Download 40–1 Infectious Disease

40–1 Infectious Disease
Section 40–1
1 FOCUS
Objectives
G
ood health is something that you might take for granted—
until you or someone close to you gets sick. Then, the value of
good health becomes all too obvious. Why do you get sick? How
do you get better? What is the best way for you to avoid getting
sick in the first place? These are questions that people have
been asking for centuries. Today, in most cases, these questions
can be answered.
A disease is any change, other than an injury, that disrupts
the normal functions of the body.
Some diseases are
produced by agents, such as bacteria, viruses, and fungi.
Others are caused by materials in the environment, such
as cigarette smoke. Still others, such as hemophilia, are
inherited. Disease-causing agents are called pathogens,
which means “sickness-makers.” Diseases caused by pathogens
are generally called infectious diseases.
The Germ Theory of Disease
For thousands of years, people believed that diseases were
caused by curses, evil spirits, or night vapors. In the midnineteenth century, a new explanation was put forth based on
the work of the French chemist Louis Pasteur and the German
bacteriologist Robert Koch. The observations of Pasteur and
Koch led them to conclude that infectious diseases were caused
by microorganisms of different types, commonly called germs.
This idea is now known as the germ theory of disease.
The world is filled with microorganisms of every shape and
description. How can scientists be sure that a particular organism
causes a certain disease? In 1975, Allen Steere of Yale University
had a chance to ask that question. In a small area of Connecticut,
Steere found 39 children and several adults suffering from pain
and joint inflammation. Their symptoms looked like a
rare form of childhood arthritis. However, Steere thought
that there were far too many cases of arthritis for such a
small population. He looked for another explanation. The
rural location of the outbreak and the fact that most of
the cases had started in summer or early fall made Steere
suspect, at first, that this could be an infectious disease
carried by an insect.
Figure 40–1
Diseases can be inherited,
caused by materials in the environment, or
produced by pathogens. Certain species of
ticks often carry bacteria or viruses, so their
bites can transmit disease.
40.1.1 Identify the causes of disease.
40.1.2 Explain how infectious diseases are transmitted.
40.1.3 Describe how antibiotics
fight infection.
Key Concepts
• What causes disease?
• How are infectious diseases
transmitted?
Vocabulary
disease
pathogen
germ theory of disease
Koch’s postulates
vector
antibiotic
Vocabulary Preview
Reading Strategy:
Using Prior Knowledge
Before you read, make a list of
some of the diseases that you
have had. As you read, determine which pathogen might
have caused each disease.
Tell students that the term pathogen
refers to an agent that causes disease. Ask: How do you think the
term pathogen is related to the
germ theory of disease? (Germ is
another term for pathogen. According
to the theory, germs, or pathogens,
cause disease.)
Reading Strategy
Students are likely to list respiratory
infections such as colds and flu and
gastrointestinal infections that cause
stomachaches and diarrhea. They
should determine which pathogen
might have caused each disease.
2 INSTRUCT
Address Misconceptions
Explain that some diseases have multiple causes. For example, some types of
cancer, such as lung cancer, are caused
by environmental factors, for example,
cigarette smoke. Other types of cancer, such as cervical cancer, are caused
by pathogens (for cervical cancer,
human papilloma virus).
The Germ Theory
of Disease
(magnification: about 30⫻)
Demonstration
SECTION RESOURCES
• Laboratory Manual A, Chapter 40 Lab
• Teaching Resources, Section Review 40–1
Save
• Reading and Study Workbook A,
e
Section 40–1
• Adapted Reading and Study Workbook B,
Section 40–1
• Biotechnology Manual, Lab 16
• Lesson Plans, Section 40–1
• iText, Section 40–1
• BioDetectives Videotapes, “Influenza:
Tracking a Virus”; “Hantavirus: A Tale of Mice
and People”
• Transparencies Plus, Section 40–1
Tim
Technology:
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Print:
Help students appreciate the importance of the germ theory of disease
by showing them death rates by
cause of death in the United States
population for the late 1800s and
also for a recent year. Then, ask: How
did the number of deaths caused
by infectious diseases change? (It
fell dramatically.) Add that identifying
germs as the cause of infectious diseases was the first step in bringing
these diseases under control.
The Immune System and Disease
1031
40–1 (continued)
Koch’s Postulates
Demonstration
Demonstrate the importance of using
sterile techniques when applying
Koch’s second postulate. Hold a wire
loop in the flame of a Bunsen burner
for a few seconds. Allow the loop to
cool, dip it in a bacterial culture, and
run it over sterile agar in a petri dish.
