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CHAPTER
20
Viruses
and Bacteria
Quick Review
Looking Ahead
Answer the following without referring to
earlier sections of your book.
1. List the properties of life. (Chapter 1,
Section 1)
4B TAKS 2
Section 1
Viruses
2. Define prokaryote. (Chapter 3,
Section 2)
4A
3. Describe a bacteriophage. (Chapter 9,
Section 1)
4C TAKS 3
4. Differentiate DNA from RNA. (Chapter 10,
Section 1)
6A TAKS 2
Did you have difficulty? For help, review the
sections indicated.
Reading Activity
Take a break after reading each section of this
chapter, and closely study the figures in the section. Reread the figure captions, and, for each
one, write out a question that can be answered
by referring to the figure and its caption. Refer
to your list of figures and questions as you
review the concepts addressed in the chapter
before you complete the Performance Zone
chapter review.
Opening Activity
Location of Bacteria Ask students to make a list of places where
they might find bacteria. Tell students that every answer is correct
because bacteria live everywhere—
in the human body and on everything we touch and eat. Emphasize
that bacteria are an important part
of the environment.
Quick Review
Answers
1. Properties of life include cellular structure and function,
reproducing, metabolizing to
obtain and use energy, maintaining homeostasis, passing
on traits through heredity,
changing over time, and
depending on one another
and the environment
Is a Virus Alive?
Viral Structure
Viral Reproduction
How HIV Infects Cells
Viral Diseases
Section 2
Bacteria
TAKS 2 Bio 4B
Bacterial Structure
Eubacteria and Archaebacteria
Pathogenic Bacteria
Antibiotics
Importance of Bacteria
2. Prokaryotes are single-celled
organisms that lack a
nucleus and other internal
compartments. Bio 4A
3. A bacteriophage is a virus that
infects bacteria. It consists of a
nucleic acid surrounded by a
protein coat. TAKS 3 Bio 4C
4. DNA is double stranded and
contains thymine and deoxyribose. RNA is single stranded
and contains uracil and ribose.
TAKS 2 Bio 6A
www.scilinks.org
Reading Activity
National Science Teachers Association sci LINKS Internet
resources are located throughout this chapter.
Streptococcus bacteria include a number of strains
that can produce a wide range of illnesses. Some, like
“strep throat,” are easily treated. Others are rare and
require immediate medical attention.
TEKS
Bio 3D
Bio 3F
Bio 4A
Bio 9A
Describe the connection between biology and future careers.
Research and describe the history of biology and contributions of scientists.
To identify the parts of prokaryotic and eukaryotic cells.
Compare the structures and functions of different types of biomolecules
such as carbohydrates, lipids, proteins, and nucleic acids.
Bio 11D summarize the role of microorganisms in maintaining and disrupting
equilibrium including diseases in plants and animals and decay in an
ecosystem.
Bio 12C Compare variations, tolerances, and adaptations of plants and animals in
different Biomes.
Bio/IPC 3C Evaluate the impact of research on scientific thought, society, and
the environment.
Answers
433
Students should examine the
chapter figures closely. A typical
question written for Figure 4, for
example, might compare and contrast the lytic and lysogenic cycles
of viral replication.
Chapter Resource File
• Lesson Plans
• Vocabulary Worksheets
• Concept Mapping
Chapter 20 • Viruses and Bacteria
433
Section 1
Section 1
Viruses
Focus
Objectives
Overview
Before beginning this section
review with your students the
objectives listed in the Student
Edition. This section introduces
students to the structure of viruses
and examines how they replicate.
The section also examines how
viruses cause disease. Viral characteristics are discussed as they apply
to HIV. TAKS 3 Bio 4C
Bellringer
Distribute newspapers or news
magazines to student groups and
ask students to find an article
about viruses. Have them quickly
read the article and write a question about material in the article.
Most newspapers will contain at
least one article about viruses, for
example, articles on HIV or West
Nile virus. TAKS 3 Bio 4C
● Describe why a virus is
not considered a living
organism.
4B 4C
Throughout the book, you have learned about the properties of life.
All living things are made of cells, are able to grow and reproduce,
and are guided by information stored in their DNA. The smallest
TAKS 2, TAKS 3
organisms that have these properties are prokaryotes. Viruses are
● Summarize the discovery of
the tobacco mosaic virus.
3F segments of nucleic acids contained in a protein coat. Viruses are not
cells. Viruses are smaller than prokaryotes and range in size from
● Describe the basic structure
about 20 nm to 250 nm (0.02–0.25 µm) in diameter. (One nanometer
of a virus.
4C TAKS 3
is equal to 0.001µm or 0.00000004 in.) Most viruses, such as the Ebola
● Summarize the steps of
virus shown in Figure 1, can be seen only with an electron microviral replication.
4C TAKS 3
scope. Viruses are pathogens —agents that cause disease. Viruses
● Explain how HIV infects
replicate by infecting cells and using the cell to make more viruses.
4C
immune system cells.
TAKS 3 Because viruses do not have all the properties of life, biologists do not
consider them to be living. Viruses do not grow, do not have homeKey Terms
ostasis, and do not metabolize. Because they cause diseases in many
virus
organisms, viruses have a major impact on the living world.
pathogen
capsid
envelope
glycoprotein
bacteriophage
lytic
provirus
lysogenic
prion
viroid
Motivate
Discussion/
Question
GENERAL
Ask students what tomatoes, white
potatoes, and garden peppers have
in common. (All three are from the
nightshade family, Solanaceae, and
they are vulnerable to the same diseases.) Tell students that tobacco is
also a member of the nightshade
family. A virus that plagues this
family, the tobacco mosaic virus
(TMV), was first recognized in
tobacco. Have students speculate as
to why TMV infects only members
of this family. (Students may mention specific receptor sites on the
plants’ cell surfaces.) TAKS 3 Bio 4C
Figure 1 Ebola virus.
This virus causes an
often-fatal disease and has
been recognized only
since 1976.
Discovery of Viruses
Near the end of the nineteenth century, scientists were trying to find
the cause of tobacco mosaic disease, which stunts the growth of
tobacco plants. Scientists filtered bacteria from the sap of infected
plants. They were surprised to find that the filtered sap could still
cause uninfected plants to become infected. The scientists concluded that the pathogen is
smaller than a bacterium. The
pathogen was called a virus, a
Latin word meaning “poison.”
For many years after this
discovery, viruses were thought
to be tiny cells. In 1935, biologist Wendell Stanley of the
Rockefeller Institute purified
tobacco mosaic virus (TMV).
He determined that the purified virus is a crystal. Stanley
concluded that TMV is a chemical rather than an organism.
Each particle of TMV is
composed of RNA and protein.
Scientists were able to separate
the RNA from the protein and
reassemble the virus so that it
could infect plants.
434
Chapter Resource File
• Lesson Plan GENERAL
• Directed Reading
• Active Reading GENERAL
pp. 434–435
Student Edition
TAKS Obj 2 Bio 4B
TAKS Obj 3 Bio 4C
TEKS Bio 3F, 4B, 4C
Teacher Edition
TAKS Obj 4 IPC 7D
TEKS Bio 4C
TEKS IPC 7D
434
Is a Virus Alive?
Chapter 20 • Viruses and Bacteria
Planner CD-ROM
• Reading Organizers
• Reading Strategies
• Occupational Applications
Worksheet Sanitarian GENERAL
• Supplemental Reading Guide
Microbe Hunters
Viral Structure
The virus protein coat, or capsid, may contain either RNA or DNA,
but not both. RNA viruses include the human immunodeficiency
virus (HIV), which causes AIDS, influenza viruses, and rabies virus.
DNA viruses include those viruses that cause warts, chickenpox, and
mononucleosis. Many viruses, such as the influenza virus shown in
Figure 2, have a membrane, or envelope, surrounding the capsid.
The envelope helps the virus enter cells. It consists of proteins,
lipids, and glycoproteins (glie koh PROH teenz), which are proteins
with attached carbohydrate molecules that are derived from the
host cell. Some viruses also contain specific enzymes.
Viruses exist in a variety of shapes. Some viruses, such as the
Ebola virus, shown in Figure 1, are long rods that form filaments.
Spherical viruses, such as the influenza virus shown in Figure 2,
typically are studded with receptors. These receptors help the virus
enter cells. A helical virus, like the tobacco mosaic virus shown in
Figure 2, is rodlike in appearance, with capsid proteins winding
around the core in a spiral. Polyhedral viruses have many sides and
are roughly spherical. The capsid of most polyhedral viruses has 20
triangular faces and 12 corners. This odd shape is an efficient one
for containing a viral genome. Figure 2 shows the polyhedral shape
of a adenovirus, which can cause several different kinds of infections in humans.
Viruses that infect bacteria, called bacteriophages , have a complicated structure. A T4 bacteriophage, for example, has a polyhedron
capsid attached to a helical tail. A long DNA molecule is coiled within
the polyhedron.
Compare and Contrast
To compare and contrast
the properties of life as
defined in Chapter 1 and the
properties of viruses, make
a two-column list. In one
column, write the properties
of life. In the other column,
write the properties of life
that viruses have.
Figure 2 Viral structures
Magnification: 1,250,000ⴛ
READING
SKILL
BUILDER
K-W-L Before students read this
section, have them write short individual lists of all the things they
already Know (or have heard)
about viruses. When students have
finished their lists, ask them to contribute their entries to a class list on
the board or overhead. Then have
students list things they Want to
know about viruses. Have students
save their lists for later use in
Reteaching at the end of Section 1.
Teaching Tip
Viruses can have characteristic shapes.
Magnification: 202,500ⴛ
Teach
Magnification: 135,000ⴛ
GENERAL
Design a Virus Have students create a fictitious virus. They should
produce a drawing or a model of
their virus and provide information
about the origin of the virus, its
components, the host it infects,
how the virus is transmitted, and
the effects of the virus on the host.
Have students share their creations
with the class.
LS Kinesthetic
Using the Figure
Influenza (enveloped)
Tobacco mosaic virus (helical)
Adenovirus (polyhedral)
435
CHEMISTRY
IPC Benchmark Fact
TAKS 3 Bio 4C
CONNECTION
Only a few different kinds of proteins are
found in a viral capsid. For example, the capsid
of TMV contains more than 1,000 protein
molecules, but they are all copies of the same
protein. This means that one gene can code all
of the capsid components. TAKS 3 Bio 4C
Use Figure 2 to point out two
important parts of a virus: the capsid (made of protein) and the
nucleic acid (RNA or DNA). Some
viruses contain DNA, whereas others contain RNA. Ask students
what constitutes the membranous
envelope surrounding the capsid of
the influenza virus. (proteins, lipids,
and glycoproteins from the host cell)
Emphasize that different viruses
can have very different appearances; some are larger and more
complex than others. LS Visual
Due to the way in which elements interact and form
bonds, viruses have characteristic shapes (helical or
polyhedral). In a similar way, water also has a characteristic shape because the hydrogen atoms are
arranged with the oxygen atom to form a specific
angle, which is the same for all water molecules (i.e.,
104.45°). Because oxygen is more electronegative
than hydrogen, oxygen has a greater tendency to
attract electrons. The unequal sharing of bonding
electrons produces water’s polar property.
