Download Chapter 18 Interactive Reader

18
CHAPTER
Viruses and
Prokaryotes
GETTING READY TO LEARN
Preview Key Concepts
18.1 Studying Viruses and Prokaryotes
Infections can be caused in several ways.
18.2 Viral Structure and Reproduction
Viruses exist in a variety of shapes and sizes.
18.3 Viral Diseases
Some viral diseases can be prevented with vaccines.
18.4 Bacteria and Archaea
Bacteria and archaea are both single-celled prokaryotes.
18.5 Beneficial Roles of Prokaryotes
Prokaryotes perform important functions for organisms and ecosystems.
18.6 Bacterial Diseases and Antibiotics
Understanding bacteria is necessary to prevent and treat disease.
Review Academic Vocabulary
Write the correct word for each definition.
archaea
homeostasis
lipid
1.
: prokaryotes belonging to one of the three
domains of life
2.
: nonnpolar molecule made of carbon,
hydrogen, and oxygen
3.
: condition of constant internal conditions
Preview Biology Vocabulary
To see how many key terms you already know from this chapter, choose
the word that makes sense in each sentence.
antibiotic
toxin
vaccine
1. A doctor may prescribe a(n)
bacterial infection.
if you have a
2. You may have received a(n)
shot to prevent getting the flu.
in the form of a
3. Any poison produced by an organism, including the oil produced by
poison ivy, is a(n)
.
296
Student text pages
544–545
SECTION
Viruses
18.1 Studying
and Prokaryotes
KEY CONCEPT Infections can be caused in several ways.
Viruses, bacteria, viroids, and prions can all
cause infection.
Any living organism or particle* that can cause an infectious disease is
called a pathogen. An infectious disease is an illness that can be passed
from one organism to another. Bacteria, viruses, viroids, and prions can
all be pathogens. Although many types of bacteria are helpful—and even
necessary—for your health, some types of bacteria can make you sick.
RELATIVE SIZES OF CELLS AND INFECTIOUS PARTICLES
Bacteria, viruses, viroids, and prions can all cause infection. Eukaryotic cells can be
microscopic, but they are larger than prokaryotic cells, like bacteria. Prokaryotes are
larger than viruses, viroids, and prions.
1 nanometer (nm) = one billionth of a meter
100 nm
eukaryotic cells
10,000–100,000 nm
viruses
50–200 nm
prokaryotic cells
200–10,000 nm
viroids
5–150 nm
prion
2–10 nm
Bacteria These single-celled organisms are prokaryotes. Bacteria are
living things—they contain DNA, use nutrients and energy, grow and
reproduce, and respond to their environment.
Viruses A virus is an infectious particle made only of a piece of DNA or
RNA surrounded by a protein coat. Viruses have some characteristics of
living things, but not all. For example, they cannot reproduce on their
own. They need living cells to help them reproduce and to make proteins.
Viroids A viroid is a piece of single-stranded RNA without a protein
coat. Viroids cause diseases in plants, and are passed through seeds or
pollen. Like a virus, a viroid cannot reproduce without the help of
living cells.
* ACADEMIC VOCABULARY
particle a little piece of something
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297
Prions A prion (PREE-ahn) is an infectious
particle made only of proteins. Recall from
Chapter 2 that proteins have a three-dimensional shape. Prions cause proteins to fold
incorrectly, so they end up with the wrong
shape and do not work properly. Prions are
different from other pathogens because they
have no genetic material, but can still cause
disease. Prion diseases are always deadly,
because the body has no immune response
against a protein. The illness commonly called
mad cow disease is caused by prions.
Circle the names of four pathogens presented above.
18.1
Mark It Up
Vocabulary Check
virus
pathogen
Go back and highlight
each sentence that
has a vocabulary
word in bold.
viroid
prion
Match each clue below to the
correct term from the list above.
1. made of protein only
2. made of DNA or RNA and a protein coat
3. causes infectious disease
4. made of RNA only
18.1
The Big Picture
5. Fill in the table below with the following terms: bacteria, viruses,
viroids, and prions.
PATHOGENS
LIVING CELLS
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McDougal Littell Biology
NOT LIVING CELLS
This drawing shows the
three-dimensional structure of the blood protein
hemoglobin. The proper
function of a protein is
based on its shape. Prions affect the shape of
proteins. As a result, the
proteins will not work
properly.