(CAUTION: Use a safe strain of bacteria, such as E. coli, from a scientific
supply company, and apply sterile
techniques to the handling of the
bacterial culture.) Sterilize the loop
again, let it cool, and run it over sterile agar in a second petri dish.
Incubate both dishes at 37°C for 24
hours, and then have students
observe the differences in the agar.
(Bacteria should be visible growing in
the first petri dish but not the second.)
Ask: Which step of the demonstration caused the different outcomes
in the two petri dishes? (The resterilization of the wire loop) How does
this demonstration relate to Koch’s
second postulate? (If you had been
trying to isolate and grow a pathogen
in the petri dishes, only the second dish
would produce a pure culture. The first
petri dish would have produced bacteria in addition to the pathogen.)
Pathogen (Borrelia burgdorferi) identified
Pathogen grown in pure culture
Pathogen injected into healthy lab mouse
Sure enough, many of the children reported
that their problems began with what they thought
was an insect bite. The bite was followed by an
expanding skin rash. Steere called the infection
Lyme disease after the town of Lyme,
Connecticut, where it was first discovered.
Steere and his colleagues were able to link
the skin rash to the bite of the tiny deer tick
(Ixodes scapularis). One of Steere’s colleagues,
Dr. Willy Burgdorfer, found an unusual spiralshaped bacterium (Borrelia burgdorferi) in the
ticks. Steere found the same bacterium in
patients with Lyme disease. Could this bacterium be the cause of Lyme disease?
For ethical reasons, Steere did not try to
infect healthy children with the bacterium.
However, when the bacterium was injected into
laboratory mice, they developed arthritis and
other symptoms, just as the children had. From
the sick mice, Steere recovered the bacteria,
which were then injected into healthy mice. The
healthy mice then developed the disease. Steere
and his colleagues had found the organism that
caused Lyme disease. The process Steere used is
shown in Figure 40–2.
Koch’s Postulates
Healthy mouse becomes sick
Pathogen (Borrelia burgdorferi) recovered
왖 Figure 40–2
Allen Steere followed
Koch’s postulates to test his theory
that the bacterium Borrelia burgdorferi
caused Lyme disease. Inferring Why
must the pathogen be grown in a pure
culture?
The groundwork for Allen Steere’s work with
Lyme disease was actually laid more than a
hundred years earlier by Robert Koch. From his
studies with various bacteria, Koch developed a
series of rules still used today to identify the
microorganism that causes a specific disease.
These rules are known as Koch’s postulates.
Koch’s postulates can be stated as follows:
1. The pathogen should always be found in the
body of a sick organism and should not be
found in a healthy one.
2. The pathogen must be isolated and grown in
the laboratory in pure culture.
3. When the cultured pathogens are placed in a
new host, they should cause the same disease
that infected the original host.
4. The injected pathogen should be isolated from
the second host. It should be identical to the
original pathogen.
Why are these rules important? Because
identifying pathogens that cause disease is the
first step toward preventing or curing the ailments they produce.
Less Proficient Readers
Reinforce the material for less proficient readers by
having them make posters that show ways infectious diseases can be spread and also how their
spread can be prevented. For example, students
might use a picture of two people shaking hands
to illustrate the spread of diseases through physical contact and beside it a picture of someone
washing hands to prevent the spread of diseases
in this way.
1032
Chapter 40
Advanced Learners
Have students who need extra challenges learn
more about Lyme disease. Students might investigate the current distribution of the disease in the
United States, the number of people who are
infected, how the disease is treated, and whether
it can be transmitted by other vectors. Students
should share what they learn in an oral report
illustrated with visuals, such as a map showing the
distribution of Lyme disease.
Agents of Disease
Agents of Disease
For many pathogens, the human body provides just the right
conditions for growth—a suitable body temperature, a watery
environment, and an abundance of nutrients. The large intestine, for example, harbors dense colonies of bacteria that help in
the process of digestion. Bacteria and yeast are also found in the
mouth and throat. Fortunately, most of these organisms are
harmless, and many are actually beneficial.
If this is true, then exactly how do pathogens cause disease?
Some pathogens, including viruses and some bacteria, destroy
cells as they grow. Other bacteria release toxins that harm an
organism. Still others, especially parasitic worms, produce
sickness when they block the flow of blood, remove nutrients
from the digestive system, and disrupt other bodily functions.
The Ascaris worm in Figure 40 –3 is a parasitic worm.
To see how
scientists test a
hypothesis about
how a disease is
caused and transmitted, view the segment
“Hantavirus: A Tale of Mice and People,”
on Videotape Three.
Build Science Skills
Viruses Viruses are tiny particles that invade and replicate
within living cells. Viruses attach to the surface of a cell, insert
their genetic material in the form of RNA or DNA, and take over
many of the functions of the host cell. Viruses can infect nearly
every type of organism—including plants, animals, and bacteria.
