpose (Figure 1.13e). For example, a systems biologist may
conduct experiments that try to characterize an entire cellular
process, which is driven by dozens of different proteins.
Cell biologists often use
microscopes to learn how
cells function.
(c) Cell biology— cellular levels
Molecular biologists and
biochemists study the
molecules and
macromolecules that
make up cells.
(d) Molecular biology—
atomic/molecular levels
Systems biologists may study
groups of molecules. The
microarray shown in the inset
determines the expression of
many genes simultaneously.
(e) Systems biology—all levels, shown here at the molecular level
Figure 1.13 Biological investigation at different levels of
organization. a: Purestock/SuperStock; b: Diane Nelson; c: Erik Isakson/Blend
Images; d: Dmytro Zinkevych/Alamy Stock Photo; e: Andrew Brookes/Corbis/Getty
Images; e (inset): Alfred Pasieka/Science Source
13
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14
CHAPTER 1
∙∙ However, systems biology is not new. Animal and plant
physiologists have been studying the functions of complex
organ systems for centuries. Likewise, ecologists have been
characterizing ecosystems for a very long time. The excitement
surrounding systems biology in recent years has been the result
of new experimental tools that allow biologists to study complex
interactions at the molecular level.
A Hypothesis Is a Proposed Idea, Whereas
a Theory Is a Broad Explanation Backed
by Extensive Evidence
Let’s now consider the process of science. In biology, a hypothesis
is a proposed explanation for a natural phenomenon. It is a proposition based on previous observations or experimental studies. For
example, with knowledge of seasonal changes, you might hypothesize
that maple trees drop their leaves in the autumn because of the shortened amount of daylight. An alternative hypothesis might be that the
trees drop their leaves because of lower temperatures. In biology, a
hypothesis requires more work by researchers to evaluate its validity.
A useful hypothesis must make predictions—expected outcomes
that can be shown to be correct or incorrect. In other words, a useful
hypothesis is testable, which means that the hypothesis can be shown
to be consistent or inconsistent with data that are obtained via experimentation. If a hypothesis is incorrect, it should be falsifiable—it can
be shown to be incorrect by additional observations or experimentation. Alternatively, a hypothesis may be correct, so further work will
not disprove it. In such cases, we say that the researchers have failed
to reject the hypothesis.
Even so, in science, a hypothesis is never really proven but rather
always remains provisional. Researchers accept the possibility that perhaps they have not yet conceived of the correct hypothesis. After many
experiments, biologists may conclude that a hypothesis is consistent
with known data, but they should never say the hypothesis is proven.
By comparison, a theory, as the term is used in biology, is a broad
explanation of some aspect of the natural world that is substantiated by
a large body of evidence. Biological theories incorporate observations,
hypothesis testing, and the laws of other disciplines such as chemistry and physics. Theories are powerful because they allow us to make
many predictions about the properties of living organisms.
As an example, let’s consider the theory that DNA is the genetic
material and that it is organized into units called genes. An overwhelming body of evidence has substantiated this theory. Thousands
of living species have been analyzed at the molecular level. All of
them have been found to use DNA as their genetic material and to
express genes that produce the proteins that lead to their characteristics. This theory makes many valid predictions. For example, certain
types of mutations in genes are expected to affect the traits of organisms. This prediction has been confirmed experimentally. Similarly,
this theory predicts that genetic material is copied and transmitted
from parents to offspring. Through comparisons of the DNA of parents and offspring, this prediction has also been confirmed. Furthermore, the theory explains the observation that offspring resemble
their parents. Overall, two key attributes of a scientific theory are
(1) consistency with a vast amount of known data and (2) the ability
to make many correct predictions.
The meaning of the term theory is sometimes muddled, because
the word is used in different situations. In everyday language, a theory is often viewed as little more than a guess. For example, a person might say, “My theory is that Professor Simpson did not come
to class today because he went to the beach.” However, in biology, a
theory is much more than a guess. A theory is an established set of
ideas that explains a vast amount of data and offers valid predictions
that can be tested. Like a hypothesis, a theory can never be proven
to be true. Scientists acknowledge that they do not know everything.
Even so, biologists would say that theories are extremely likely to
be true, based on all known information. In this regard, theories are
viewed as knowledge, which is the awareness and understanding of
information.
Discovery-Based Science and Hypothesis
Testing Are Scientific Approaches That Help
Us Understand Biology
The path that leads to an important discovery is rarely a straight line.
Rather, scientists ask questions, make observations, ask modified questions, and may eventually conduct experiments to test their hypotheses.
The first attempts at experimentation may fail, and new experimental
approaches may be needed. To suggest that scientists follow a rigid
scientific method is an oversimplification of the process of science.
Scientific advances often occur as scientists dig deeper and deeper into
a topic that interests them. Curiosity is the key phenomenon that sparks
scientific inquiry. How is biology actually conducted? As discussed
next, researchers typically follow two general types of approaches:
discovery-based science and hypothesis testing.