TAKS 4 IPC 7D (grade 11 only)
Transparencies
TT Bellringer
TT Viral Replication in Bacteria
TT Structures of Adenovirus and
Bacteriophage
TT Structures of TMV and Influenza
Virus
TT Important Viral Diseases
Chapter 20 • Viruses and Bacteria
435
Magnification: 32,512ⴛ
Viruses lack the enzymes necessary for metabolism and have no
structures to make protein. Therefore, viruses must rely on living
cells (host cells) for replication, as shown in Figure 3. Before a virus
can replicate, it must first infect a living cell. A plant virus, like
TMV, enters a plant cell through tiny tears in the cell wall at points
of injury. An animal virus enters its host cell by endocytosis. A bacterial virus, or bacteriophage, punches a hole in the bacterial cell
wall and injects its DNA into the cell.
Teach, continued
continued
Demonstration
GENERAL
Show students labels from tomato
plants or ads in nursery catalogs
that state that the plants are resistant to TMV. Explain that people
who handle tobacco products can
carry the virus on their hands and
infect plants by touching them. An
infected plant will develop light
and dark patches on its leaves—the
mosaic-like symptoms of the
disease. LS Visual TAKS 3 Bio 4C
Using the Figure
Figure 3 Bacteriophage
infecting a bacterium.
Bacteriophages (pink) first
attach to a bacterial cell (blue)
and then push their DNA into
it. The cell then produces
more viruses.
GENERAL
Point out that some of the capsids
in Figure 3 appear empty. Ask students to explain why. (Those capsids
that appear empty have already delivered their DNA to the bacterial cell.
Those capsids that appear dark
still contain
English Language
Learners
their DNA.)
Figure 4 Viral replication
in bacteria. Bacterial viruses
provide a model by which
viruses replicate through the
lytic cycle or lysogenic cycle.
TAKS 3 Bio 4C
Lytic Cycle
The reproduction of bacterial viruses has been well studied. Once
inside a cell, the virus will set out on one of two different paths: the
lytic cycle or the lysogenic cycle.
In bacterial viruses, the cycle of viral infection, replication, and
cell destruction is called the lytic cycle. After the viral genes have
entered the cell, they use the host cell to replicate viral genes and to
make viral proteins, such as capsids. The proteins are then assembled with the replicated viral genes to form complete viruses. The
host cell is broken open and releases newly made viruses. Though
reproduction in bacterial viruses is illustrated here, these stages are
common to infections by other viruses as well. The lytic cycle is
shown in Figure 4.
Lysogenic Cycle
During an infection, some viruses stay inside the cells but do not
make new viruses. Instead of producing virus particles, the viral
gene is inserted into the host chromosome and is called a provirus .
Lytic cycle
Teaching Tip
GENERAL
1
Viral Reproduction Tell students
that a single virus that infects a
bacterial cell can produce about
100 new viruses in 20 minutes.
Have students calculate how many
viruses would exist after 1 hour,
assuming that there are sufficient
cells to support continuous viral
replication. (1 million) LS Logical
BUILDER
Graphing Have students graph the
number of viruses described in the
Teaching Tip above. Students
should graph the number of viruses
present at 0, 20, 40, and 60 minutes. Student graphs should show
exponential growth.
The virus attaches
to a cell and
injects DNA.
Lysogenic cycle
Bacterial
chromosome
5
The provirus may
enter the lytic cycle.
Many
cell
divisions
4
SKILL
Viral Reproduction
The cell
breaks open
and releases
viruses.
3
New viruses are
made.
2
4
Viral DNA
enters the
lytic cycle
or lysogenic
cycle.
3
The host cell
divides normally.
Viral DNA integrates
with host DNA.
436
REAL WORLD
CONNECTION
pp. 436–437
Student Edition
TAKS Obj 3 Bio 4C
TEKS Bio 4C
Teacher Edition
TAKS Obj 3 Bio 4C
TEKS Bio 3D, 4C
436
Chapter 20 • Viruses and Bacteria
Commonly called the flu, influenza has been
perhaps the most lethal viral disease in
human history. Because the influenza virus is
airborne, it is highly contagious. A common
flu virus can be lethal to people who have
respiratory ailments or compromised
immune systems, as well as to elderly people
and young children. Sometimes a new type
of flu virus is very lethal. For example, in
1918 and 1919, a new type of influenza
killed 22 million people—more people than
were killed in combat during World War I.
TAKS 3 Bio 4C
Whenever the cell divides, the provirus also divides, resulting in two
infected host cells. In this cycle, called the lysogenic (lie soh JEHN
ihk) cycle, the viral genome replicates without destroying the host
cell. This cycle is shown in Figure 4. In some lysogenic viruses, a
change in the environment can cause the provirus to begin the lytic
cycle. This results in the destruction of the host cell.
In animal cells, viruses can replicate slowly so that the host cell
is not destroyed by the virus. For example, the virus that causes
cold sores in humans hides deep in the nerves of the face. When the
conditions in the body become favorable for the virus, such as
when a person is under stress, the virus then begins to cause tissue
damage that is seen as a cold sore or fever blister.
READING
SKILL
BUILDER
Paired Summarizing Have pairs
of students silently read about the
two methods of viral replication.
As they read, have them note passages they do not understand. After
students finish, ask one member of
each pair to summarize the passage, referring to the text as
needed. The listener should add
anything omitted and continue the
discussion by pointing out what he
or she did not understand. Partners
should work together to clarify
what was not clear and to formulate questions to present to the class.
Host Cell Specificity
Viruses are often restricted to certain kinds of cells. For example,
TMV infects tobacco and related plants, but does not infect animals.
Scientists hypothesize that this specificity may be due to the viruses’
origin. Viruses may have originated when fragments of host genes
escaped or were expelled from cells. The hypothesis that viruses
originated from a variety of host cells may explain why there are so
many different kinds of viruses. Biologists think there are at least as
many kinds of viruses as there are kinds of organisms.
Co-op Learning
Structure of HIV—an
Enveloped Virus
Many viruses that infect only animals,
such as the influenza virus shown in
Figure 2, have an exterior viral envelope. Figure 5 shows human immunodeficiency virus (HIV), the virus that
causes acquired immune deficiency
syndrome (AIDS). Figure 5 illustrates
the envelope and other features common to several animal viruses. In
many cases, the viral envelope is composed of a lipid bilayer derived from
the membrane of the host cell. On the
surface of the virus, glycoproteins are
embedded within the envelope.
Within the envelope lies the capsid,
which in turn encloses the virus’s
genetic material. In the case of HIV,
the genetic material is composed of
two molecules of single-stranded
RNA. The approximately 9,000 nucleotides of HIV make up nine genes.
Three of these genes are common to
many different viruses.
English Language
Learners
Teaching Tip
Figure 5 HIV. HIV infects
human white blood cells.
Glycoprotein
Envelope
Capsid
County Health Department Ask
a county public health official to
speak to your class about the kind
of work the county public health
department does to prevent viral
diseases. Be sure to ask the speaker
to discuss viral diseases that are of
concern in your county (e.g., mosquito-transmitted viral encephalitis,
measles, polio, and influenza,
HIV). Check with your school’s
guidelines about the kinds of subject areas that are appropriate. Ask
the speaker to bring samples of
equipment that the county uses in
its health work. LS Intrapersonal
Bio 3D
RNA
437
Career
Epidemiologist Epidemiologists are
employed by hospitals, health departments,
universities, and private consulting firms. Their
work is often a combination of biology, medicine, and detective-like problem solving.
Epidemiologists study human health and disease, investigate and identify new cases, and
work to prevent epidemics. A strong background in biology—especially microbiology—
statistics, and evolution is vital. Many
epidemiologists also have advanced degrees
in public health or medicine. Bio 3D
Chapter 20 • Viruses and Bacteria
437
How HIV Infects Cells
HIV, shown in Figure 6, provides a good example of how animal
viruses enter cells. HIV entry is a two-step process. First, the virus
attaches to the cell at specific sites called receptors. Second, this
attachment triggers endocytosis. Recall that during endocytosis,
the cell membrane pushes inward, carrying a particle—in this case
HIV—with it into the cell.
Teach, continued
continued
READING
SKILL
BUILDER
Brainstorming Ask students what
becomes of the proteins made by the
host cell under the direction of the
viral genome. (The proteins become
the capsids for the new viruses and the
enzymes needed for English Language
replication.)
Learners
Activity
Attachment
Studding the surface of each HIV are spikes composed of a glycoprotein. This particular glycoprotein precisely fits a human cell
surface receptor called CD4. Thus the HIV glycoprotein can bind to
any cell that possesses CD4 receptors. In humans, immune system
cells called lymphocytes and macrophages, as well as certain cells in
the brain, possess CD4 receptors.
Entry into Macrophages
GENERAL
Writing
HIV cannot enter a cell merely by docking onto a CD4 receptor.
Rather, the glycoprotein must also activate a second co-receptor,
called CCR5. It is this event at CCR5 that starts endocytosis, illustrated in Figure 7. Because human macrophages possess both CD4
and CCR5 receptors, HIV can enter macrophages. Lymphocytes,
which are critical to immune system function, do not have CCR5
receptors. HIV therefore does not enter lymphocytes.
Future Headlines
Ask students to write headlines about HIV that they might
expect to see in 10 years. Discuss
the headlines and the predictions
behind them with the class. Then
have students write short essays to
explain their predictions about
AIDS in the future. Post the headlines and essays around the room.
Replication
LS Verbal Bio/IPC 3C; Bio 11D
www.scilinks.org
Topic: AIDS Research
in Texas
Keyword: HXX4001
Once inside a cell, the HIV particle sheds its capsid. The particle
then releases an enzyme called reverse transcriptase. Reverse transcriptase copies the naked viral RNA into a complementary DNA
version. This process is mistake-prone, so it creates many new
mutations. Translation of the viral DNA by the host cell’s machinery directs the production of many copies of the virus. HIV doesn’t
rupture and kill the cell; instead, the new viruses are released from
the cell by budding. The new virus particle is thus covered with an
envelope derived from the cell membrane.
Figure 6 HIV. The spherical
structure of HIV is visible in this
transmission electron micrograph
of individual virus particles.