Diseases caused by viruses include the common cold, influenza,
smallpox, and warts.
Figure 40–3 Protists and worms
often cause disease in humans and
other animals. The protist
Trypanosoma (purple objects) causes
African sleeping sickness. The Ascaris
worm matures in the intestine and
causes severe malnutrition in its hosts.
Bacteria Most bacteria are harmless to humans. Unfortunately,
the few that are pathogens cause serious diseases. Bacteria cause
disease in one of two ways—either by breaking down the tissues
of the infected organism for food or by releasing toxins that harm
the body. Bacterial diseases include streptococcus infections,
diphtheria, botulism, and anthrax.
Protists You may not associate protists with disease, but a
protist causes what may be the single most damaging infectious
disease afflicting humans—malaria. Malaria is caused by
Plasmodium, a protist that is spread from person to person by
mosquitoes. Insects also spread another protist known as
Trypanosoma. Trypanosoma protists live in the bloodstreams of
vertebrate animals. The protist feeds off the nutrients in the
host organism’s blood. Trypanosoma causes African sleeping
sickness. Contaminated water supplies are responsible for amebic
dysentery, a serious infection caused by the protist Entamoeba.
Drawing Conclusions Assign one
student to research an example of
each of the types of pathogens
described on this page. Students
should find out how the pathogen
causes disease and report back to the
class. (Findings will vary depending on
the pathogen. For example, the bacterium that causes tetanus produces a
toxin that causes involuntary muscle
spasms, especially of the jaw.) After all
the students have reported, ask:
Based on these findings, what conclusions can you draw about
different types of pathogens and
how they cause disease? (Students
might conclude, for example, that
worms cause disease by removing
nutrients from the digestive system or
by injuring tissues.)
Address Misconceptions
Trypanosoma Among Red Blood Cells
Worms Flatworms and roundworms are also responsible for a
number of serious human diseases. People in many tropical
regions of the world can become infected by a parasitic flatworm
known as Schistosoma. These flatworms live part of their lives
in snails and then leave the snails to enter the fresh water of
streams and rice paddies. Schistosoma worms frequently infect
people working in rice fields. Other parasitic worms that infect
humans include tapeworms and hookworms.
What are three diseases caused by protists?
Encourage students
to view the segment “Hantavirus:
A Tale of Mice and People” on
Videotape Three.
Explain that symptoms of infectious
diseases are sometimes due to the
response of the immune system to
the presence of a pathogen. For
example, the sneezing and runny
nose associated with a cold are due
to the production of histamines in
response to the presence of the cold
virus. Students may think that all
infectious diseases are contagious.
Explain that contagious diseases are
spread from person to person by
direct or indirect contact. Measles
and influenza are contagious; tetanus
is not.
Ascaris Worm in Intestine
FACTS AND FIGURES
All about tetanus
Although tetanus was described by Hippocrates
2400 years ago, its prevalence has been masked
because it strikes individuals and does not cause
epidemics. The organism that causes tetanus, the
bacillus Clostridium tetani, is found mainly in soil.
It can enter the body through any break in the
skin, from a superficial scratch to a puncture
wound. Because C. tetani is anaerobic, it grows
best in deeper tissues, so puncture wounds are
especially prone to developing tetanus infections.
The bacterium produces one of the most powerful toxins known. It affects the nervous system
and causes painful muscle contractions, especially
in the muscles of the neck, jaw, and thorax. It frequently leads to death. Fortunately, tetanus can
be prevented with a vaccine.
Answers to . . .
Malaria, African sleeping
sickness, and amebic dysentery
Figure 40–2 To make sure that only
the suspected pathogen has been
transferred to the new host
The Immune System and Disease
1033
Fungi Most fungi are harmless, but a few are capable of
40–1 (continued)
N S TA
N S TA
For: Links on diseases
Visit: www.SciLinks.org
Web Code: cbn-0401
Download a worksheet
on diseases for students to complete, and find additional teacher
support from NSTA SciLinks.
How Diseases Are Spread
Infectious diseases can be transmitted in a number of ways.
Some infectious diseases are spread from one person
to another through coughing, sneezing, or physical
contact. Other infectious diseases are spread through
contaminated water or food. Still others are spread by
infected animals.
How Diseases Are
Spread
Build Science Skills
Designing Experiments Challenge
students to design an experiment to
measure the effects of frequent handwashing on the transmission of
infectious diseases such as the common cold. Each experimental design
should include a clearly stated
research question, a description of
the variables to be tested and how
they will be measured, and an explanation of how other variables will be
controlled.