Discovery-Based Science The collection and analysis of data
without the need for a preconceived hypothesis is called discoverybased science, or simply discovery science. Why is discovery-based
science carried out? The information gained from discovery-based science may lead to the formation of new hypotheses and, in the long run,
may have practical applications that benefit people. Researchers, for
example, have identified and begun to investigate previously unknown
genes within the human genome without already knowing the function
of those genes. The goal is to gather additional clues that may eventually allow them to propose a hypothesis that explains a gene’s function.
Discovery-based science often leads to hypothesis testing.
Hypothesis Testing In biological science, the scientific method,
also known as hypothesis testing, is usually followed to formulate
and test the validity of a hypothesis. This strategy may be described
as a five-step method:
1. Observations are made regarding natural phenomena.
2. These observations lead to a hypothesis that tries to explain the
phenomena. A useful hypothesis is one that is testable because it
makes specific predictions.
3. Experimentation is conducted to determine if the predictions are
correct.
4. The data from the experiment are analyzed.
5. The hypothesis is considered to be consistent with the data, or it
is rejected.
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AN INTRODUCTION TO BIOLOGY
1
OBSERVATIONS The leaves on maple trees fall in autumn when the days get colder and shorter.
2
HYPOTHESIS The shorter amount of daylight causes the leaves to fall.
3
EXPERIMENTATION
Small maple trees are grown in
2 greenhouses where the only
variable is the length of daily light.
Control group:
Amount of daily light remains
constant for 180 days.
5
THE DATA
Number of leaves dropped
per tree after 180 days
4
200
A statistical analysis
can determine if
the control and the
experimental data
are significantly
different. In this
case, they are.
100
Control Experimental
group
group
The scientific method is intended to be an objective way to gather
knowledge. As an example, let’s return to the question of why maple
trees drop their leaves in autumn. By observing the length of daylight
throughout the year and comparing that data with the time of the year
when leaves fall, one hypothesis might be that leaves fall in response
to shorter periods of daylight (Figure 1.14). This hypothesis makes
a prediction—exposure of maple trees to shorter periods of daylight
will cause their leaves to fall. To test this prediction, researchers
would design and conduct an experiment.
How is hypothesis testing conducted? Although hypothesis testing may follow many paths, certain experimental features are common to this approach. First, data are often collected in two parallel
ways. One set of experiments is done on the control group, whereas
another set is conducted on the experimental group. In an ideal
experiment, the control and experimental groups differ by only one
factor. For example, an experiment could be conducted in which two
groups of trees are observed, and the only difference between their
environments is the length of light each day.
To conduct such an experiment, researchers would grow small
trees in a greenhouse where they could keep other factors such as
temperature, water, and nutrients the same between the control and
experimental groups, while providing the two groups with different amounts of light via artificial lighting. In the control group, the
15
Experimental group:
Amount of daily light becomes
progressively shorter for 180 days.
CONCLUSION The hypothesis cannot be rejected.
Figure 1.14 The steps of the scientific method, also known as
hypothesis testing.
Core Skill: Process of Science In this example, the goal
is to test the hypothesis that maple trees drop their leaves
in the autumn due to the shorter amount of daylight.
Concept Check:
testing?
What is the purpose of a control group in hypothesis
number of hours of light provided would be kept constant each day,
whereas in the experimental group, the amount of light provided each
day becomes progressively shorter to mimic seasonal light changes.
The researchers would then record the number of leaves dropped by
the two groups of trees over a certain period of time.
Another key feature of hypothesis testing is data analysis. The
result of experimentation is a set of data from which a biologist tries
to draw conclusions. Biology is a quantitative science. When experimentation involves control and experimental groups, a common form
of analysis is to determine if the data collected from the two groups
are truly different. Biologists apply statistical analyses to their data to
determine if the outcomes from the control and experimental groups
are likely to differ because of the single variable that is different
between the two groups. When differences between the control and
experimental data are statistically significant, they are not likely to
have occurred as a matter of random chance.
In our example in Figure 1.14, the trees in the control group
dropped far fewer leaves than did those in the experimental group. A
statistical analysis could determine if the data collected from the two
greenhouses are significantly different from each other. If the two sets
of data are found not to be significantly different, the hypothesis will
be rejected. Alternatively, if the differences between the two sets of
data are significant, as shown in Figure 1.14, biologists can conclude
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16
CHAPTER 1
that the hypothesis is consistent with the data, though it is not proven.
A hallmark of science is that valid experiments are repeatable, which
means that similar results are obtained when an experiment is conducted on multiple occasions. For our example in Figure 1.14, the
data would be valid only if the experiment was repeatable.
As described next, discovery-based science and hypothesis testing are often used together to learn more about a particular scientific
topic. As an example, let’s look at how both approaches led to successes in the study of the disease called cystic fibrosis.