Student text pages
547–551
SECTION
Structure
18.2 Viral
and Reproduction
KEY CONCEPT Viruses exist in a variety of shapes and sizes.
Viruses differ in shape and in ways of entering
host cells.
Not all viruses are the same. They can be simple or complex in structure,
and they have different ways of getting into host cells. Host cells are cells
that are infected by a virus. Viruses can only reproduce after they have
infected host cells.
The Structure of Viruses
Viruses are made up of two main parts: a piece of genetic material, and a
protein covering, or coat, called a capsid. Unlike eukaryotes and prokaryotes, the genetic material of viruses may be either DNA or RNA.
The shape of a virus plays an important role in how it works. The
proteins on the surface of a viral capsid match a particular host—like a
key fits a lock. Each type of virus can infect only certain hosts. Some
viruses can infect several species. Others can infect only a single species.
VIRAL SHAPES
The different proteins that make up a viral capsid give viruses a variety of shapes.
capsid
genetic material
(DNA or RNA)
surface
proteins
Some viruses are shaped like
a ball.
surface proteins
surface capsid
proteins
genetic material
(DNA or RNA)
capsid
genetic material
(DNA or RNA)
Some viruses have a long
twisted or coiled shape.
Some viruses are
many-sided.
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Viruses that Infect Bacteria
Bacteriophages (bak-TEER-ee-uh-FAYJ-ihz) are a
group of viruses that infect bacteria. Bacteriophages are
often called “phages” for short. Phages attach to the
outside of a bacterium, and inject their DNA into
the cell.
Viruses that Infect Eukaryotes
Viruses that infect eukaryotes enter a host cell differently than phages enter host bacterial cells. For example, viruses that infect eukaryotes may get taken into a
cell through endocytosis. Once inside the eukaryotic
cell, the virus finds the nucleus, where the host cell’s
DNA is located.
capsid
DNA
This part of the
phage attaches to a
bacterium and
pierces the cell wall.
The viral DNA then
gets injected into
the bacterium.
Bacteriophage
What are the two main structural parts of a virus?
Viruses cause two types of infections.
Once inside a host cell, there are two basic pathways of infection that
are similar for all viruses. A virus may end up destroying the host cell,
or it may add its genetic material to the host cell without destroying it.
These two pathways are shown for bacteriophages on the next page.
Lytic Infection
Visual Connection
A lytic infection (LIHT-ihk) results in the host cell bursting open and
releasing new viral offspring into the host’s system. First, the virus enters
the host cell. Then, the viral DNA directs the host cell to copy the viral
DNA and produce more capsids. The capsids and viral DNA come
together to make new virus particles. The host cell is destroyed and the
viral offspring are released. They can then infect other cells.
See bacteriophages
attack a bacterium:
student text, pg. 549
Lysogenic Infection
A lysogenic infection (LY-suh-JEHN-ihk) results in the viral DNA
combining with the host cell’s DNA. The phage DNA inserted into the
host cell’s DNA is called a prophage. When the host cell goes through
mitosis, the prophage gets copied and passed on to daughter cells along
with the host cell’s DNA. The prophage can remain a permanent part
of the host cell’s DNA. Or, it can enter the lytic cycle and produce
new viruses.
300
Endocytosis is a process
in which a substance is
surrounded by the cell
membrane, and then
released into the cell.
McDougal Littell Biology
LYTIC INFECTION
A lytic infection results in the lysis, or breaking
apart, of the host cell and release of new viral
particles. A lysogenic infection
does not destroy the
host cell.
host bacterium
The bacteriophage attaches
and injects its DNA into a
host bacterium.
The viral DNA
forms a circle.
The host bacterium breaks apart,
or lyses. Bacteriophages are able
to infect new host cells.
The viral DNA directs the host
cell to produce new viral parts.
The parts assemble into new
bacteriophages.
The virus may enter the
lysogenic cycle, in which the
host cell is not destroyed.
LYSOGENIC INFECTION
The viral DNA is called
a prophage when it
combines with the
host cell’s DNA.
The prophage may leave
the host’s DNA and enter
the lytic cycle.
Many cell divisions produce a
colony of bacteria infected
with prophage.
Although the prophage is not
active, it is copied along with
the host cell’s DNA.
An infected cell may stay in the lysogenic cycle for a long time. A
trigger, such as stress, can push the virus into the lytic cycle. The virus
will then use the cell to produce new viruses.
In which cycle of infection are new viral particles released—
lytic or lysogenic?