Make Connections
Environmental Science List some
vector-borne diseases found in the
United States and the vectors that
spread them, such as Rocky
Mountain spotted fever, which is
spread by ticks, and encephalitis,
which is spread by mosquitoes. Ask:
What are some ways you could
reduce the spread of these diseases? (Students are likely to say by
eliminating the vectors, for example, by
spraying with pesticides, or by avoiding
contact with the vectors, for example,
by wearing protective clothing.) Are
there any drawbacks to these
approaches? (Unless pesticides are
pathogen-specific, they can harm other
organisms.)
causing serious problems. One genus of fungi, Tinea, is
particularly adept at penetrating the outer layers of skin. When
it attacks the skin between the toes it produces the infection
known as athlete’s foot. The same fungus can infect the scalp,
where it results in rough, scaly patches known as ringworm.
Other types of fungi infect the mouth, the throat, and even the
fingernails and toenails.
Physical Contact Some infectious diseases can be spread by
왖 Figure 40– 4
Some infectious diseases are spread from
person to person by sneezing.
Thousands of pathogen particles
can be released by a sneeze.
direct physical contact. For example, a disease may be transmitted when a healthy person touches a person with a disease.
Some of the most dangerous pathogens are spread from one
person to another by sexual contact.
Most diseases are spread by indirect contact. For example,
some pathogens can be carried through the air. If a person with
a cold or virus coughs or sneezes, thousands of droplets are
released, as shown in Figure 40 – 4. The pathogens can also
settle on objects. If you touch those objects, the pathogens can be
transferred to your hands, and you can infect yourself by touching your mouth or nose.
Some behaviors can help to control transmission of diseases
spread by physical contact. Simple measures, such as covering
your mouth with a tissue when you cough, can limit the spread
of infection. Washing your hands thoroughly and often also
helps to prevent the spread of many pathogens.
Contaminated Food and Water Have you ever had food
poisoning? Food poisoning is caused by eating food that contains
pathogens. Bacteria are always present in uncooked meat. Bacteria
also grow quickly in warm, partially cooked food. If food is cooked
thoroughly, the risk of food poisoning due to contamination may be
reduced. Contaminated water also causes disease, especially in
parts of the world with poor sanitation and untreated sewage.
Infected Animals Animals, such as the mosquito shown in
Figure 40–5, also spread infectious disease. Animals that carry
pathogens from person to person are called vectors. Malaria,
Lyme disease, West Nile virus, and rabies are diseases carried
by vectors. Avoiding tall grass and wooded areas where deer and
field mice dwell will limit your exposure to ticks that carry Lyme
disease. Staying away from wild animals can reduce your risk of
being bitten by a rabid animal.
HISTORY OF SCIENCE
The black death
Bubonic plague—or the black death, as it was
referred to in the Middle Ages—is caused by a
bacillus, Yersinia pestis, that is transmitted by fleas.
Y. pestis is usually spread among wild rodent populations, but it can also spread to other mammals,
including humans. Huge epidemics of bubonic
plague have afflicted human populations
throughout history. For example, in the mid1300s, bubonic plague swept across Europe and
1034
Chapter 40
killed roughly a quarter of the human population.
Between 1890 and 1930, more than 13 million
people worldwide died of plague. Most people
are surprised to learn that plague is still present
today in wild rodent populations in many areas of
the world, including some parts of the United
States, and that local outbreaks of plague occasionally occur in human populations. Fortunately,
the disease now can be treated successfully with
antibiotics.
Fighting Infectious
Diseases
Fighting Infectious Diseases
Because prevention isn’t always possible, drugs have
been developed for use against some types of pathogens.
Antibiotics are perhaps the most useful single class of
infection-fighting drugs. Antibiotics are compounds
that kill bacteria without harming the cells of the
human or animal hosts. Antibiotics work by interfering
with the cellular processes of microorganisms.
Make Connections
Discovery of Antibiotics Many antibiotics are
produced naturally by living organisms. Other antibiotics are synthetic. One antibiotic, penicillin, was discovered accidentally in 1928 by the Scottish bacteriologist
Alexander Fleming. Fleming had been growing
Staphylococcus bacteria in a culture dish. One day, he
noticed that the culture of bacteria had been contaminated by a species of green mold called Penicillium
notatum. On closer observation, Fleming saw something
surprising. The bacteria were not growing near the mold.
Something produced by the mold was apparently inhibiting their
growth. Later, researchers discovered that penicillin—the name
Fleming gave the antibiotic—interferes with the growth of
bacteria.
Antibiotics have no effect on viruses. However, antiviral
drugs have been developed to fight certain viral diseases. These
drugs generally inhibit the ability of viruses to invade cells and
to multiply once inside cells.