The Study of Cystic Fibrosis Provides
Examples of Discovery-Based Science
and Hypothesis Testing
Let’s consider how biologists made discoveries related to the disease
cystic fibrosis (CF), which affects about 1 in every 3,500 Americans.
Persons with CF produce abnormally thick and sticky mucus that
obstructs the lungs and leads to life-threatening lung infections. The
thick mucus also blocks ducts in the pancreas, which prevents the
digestive enzymes this organ produces from reaching the intestine.
Without these enzymes, the intestine cannot fully absorb amino acids
and fats, which can cause malnutrition. Persons with this disease may
also experience liver damage because the thick mucus can obstruct
the liver. On average, people with CF in the United States currently
live into their late 30s. Fortunately, as more advances have been made
in treatment, this number has steadily increased.
Because of its medical significance, many scientists are interested in CF and are conducting studies aimed at gaining greater
information regarding its underlying cause. The hope is that knowing
more about the disease may lead to improved treatment options, and
perhaps even a cure. As described next, discovery-based science and
hypothesis testing have been critical to gaining a better understanding
of this disease.
The CFTR Gene and Discovery-Based Science In 1935,
American physician Dorothy Andersen determined that cystic fibrosis
is a genetic disorder. Persons with CF have inherited two faulty CFTR
genes, one from each parent. (We now know this gene encodes a protein named the cystic fibrosis transmembrane regulator, abbreviated
CFTR.) In the 1980s, researchers used discovery-based science to
identify this gene. Their search for the CFTR gene did not require any
preconceived hypothesis regarding the function of the gene. Rather,
they used genetic strategies similar to those described in Chapter 21.
Research groups headed by Lap-Chee Tsui, Francis Collins, and John
Riordan identified the CFTR gene in 1989.
The discovery of the CFTR gene made it possible to devise diagnostic testing methods to determine if a person carries a faulty version of that gene. In addition, the characterization of the CFTR gene
provided important clues about its function. Researchers observed
striking similarities between the CFTR gene and other genes that
were already known to encode proteins that function in the transport
of substances across membranes. Based on this observation, as well
as other kinds of data, the scientists hypothesized that the function of
the normal CFTR gene is to encode a transport protein. In this way,
the identification of the CFTR gene led them to conduct experiments
aimed at testing a hypothesis about its function.
Proper Cl – export
occurs, and water
balance is normal.
Cl –
Cl – export is defective, affecting
water balance and causing an
abundance of sticky mucus.
Cl –
Mucus
Cl
Transporter encoded with
normal CFTR gene
Defective
transporter
Cl
Lung cell with normal CFTR gene
Lung cell with faulty CFTR gene
Figure 1.15 A hypothesis suggesting an explanation for the
defective function of a gene in patients with cystic fibrosis. The
normal CFTR gene, which does not carry a mutation, encodes a
protein that transports chloride ions (Cl−) across the plasma
membrane to the outside of the cell. In persons with CF, this protein is
defective due to a mutation in the CFTR gene.
Concept Check: Explain how discovery-based science helped researchers
to hypothesize that the CFTR gene encodes a transport protein.
The CFTR Gene and Hypothesis Testing Researchers interested in
the CFTR gene also considered studies showing that patients with CF
have an abnormal regulation of salt balance across their plasma membranes. They hypothesized that the normal CFTR gene encodes a protein
that functions in the transport of chloride ions (Cl−) across the membranes of cells (Figure 1.15). This hypothesis led to experimentation that
tested normal cells and cells from CF patients for their ability to transport
Cl−. The CF cells were found to be defective in chloride transport.
In 1990, scientists successfully transferred the normal CFTR gene
into cells from CF patients in the laboratory. The introduction of the
normal gene corrected the cells’ defect in chloride transport. Overall,
the results showed that the CFTR gene encodes a protein that transports
Cl− across the plasma membrane. A mutation in this gene causes it to
encode a defective protein, leading to a salt imbalance that affects water
levels outside the cell, which explains the thick and sticky mucus in CF
patients. In this example, hypothesis testing provided a way to evaluate
a hypothesis about how a disease is caused by a genetic change.
Biology Is a Social Discipline
Finally, it is worthwhile to point out that biology is a social as well
as a scientific discipline. Several laboratories often collaborate on
scientific projects. After performing observations and experiments,
biologists communicate their results in various ways. Most importantly, papers are submitted to scientific journals. Following submission, a paper usually undergoes a peer-review process in which other
scientists, who are experts in the area, evaluate the paper and make
comments regarding its quality. As a result of peer review, a paper is
accepted for publication or rejected, or the authors of the paper may
ISTUDY
AN INTRODUCTION TO BIOLOGY
17
Figure 1.16 One of the social aspects of science.
Dita Alangkara/AP Photo
Core Skill: Communication and
Collaboration At scientific meetings,
researchers from various disciplines
gather together to discuss new data
and discoveries. Research that is
conducted by professors, students, lab
technicians, and industrial participants
is sometimes hotly debated.
be given suggestions for how to revise the work or conduct additional
experiments to make it acceptable for publication.