438
MISCONCEPTION
ALERT
pp. 438–439
Student Edition
TAKS Obj 2 Bio 4B
TAKS Obj 2 Bio 6C
TAKS Obj 3 Bio 4C
TEKS Bio 4C, 6C, 11D
Teacher Edition
TAKS Obj 1 Bio/IPC 2A
TAKS Obj 3 Bio 4C
TEKS Bio 3F, 4C, 11D
TEKS Bio/IPC 2A, 3C
438
HIV Infection and AIDS Students may
not realize that an individual who has been
infected with HIV can pass the virus to
others even though he or she shows no
symptoms of AIDS. During the long latency
period between infection and the appearance of AIDS, typically 8 to 10 years, the
virus multiplies in the body but does not
kill the cells. Eventually, however, the
tissues of the lymphatic system cease to
function, and AIDS develops. TAKS 3 Bio 4C
Chapter 20 • Viruses and Bacteria
IPC Benchmark Fact
Have students identify and describe the strengths and
weaknesses of the hypothesis concerning the origin
of viral specificity. Ask them if they can think of a way
this hypothesis might be tested. TAKS 1 Bio/IPC 2A
CCR5
receptor
HIV
CH4
coreceptor
HIV RNA
SKILL
New
DNA
Writing Skills The first
cases of AIDS were reported
in the early 1980s. Have students
obtain statistics on the spread of
AIDS from its discovery to the
present time. Ask students to present the information in brief reports,
including a bar graph that compares the number of AIDS-related
deaths over the past few decades.
Reverse
transcriptase
Immune
system cell
The glycoprotein on HIV’s surface docks at
a CD4 receptor. A second receptor, CCR5,
helps pull HIV into the cell.
BUILDER
Writing
The viral envelope is left outside the cell.
The capsid fragments are located inside the
HIV cell. A DNA copy of the HIV RNA is made
by the cell.
LS Verbal TAKS 2 Bio 4C; Bio 11D
Group Activity
HIV
RNA
HIV
HIV
proteins
Budding
The new viral DNA directs synthesis of
new HIV proteins and HIV RNA.
New HIV particles leave macrophages
by budding. HIV particles leave T cells by
budding or bursting through the membrane.
AIDS
For years after the initial infection, HIV continues to replicate (and
mutate). Eventually and by chance, HIV’s surface glycoproteins
change to the point that they now recognize a new cell surface receptor. This receptor is found on the subset of lymphocytes called T cells.
Unlike its activity in macrophages, HIV reproduces in T cells and
then destroys them. This increases the number of virus particles in
the blood, which then infect other T cells, widening the circle of cell
death. It is this destruction of the body’s T cells that blocks the body’s
immune response and signals the onset of AIDS. AIDS is a disease in
which an individual is unable to defend his or her own body against
infections that do not normally occur in healthy individuals.
Usually, HIV-infected people do not develop AIDS symptoms until
years after infection. As a result, an HIV-infected individual can feel
healthy and still spread the virus to others. HIV is not passed from an
infected person to a healthy one through casual contact. It is transmitted in body fluids (such as semen or vaginal fluid) through sexual
contact and in blood through the sharing of nonsterile needles. It is
also transmitted to infants during pregnancy or through breast milk.
Figure 7 HIV infection.
HIV docks at specific receptors
on cell membranes. The virus
is reproduced by the infected
cell.
GENERAL
AIDS Drug Ask student groups to
design a hypothetical drug that will
disable the infection cycle of HIV.
Students’ drugs can target any step
within the viral replication cycle,
such as preventing the virus from
attaching to white blood cells,
inhibiting endocytosis of the virus,
or destroying reverse transcriptase.
Ask students to make diagrams of
the HIV infection cycle that show
their drug at work. Remind students that prevention is the best
way to fight
English Language
Learners
AIDS.
TAKS 1 Bio/IPC 2A
READING
SKILL
BUILDER
Interactive Reading Assign
Chapter 20 of the Holt Biology
Guided Audio CD Program to help
students achieve greater success in
reading the chapter.
439
Immunity to AIDS A small number of individuals have a natural resistance to HIV. This
resistance seems to be due to their having a
defective cell surface receptor for HIV.
Researchers are trying to make use of this
mutation to develop a vaccine for AIDS. Bio 3F
Chapter 20 • Viruses and Bacteria
439
Viral Diseases
Diseases caused by viruses have been known and feared for thousands of years. Perhaps the most lethal virus in human history is
the influenza virus. Commonly known as the flu, influenza is characterized by chills, fever, and muscular aches. The virus infects cells
of the upper respiratory tract. There the viruses replicate and
spread to new cells. About 22 million Americans and Europeans
died of flu during an 18-month period in 1918–1919. Table 1 lists
some familiar viral diseases.
Certain viruses can also cause some types of cancer. Recall that
cancer is a condition in which cells reproduce uncontrollably as a
result of the failure of mechanisms that control cell growth and
division. Viruses associated with human cancers include hepatitis B
(liver cancer), Epstein-Barr virus (Burkitt’s lymphoma), and human
papilloma virus (cervical cancer).
Teach, continued
continued
Teaching Tip
Eradicating Smallpox Tell students that smallpox is the first
disease to be eradicated globally.
Then tell students that the World
Health Organization was able to
wipe out the disease through a
highly effective worldwide vaccination strategy. The last known
smallpox case outside of the lab
was reported in 1977 in Somalia.
Although officially declared eradicated in 1980, samples of the
smallpox virus are stored in the
United States and in Russia.
Controversy exists over whether to
destroy these samples or maintain
them for future study. Have a class
discussion about this controversy,
and ask students for their views.
Table 1 Important Viral Diseases
Disease
Description of illness
How the disease is transmitted
AIDS
Immune system failure
Sexual contact, contaminated
blood, or contaminated needles
Common cold
Sinus congestion, muscle aches, cough, fever
Inhalation, direct contact
Ebola
High fever, uncontrollable bleeding
Body fluids
Bio 3F
Hepatitis A
Flulike symptoms, swollen liver,
yellow skin, painful joints
Contaminated blood, food, or water
Teaching Tip
Hepatitis B
Flulike symptoms, swollen liver, yellow skin,
painful joints; can cause liver cancer
Sexual contact, contaminated
blood, or contaminated needles
Influenza (flu)
Fever, chills, fatigue, cough, sore throat,
muscle aches, weakness, headache
Inhalation
Mumps
Painful swelling in salivary glands
Inhalation
Polio
Fever, headache, stiff neck, possible paralysis
Contaminated food or water
Rabies
Mental depression, fever, restlessness,
difficulty swallowing, paralysis,
convulsions; fatal
Bite of infected animal
Smallpox
Blisters, lesions, fever, malaise, blindness,
disfiguring scars; often fatal
Inhalation
Yellow fever
Rash, swollen glands, fever; fatal to developing
infant in pregnant woman
Bite of infected mosquito
Prions Disease-causing prions
have the same amino acid sequence
as the normal prion protein, but
the disease-causing prions are
folded in a way that changes their
function and physical characteristics. Have students research the
shape of a disease-causing prion
and that of its normal protein and
make diagrams showing the
differences. LS Visual
440
Cultural
Awareness
pp. 440–441
Student Edition
TAKS Obj 3 Bio 4C
TEKS Bio 3F, 4C
TEKS Bio/IPC 3C
Teacher Edition
TAKS Obj 3 Bio 4C
TEKS Bio 3C, 3F, 4C
440
Accidental Spread of Viral Diseases
Isolated communities are at particular risk
of epidemics when outsiders visit. Diseases
spread by travelers can wipe out a small isolated community. Spanish conqueror Hernán
Cortés was aided in his conquest of the
Aztecs by a smallpox epidemic that struck
those Native Americans. Prior to the arrival
of the Europeans, smallpox had been
Chapter 20 • Viruses and Bacteria
unknown in the New World. The disease
killed millions of Native Americans.
Today, the Yanomamo tribe of Brazil and
Venezuela is being decimated because of the
onslaught of malaria, influenza, measles,
and chicken pox brought by miners in search
of gold. TAKS 3 Bio 4C
Emerging Viruses
Viruses that evolve in geographically isolated areas and are pathogenic to humans are called emerging viruses. These new pathogens
are dangerous to public health. People become infected when they
have contact with the normal hosts of these viruses.
In 1999, a mosquito-borne virus called West Nile virus began to
spread across the United States. West Nile virus probably was
brought from overseas to America by an infected bird. While it is an
emerging virus in North America, West Nile virus is common in
Africa, eastern Europe, and western Asia. People who are infected
with the virus from mosquito bites typically experience mild flulike
symptoms. In some people, particularly the elderly, inflammation
of the brain may occur, which can be fatal.
First detected in the southwestern United States, hantavirus is
spread in rodent droppings and can cause a lethal illness in humans.
At least 38 percent of its human victims die.
www.scilinks.org
Topic: Viral Diseases
Keyword: HX4186
Close
Reteaching
Prions and Viroids
In 1982, the American scientist Stanley Pruisner, of Stanford University, described a new class of pathogens that he called prions
(PREE awnz). Prions are composed of proteins but have no nucleic
acid. A disease-causing prion is folded into a shape that does not
allow the prion to function. Contact with a misfolded prion will
cause a normal prion to misfold, too. In this way the misfolding
spreads like a chain reaction.
Prions were first linked to a brain disease in
sheep called scrapie. Later, brain diseases such
as mad cow disease, displayed by the cow shown
in Figure 8, and Creutzfeldt-Jakob disease were
also associated with prions. Eating meat containing the disease-causing prion can cause
infection.
A viroid (VEER oid) is a single strand of RNA
that has no capsid. Viroids are important infectious disease agents in plants. Viroids have
affected economically important plants such as
cucumbers, potatoes, avocados, and oranges.
Figure 8 Infected cow.
This cow, which is unable to
stand and walk, is showing
signs of mad cow disease.
K-W-L Have students return to
their lists of things they Want to
know about viruses that they created when they began this section.
Have them check off the questions
that they can now answer. Students
should then make a list of what
they have Learned. Conclude by
asking:
• Which questions are still
unanswered?
• What new questions do you
have?
You may wish to have students
research their unanswered
questions. LS Verbal
Quiz
GENERAL
1. What is the genetic material of
HIV? (HIV is composed of two
molecules of single-stranded RNA.)
2. What is a bacteriophage?
(A bacteriophage is a virus that
infects bacteria.)
3. What is the general structure of a
virus? (A virus has a nucleic acid
core surrounded by a protein coat.)
Alternative
Assessment
Section 1 Review
GENERAL
Writing
Compare the properties of viruses with the
properties of cells.
Describe how HIV causes AIDS.