왖
Figure 40– 5
Some infectious diseases are spread by insects.
This Anopheles mosquito may be a
carrier of the protist that causes
malaria.
Call on students at random to name
the agents of disease. Call on other
students to give an example of each
agent.
buy many medicines without a prescription. These medicines,
called over-the-counter drugs, treat only the symptoms of the
disease—including cough, congestion, and fever. These medicines help you feel better, but they do not actually treat the
cause of the infection. The best treatment for most infections
includes rest, a well-balanced diet, and plenty of fluids.
Reteach
Have students write each of Koch’s
postulates, unnumbered, on an index
card. Then, have students shuffle the
cards and try to put them back in the
correct order.
40–1 Section Assessment
Key Concept Describe
some of the causes of disease.
2.
Key Concept What are
the ways in which infectious
diseases are spread?
3. How do vectors spread disease?
4. What are antibiotics?
5. Critical Thinking Inferring
Why did Koch require all four
steps in determining the cause of
an infectious disease? Could you
eliminate one of the steps?
Explain your answer.
3 ASSESS
Evaluate Understanding
Over-the-Counter Drugs You probably know that you can
1.
Health Science Introduce the concept of bacterial resistance to
antibiotics. Explain that it occurs
when people fail to take antibiotics
long enough to kill all the bacteria
that are causing an infection. Ask:
Why does this lead to the bacteria’s developing resistance to the
antibiotic? (The remaining bacteria
are those that have some resistance to
the antibiotic. Through time, repeated
selection in this way for the most resistant bacteria leads to bacteria that are
almost completely resistant to a particular antibiotic.)
Descriptive Writing
Describe how Allen Steere
used Koch’s postulates to
discover the cause of Lyme
disease. You may want to start
by listing the postulates in
one column of a table and, in
another column, listing the
steps used by Steere.
Students’ explanations should
include the information described
in the text on pp. 1031–1032.
If your class subscribes to the iText,
use it to review the Key Concepts in
Section 40–1.
40–1 Section Assessment
1. Inherited factors, materials in the environment, and pathogens
2. By coughing, sneezing, or physical contact;
contaminated water and food; and infected
animals
3. By carrying pathogens from person to person
4. Compounds that kill bacteria without harming human or animal cells
5. Answers will vary. Most students will say
that you could not eliminate one of Koch’s
steps. However, accept all logical answers
that have an adequate explanation.
The Immune System and Disease
1035
Section 40–2
40–2 The Immune System
1 FOCUS
Objectives
40.2.1 Identify the body’s nonspecific defenses against
invading pathogens.
40.2.2 Describe the function of the
immune system.
W
Key Concepts
• What is the function of the
immune system?
• What are the body’s nonspecific defenses against
invading pathogens?
Vocabulary
Vocabulary Preview
Explain that immunity means resistance to infection. Then, challenge
students to fill in the blanks in the
following statements with the correct
Vocabulary terms containing the
word immunity. Immune response
outside cells, involving antibodies,
is called
immunity. (humoral)
Immunity involving killer T cells is
called
immunity. (cellmediated) When the body is injected
with antibodies, it is called
immunity. (passive) When the body
makes antibodies in response to an
antigen, it is called
immunity. (active) After students read the
section, they should check to see if
their answers were correct.
immunity
inflammatory response
fever
interferon
immune response
antigen
humoral immunity
cell-mediated immunity
antibody
vaccination
active immunity
passive immunity
Reading Strategy:
Finding Main Ideas Before
you read, skim the section to
identify the key ideas. Then,
carefully read the section,
making a list of supporting
details for each main idea.
Nonspecific Defenses
Nonspecific defenses do not discriminate between one threat and
another. These defenses include physical and chemical barriers.
First Line of Defense The function of the first line of
defense is to keep pathogens out of the body. This role is carried
out by skin, mucus, sweat, and tears.
Your body’s most
important nonspecific defense is the skin. Very few
pathogens can penetrate the layers of dead cells at the skin’s
surface. The importance of the skin as a barrier against infection becomes obvious as soon as the skin is broken. When that
happens, pathogens can enter your body and multiply. As they
grow, they cause the symptoms of an infection, such as swelling,
redness, and pain.
Many secretions of the body, including mucus, saliva, and
tears, contain lysozyme, an enzyme that breaks down the cell
walls of many bacteria. In addition, oil and sweat glands
in the skin produce an acidic environment that kills many
bacteria.
Reading Strategy
Have students preview the section by
studying the figures and reading the
captions.
2 INSTRUCT
Nonspecific Defenses
Build Science Skills
Applying Concepts Ask: If you eat
food that contains bacteria, which
nonspecific defenses will help protect your body from illness?