Another social aspect of research is that biologists often attend
meetings where they report their most recent work to the scientific
community (Figure 1.16). They comment on each other’s ideas and
results, eventually putting together the information that builds into
scientific theories over many years. As you develop your skills at
scrutinizing experiments, it is helpful to discuss your ideas with other
people, including fellow students and faculty members. Importantly,
you do not need to know all the answers before you enter into a scientific discussion. Instead, a more realistic way to view science is as an
ongoing and never-ending series of questions.
1.6
Core Skills of Biology
Learning Outcomes:
1. CoreSKILL » Describe the core skills of biology as identified by
Vision and Change.
2. CoreSKILL » Explain the process of science.
3. CoreSKILL » Describe what a model is in biology, and explain
why models are useful.
4. CoreSKILL » List the types of problem-solving skills you will
develop by completing BioTIPS.
In addition to the five core concepts of biology (see Section 1.2), the
participants in Vision and Change also identified certain skills that
students should develop so that they can become successful in careers
in biology. Educators need to focus on these core skills, which are
also referred to as core competencies:
∙∙ The ability to apply the process of science
∙∙ The ability to use quantitative reasoning
∙∙ The ability to use models and simulation
∙∙ The ability to tap into the interdisciplinary nature of science
∙∙ The ability to communicate and collaborate with professionals
in other disciplines
∙∙ The ability to understand the relationship between science and
society
In this section, we will consider the features of this textbook that
will help you to develop these skills. These features are summarized
below:
∙∙ Each chapter has a Feature Investigation that allows you to apply
the process of science. Likewise, the BioTIPS features are aimed
at helping you refine and apply your problem-solving skills.
∙∙ Quantitative reasoning is also a key component of the Feature
Investigations. It is involved in answering many of the questions
at the end of Feature Investigations, as well as many end-ofchapter questions and BioTIPS questions.
∙∙ A key feature of the sixth edition, which is described later in
this section, is the Modeling Challenges. After learning about a
particular topic in biology, you will be asked to either interpret a
given model or propose your own model based on a scenario or
some data.
∙∙ The interdisciplinary nature of science is highlighted in features
titled Connections that follow some figure legends.
∙∙ Another feature of the sixth edition is the addition of a core
skill called Science and Society following some of the figure
legends.
The Vision and Change icon,
, that highlights core concepts
throughout the text, also highlights material that promotes the core
skills.
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18
CHAPTER 1
Core Skill: Process of Science
Feature Investigation | Observation and Experimentation Form the Core of Biology
Biology is largely about the process of discovery. Therefore, a recurring theme of this textbook is how scientists design experiments, analyze data, and draw conclusions. Although each chapter contains many
examples of data collection and experiments, a consistent element is
a Feature Investigation—which presents an actual study by current or
past researchers. Some of these involve discovery-based science, in
which biologists collect and interpret data in an attempt to make discoveries that are not hypothesis-driven. Most Feature Investigations,
however, involve hypothesis testing in which a hypothesis is stated
and the experiment and resulting data are presented. Figure 1.14, illustrating the experiment with maple trees, shows the general form of
Feature Investigations.
The Feature Investigations allow you to appreciate the connection between science and scientific theories. As you read a
Model-Based Learning Will Enhance Your
Understanding of Biological Concepts and
Improve Your Critical-Thinking Skills
What is a model? A scientific model, or simply a model, is a conceptual, mathematical, or physical depiction of a real-world phenomenon. A model is a simplification and abstraction of a researcher’s
perception of reality. In biology, models are testable ideas that are
usually derived from observations and experiments. Because of the
vast amount of complexity and variation found in nature, all but the
simplest models are imperfect depictions of living things, their working parts, and their interactions with the environment. The majority
of figures in this textbook are models, based on the ideas of biologists
and drawn by professional illustrators.
Why are models useful? One reason is they promote communication. Models allow scientists to convey their ideas in a
relatively simple way. For example, a model of the human heart
depicts how the parts of the heart work together to pump blood
(look ahead to Figure 48.6). Another useful aspect of a model is
that it can be used as a working hypothesis that helps researchers
visualize or explain biological phenomena. Such models form the
basis for conducting further experiments. Models are evaluated by
their consistency with experimental data, which enables researchers to accept, reject, or refine them. Likewise, models allow biologists to make meaningful predictions. Such predictions can be
refuted or supported via experimentation. A model for gene regulation in Chapter 14 predicts that a repressor protein inhibits gene
expression (look ahead to Figure 14.7). This prediction was verified by experimentation, as shown in Figure 14.9. Finally, models
can lead to conceptual frameworks. For example, the concept of a
species niche, which is described in Chapter 57, was derived from
species competition models and has subsequently become one of
the most important concepts in ecology.
Models take on many different forms. Let’s consider some common categories of models that you will see.