Critical Thinking Evaluate the argument that
Describe Stanley’s experiment with the
tobacco mosaic virus.
4C
4C
emerging viruses are new viruses.
3C 3F
Name the parts of a virus.
4C
List the steps by which viruses replicate.
4C
Have students write
a story telling how an HIV
virus infects a cell. LS Verbal
4C
TAKS Test Prep Viruses differ from cells
4C
because viruses
A can grow.
C have homeostasis.
B do not metabolize. D lack nucleic acids.
441
Answers to Section Review
1. Cells metabolize, grow, maintain homeostasis,
and reproduce. Viruses reproduce, but not
without the help of a host cell. TAKS 3 Bio 4C
2. Stanley purified the tobacco mosaic virus, found
that it was crystalline, and then used the crystal
to infect healthy tobacco plants. Bio/IPC 3C, Bio 3F
3. Viruses consist of a nucleic acid core, a
protein capsid, and may be surrounded by
a membranous envelope (proteins, lipids, and
glycoproteins). TAKS 3 Bio 4C
4. Viruses enter the host cell. This is followed by
replication of the viral genome, which is then
used to build viral proteins. The proteins and
nucleic acids are assembled into new viruses,
which cause the cell to burst, releasing new
viruses. TAKS 3 Bio 4C
5. HIV replicates in macrophages over a period of
years. Eventually, the HIV surface glycoproteins
change and they attack T cells, killing them. This
destroys the body’s immune system. TAKS 3 Bio 4C
6. Emerging viruses have been recorded only
recently as causing diseases. However, these
viruses may not be new; they simply may have
gone unnoticed or unrecorded. TAKS 3 Bio 4C
7.
A. Incorrect. Viruses do not
grow. B. Correct. Viruses do not metabolize.
C. Incorrect. Viruses do not maintain homeostasis. D. Incorrect. Viruses have nucleic acids. TAKS 3 Bio 4C
Chapter 20 • Viruses and Bacteria
441
Section 2
Bacteria
Section 2
Focus
Before beginning this section
review with your students the
objectives listed in the Student
Edition. This section introduces
students to Eubacteria and
Archaebacteria, their structure, and
their methods of obtaining energy.
Their ability to cause disease and
their importance to humans are
also discussed. The section ends
with a discussion of antibiotic
resistance in bacteria. TAKS 3 Bio 4D
● List seven differences
between bacteria and
eukaryotic cells.
4A
The prokaryotes referred to in this chapter as bacteria include the
organisms that compose the kingdom Eubacteria (Domain Bacteria)
and the organisms that compose the kingdom Archaebacteria (Domain
Archaea). Bacteria differ from eukaryotes in at least seven ways.
● Describe three different
ways bacteria can obtain
energy.
4B TAKS 2
Have students make individual lists
of as many beneficial uses of bacteria as they can think of.
Motivate
GENERAL
Ask students which of the following diseases are caused by viruses
and which by bacteria: measles,
AIDS, tuberculosis, syphilis,
influenza, chicken pox, botulism,
bubonic plague, polio, mumps,
Lyme disease, strep throat, and the
common cold. (Measles, AIDS,
influenza, chicken pox, polio,
mumps, and colds are caused by
viruses; the other diseases are caused
by bacteria.) Ask whether antibiotics can cure all these diseases
and, if not, why. Explain that
although antibiotics can cure many
bacterial infections, they are not
effective at curing viral infections.
TAKS 3 Bio 4C, 4D
1. Internal compartmentalization. Bacteria are prokaryotes.
Unlike eukaryotes, prokaryotes lack a cell nucleus. Bacterial
cells have no internal compartments or membrane systems.
● Describe the external and
internal structure of
Escherichia coli.
4A
● Distinguish two ways that
4D
bacteria cause disease.
2. Cell size. Most bacterial cells are about 1 µm in diameter; most
eukaryotic cells are more than 10 times that size.
3. Multicellularity. All bacteria are single cells. Some bacteria may
stick together or may form strands. However, these formations
are not truly multicellular because the cytoplasm in the cells does
4D
not directly interconnect, as is the case with many multicellular
TAKS 3
eukaryotes. Also, the activities of the cells are not specialized.
TAKS 3
● Identify three ways that
bacteria benefit humans.
Key Terms
Bellringer
Identifying
Preconceptions
Bacterial Structure
Objectives
Overview
4. Chromosomes. Bacterial chromosomes consist of a single circular piece of DNA. Eukaryotic chromosomes are linear pieces
of DNA that are associated with proteins.
pilus
bacillus
coccus
spirillum
capsule
antibiotic
endospore
conjugation
anaerobic
aerobic
toxin
5. Reproduction. Bacteria reproduce by binary fission, a process
in which one cell pinches into two cells. In eukaryotes, however,
microtubules pull chromosomes to opposite poles of the cell during mitosis. Afterward, the cytoplasm of the eukaryotic cell
divides in half, forming two cells.
Pilus
6. Flagella. Bacterial flagella are simple structures composed of a
single fiber of protein that spins like a corkscrew to move the cell.
Eukaryotic flagella are more-complex structures made of microtubules that whip back and
Magnification: 69,230ⴛ
forth rather than spin. Some
bacteria also have shorter,
thicker outgrowths called pili
(PIHL ee) (singular, pilus),
shown in Figure 9. Pili enable
bacteria to attach to surfaces
or to other cells.
Flagellum
Figure 9 Flagella and
pili. Bacteria have
flagella that provide them
with movement and pili
that enable adherence to
surfaces.
Proteus mirabilis
442
Chapter Resource File
• Lesson Plan GENERAL
• Directed Reading
• Active Reading GENERAL
pp. 442–443
Student Edition
TAKS Obj 2 Bio 4B
TAKS Obj 3 Bio 4D
TEKS Bio 4A, 4B, 4D
Teacher Edition
TAKS Obj 2 Bio 4B
TAKS Obj 3 Bio 4C, 4D
TEKS Bio 4A, 4B, 4C, 4D
442
7. Metabolic diversity. Bacteria
have many metabolic abilities
that eukaryotes lack. For example, bacteria perform several
different kinds of anaerobic
and aerobic processes, while
eukaryotes are mostly aerobic
organisms.
Chapter 20 • Viruses and Bacteria
Planner CD-ROM
• Reading Organizers
• Reading Strategies
• Supplemental Reading Guide
The Andromeda Strain
Bacterial Cell Shapes
A bacterial cell is usually one of three basic shapes, as shown in
Figure 10: bacillus (buh SIHL uhs), a rod-shaped cell; coccus
(KAHK us), a round-shaped cell; or spirillum (spy RIHL uhm), a
spiral cell. A few kinds of bacteria aggregate into strands. Species
that form filaments are indicated by the prefix strepto-, while
species that form clusters are indicated by the prefix staphylo-.
Members of the kingdom Eubacteria have a cell wall made of peptidoglycan, a network of polysaccharide molecules linked together
with chains of amino acids. Outside the cell wall and membrane,
many bacteria have a gel-like layer called a capsule . Members of the
kingdom Archaebacteria often lack cell walls.
Reviewing Information
Prepare flash cards for each
of the Key Terms in this
chapter. On each card, write
the term on one side and its
definition on the other side.
Use the cards to review
meanings of the Key Terms.
Cell walls Eubacteria can have two types of cell walls, distinguished by a dye staining technique called the Gram stain. One
group is called Gram-negative, and the other Gram-positive.
Gram staining is important in medicine because the two groups
of eubacteria differ in their susceptibility to different antibiotics.
Antibiotics are chemicals that interfere with life processes in bacteria. Thus, Gram staining can help determine which antibiotic
would be most useful in fighting an infection.
Pili Pili enable bacteria to adhere to the surface of sources of nutrition, such as your skin. Some kinds of pili enable bacteria to
exchange genetic material through a process called conjugation.
Conjugation (kahn juh GAY shuhn) is a process in which two
organisms exchange genetic material. In prokaryotes, pili from one
bacterium adhere to a second bacterium, and genetic material is
transferred from the first bacterium to the second bacterium. Conjugation enables bacteria to spread genes within a population.
Magnification: 117,300ⴛ
Bacillus (rod-shaped)
E. coli
Coccus (round-shaped)
Micrococcus luteus
READING
SKILL
BUILDER
Brainstorming Ask students to discuss whether the following statement
is true or false: Bacteria are successful in part because they have cellular
structures that enable them to live
in a wide variety of environments.
Students should give examples supporting their viewpoints.
Teaching Tip
Endospores Some bacteria form thick-walled endospores (EHN
doh spohrz) around their chromosomes and a small bit of cytoplasm when they are exposed to harsh conditions. These conditions
can be the depletion of nutrients, a drought, or high temperatures.
Endospores can survive environmental stress and may germinate
years after they were formed, releasing new, active bacteria.
Teach
www.scilinks.org
Topic: Bacteria
Keyword: HX4018
Figure 10 Bacterial
shapes. Bacteria are usually
one of three shapes.
Magnification: 2,295ⴛ
GENERAL
Movement and Locomotion
Explain that bacteria have several
mechanisms of locomotion, including sliding over slimy surfaces,
twisting through fluids, and propelling themselves with flagella.
However, not all bacteria move.
Bacteria that are capable of movement are called motile bacteria.
Those that cannot move on their
own are called nonmotile bacteria.
Have students discuss how nonmotile bacteria might move from
place to place. (Possible answers are
transport by other organisms,
through the air, through water.)
TAKS 2 Bio 4B; Bio 4A
Spirillum (spiral-shaped)
Spirillum volutans
443
Transparencies
TT
TT
TT
TT
TT
Bellringer
Three Bacterial Cell Shapes
Gram Staining
Escherichia coli
Important Bacterial Diseases
Bacterial Flagella Flagella are composed of
proteins. A flagellum is connected to a protein
shaft, which passes through the capsule of the
bacteria. The shaft attaches to a double set of
rings in the cell wall, much like rings of ball
bearings. When the inner ring turns, the flagellum rotates. The outer ring is fixed to the cell
wall and does not move. Interested students
may be interested in making a model of a bacterial flagellum. Bio 4A
Chapter 20 • Viruses and Bacteria
443
Obtaining Energy
Teach, continued
continued
SKILL
BUILDER
GENERAL
Math Skills Explain to students
that, in theory, each colony on a
Petri dish arose from a single bacterium and that bacteriologists use
this understanding to count the
number of bacteria in a sample.
Give students the following problem. A 1-mL sample of bacterial
culture was diluted 1,000 times in
water, and then 0.1 mL was added
to a Petri dish. Twenty-four hours
later, 38 colonies were counted.