(Lysozyme in saliva and stomach acid
and digestive enzymes in the stomach)
왗 Figure 40–6
The immune system fights infection. The
production of mucus is one of your body’s defenses. Pathogens can
get trapped in mucus the way the long brown strand of dirt shown in
the micrograph is trapped.
(magnification: 1100⫻)
SECTION RESOURCES
Technology:
• Laboratory Manual B, Chapter 40 Lab
• Teaching Resources, Section Review 40–2,
Save
Chapter 40 Real-World Lab
e
• Reading and Study Workbook A,
Section 40–2
• Adapted Reading and Study Workbook B,
Section 40–2
• Lesson Plans, Section 40–2
• iText, Section 40–2
• Animated Biological Concepts Videotape
Library, 44 Inflammatory Response,
45 Humoral Immunity, 46 Cell-Mediated
Immunity
• Transparencies Plus, Section 40–2
Tim
Print:
Chapter 40
r
1036
ith pathogens all around us, it might seem like a miracle
that you aren’t sick all of the time. There’s a reason, of
course, why most of us enjoy good health. Our bodies have a
protective system—a series of defenses that guard against
disease.
The immune system is the body’s main defense against
pathogens. The immune system recognizes, attacks, destroys,
and “remembers” each type of pathogen that enters the body. It
does this by producing specialized cells that inactivate
pathogens. For each kind of pathogen, the immune system
produces cells that are specific to that pathogen.
The
function of the immune system is to fight infection
through the production of cells that inactivate foreign
substances or cells. This process is called immunity.
The immune system includes two general categories of
defense mechanisms against infection: nonspecific defenses and
specific defenses. Nonspecific defenses are like the fortress walls
of the system. They guard against infections by keeping most
things out of the body. Specific defenses work like security
guards. They track down harmful pathogens that have managed
to break through the body’s nonspecific defenses.
Demonstration
Use a microprojector and a drop of
pond water on a slide to show students how amoebas feed. Point out
the amoebas on the slide. As students watch their activity, ask: What
do amoebas do to consume their
prey? (They engulf, or surround, their
prey.) Explain that phagocytes engulf
bacteria and other pathogens in the
same way.
Wound
Skin
Phagocytes move into
the area and engulf the
bacteria and cell debris
Bacteria enter
the wound
Make Connections
Capillary
Pathogens can also enter your body through other body
openings, including your mouth and nose. Your body has other
nonspecific defenses that protect these openings. Mucus in your
nose and throat helps to trap pathogens. The cilia that line your
nose and throat help to push pathogens away from your lungs.
Stomach acid and digestive enzymes destroy many pathogens
that make their way to your stomach.
왖 Figure 40–7
The inflammatory response is a nonspecific
defense reaction to tissue damage caused by injury or infection.
When pathogens enter the body,
phagocytes move into the area and
engulf the pathogens. In addition,
platelets and clotting factors leak
from the capillaries.
Second Line of Defense If pathogens do manage to enter
your body, they may multiply quickly, releasing toxins into your
tissues. When this happens, the inflammatory response —a
second line of defense—is activated.
The inflammatory
response is a nonspecific defense reaction to tissue
damage caused by injury or infection. When pathogens are
detected, the immune system produces millions of white blood
cells, which fight the infection. Blood vessels near the wound
expand, and white blood cells move from the vessels to enter the
infected tissues. Many of these white blood cells are phagocytes,
which engulf and destroy bacteria. The infected tissue may
become swollen and painful. The inflammatory response is
summarized in Figure 40–7.
The immune system also releases chemicals that increase the
core body temperature. You may have experienced this elevated
body temperature, called a fever. The increased body temperature is advantageous because many pathogens can survive only
within a narrow temperature range. An elevated temperature
slows down or stops the growth of such pathogens. The higher
body temperature also increases the heart rate so that the white
blood cells get to the site of infection faster. Physicians know that
a fever and an increased number of white blood cells are two
indications that the body is hard at work fighting infection.
What is the role of phagocytes in the inflammatory
Health Science Explain that since
interferons were discovered in 1957,
doctors have been excited about the
possibility of using them to prevent
disease. In 1980, an interferon
became the first biopharmaceutical
to be successfully mass-produced
using genetic engineering. Mass production made interferons available
for research and clinical purposes.
Challenge interested students to find
out the results of interferon research
since 1980 and report to the class on
what they learn. (Students will find
that interferons show promise against
many viral diseases and some cancers.)
Macrophage means a large cell that
eats or engulfs.
Phagocyte comes from the
Greek phag, meaning “eat,” and
kutos, meaning “cell.” Thus, a
phagocyte is a cell that eats or
engulfs. If the Greek prefix
macro- means “large,” what
might the word macrophage
mean?
response?