Feature Investigation, you may find yourself thinking about different
approaches and alternative hypotheses. Different people can view the
same data and arrive at very different conclusions. As you progress
through the experiments in this textbook, we hope you will try to
develop your own skills at formulating hypotheses, designing experiments, and interpreting data.
Experimental Questions
1. Discuss the difference between discovery-based science and
hypothesis testing.
2. What are the steps in the scientific method, also called
hypothesis testing?
3. CoreSKILL » In an experiment, explain how a control group and
an experimental group differ from each other.
∙∙ Structural models. A structural model shows the physical
structures of components that make up living organisms.
Biochemists and biologists have proposed many different
models that depict biological structures at the cellular and
molecular level. Figure 3.14 is a collection of 20 models of the
structures of amino acids that are found in proteins.
∙∙ Mechanistic models. A mechanistic model (also called a physiological model) describes the workings of the individual parts of
a complex system, and the manner in which they interact. As
an example, plant biologists have proposed two models, called
symplastic and apoplastic transport, which describe two possible
pathways by which minerals are taken into the root of a plant
(look ahead to Figure 39.7).
∙∙ Mathematical models. A mathematical model is a description
of a process or a system using mathematical concepts, symbols,
and diagrams. Many mathematical models are presented as
one or more equations. For example, ecologists use equations
to describe two different modes of population growth, termed
exponential and logistic growth. Such equations allow biologists
to make predictions about population growth, which can be
illustrated graphically (look ahead to Figure 56.9).
∙∙ Temporal models. A temporal model depicts a biological
process as it occurs over a short or long period of time. In cell
biology, some processes occur very quickly. For example, the
absorption of light energy during photosynthesis occurs in
less than a second (look ahead to Figure 8.11). In contrast, the
evolution of new groups of species may occur on a timescale of
millions of years (look ahead to Figure 26.4).
∙∙ Hierarchical models. In a hierarchical model, organisms, parts
of organisms, or observations fall into nested levels. For example,
the field of taxonomy organizes species into progressively smaller
groups, such as kingdom, family, and genus (plural, genera). One
or more genera are found within a family, and many different
families are found within a kingdom (see Figure 1.12).
ISTUDY
AN INTRODUCTION TO BIOLOGY
Some models incorporate two or more of these categories. Take a
look at the model for DNA replication in Figure 11.18, which is a combination of a structural model, a mechanistic model, and a temporal model.
Model-based learning is an educational approach in which students evaluate or generate models as a way to enhance their understanding of scientific concepts and improve their critical-thinking
skills. In this textbook, you will be engaged in this strategy via figures that present a modeling challenge. Each of these figures shows
a model that pertains to a particular topic in biology. After you study
this model, your modeling skills will be challenged in one of two
different ways. In some cases, you will be given a second model and
asked to explain it or describe what types of predictions can be made
based on it (Figure 1.17). In other cases, you will be given a scenario
and asked to generate your own model that is consistent with the scenario (Figure 1.18). Even though explaining and generating models
3ʹ
Amino acid attachment site
at the 3ʹ single-stranded region
19
Outer
membrane
Intermembrane
space
Inner
membrane
Mitochondrial
matrix
Cristae
Cytosol
5ʹ
0.3 μm
Figure 1.18 A modeling challenge to make a prediction. This
figure shows the structure of a mitochondrion. It emphasizes the
membrane organization of the mitochondrion, which has outer and
inner membranes. The invaginations (infoldings) of the inner
membrane, which are called cristae, occur because of the large
surface area of that membrane. The modeling challenge below
involves proposing an altered model. Don W. Fawcett/Science Source
Stem-loop
Hydrogen bonds
G
G C
Anticodon
Figure 1.17 A modeling challenge to explain a revised model.
This figure shows a model for the structure of a tRNA molecule, which is
described in Chapter 12. The stem regions are regions where the RNA
is double-stranded as a result of complementary base pairing, in which
A hydrogen-bonds to U, and G hydrogen-bonds with C. The modeling
challenge below involves an alteration in this model.
Core Skill: Modeling In this modeling
challenge, you are asked to explain
how the model shown here differs
from the one in Figure 1.17.
Modeling Challenge: In a tRNA
molecule, four of the bases were
changed. One A was changed to
a G, and three C’s were changed
to U’s. A model of the structure of
this altered tRNA is shown to the right.
Explain where the altered bases are
located and how the alteration affects
the structure of the tRNA.
Core Skill: Modeling This modeling challenge asks
you to propose a model for the structure of a
mitochondrion in the presence of a drug that
decreases the surface area of the inner membrane.
Modeling Challenge: Let’s suppose a cell is exposed to a
drug that decreases the surface area of the inner mitochondrial membrane, but has no effect on the outer mitochondrial
membrane. Draw a model of the structure of the mitochondrion in the presence of this drug.
can be a challenge, the educational benefits are worth it. Give the
modeling challenges a try.
BioTIPS Will Help You Improve Your
Problem-Solving Skills
As you progress through this textbook, your learning will involve two
general goals:
∙∙ You will gather foundational knowledge. In other words, you
will be able to describe basic ideas and discoveries in biology.