Ask students to calculate how
many bacteria were in the original
sample. (38 ⫻ 1,000 ⫻ 10 ⫽
380,000 bacteria per mL) Then ask
students to calculate how many
bacteria would have been in the
sample if the dilution factor had
been only 1 to 250. (38 ⫻ 250 ⫻ 10
⫽ 95,000 bacteria per mL)
Real Life
Big, big bacteria
In 1999, scientists
announced the discovery
of the largest bacteria ever
discovered. Thiomargarita
namibiensis was found off
the coast of Namibia.
More than 100 times larger
than the previously known
largest bacterium, T. namibiensis is 0.5 mm wide.
Photosynthesizers
Figure 11 Photosynthetic
bacterium. Anabaena is a
photosynthetic cyanobacterium in which individual cells
adhere in filaments. The two
large orange-colored cells are
encased in a structure where
nitrogen fixation occurs.
LS Logical
Teaching Tip
GENERAL
Nitrogen-Fixing Bacteria Ask
students what would happen if all
nitrogen-fixing bacteria were eliminated. (The amount of nitrogen
available to plants would fall, plant
growth would be reduced, and the
amount of organic compounds
available at higher trophic levels
would decline.) TAKS 2 Bio 4B
Bacteria called chemoautotrophs (KEE moh AW toh trohfs)
obtain energy by removing electrons from inorganic molecules such as ammonia, NH3, and hydrogen sulfide, H2S, or
from organic molecules such as methane, CH4. In the presence
of one of these hydrogen-rich chemicals, chemoautotrophic
bacteria can manufacture all their own amino acids and proteins. Chemoautotrophic bacteria that live in the soil, such as
Nitrosomonas and Nitrobacter, are of great importance to the
environment and to agriculture. They have an important role
in the nitrogen cycle called nitrification. Nitrification, as you
may recall from an earlier chapter, is the process in which bacteria oxidize ammonia into nitrate. Nitrate is the form of
nitrogen most commonly used by plants.
444
Cultural
Awareness
TAKS 2 Bio 4B
pp. 444–445
Student Edition
TAKS Obj 2 Bio 4B
TAKS Obj 2 Bio 8C
TAKS Obj 3 Bio 4D
TAKS Obj 3 Bio 7B
TEKS Bio 4B, 4D, 7B, 8C
Teacher Edition
TAKS Obj 2 Bio 4B
TEKS Bio 4B, 9A, 12C
444
A significant fraction of the world’s photosynthesis is carried out by
bacteria. Photosynthetic bacteria can be classified into four major
groups based on the photosynthetic pigments they contain: purple
nonsulfur bacteria, green sulfur bacteria, purple sulfur bacteria,
and cyanobacteria. Green sulfur bacteria and purple sulfur bacteria
grow in anaerobic (oxygen-free) environments. They cannot use
water as a source of electrons for photosynthesis and instead use
sulfur compounds, such as hydrogen sulfide, H2S. Purple nonsulfur
bacteria use organic compounds, such as acids and carbohydrates,
as a source of electrons for photosynthesis.
Of particular importance are the cyanobacteria, which
often clump together in large mats of filaments. Recall that
cyanobacteria are thought to have made the Earth’s oxygen
atmosphere. Each filament is a chain of cells encased in a
continuous jellylike capsule. Many cyanobacteria, such as
species of Anabaena, shown in Figure 11, are capable of fixing nitrogen.
Chemoautotrophs
Activity
Organizing Bacteria Have students make a table classifying
common bacteria by the way they
obtain energy. Tables should divide
bacteria into three groups: photosynthetic, chemoautotrophic, and
heterotrophic. LS Logical
Over 4,000 species of bacteria have been named, and probably many
more haven’t yet been discovered. Bacteria occur in the widest possible range of habitats and play key ecological roles in nearly all of
them. As you may recall from an earlier chapter, bacteria thrive in
hot springs, frigid arctic seas, and groundwater. They are even found
at high pressures in the deep sea and inside solid rock.
Bacteria can be classified in several different ways. Classifying
bacteria by the different ways in which they obtain energy, for example, gives a good general sense of the great diversity among bacteria.
Bacteria can also be classified according to their phylogenetic
relationships. By comparing the sequence of their ribosomal RNA,
scientists have determined that there are at least 12 phyla of eubacteria and four phyla of archaebacteria.
Making Yogurt Yogurt was first made by
nomadic Middle Eastern tribes. The hot
desert sun, aided by the gentle rocking of
camel transportation, provided the perfect
environment for making yogurt. Yogurt is
created from milk that has been curdled by
two types of bacteria: Lactobacillus bulgaricus and Streptococcus thermophilus.
Chapter 20 • Viruses and Bacteria
Heterotrophs
Most bacteria are heterotrophs. Together with fungi,
heterotrophic bacteria are the principal decomposers
of the living world; they break down the bodies of dead
organisms and make the nutrients available to other
organisms. Many are aerobic , that is, they live in the
presence of oxygen. Some other bacteria can live without oxygen.
Other activities of heterotrophic bacteria may be
helpful or harmful to humans. For example, more
than half of our antibiotics are produced by several
species of Streptomyces, a filamentous bacterium
found in soil. On the other hand, one species of
Staphylococcus can secrete a poison into food. This
poison causes nausea, diarrhea, and vomiting in people who eat the Staphylococcus-contaminated food.
Species of the symbiotic bacteria Rhizobium are by
far the most important of all nitrogen-fixing organisms. Rhizobium species are heterotrophic bacteria
that usually live within lumps on the roots of legumes
(plants such as soybeans, beans, peas, peanuts, alfalfa, and clover),
as shown in Figure 12. Farmers take advantage of Rhizobium’s
nitrogen-fixing abilities when they “rotate” their crops every few
years and grow legumes, which replenish the soil with nitrogencontaining compounds.
Drilling for Buried
Obj 2 Bio 8C;
Bacteria TAKS
Bio 12C
Magnification: 1,440ⴛ
Figure 12 Nitrogen-fixing
bacteria. The bacteria inside
the lumps on these soybean
roots contain Rhizobium, a
nitrogen-fixing bacteria.
TAKS 2
ne of the least known
ecosystems on Earth consists of bacteria that live at the
bottom of the ocean, buried deep
in sediment. These microorganisms have been recovered from
depths as great as 800 m below
the ocean floor. In this completely
dark environment, they rely on a
variety of chemoautotrophic and
heterotrophic processes to obtain
energy and nutrients. Found at
every site where scientists have
looked for them, deep-ocean
bacteria are extremely abundant.
Scientists estimate that they comprise between 10 and 30 percent
of the Earth’s biomass.
Ocean Drilling Program
Researchers in the Ocean Drilling
Program (ODP) are collecting sediment from several sites in the
Pacific Ocean. They drill into the
ocean floor from the ODP’s
research ship, JOIDES Resolution. The ship can drill in waters
over 8,200 m deep. Texas A&M
University runs the ship and
stores the sediment samples.
As the drilling proceeds, sediment is pulled up through the drill
pipe and kept under sterile,
anaerobic conditions until the
bacteria in them can be studied.
Scientists are identifying bacteria
from different depths and learning
Discussion
• What sources of contamination do the researchers have to
avoid? (sea water, liquids from
the drill, the equipment itself,
contamination by humans)
• Why is it important to keep
the samples under high pressure? (The organisms in the
sample live under high pressure
in the ocean depths; changing
the pressure might kill the
organisms.)
Drilling for Buried Bacteria
O
Teaching Strategies
• Ask students why the sediment sections must be kept
under anaerobic conditions.
(The anaerobic bacteria might
die in the presence of oxygen.)
• The purpose of the project is
to determine the kinds and
numbers of microbes in the
rocks of the suboceanic crust.
how these bacteria affect Earth’s
oceans and atmosphere.
www.scilinks.org
Topic: Ocean Drilling
Keyword: HXX4019
445
REAL WORLD
CONNECTION
Encourage students to research the roles of
bacteria and heat in making cheese. The production of cheese involves bacteria that break
down lactose in milk, producing lactic acid as
a waste product. The acid causes the milk to
separate into curds—solid components from
which cheese is made, and whey—a liquid
product that is removed. Cheeses require a
heating process that can destroy the bacteria
when the cheese is done. Different types of
cheeses are made with different kinds of bacteria. For example, cheddar cheese is made with
bacteria that require moderate temperatures,
whereas Swiss cheese is made with bacteria
that can tolerate higher temperatures. Bio 9A
Chapter 20 • Viruses and Bacteria
445
Up Close
Up Close
Escherichia coli TAKS 2 TAKS 3
Escherichia coli TAKS 2 Bio 8C
TAKS 3 Bio 4D; Bio 11D
Discussion
• Is E. coli a gram-positive or
gram-negative bacterium?
(gram-negative)
• How does E. coli reproduce?
(binary fission) How fast can the
cells divide? (as often as every
20 minutes)
• Describe the genetic material of
an E. coli cell. (It has one circular
DNA molecule containing about
5,000 genes.)
• What is the function of pili?
(Pili serve to attach E. coli to surfaces and to join bacterial cells in
conjugation.)
Scientific name: Escherichia coli
●
Size: Up to 1 µm
●
Habitat: Inhabits the intestines of many mammals
●
Mode of nutrition: Heterotrophic
Characteristics
Cell structure E. coli is a Gram-
Genetic material Like all bacteria,
negative eubacterium. It has a rigid cell
wall composed of peptidoglycan. Outside
the cell wall lies the outer membrane,
E. coli has a single DNA molecule in the
form of a loop. E. coli has approximately 5,000 genes.
▲
Teaching Strategies
Tell students that in 1993, four
children died from infection with
a strain of E. coli O157:H7 found
in undercooked hamburger meat,
and more than 600 cases of food
poisoning were reported in northwestern states. The symptoms of
E. coli O157:H7 food poisoning
include bloody diarrhea and kidney failure. Severe cases can cause
permanent damage to organs
or even death. The Centers for
Disease Control and Prevention
estimates that approximately
20,000 individuals suffer symptoms of E. coli O157:H7 poisoning
each year from undercooked food.
Ask students how they can avoid
food poisoning. (Possible answers
include cooking meat thoroughly,
choosing clean restaurants, and making sure that foods are served and
stored at their proper temperatures.)
●
Cell wall
which is composed of lipids
and polysaccharides.
Outer membrane
▲ DNA
Cell membrane
Ribosome
▼ Flagellum
Locomotion By
rotating its slender,
whiplike flagella, E. coli
propels itself through
its environment.
Peptidoglycan
▼ Pili
Adherence Like many Gram-negative
bacteria, E. coli has pili—short, thin, hairlike
Reproduction Most bacteria
reproduce by binary fission, a process
by which a single cell divides into two
identical new cells. E. coli can divide
as often as every 20 minutes.
appendages. Pili can adhere to surfaces,
including the surfaces of intestinal-lining
cells. Pili also join bacterial cells prior to
conjugation.