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18.2
Vocabulary Check
capsid
bacteriophage
lytic infection
lysogenic infection
prophage
Mark It Up
Go back and highlight
each sentence that
has a vocabulary
word in bold.
Circle the correct term from each pair to
complete the sentences below.
1. Viral DNA combined with the host cell’s DNA is called a prophage /
bacteriophage.
2. A virus is made of two main parts, genetic material and a
bacteriophage / capsid.
3. In a lysogenic infection / lytic infection the viral DNA becomes part
of the host cell’s DNA and the host cell is not destroyed.
4. In a lysogenic infection / lytic infection the host cell bursts, releasing
new viral offspring into the host’s system.
18.2
The Big Picture
5. What do viruses need to reproduce?
6. What is a main difference between the lytic and lysogenic cycles of
infection?
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Student text pages
552–554
SECTION
18.3 Viral Diseases
KEY CONCEPT Some viral diseases can be prevented with vaccines.
Viruses cause many infectious diseases.
Your body has defenses against viruses. Skin is your body’s first defense.
A virus cannot get through your skin unless there is an opening such as a
cut or a scrape. A virus can also enter your body through other openings,
such as the mouth, nose, genital areas, eyes, and ears. Some viral infections are deadly and others are barely noticeable. Several human illnesses
caused by viruses are listed below.
The Common Cold
More than 200 viruses cause the illness that we call the common cold. It is
hard to find a cure for the common cold because it is caused by so many
different viruses that mutate rapidly.
Influenza
The influenza virus is often called the flu for short. The flu spreads
quickly. There are often flu epidemics, or rapid outbreaks that affect
many people. Subtypes of the flu can infect birds, horses, pigs, whales,
and seals. Currently, only three subtypes infect humans. The flu can be
controlled with a vaccine (vak-SEEN), a substance that gets the body’s
immune system to prepare a response against a virus. Flu viruses mutate
rapidly, so a new vaccine must be made every year.
SARS
SARS (severe acute respiratory disease) has symptoms similar to
the flu, including fever and coughing. SARS first appeared in Asia
in 2002. By the following summer it had spread to other countries.
Replication
9C6
9C6
Transcription
HIV
HIV (human immunodeficiency virus) is a type of virus called a
retrovirus. Retro- means “backward.” A retrovirus copies its
genetic material “backwards.” Usually, DNA is used to make a copy
of RNA, but a retrovirus contains RNA that gets used to make
DNA. The DNA then becomes part of the host cell’s DNA.
GC6
GC6
Translation
cjXaZjh
XnideaVhb
EgdiZ^c
EgdiZ^c
Usually, DNA is used to make
RNA. But retroviruses can use
RNA to make DNA.
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HIV can remain part of the host cell’s DNA for many years with no
symptoms. When the virus becomes active, it makes more viral particles.
The host cells burst, and the new viruses can infect other cells. This stage
of the disease destroys the host’s white blood cells.
White blood cells are a very important part of the human immune
response. The loss of white blood cells leads to AIDS, or acquired
immune deficiency syndrome. Once a person’s white blood cells are
destroyed, she or he may be unable to fight off the common microorganisms that humans come into contact with every day.
HIV mutates very quickly, which makes it a challenge to treat. However, there are medicines that can help to slow the spread of the virus
once a person is infected.
Name three infectious diseases that are caused by viruses.
VIRAL DISEASE
VIRAL
INFECTION
SYMPTOMS OF
DISEASE
TRANSMISSION OF DISEASE
U.S. VACCINE RECOMMENDATION
Chickenpox
rash, itchy skin, fever,
fatigue*
contact with rash, droplet
inhalation
for children between 12 and 18 months
Hepatitis A
yellow skin, fatigue,
abdominal pain
contact with contaminated
feces
for people traveling to infected locations and protection during outbreaks
Mumps
painful swelling in salivary glands, fever
droplet inhalation
for children between 12 and 15 months
and again at 4 to 6 years
Rabies
anxiety, paralysis, fear
of water
bite from infected animal
for veterinarians and biologists in
contact with wildlife
West Nile
fever, headache, body
ache
bite from infected mosquito
no available vaccine
Vaccines are made from weakened pathogens.
In the United States, most children are vaccinated against diseases such
as measles, mumps, and chicken pox. Every year, millions of people are
vaccinated against influenza.