For example, you will be able to explain how photosynthesis
works.
∙∙ You will develop skills that will allow you to apply that foundational knowledge in different ways. For example, you will learn
how to use statistics to determine if a hypothesis is consistent
with experimental data.
ISTUDY
20
CHAPTER 1
The combination of foundational knowledge and skills will enable
you not only to understand biology but also to apply your knowledge
in different situations. To help you develop these skills, Chapters 2
through 60 contain solved problems called BioTIPS, where the ending stands for Topic, Information, and Problem-Solving Strategy.
These solved problems follow a consistent pattern.
BIO TIPS
THE QUESTION All of the BioTIPS begin with a
question. As an example, let’s consider the following question:
The following base sequence is found within a messenger RNA
molecule:
AUG GGC CUU AGC
This segment carries the information to make a region of a
polypeptide with the amino acid sequence methionine-glycineleucine-serine. What would be the consequences if a mutation in
the gene that encodes this mRNA changed the second cytosine (C)
in the base sequence to an adenine (A)?
T OPIC What topic in biology does this question address? The
topic is gene expression. More specifically, the question is about
the relationship between a base sequence and the genetic
code.
I NFORMATION What information do you know based on the
question and your understanding of the topic? In the question,
you are given the base sequence of a short segment of an
mRNA and told that one of the bases has been changed. From
your understanding of the topic, you may remember that a
polypeptide sequence is determined by reading the mRNA
(transcribed from a gene) in groups of three bases called
codons.
P ROBLEM-SOLVING S TRATEGY Compare and contrast.
Predict the outcome. One strategy to begin to solve this
problem is to compare the mRNA sequence before and after
the mutation:
Original: AUG GGC CUU AGC
Mutant: AUG GGC AUU AGC
↑
ANSWER The mutation has altered the sequence of bases in
the mRNA, changing the third codon from CUU to AUU (see the
arrow). Because codons specify amino acids, this may change the
third amino acid in the polypeptide to something else. Note: If you
look ahead to Table 12.1, you will see that CUU specifies leucine,
whereas AUU specifies isoleucine. Therefore, you can predict
that the mutation will change the third amino acid from leucine to
isoleucine.
Though many different problem-solving strategies exist, BioTIPS
will focus on 11 strategies that will help you solve problems. You will
see these strategies over and over again as you progress through this
textbook:
1. Make a drawing. Biology problems are often difficult to solve
in your head. Making a drawing may make a big difference in
your ability to see the solution.
2. Compare and contrast. Making a direct comparison between
two biological structures or processes may help you understand
how they are similar and how they are different.
3. Relate structure and function. A recurring theme in biology is
that structure determines function. This relationship holds true
at many levels of biology, including the molecular, microscopic,
and macroscopic levels. For some questions, you will need to
understand how certain structural features are related to their
biological functions.
4. Sort out the steps in a complicated process. At first, some
questions may be difficult to understand because they involve
mechanisms that occur in a series of several steps. Sometimes,
if you sort out the steps, you will be able to identify the key step
that you need to understand to solve the problem.
5. Propose a hypothesis. A hypothesis is an attempt to explain an
observation or data. Hypotheses may be made in many forms
including statements, models, equations, and diagrams.
6. Design an experiment. Experimental design lies at the heart
of science. In many cases, an experiment begins with some
type of starting material(s), such as strains of organisms or
purified molecules, and then the starting materials are subjected
to a series of steps. The Feature Investigations throughout
the textbook will also help you refine the skill of designing
experiments.
7. Predict the outcome. Biologists may want to predict the
outcome of an experiment.
8. Interpret data. Experimentation involves the analysis of
data. Such an analysis often involves the use of statistics
to determine if the experimental and control data show
significant differences. The interpretation of data allows
scientists to propose models that describe what the data
may mean.
9. Use statistics. A variety of different statistical methods are
used to analyze data and make conclusions about what they
mean.
10. Make a calculation. Biology is a quantitative science.
Researchers have devised mathematical relationships that
help them understand and predict biological phenomena.
Becoming familiar with these mathematical relationships
will help you to better understand biological concepts and to
make predictions.
11. Search the literature. The goal here is to be able to read and
explain a scientific article, and extract useful information.
For most problems in this textbook, one or more of these strategies
may help you arrive at the correct solution. BioTIPS will provide you
with practice in applying these problem-solving strategies.
ISTUDY
AN INTRODUCTION TO BIOLOGY
∙∙ Discovery-based science is an approach in which researchers conduct
experiments and analyze data without a preconceived hypothesis.
Summary of Key Concepts
1.1
∙∙ Biology is the study of life. Discoveries in biology help us
understand how life exists, and they also have many practical
applications, such as the development of drugs to treat human
diseases (Figures 1.1, 1.2, Table 1.1.).