446
MISCONCEPTION
ALERT
pp. 446–447
Student Edition
TAKS Obj 2 Bio 4B
TAKS Obj 3 Bio 4D
TAKS Obj 3 Bio 7B
TEKS Bio 4B, 4D, 7B
Teacher Edition
TAKS Obj 2 Bio 8C
TAKS Obj 3 Bio 4C, 4D
TEKS Bio 4C, 4D, 8C, 11D
446
“Bad” Bacteria Students tend to think of
bacteria as “bad” organisms because they are
often described as sources of disease. Of the
thousands of kinds of bacteria, however, only
a few are harmful. Bacteria are nature’s recyclers, and scientists are finding ways to use
bacteria to produce desirable materials and
Chapter 20 • Viruses and Bacteria
degrade wastes. Biotechnologists insert genes
into bacterial cells that allow them to make
plastics, pharmaceuticals, pesticides, and
foods. Bacteria can even be used to mine metals, such as copper and gold, and to clean up
industrial wastes. TAKS 3 Bio 4D
Pathogenic Bacteria
In order to understand infectious diseases, think of your
body as a treasure chest full of resources. Your body has protein, minerals, fats, carbohydrates, and vitamins. You may
want to keep and use these resources, but so do many other
organisms, including the bacteria on and in your body. Bacteria have evolved various means of obtaining these
resources from you. In some cases, the competition for the
resources in your body can result in your becoming ill.
Using the Table
Bacteria Can Metabolize Their Host
Heterotrophic bacteria obtain nutrients by secreting
enzymes that break down complex organic structures in
their environment and then absorbing them. If that environment is your throat or lungs, this can cause serious problems.
For example, tuberculosis, a disease of the lungs, is caused by
Mycobacterium tuberculosis, shown in Figure 13. Tuberculosis was
once one of the most common causes of death. In most cases, infection occurs when tiny droplets of moisture that contain the bacteria
are inhaled. Some bacteria settle in the lungs, where they grow
using human tissue as their nutrients. The bacteria may also spread
to other parts of the body. Symptoms may include coughing up sputum and blood, chest pain, fever, fatigue, weight loss, and loss of
appetite. If left untreated, death may occur as quickly as within 18
months but more commonly within 5 years. Other important bacterial diseases are described in Table 2.
Table 2
Figure 13 Tuberculosis
in a lung. The red-stained
structures in this light
micrograph are Mycobacterium
tuberculosis, which cause
tuberculosis.
Disease
Description of illness
Bacterium
TAKS 3 Bio 4C, 4D; Bio 11D
Demonstration
Important Bacterial Diseases
How the disease is
transmitted or caused
GENERAL
Have students examine Table 2 and
suggest ways that bacterial and
viral infections can be prevented.
Lead students to consider ways that
pathogens can be spread such as
through air, water, blood, food,
pets, rodents, and so on. (Students
may suggest that diseases can be prevented by sanitation, good hygiene,
lifestyle changes, vaccinations,
healthy immune systems, and proper
storage and preparation of food.)
GENERAL
Ask students to bring in newspaper
and magazine articles that discuss
specific bacterial or viral infections.
Make a list on the board or overhead of the diseases discussed in
each article, and have students indicate whether each pathogen is a
bacterium or virus. Have students
discuss the methods of contracting
each disease, the people commonly
affected, and potential treatments.
LS Interpersonal
Anthrax
Fever, severe difficulty breathing
Bacillus anthracis
Inhalation of spores
Bubonic plague
Fever, bleeding, lymph nodes that form
swellings called buboes; often fatal
Yersinia pestis
Bite of an infected flea
Cholera
Severe diarrhea and vomiting;
fatal if not treated
Vibrio cholerae
Drinking contaminated water
Dental cavities
Destruction of minerals in tooth
Streptococus mutans
Dense collections of bacteria
in mouth
Lyme disease
Rash, pain, swelling in joints
Borrelia burgdorferi
Bite of an infected tick
Tuberculosis
Fever, difficulty breathing
Mycobacterium
Inhalation
Typhus
Headache, high fever
Rickettsia
Bite of infected flea or louse
TAKS 3 Bio 4C, 4D; Bio 11D
447
HISTORY
CONNECTION
The plague that spread through Europe in the
fourteenth century killed more than 25 million
people. Introduced by rats from the Black Sea
region, it spread through trade routes to
Europe. The disease is caused by the bacterium Yersinia pestis and is transmitted by
fleas. It causes enlarged lymph nodes, called
buboes—hence, the name bubonic plague.
Fever, pain, and necrosis, or blackening of the
skin, can also occur. This last symptom lead to
the disease’s other name: Black Death.
TAKS 3 Bio 4D
Chapter 20 • Viruses and Bacteria
447
Not all bacteria are lethal. For example, some bacteria cause
everyday health problems, such as acne. Acne occurs in about 85
percent of teenagers. Bacteria, such as Propionibacterium acnes,
normally grow in an oil gland of the skin. They metabolize a certain
kind of oil produced by those glands. During puberty the oil glands
increase the amount of oil produced, and the bacterial population
on the skin increases greatly. The bacteria grow in the pores where
the oil normally flows, forming pimples and blackheads.
Teach, continued
continued
Using the Figure
Have students examine Figure 14.
Point out that the zone of clearance
around the bacterial colony represents the destruction of red blood
cells by Streptococcus. Ask students
if they think Streptococcus species
are the only bacteria that lyse red
blood cells. (Hemolysins are also
produced by Staphylococcus and
Clostridium English Language TAKS 3
Learners
Bio 4D
species.)
SKILL
BUILDER
Bacterial Toxins
Figure 14 The effect of
bacterial toxins. This species
of Streptococcus secretes a
toxin that destroys red blood
cells. The agar contains red
blood cells and clearly shows a
zone around the bacteria
where the toxin has destroyed
the red blood cells.
Writing
Writing Skills Have students
research and write a report
about the guidelines for food handling and storage that are recommended by the Centers for Disease
Control and Prevention. LS Verbal
SKILL
BUILDER
Graphing For decades the tuberculosis (TB) death rate in the United
States was in decline. In the 1940s,
health workers believed TB would
be eradicated because the disease
seemed to be under control. By 1985,
the number of reported cases had
plunged to only 22,201—one-fourth
of the number of cases reported in
1953. However, the number of cases
began to rise in 1986. Although TB
is treatable and preventable, a cure
takes about 6 months once a person’s lungs are infected. Many
patients stop taking their medication before they are completely
cured. Have students research the
number of TB cases from the 1940s
to the present and make a bar
graph showing the number of cases
in each decade. LS Logical
TAKS 1 Bio/IPC 2C; TAKS 3 Bio 4C; Bio 11D
pp. 448–449
Student Edition
TAKS Obj 2 Bio 6C
TAKS Obj 3 Bio 4D
TEKS Bio 4D, 6C, 11D
Teacher Edition
TAKS Obj 1 Bio/IPC 2C
TAKS Obj 3 Bio 4C, 4D
TAKS Obj 4 IPC 7D
TEKS Bio 4C, 4D, 9A, 11D
TEKS Bio/IPC 2C
TEKS IPC 7D
448
The second way bacteria cause disease is by secreting chemical
compounds into their environment. These chemicals, called toxins,
are poisonous to eukaryotic cells, as shown in Figure 14. Toxins can
be secreted into the body of an infected person or into a food in
which bacteria are growing.
When bacteria grow in food and produce toxins, the toxins can
cause illness in humans who eat those contaminated foods. This
kind of illness is called an intoxication. For example, Staphylococcus aureus causes the most common type of food poisoning. The
symptoms include nausea, vomiting, and diarrhea. This type of poisoning is painful but is seldom fatal.
Another type of intoxication that is fatal occurs when food is not
canned properly. Sometimes canned food is not heated enough to
kill endospore-forming bacteria, such as Clostridium botulinum.
The bacteria can then grow and produce a deadly toxin that affects
the nervous system. A person who eats food that contains this toxin
then becomes ill with a disease called botulism, whose symptoms
include double vision and paralysis. People with botulism may die
because they are unable to breathe.
Some bacteria are responsible for other diseases reported in the
news, such as E. coli O157:H7, the cause of several outbreaks of
food poisoning in the United States. E. coli normally lives in our
intestines. However, if it acquires DNA that codes for the toxin
through conjugation, it can produce the toxin. E. coli poisoning is
associated with raw or improperly cooked ground beef.
Most bacteria can be killed by boiling water or various chemicals. Using hot, soapy water to prevent contamination of our food
utensils and food supply is one way of preventing disease. Many
commercial antibacterial products can also be used to prevent bacterial contamination in the kitchen and in industrial food factories.
Biowarfare
448
Biowarfare is the deliberate exposure of people to biological toxins or
pathogens such as bacteria or viruses. The United States government
is justifiably concerned about the use of bioweapons—biological
toxins or pathogens suitable for mass infection—against military
personnel overseas and against civilians within the United States.
Biologists are working on new approaches to recognize the onset of
an attack with a bioweapon, to treat infected people, and to slow the
spread of any outbreak of disease.
did you know?
Bacterial Toxins Some bacterial toxins can be
used for medical purposes. Botulinum toxin is
used to treat dystonia, an abnormal muscle
rigidity that causes painful muscle spasms. The
toxin inhibits the release of acetylcholine from
the neurons in the neuromuscular junction,
allowing the muscles to relax. Dermatologists
are using the same toxin to erase “frown lines”
and wrinkles on the face. Diluted toxin is
injected under the skin to relax facial muscles
and smooth out the wrinkles. The effect is temporary and must be repeated every 6 months.
Bio 9A
Chapter 20 • Viruses and Bacteria
IPC Benchmark Review
To prepare students for the TAKS and accompany
the discussion of bacteria, have students review
Chemical Behavior of Elements, TAKS 4 IPC 7D on
pp. 1050–1051 of the IPC Refresher in the Texas
Assessment Appendix of this book.
Antibiotics
Fungus
In 1928, the British bacteriologist Alexander Fleming
noticed a fungus of the genus Penicillium growing on a
culture of S. aureus. He saw that bacteria did not grow near
the fungus. He concluded that the fungus was secreting a
substance that killed the bacteria, as shown in Figure 15.
Fleming isolated the substance and named it penicillin.
In the early 1940s, scientists found that penicillin was effective in treating many bacterial diseases, such as pneumonia.
Different antibiotics interfere with different cellular
processes. Because these processes do not occur in viruses,
antibiotics are not effective against them. Other antibiotics, such as tetracycline and ampicillin, have been
discovered in nature or imitated chemically.
Antibiotic-Resistant Bacteria
In recent years, some bacteria have become resistant to antibiotics.