* ACADEMIC VOCABULARY
fatigue a feeling of tiredness
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McDougal Littell Biology
A vaccine contains the weakened virus or parts of the virus that it is
supposed to protect against. A vaccine triggers the body’s immune system
response. Because the vaccine contains a weakened virus, it does not
cause illness. But if the virus enters the body again, the body will be
prepared to start an immune response before the virus can cause damage.
What main substance would an influenza vaccine contain?
18.3
Vocabulary Check
epidemic
vaccine
retrovirus
Mark It Up
Go back and highlight
each sentence that
has a vocabulary
word in bold.
Write a short definition for each vocabulary term.
1. epidemic:
2. vaccine:
3. retrovirus
18.3
The Big Picture
4. What is the body’s first defense against infection?
5. How does a vaccine protect a person against infection?
6. Why is a person with AIDS more easily infected by pathogens than a
person without AIDS?
Interactive Reader
305
SECTION
18.4 Bacteria and Archaea
Student
text pages
@E;@8E8JK8E;8I;J
555–558
B.8.3
KEY CONCEPT Bacteria and archaea are both single-celled prokaryotes.
Prokaryotes are widespread on Earth.
Bacteria and archaea live just about everywhere on Earth—even inside
rocks and in polar ice caps. A drop of your saliva may contain 40 million
bacterial cells. A gram of soil may contain 5 billion bacterial cells from
over 10,000 types of bacteria. Prokaryotes are an important part of the
communities in which they live.
Prokaryotes can be divided into groups based on their need for oxygen.
• An obligate anaerobe (AHB-lih-giht AN-uh-ROHB) cannot
survive in the presence of oxygen.
• An obligate aerobe (AHB-lih-giht AIR-ohb) needs oxygen to
survive.
• A facultative aerobe (FAK-uhl-tay-tihv AIR-ohb) can survive
whether or not oxygen is present.
What is the difference between an obligate anaerobe and an
obligate aerobe?
Bacteria and archaea are structurally similar but
have different molecular characteristics.
All prokaryotes either belong to the domain Archaea or the domain
Bacteria. The two groups of organisms have similar appearances but
have many differences in their genetics and biochemistry.
Structural Comparison
• Cell shape Archaea come in many shapes. Bacteria have three common forms: rod-shaped, spiral-shaped, and spherical-shaped.
• No organelles Prokaryotes have no nucleus or other membranebound organelles.
• DNA Prokaryotic DNA is in the shape of a loop, or a circle, and is
located in the cytoplasm.
• Plasmids Prokaryotes can also have plasmids. A plasmid is a small
piece of DNA that replicates separately from the main chromosome.
• Movement Many bacteria and archaea use flagella to move. A
flagellum (fluh-JEHL-uhm) is a long structure outside of the cell
that is used to move. The flagella of bacteria and archaea look similar
but they are structurally different.
• Pili Many prokaryotes have structures called pili, which are shorter
and thinner than flagella. Pili help prokaryotes to stick to surfaces.
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McDougal Littell Biology
VOCABULARY
Something that is
obligatory is something
that must happen. Something that is facultative
is something that may
happen but does not have
to happen.
PROKARYOTE STRUCTURE
pili
flagellum
chromosome
plasmid
cell wall
plasma
membrane
Molecular Comparison
Archaea and bacteria are very different on a molecular level. Molecular
evidence suggests that archaea have at least as much in common with
eukaryotes as they do with bacteria. The cell walls and cell membranes
of archaea and bacteria have very different chemical components. For
example, archaea have a type of lipid in their membranes that is not
found in any other living organism.
What
one
way archaea
in whichand
archaea
anddiffer?
bacteria differ?
What is one
wayisin
which
bacteria
JK8E;8I;J
:?<:B
Bacteria have various strategies for
survival.
You might use a thoughtful plan, or a strategy, for playing a
game. In science, a strategy also means an adaptation that
improves a species’ chance for survival. The exchange of genetic
material through conjugation and the formation of endospores
are two bacterial strategies for survival.
Bacteria reproduce asexually. However, through a process
called conjugation (KAHN-juh-GAY-shuhn), two or more bacterial cells can exchange DNA. This process allows bacteria to
adapt quickly to different environmental conditions.
VISUAL VOCAB
In conjugation, genetic material
transfers between prokaryotes, producing genetic variation. DNA passes
through a structure called a conjugation bridge which connects the cells.
conjugation bridge
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When conditions are very bad for growth and survival, some bacteria
can produce an endospore. An endospore is a specialized cell with a
thick, protective wall that can survive drying out, temperature changes,
and even disinfectants. Endospores can last for hundreds of years.