∙∙ The scientific method, also called hypothesis testing, is a series
of steps to formulate and test the validity of a hypothesis. The
experimentation often involves a comparison between control and
experimental groups (Figure 1.14).
Levels of Biology
∙∙ The study of cystic fibrosis provides an example in which both
discovery-based science and hypothesis testing led to key insights
regarding the nature of the disease (Figure 1.15).
∙∙ Living organisms can be viewed at different levels of biological
organization: atoms, molecules and macromolecules, cells, tissues,
organs, organisms, populations, communities, ecosystems, and the
biosphere (Figure 1.3).
∙∙ Biology is a social discipline in which scientists often work in teams.
To be published, a scientific paper is usually subjected to a peerreview process in which other scientists evaluate the paper and make
suggestions regarding its quality. Advances in science often occur
when scientists gather and discuss their data (Figure 1.16).
1.2 Core Concepts of Biology
∙∙ Vision and Change has identified five core concepts in biology
(Figure 1.4). These are evolution; structure and function; information
flow, exchange, and storage; pathways and transformations of energy
and matter; and systems.
1.3
Biological Evolution
∙∙ Changes in species often occur as a result of modification of preexisting structures (Figure 1.5).
∙∙ During vertical evolution, mutations in a lineage alter the
characteristics of species from one generation to the next. Individuals
with greater reproductive success are more likely to contribute their
characteristics to future generations, a process known as natural
selection. Over the long run, this process alters species and may
produce new species (Figure 1.6).
∙∙ Horizontal gene transfer is the transfer of genetic material from
one organism to another organism that is not its offspring. Along
with vertical descent with mutation, it is an important process in
biological evolution, producing a web of life (Figures 1.7, 1.8).
∙∙ An analysis of genomes and proteomes helps us to understand how
information at the molecular level relates to the characteristics
of individuals and how they survive in their native environments
(Figure 1.9).
∙∙ Artificial selection can change the characteristics of a population
from generation to generation, such as promoting tame behavior in
red foxes (Figure 1.10).
1.4
Classification of Living Things
∙∙ Taxonomy is the grouping of species according to their evolutionary
relatedness to other species. Going from broad to narrow groups,
each species is placed into a domain, a supergroup, a kingdom, a
phylum, a class, an order, a family, and a genus (Figures 1.11, 1.12).
∙∙ Biologists use a two-part description, called binomial nomenclature,
to provide each species with a unique scientific name.
1.5
Biology as a Scientific Discipline
∙∙ Biological science is the observation, identification, experimental
investigation, and theoretical explanation of natural phenomena.
∙∙ Biologists study life at different levels, ranging from ecosystems to
the molecular components in cells (Figure 1.13).
∙∙ A hypothesis is a proposal to explain a natural phenomenon. A useful
hypothesis makes a testable prediction. A biological theory is a broad
explanation that is substantiated by a large body of evidence.
21
1.6
Core Skills of Biology
∙∙ Vision and Change recognized the need to focus on the development
of certain skills in students: the ability to apply the process of
science; the ability to use quantitative reasoning; the ability to use
models and simulation; the ability to tap into the interdisciplinary
nature of science; the ability to communicate and collaborate with
professionals in other disciplines; and the ability to understand the
relationship between science and society.
∙∙ Each chapter in this textbook has a Feature Investigation, an actual
study by current or past researchers that highlights the experimental
approach and helps you appreciate how science has led to key
discoveries in biology.
∙∙ Biologists use models to convey their ideas, evaluate experiments,
and make predictions that apply to their research studies. Modeling
challenges will help you to understand and propose models
(Figures 1.17, 1.18).
∙∙ BioTIPS are intended to develop your problem-solving skills.
Assessing Your Knowledge and Skills
Foundational Knowledge
Multiple Choice
1. Populations of organisms change over the course of many generations.
Many of these changes result in increased survival and reproduction.
This phenomenon is
a. evolution.
b. homeostasis.
c. development.
d. genetics.
e. metabolism.
2. Which of the following is an example of horizontal gene transfer?
a. the transmission of an eye color gene from father to daughter
b. the transmission of a mutant gene causing cystic fibrosis from father
to daughter
c. the transmission of a gene conferring pathogenicity (the ability to
cause disease) from one bacterial species to another
d. the transmission of a gene conferring antibiotic resistance from a
mother cell to its two daughter cells
e. all of the above
ISTUDY
22
CHAPTER 1
3. The scientific name for humans is Homo sapiens. The name Homo
is the __________ to which humans are classified.
a. kingdom
d. genus
b. phylum
e. species
c. order
b. A new mutation arose in E. coli from a single patient, conferring
ampicillin resistance, and this strain of E. coli was transmitted to the
other 10 patients.
c. Streptococcus pneumoniae and E. coli can easily exchange genetic
material. Antibiotic resistance was passed from Streptococcus
pneumoniae to E. coli by horizontal gene transfer in each of the
co-infected patients.
d. The 11 patients probably had acquired the ampicillin-resistant E. coli
strain prior to coming to the hospital but the symptoms did not
appear until after they entered the hospital.
e. Both b and d are equally likely.