Susceptible bacteria are eliminated from the population, and resistant bacteria survive and reproduce, thus passing on their resistance
traits. Mutations for antibiotic resistance arise spontaneously in
bacterial populations as errors in DNA replication. There are many
individuals in a bacterial population, and bacteria multiply very
rapidly (doubling their numbers in as few as 20 minutes). Therefore,
a mutation that gives the bacteria a selective advantage can quickly
spread throughout a population.
Group Activity
Writing
Bacteria
Figure 15 Antibiotics
are naturally produced.
Alexander Fleming saw a plate
of agar very similar to this one.
Notice how the bacteria do
not grow next to this fungus.
”Rational” Drug
Design One strategy that
researchers are using to control
resistant bacterial strains is called
“rational” drug design. By looking
at the genes and enzymes involved
in drug resistance, scientists are trying to create drugs that bind to the
active sites of the enzymes and render them inactive. Have student
groups research this work and
prepare presentations for class.
Presentations might include models
of enzyme action. Co-op Learning
Bio 9A
Group Activity
GENERAL
Breakthroughs in Science
Organize students into small
groups to discuss the technological
uses of bacteria. Have students
propose future uses of bacteria
and ask them to imagine the
potential impact of their breakthroughs. Encourage students to
consider potentially harmful, beneficial, and benign effects of their
ideas on quality of life, economy,
health, and the environment. Then
have students produce a diagram
illustrating the topic of their discussion to share with the class.
Diagrams might feature the technological development in the
center with its effects on society
represented by spokes radiating
outward.
Antibiotic Misuse Mutations that confer resistance to antibiotics are
strongly favored in bacterial populations being treated with an antibiotic. Usually, if the full course of the antibiotic is administered, all
the targeted bacteria are killed and there is no chance for a resistant
strain to develop. If antibiotic treatment ends prematurely, some of
the bacteria may survive. Which ones? The ones most resistant to the
antibiotic. A patient who does not take the full course of a prescribed
antibiotic is setting the stage for the development of antibioticresistant bacteria.
Multiple-antibiotic Resistance A related problem can arise in a
patient being treated with two or more antibiotics at the same time.
This practice selects for bacteria that have acquired several antibiotic-resistance genes. A number of strains of Staphylococcus aureus
associated with severe infections of hospital patients (so-called hospital staph) have appeared in recent years. These strains are resistant to penicillin and a wide variety of other antibiotics, so
infections caused by these strains are very difficult to treat.
Recently, concern has arisen over the common use of antibacterial soaps. Antibacterial soaps are marketed as a means of protecting
people from harmful bacteria. Their routine use, however, may favor
bacteria resistant to the antibacterial agents in the soap. Ultimately,
routine use of antibacterial soaps could reduce our ability to treat
common bacterial infections.
Co-op Learning
English Language
Learners
TAKS 3 Bio 4D
449
IPC Benchmark Mini-Lesson
Biology/IPC Skills TAKS 4 IPC 7D (grade 11 only)
Relate the chemical behavior of an element including
bonding to its placement on the periodic table
Activity Many compounds loose their shape, or
denature, under harsh conditions such as in acid or
high temperatures. Proteins have a specific shape
caused by weak attractions between the molecules
that make up the protein. Ask students how they think
heat is able to kill bacteria. (It denatures membrane
proteins, causing the cell wall and cell membrane of
the bacteria to rupture.)
Trends in Genetic Engineering
Engineered Bacteria Show students pictures
of an oil spill and a field with a growing crop.
Ask students what useful roles bacteria might
play in these pictures. Explain that bacteria are
being genetically modified by biotechnologists
to perform a variety of useful tasks, including
cleaning up spilled petroleum products and
removing PCBs from the environment. In agriculture, bacteria can take the place of some
fertilizers and pesticides and can be used to
prevent frost damage in strawberry plants.
Human insulin, human growth hormone, and
TPA (which dissolves blood clots) are now
being made using engineered bacteria. TAKS 3 Bio 4D
Chapter 20 • Viruses and Bacteria
449
Importance of Bacteria
Despite the misery that some bacteria cause humans in the form of
disease and food spoilage, much of what bacteria do is extremely
important to our health and economic well-being.
Close
Reteaching
Food and Chemical Production
Have students research the proliferation of Staphylococcus infections
that are contracted in hospitals.
How are they spread? What strains
are involved? Why are they particularly dangerous? How can they be
prevented? Have students present
their findings in a short written
report. TAKS 3 Bio 4D; Bio 11D
Quiz
Figure 16 Swiss cheese.
In making Swiss cheese, bacteria grow in the cheese and
produce gas. As the cheese
hardens these pockets of gas
remain, giving the cheese its
characteristic holes.
GENERAL
1. What are the three basic shapes
Many of the foods that we eat are processed by specific kinds of
bacteria. For example, many fermented foods are produced with
the assistance of bacteria, as shown in Figure 16. These foods
include pickles, buttermilk, cheese, sauerkraut, olives, vinegar,
sourdough bread, and even some kinds of sausages.
Humans are able to use different bacteria to produce different
kinds of chemicals for industrial uses, as shown in Figure 17. For
example, different kinds of Clostridium species can make either
acetone or butanol. These chemicals can be used to produce a large
variety of other useful chemicals.
Genetic engineering companies use genetically engineered
bacteria to produce their many products, such as drugs for
medicine and complex chemicals for research.
of bacteria? (bacillus, coccus,
spirillum)
2. How do heterotrophic bacteria
obtain energy? (They obtain
energy by feeding on organic material produced by other organisms.)
Mining and Environmental Uses of Bacteria
Mining companies can use bacteria to concentrate desired elements from low-grade ore. Low-grade ore has a low percentage
of the desired mineral, but it also has sulfur compounds.
Chemoautotrophic bacteria can convert the sulfur into a soluble compound, leaving the desired mineral behind. The sulfur
compound can be washed away with water, leaving only the
desired mineral. This technique can be used to harvest copper
or uranium.
Bacteria metabolize different organic chemicals and are
therefore used to help clean up environmental disasters such as
petroleum and chemical spills. Powders containing petroleummetabolizing bacteria are used to help clean oil spills.
3. In what two ways do bacteria
produce disease? (They metabolize their host’s body and produce
toxins.)
Alternative
Assessment
Figure 17 Industrial
fermenter. Bacteria can be
used to produce useful chemicals such as in this fermenter.
GENERAL
Have students give a class presentation on composting to show that
bacteria are an essential part of the
decay process. Students should
explain the type of metabolism
used by the bacteria (heterotrophic)
and the conditions under which the
bacteria live in the compost pile.
The presentation should also
address the question of whether
decay could occur in the absence
of bacteria. Bio 11D
Section 2 Review
Construct a table that lists the seven ways
4A
bacteria differ from eukaryotic cells.
List the structures found in E. coli.
4A
Identify the relationship between photosyn-
thesis, heterotrophic metabolism, and
4B
chemoautotrophic metabolism.
Describe the relationship between metabolism,
toxins, bacteria, and disease.
4B 4C 4D
List three ways bacteria are helpful.
Critical Thinking
Defending a Theory
How does the growth of antibiotic resistance in
bacteria support the theory of evolution by
7B
natural selection?
TAKS Test Prep Which disease is caused by
inhaling a bacterium?
4D
A cholera
B botulism
C E. coli food poisoning
D tuberculosis
4D
450
Answers to Section Review
pp. 450–451
Student Edition
TAKS Obj 2 Bio 4B
TAKS Obj 3 Bio 4C, 7B
TAKS Obj 3 Bio 4D
TEKS Bio 4A, 4B, 4C, 4D, 7B, 11D
Teacher Edition
TAKS Obj 2 Bio 4B
TAKS Obj 3 Bio 4C, 4D, 7B
TEKS Bio 4A, 4B, 4C, 4D, 7B, 11D
450
1. Differences include internal compartmentalizachemicals, the fixation of nitrogen, mining, and
tion, cell size, multicellularity, chromosomes,
environmental restoration. TAKS 3 Bio 4D
reproduction, flagella, and metabolic diversity. Bio 4A 6. Natural selection favors those organisms best
2. cell wall, pili, flagella, ribosomes, circular DNA Bio 4A
suited to their environment. When an antibiotic
is present, bacteria that are naturally resistant
3. All are methods by which bacteria obtain
to it will survive over nonresistant bacteria.
energy. Photosynthesizers use light energy,
The resistant bacteria will eventually outnumchemoautotrophs use simple chemicals, and
ber the less well-adapted bacteria. TAKS 3 Bio 7B
heterotrophs use complex organic material
made by other organisms. TAKS 2 Bio 4B
7.
A. Incorrect. Cholera is caused
by drinking contaminated water. B. Incorrect.
4. Bacteria may cause disease by metabolizing the
Botulism is caused by eating contaminated
host’s cells or by secreting toxins.
TAKS 2 Bio 4B; TAKS 3 Bio 4C, 4D
food. C. Incorrect. E. coli food poisoning is
caused by eating contaminated food.
5. Bacteria are used in the processing of many
D. Correct. TAKS 3 Bio 4D
foods, the creation of medical and industrial
Chapter 20 • Viruses and Bacteria
Study
CHAPTER HIGHLIGHTS
ZONE
Key Concepts
●
●
●
●
●
●
virus (434)
pathogen (434)
capsid (435)
envelope (435)
glycoprotein (435)
bacteriophage (435)
lytic (436)
provirus (436)
lysogenic (437)
prion (441)
viroid (441)
Viruses consist of segments of a nucleic acid contained in a
protein coat, and some have an envelope.
Viruses do not have all of the characteristics of life and are
therefore not considered to be alive.
Viruses replicate inside living cells. They enter a cell by
injecting their genetic material into the cell, by slipping
through tears in the plant cell wall, or by binding to molecules on the cell surface and triggering endocytosis.
Viruses replicate through a lytic cycle or a lysogenic cycle.
HIV replicates inside immune system cells, eventually
destroying them, leaving the host without adequate defense
against disease.
Emerging viruses are geographically isolated viruses that
cause disease in humans.
Viroids are infectious RNA molecules that cause disease in
plants, and prions are infectious proteins that cause disease
in certain animals.
Chapter Resource File
●
●
●
●
●
●
• Science Skills Worksheet GENERAL
• Critical Thinking Worksheet
• Test Prep Pretest GENERAL
• Chapter Test GENERAL
Section 2
2 Bacteria
●
GENERAL
Have students choose two diseases,
one caused by a bacterium and one
caused by a virus. Students can use
information from the textbook, do
outside research, or create fictitious
diseases. Ask students to draw
plausible structures for the
pathogens and to describe the
method of infection, prevention,
and treatment. Students’ drawings
must depict the characteristics of
bacteria and viruses described in
this chapter.