Why is conjugation considered a survival strategy?
18.4
Vocabulary Check
obligate anaerobe
obligate aerobe
facultative aerobe
plasmid
flagellum
conjugation
endospore
Mark It Up
Go back and highlight
each sentence that
has a vocabulary
word in bold.
1. Which type of bacterium is likely to live at the bottom of a lake,
where there is no oxygen?
2. Look back at the figure of prokaryote structure on page 307.
- Draw an arrow that points to the flagellum.
- Circle a plasmid.
3. Name one process and one structure that are bacterial strategies for
survival.
18.4
The Big Picture
4. Where can bacteria and archaea live?
5. Bacteria and archaea look very similar. In what main way do they differ?
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Student
text pages
@E;@8E8JK8E;8I;J
559–561
SECTION
Roles
18.5 Beneficial
of Prokaryotes
B.4.4
KEY CONCEPT Prokaryotes perform important functions
for organisms and ecosystems.
Prokaryotes provide nutrients to humans and
other animals.
Bacteria are important parts of animal digestive systems. Both the
bacteria and the host animal benefit from this relationship. The bacteria
benefit from a stable home and source of food. The host animal benefits
because the bacteria help break down foods and produce vitamins and
other nutrients.
Prokaryotes are also important to human nutrition because they are
used to make many common foods. Cheese, sour cream, yogurt, butter,
pickles, soy sauce, sauerkraut, vinegar, and many other foods all depend
on fermentation by prokaryotes to produce their flavors.
You may have heard about food poisoning caused by bacteria.
Although some types of bacteria in food can be harmful, eating food
produced by bacteria is not dangerous—as long as it’s the right kind of
bacteria!
Many types of foods are made using bacteria. Which of the
foods listed above have you tried?
Prokaryotes play
important roles in
ecosystems.
You cannot see prokaryotes with your
bare eyes, so it may be easy to forget
about them. But they play very important roles in every ecosystem. For
example, some prokaryotes produce
oxygen through photosynthesis.
Others help cycle carbon, nitrogen,
hydrogen, and phosphorous through
the environment.
One example of prokaryotes’ roles in
nutrient cycles is shown in this drawing.
Bacteria in the soil help to cycle nitrogen
through the environment.
NITROGEN CYCLE
Much of the nitrogen cycle occurs underground, where
bacteria transform nitrogen into a form that can be used
by plants.
nitrogen in
atmosphere
animals
plants
denitrifying
bacteria
decomposers
nitrogen-fixing
bacteria
nitrifying
bacteria
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Prokaryotes can break down many natural substances. They can
also break down many substances made by humans. Because of this
ability, scientists use prokaryotes in a process called bioremediation.
Bioremediation (BY-oh-rih-MEE-dee-AY-shuhn) is a process that uses
living things to break down pollutants. For example, some types of
bacteria can digest oil. These bacteria are used to help clean up oil spills
and other industrial accidents.
What
is one of
example
of a pollutant
thatcan
bacteria
can
What is one
example
a pollutant
that bacteria
help to
JK8E;8I;J
:?<:B
help to break down?
break down?
18.5
Vocabulary Check
bioremediation
Mark It Up
Go back and highlight
each sentence that
has a vocabulary
word in bold.
1. Remediation means “fixing a problem.” The prefix bio- means
“life.” Explain how these word parts contribute to the meaning of
bioremediation.
18.5
The Big Picture
2. What are two ways that prokaryotes provide nutrients to humans?
3. What is one important role that prokaryotes play in ecosystems?
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Student text pages
563–565
SECTION
Diseases
18.6 Bacterial
and Antibiotics
KEY CONCEPT Understanding bacteria is necessary to prevent and
treat disease.
Some bacteria cause disease.
Some bacteria can cause disease in plants and animals. Bacteria can
cause illness in two basic ways:
1. Bacteria can attack the cells in one of the body’s tissues. For example,
the disease tuberculosis, sometimes called TB, is caused by bacteria
that invade the lungs and use the tissue for nutrients.
2. Bacteria can make poisons, called toxins, that can be carried in the
blood to other parts of the body. A toxin is a poison released by an
organism. For example, the most common source of food poisoning
is from toxins released by a type of bacteria.