4. The underlying factor that explains the unity and diversity of modern
species is
a. energy.
d. systems biology.
b. evolution.
e. all of the above.
c. information.
5. In science, a theory should
a. be equated with knowledge.
b. be supported by a substantial body of evidence.
c. provide the ability to make many correct predictions.
d. do all of the above.
e. do b and c only.
Short Answer
1. Explain how it is possible for evolution to result in unity among different
species yet also produce amazing diversity.
2.
Core Concepts Which core concept of biology is illustrated
by the observation that plants can utilize sunlight to synthesize
carbohydrates? Briefly explain.
Critical-Thinking Skills
Multiple Choice
1. Refer back to Figure 1.12 to answer this question. Based on taxonomic
classification, which of the following species is most closely related to
the clownfish (Amphiprion ocellaris)?
a. cauliflower jellyfish (Cephea cephea); kingdom: Animalia; phylum:
Cnidaria
b. giant carpet anemone (Heteractis crispa); kingdom: Animalia;
phylum: Cnidaria
c. house mouse (Mus musculus); kingdom: Animalia; phylum:
Chordata; class: Mammalia
d. Escherichia coli (a bacterium); domain: Bacteria
e. a or b
2. Ampicillin is an antibiotic used to treat bacterial infections. A
hospital reported the occurrence of a new ampicillin-resistant strain of
Escherichia coli in 11 out of 33 patients in an intensive care unit. This
new strain was found only in patients who had developed symptoms
of pneumonia while in the hospital. This pneumonia was caused by an
ampicillin-resistant strain of Streptococcus pneumonia. Which of the
following is the most likely explanation for the development of this new
antibiotic-resistant strain of E. coli?
a. New mutations arose separately in the E. coli strains from each of
the 11 patients, leading to the independent evolution of ampicillin
resistance in E. coli from each patient.
3. An ecologist is studying the species of living organisms in a valley
in western Colorado and their interactions with the environment. In
particular, she is interested in the relative amounts of water that each
species requires. She is studying
a. an ecosystem.
d. a viable landmass.
b. a community.
e. a population.
c. the biosphere.
4. Some birds migrate from their northern breeding grounds to their
southern wintering grounds by flying over very high mountains at
elevations where oxygen levels in the air are extremely low. Even
so, these birds can produce enough muscle power to complete their
incredible journey. A possible research question involving such bird
behavior is this: Do the number of mitochondria in muscle cells of such
birds increase prior to their southern migration? At which research level
is this question?
a. molecular biology
b. cell biology
c. anatomy and physiology
d. ecology
e. systems biology
5. A plant biologist spends 2 years observing three different species of
desert plants in their native environment. Following this observation
period, the researcher proposes that all three species drop their leaves to
conserve water. This is an example of
a. a theory.
d. a hypothesis.
b. a law.
e. an experiment.
c. a prediction.
Short Answer
1. Rank the following levels of biological organization from the lowest
level of complexity to the highest level of complexity: a protein;
everything in a mountain valley in Colorado; a school of dolphins; a skin
cell; the living species in a small pond; the human heart; muscle tissue;
and a carbon atom.
2.
Core Skill: Modeling Figure 1.12 is a model that describes
the taxonomic classification of the ocellaris clownfish. What
type of model is it? Explain your choice.
ISTUDY
UNIT I
CHEMISTRY
2
Living organisms are composed of chemicals, which are
altered via chemical reactions. These reactions occur
between atoms and molecules and may require, or in some
cases release, energy. Chemical reactions and interactions
between molecules play a role in virtually all aspects of a
cell’s activities. In order to understand how living organisms function, grow, develop, behave, and interact with their
environments, therefore, we first need to understand some
basic principles of atomic and molecular structure and the
forces that allow atoms and molecules to interact with each
other. We will begin this unit with an overview of inorganic
chemistry—that is, the nature of atoms and molecules, with
the exception of those that contain rings or chains of carbon.
Such carbon-containing molecules form the basis of organic
chemistry and are covered in Chapter 3.
3
The following Core Concepts and Core Skills
will be emphasized in this unit:
• Energy and matter: We will see how the chemical energy
stored in the bonds of molecules, such as sugars and fats,
can be released and used by living organisms to perform
numerous functions that support life, including growth,
digestion, and locomotion.
• Structure and function: As described in Chapter 3, the threedimensional structure of molecules is critical in enabling them
to carry out their function.
• Information: Nucleic acids, the basis of inherited genetic
material, are first introduced in Chapter 3.
• Systems: You will learn in this unit how simple molecules are
joined to create a more complex molecule with new biological
properties. The newly created molecule has properties that
are different from those of its component atoms.
• Science and society: In Chapter 2, we will see how an
understanding of chemistry has transformed the ability of
physicians to diagnose disease in humans. One example of
an application of chemistry to medicine is the PET scan.
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