Inclusion/Special Needs
The material in this section may be difficult for
some students to understand. Encourage them to
focus mainly on the figures and captions. Name
the processes that are illustrated in Figures 40–7
through 40–10. For each figure, describe the
process, and have students follow through the
diagram and read the labels as you do. Urge students to ask questions about each process as you
describe it.
Advanced Learners
Have students who are gifted writers create a
story about nonspecific defenses. Their stories
should take the point of view of a pathogen and
correctly portray the action and order of the nonspecific defenses the pathogen must overcome
when it enters the body. Urge students to read
their work to the class. Have other students
identify the nonspecific defenses as they are
described in the stories.
Answer to . . .
Phagocytes engulf and
destroy bacteria.
The Immune System and Disease
1037
40–2 (continued)
Interferon When viruses enter the body, the body sometimes
reacts in a different way. Sometimes, virus-infected cells produce a
group of proteins that help other cells resist viral infection.
Scientists named these proteins interferons because they “interfere” with the growth of the virus. Interferons inhibit the synthesis
of viral proteins in infected cells and help block viral replication.
This process slows down the progress of infection and often gives
the specific defenses of the immune system time to respond.
N S TA
NS TA
Download a worksheet on
the immune system for students to
complete, and find additional
teacher support from NSTA
SciLinks.
For: Links on the
immune system
Visit: www.SciLinks.org
Web Code: cbn-0402
Specific Defenses
If a pathogen is able to get past the body’s nonspecific defenses,
the immune system reacts with a series of specific defenses that
attack the particular disease-causing agent. These defenses are
called the immune response. A substance that triggers this
response is known as an antigen. Viruses, bacteria, and other
pathogens may serve as antigens.
The cells of the immune system that recognize specific
antigens are two types of lymphocytes: B lymphocytes (B cells)
and T lymphocytes (T cells). B cells provide immunity against
antigens and pathogens in the body fluids. This process is called
humoral immunity. T cells provide a defense against abnormal cells and pathogens inside living cells. This process is called
cell-mediated immunity.
Specific Defenses
Use Visuals
Figure 40– 8 Point out that the
drawings are greatly simplified
abstractions of what are in reality
complex molecules. Make sure students realize that the drawing on the
right is just an enlargement of the
drawing on the left with the antigens
removed, making the antigenbinding sites easier to see.
Humoral Immunity When a pathogen invades the body, its
antigens are recognized by a small fraction of the body’s B cells.
These B cells grow and divide rapidly, producing large numbers
of plasma cells and memory B cells.
Plasma cells release antibodies. Antibodies are proteins
that recognize and bind to antigens. The antibodies are carried
in the bloodstream to attack the pathogen that is causing the
infection. As the antibodies overcome the infection, the plasma
cells die out and stop producing antibodies.
Once the body has been exposed to a pathogen, millions of
memory B cells remain capable of producing antibodies
specific to that pathogen. These memory B cells greatly
reduce the chance that the disease could develop a second
time. If the same antigen enters the body a second time, a
secondary response occurs. The memory B cells divide rapidly, forming new plasma cells. The plasma cells produce the
specific antibodies needed to destroy the pathogen.
Demonstration
Demonstrate to students how the
immune system responds to specific
pathogens. Select ten student volunteers. Have the students use poster
board, string, scissors, and markers to
make five signs (attached to string so
they can be worn around the neck)
labeled: Whooping Cough, Strep
Throat, Bacterial Pneumonia,
Diphtheria, and Tetanus. Also have
the students cut five squares of
poster board in half, each one in a
different way so that it forms two
unique pieces that fit together like
pieces of a jigsaw puzzle but that do
not fit with any of the other pieces.
Then, assign five of the students to
wear the signs and play the roles of
bacteria. Give each of them one half
of a puzzle, and have them line up at
the back of the room. Assign the
remaining five students to be B cells,
give them the other halves of the
puzzles, and have them line up at the
front of the room. Finally, tell the
bacteria to “invade” the room and
the B cells to “attack” the bacterium
that has the matching puzzle piece.
When a B cell finds the bacterium
that is its match, both should sit
down. After the last pair sits down,
ask: What do the puzzle pieces carried by the “bacteria” represent?
(Antigens) What do the puzzle
pieces carried by the “B cells”
represent? (Antibodies)
1038
Chapter 40
왔 Figure 40–8 An antibody
molecule has two identical antigenbinding sites. It is at these sites
that one or two specific antigens
bind to the antibody. Applying
Concepts How do antibodies help
in the immune response?