COMMON BACTERIAL INFECTIONS
INFECTION
BACTERIUM
SYMPTOMS
CAUSES
Acne
Propionibacterium
chronic cysts, blackheads
increased oil production in skin
Anthrax
Bacillus anthracis
fever, trouble breathing
inhaling endospores
Lyme disease
Borrelia burgdorferi
rash, aching, fever, swelling of joints
bite from infected tick
Tetanus
Clostridium tetani
severe muscle spasms, fever, lockjaw
wound contaminated with soil
Tooth decay
Streptococcus mutans
tooth cavities
large populations of bacteria in mouth
Look at the table above. Which of these common bacterial
infections have you heard of?
Antibiotics are used to fight bacterial disease.
Antibiotics are chemicals that kill or slow the growth of bacteria. Many
antibiotics work by stopping bacteria from making cell walls. Antibiotics
do not affect animal cells because animal cells do not have cell walls.
Similarly, antibiotics do not affect viruses, because viruses do not have
cell walls.
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311
Antibiotics are very important medical treatments. However, they
should only be used when necessary. Recall that bacteria are a very
important part of your digestive system. These “good” bacteria are also
affected by antibiotics. The overuse of antibiotics can kill the bacteria in
your digestive system, resulting in illness.
How do many antibiotics prevent the growth of bacteria?
Bacteria can evolve resistance to antibiotics.
Antibiotics can be life-saving medicines. However,
the inappropriate and incomplete use of antibiotics
ANTIBIOTIC RESISTANCE
has resulted in strains of bacteria that are not
A bacterium carries
affected by antibiotics. In other words, these strains
genes for antibiotic
of bacteria are resistant to antibiotics. Antibioticresistance on a plasmid.
resistant bacteria are a major public health issue.
Resistance occurs as a result of natural selection.
A copy of the plasmid is transferred through conjugation.
Any bacteria that are resistant will survive and
reproduce. Resistance can then be passed on to
Resistance is quickly
offspring and spread to other bacteria. Three
spread through
many bacteria and
factors that have contributed to resistance are
their offspring.
described below.
• Overuse Anytime antibiotics are used, there
is a chance to select for resistant bacteria.
The unnecessary use of antibiotics—such as
when bacteria are not the cause of an illness—
increases the possibility that resistant bacteria
will become more common.
• Underuse Antibiotics may make a person feel
better after just one or two days. But the whole prescription of
antibiotics must be taken. Otherwise, it is possible that only the
weakest bacteria will be killed, and the ones with some resistance
may survive.
• Misuse A large portion of the antibiotics used in the United States
are fed to livestock, such as cows, to increase their growth. Antibiotics
may therefore be added to the food of healthy animals. The misuse of
antibiotics in agriculture can lead to antibiotic resistance of bacteria
in the animals’ food.
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In summary, anytime antibiotics are used when they are not necessary, or when they are used improperly, it increases the chances for
antibiotic-resistant bacteria to become more common. An illness caused
by antibiotic-resistant bacteria is difficult or impossible to treat because
the bacteria do not respond to antibiotics.
Explain the role of natural selection in the production of
antibiotic-resistant bacteria.
18.6
toxins
Vocabulary Check
antibiotics
Fill in the blanks with the correct
term from the list above.
Mark It Up
Go back and highlight
each sentence that
has a vocabulary
word in bold.
1. Some bacterial infections can be treated with
.
2. The
produced by some bacteria cause
diseases in plants and animals.
18.6
The Big Picture
3. Give one example of a disease, illness, or infection caused by bacteria
and describe its symptoms.
4. Can colds be treated with an antibiotic? Explain your response.
5. Imagine that your friend has a ten-day prescription of antibiotics for
an illness. Your friend feels better after only two days and wants to
stop taking the medicine. Explain why your friend should complete
the full prescription of antibiotics.
Interactive Reader
313
Chapter 18 Review
1. What are four types of pathogens?
2. Is a virus a living organism? Explain your response.
3. List one way that bacteria are “helpful” to humans and one important
role they play in ecosystems.
B.4.4
4. What do retroviruses do that is different from other viruses?
a. use DNA to make RNA
b. use RNA to make DNA
c. use DNA to make DNA
d. use RNA to make RNA
5. What biological process is involved in the formation of strains of bacteria that are resistant to antibiotics?
6. All prokaryotes belong to one of two domains:
or
. B.8.3
7. How does a vaccine protect against illness?
8. Label the cell wall, a chromosome, a plasmid, and the flagellum on this
diagram of a typical prokaryote.
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B.8.5