Section 1
1 Viruses
●
Alternative
Assessment
Key Terms
Bacteria differ from eukaryotes in their cellular organization, cell structures, and metabolic diversity.
Bacteria can be classified into two groups according to their
cell wall structure. Gram staining can be used to distinguish
these two groups.
Bacteria can transfer genes to one another by conjugation.
Bacteria are grouped according to their ribosomal RNA
sequences and the way they obtain energy.
Bacteria cause disease by metabolizing nutrients in their
host or by releasing toxins, which damage their host.
Bacterial disease can usually be fought with soap, chemicals, and antibiotics.
Bacteria are used to make foods, antibiotics, and chemicals;
to fix nitrogen; to clean the environment; and to cycle
important chemicals in the environment.
pilus (442)
bacillus (443)
coccus (443)
spirillum (443)
capsule (443)
antibiotic (443)
endospore (443)
conjugation (443)
anaerobic (444)
aerobic (445)
toxin (448)
451
Answer to Concept Map
The following is one possible answer
to Performance Zone item 15 on
the next page.
Disease
can be caused by
pathogens
which include
bacteria
may cause illness
by secreting
toxins
viruses
can be treated with
cannot be treated with
antibiotics
that evolve in isolated
areas are called
emerging viruses
Chapter 20 • Viruses and Bacteria
451
Performance
CHAPTER REVIEW
ZONE
CHAPTER 20
Using Key Terms
1. c TAKS 3 Bio 4C
2. c TAKS 3 Bio 4C
3. d Bio 4A
4. a TAKS 3 Bio 4C
5. a. A capsid is the protein coat that
surrounds the viral nucleic acid.
Many viruses also have an envelope, which surrounds the capsid
and aids in cell penetration.
b. When a virus is inserted into
the host chromosome during
a lysogenic cycle, it is called
a provirus. c. Prions are pathogens
composed of protein particles and
lack nucleic acids. Viroids are protein-free pathogens consisting of a
single strand of RNA. d. Bacillus
is a rod-shaped cell, coccus is a
spherically shaped cell.
Understanding Key Ideas
6. d TAKS 2 Bio 4B; TAKS 3 Bio 4C
7. a Bio 3F
8. c TAKS 3 Bio 4C
9. c Bio 4A
10. d Bio 4A
11. c Bio 11C, 11D
12. b Bio 4A
13. The body’s immune system acts
as a selective force. Some of the
viruses are eliminated. Those
viruses that have features that
enable them to escape destruction
continue to multiply.
TAKS 3 Bio 4C, 7B
14. No. The light necessary for photosynthesis is not available in the
depths of the ocean, where these
bacteria reside. Bio 4A
15. The answer to the concept map is
found at the bottom of the Study
Zone page. Bio 3E
Using Key Terms
1. A type of virus that infects bacteria is a(n)
a. viroid.
c. bacteriophage.
b. glycoprotein.
d. emerging virus.
9. Bacteria
4A
a. always have flagella.
4C
b. are smaller than viruses.
c. have aerobic or anaerobic
metabolism.
d. have a nucleus.
2. The basic components of all viruses are a
nucleic acid and a(n)
4C
a. endospore.
c. protein coat.
b. glycoprotein.
d. icosahedron.
3. E.
a.
b.
c.
d.
coli can move by using its
pili.
nucleus.
peptidoglycan.
flagella.
10. Bacteria that do not require sunlight and
obtain energy by removing electrons from
hydrogen-rich chemicals are called
4A
a. heterotrophs.
b. photosynthetic bacteria.
c. cyanobacteria.
d. chemoautotrophs.
4A
11. Environmental spills of petroleum are
sometimes cleaned up using
11C 11D
a. viroids.
c. bacteria.
b. prions.
d. bacteriophages.
4. A bacteriophage kills its host cell
during
4C
a. a lytic cycle.
b. conjugation.
c. a lysogenic cycle.
d. assembly of the capsid.
12. Identify the pilus in the photo below.
A
5. For each pair of terms below, explain the
differences in their meanings.
a. capsid, envelope
b. virus, provirus
c. prion, viroid
d. bacillus, coccus
B
C
Understanding Key Ideas
6. Unlike cells, viruses do not
a. grow.
b. have homeostasis.
c. metabolize.
d. All of the above
4B 4C
7. What evidence led Stanley to conclude that
TMV is not a living organism?
3F
a. The extract of TMV crystallized.
b. TMV is made of RNA and protein.
c. TMV reproduces only in cells.
d. The virus poisons tobacco plants.
4C
8. HIV infects and destroys
a. skin cells.
c. immune cells.
b. red blood cells. d. bacterial cells.
13. If cold viruses invade your body, your
body’s immune system may destroy most
but not all of these viruses. How does your
body’s immune system affect the evolution
of the cold viruses?
4C 7B
14.
Are the bacteria collected by
the Ocean Drilling Program photosynthetic?
How do you know?
4A
15.
Concept Mapping Make a concept
map describing the relationships of
bacteria and viruses to diseases. Try to
include the following terms in your map:
bacteria, viruses, pathogen, emerging
viruses, antibiotics, and toxin.
3E
452
Assignment Guide
Section
1
2
pp. 452–453
Review and Assess
TAKS Obj 1 Bio/IPC 2B, 2D
TAKS Obj 2 Bio 4B
TAKS Obj 3 Bio 4C, 4D, 7B
TEKS Bio 3E, 3F, 4A, 11C, 11D
452
4A
Chapter 20 • Viruses and Bacteria
Questions
1, 2, 4, 5, 6, 7, 8, 13, 15, 16, 17, 18, 19,
20, 21, 22
3, 5, 6, 9, 10, 11, 12, 14, 15, 18
Critical Thinking
Alternative Assessment
Critical Thinking
16. Applying Information How does the
20. Finding Information Research and write a
16. Certain mutations enable HIV to
resist antiviral drugs. As the virus
is exposed to these drugs, those
HIV that are resistant will survive
and continue to multiply, becoming more common, while those
HIV not resistant will be selected
against and become less common.
increase of resistance to antiviral drugs in
HIV relate to the theory of evolution by
natural selection?
7B
17. Evaluating Results In the 1520s, the Spanish
explorer Cortés and his armies introduced
smallpox to the Americas. The death rate
among the Native American people ranged
from 50 to 90 percent compared with a
death rate of about 10 percent among
people in Europe. What accounts for the
difference in death rates?
3F 4C
18. Justifying Conclusions Explain why
microbiologists oppose use of antibiotics in
patients with viral infections and why they
say antibiotics do not help the patient.
4C
19. Evaluating Relationships If a person were
infected by HIV, and the virus did not
mutate while in the person’s body, would
that person likely experience immune system failure? Why or why not?
4C
report on a preventable viral disease, such
as polio or smallpox. In your report, discuss the process scientists followed in
identifying the cause of the disease, isolating the virus, formulating a vaccine, and
2B 2D 3F 4C 4D
testing the vaccine.
21. Summarizing Information AIDS, the disease
caused by HIV, is a major health concern
worldwide. Locate statistics on AIDS cases
for as many countries as possible. Then
draw a world map on poster paper, and
devise a color legend for the map that
shows the number of AIDS cases in countries for which you have data. Color the
map to match the legend, give it a title, and
2B 4C
display the map in your classroom.
22. Career Connection Virologist Research the
field of virology. Write a report on your
findings that includes a job description,
training required, kinds of employers,
growth prospects, and starting salary.
3D
TAKS Test Prep
The diagram below illustrates viral replication
in bacteria. Use the diagram and your knowledge of science to answer questions 1–3.
1
2. What is the virus doing to the bacterium in
4C
step 1?
F injecting its capsid
G injecting its DNA
H withdrawing proteins
J withdrawing DNA
TAKS 3 Bio 4C; Bio 3F
18. Such use of antibiotics is ineffective because a virus does not carry
out any of the life processes that
the antibiotics interrupt. Such
misuse and overuse of antibiotics
encourages the evolution of resistant strains of bacteria.
TAKS 3 Bio 4C
through a hole in the cell membrane.
2
17. The Native Americans had no
natural immunity to the virus
because they had never been
exposed to it. Many Europeans
were immune because they had
been exposed to the virus, either
through contact with it or by having and recovering from smallpox.
19. No. If HIV did not mutate, it
would remain in the macrophages. It is only after it mutates
that it infects T cells and eventually destroys the immune system.
4C
3. What is happening in step 4?
A Viruses are entering the bacterium
4
TAKS 3 Bio 7B
B Viruses are repairing the cell membrane
TAKS 3 Bio 4C
using viral proteins.
C Newly formed viruses are being released
from the bacterium.
D The bacterium is ejecting its own
chromosome inside a capsid.
20. Answers will vary depending on
the viral disease chosen.
TAKS 1 Bio/IPC 2B, 2D;
3
Test
1. Which type of cycle is represented in the
diagram?
4C
A aerobic
B anaerobic
C lysogenic
D lytic
Alternative Assessment
When using a diagram to answer questions, carefully study each part of the figure as well as any
lines or labels used to indicate parts of the drawing.
453
21. TAKS 3 Bio 4C, 4D; Bio 3F
Answers will vary depending on
the data available. Of HIV-infected
individuals worldwide, most live
in Africa and the Middle East, followed by Asia and Oceania, Latin
America and the Caribbean, North
America, and Europe.
TAKS 1 Bio/IPC 2B; TAKS 3 Bio 4C
1. A. Incorrect. The presence of oxygen is not
relevant. B. Incorrect. The absence of oxygen is
not relevant. C. Incorrect. This is not a lysogenic cycle because the virus is not inserted in
the chromosome. D. Correct. This is a lytic
cycle because the cell has lysed. TAKS 3 Bio 4C
2. F. Incorrect. The capsid is not injected into
the host bacterium. G. Correct. The viral DNA
enters the host. H. Incorrect. Viruses do not
withdraw proteins from the host. J. Incorrect.
Viruses do not withdraw DNA from the host.
TAKS 3 Bio 4C
3. A. Incorrect. Viruses do not enter host cells
through holes in the cell membrane. B. Incorrect.
Viruses do not repair host cell membranes.
C. Correct. The host cell has burst and new
viruses are being released. D. Incorrect. The
illustration shows lysis of the bacterial cell.
TAKS 3 Bio 4C
22. Virologists work with viruses and
tissue cultures that are the hosts
for viruses. Most virologists have
a medical degree or a graduate
degree in microbiology or virology. Employers may include
pharmaceutical companies, university research labs, government
research labs, public health labs,
and hospitals. Growth potential
is good. Starting salary will vary
by region. Bio 3D
Chapter 20 • Viruses and Bacteria
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