Antigen-binding sites
Antibody Structure As shown in Figure 40–8, an antiAntigen
Antibody
body is shaped like the letter Y and has two identical antigenbinding sites. Small differences in the amino acids affect the
shapes of the binding sites. The shape of the binding site
makes it possible for the antibody to recognize a specific
antigen with a complementary shape. The different shapes
give antibodies the ability to recognize a large variety of
antigens. It is estimated that a healthy adult can produce
about 100 million different types of antibodies.
TEACHER TO TEACHER
After students have learned about nonspecific
defenses and before they read about specific
defenses, I challenge them to design a cell or
cells to attack a particular pathogen. I have students work in groups and use a cold virus as the
pathogen. Then, I have each group share its
results by listing the cell specifications on the
board and explaining them to the class. After the
activity, as students read about specific defenses,
they can see how their design compares with the
“real thing.” This activity helps students anticipate the complexity of specific defense cells
before they actually read about them.
—Ruth Gleicher
Biology Teacher
Niles West High School
Skokie, IL
Make Connections
FIGURE 40 –9 HUMORAL IMMUNITY
Chemistry Explain that the stem of
each Y-shaped antibody is essentially
the same but the end of each arm
has a region that is unique. In this
area, two polypeptide chains are
folded to form a groovelike cavity
that is complementary to the contour
and electric charge of a particular
antigen. Ask: How do these differences in the antigen-binding sites
of antibodies occur? (The genes that
code for the two polypeptide chains
rearrange themselves in slightly different ways in each B cell.)
Once the body has been exposed
to a pathogen, it remains capable
of producing specific antibodies
to that pathogen. The reaction to
a second infection by the same
pathogen is much faster.
Antigen
Antigen
binding to
B cell
B cell
Some B cells develop
into plasma cells.
Plasma cells produce
antibodies that are
released into the
bloodstream.
B cells grow and
divide rapidly.
Some B cells
develop into
memory
B cells.
Use Visuals
Figure 40–9 Have students follow
the flowchart as you read the captions, starting with the first step and
ending with the last. Make sure students can identify the cells involved
in each step.
Plasma cell
Memory B cell
Production of many
more plasma cells
and antibodies
Second exposure
to same antigen
Production of
memory B cells
FACTS AND FIGURES
Phagocyte power
Phagocytes develop from stem cells in bone marrow. Types of phagocytes include neutrophils,
eosinophils, and monocytes, which mature into
macrophages. Phagocytes are drawn by altered
chemical gradients into an area of damaged or
invaded tissues. There, they engulf and destroy
pathogens and other foreign substances by endocytosis. In endocytosis, the plasma membrane of
the phagocyte encloses the pathogen at or near
the cell surface of the phagocyte. Then, the membrane pinches off to form a closed endocytic
vesicle around the pathogen. The endocytic vesicle provides a “traveling compartment” that
enables the pathogen to be transported into the
cytoplasm of the phagocyte. Once inside the cytoplasm, the endocytic vesicle fuses with lysosomes,
and the pathogen is destroyed.
Answer to . . .
Figure 40–8 By binding to antigens
on the surfaces of pathogens and linking pathogens together in a large
mass, which attracts phagocytes and
makes engulfment easier
The Immune System and Disease
1039
40–2 (continued)
Use Visuals
Figure 40–10 Check students’ comprehension of the flowchart by
asking: What causes a T cell to
become a helper T cell? (Activation
by a macrophage) What causes a
killer T cell to attack the infected
cell? (Activation by a helper T cell)
Build Science Skills
Applying Concepts Point out that
cell-mediated immunity is particularly
important for diseases caused by
eukaryotic pathogens. Ask: Which
pathogens are eukaryotic, and
what are some of the diseases they
cause? (Protists, fungi, and worms are
eukaryotic pathogens. Some of the diseases they cause include malaria, beef
tapeworm, and athlete’s foot.)
Macrophage
T cell binds
to activated
macrophage.
Antigens are
displayed on
surface of
macrophage.
T cell, activated
by macrophage,
becomes a
helper T cell.
T Cell
Helper
T Cell
Helper T cell
activates killer
T cells and
B cells.
Killer
T Cell
Infected
Cell
Killer T cells bind
to infected cells,
disrupting their cell
membranes and
destroying them.
Cell-Mediated Immunity The body’s
primary defense against its own cells when they
have become cancerous or infected by viruses is
known as cell-mediated immunity. Cell-mediated
immunity is also important in fighting infection
caused by fungi and protists. When viruses or
other pathogens get inside living cells, antibodies
alone cannot destroy them.
During cell-mediated immunity, T cells divide
and differentiate into killer T cells (cytotoxic T
cells), helper T cells, suppressor T cells, and
memory T cells. Killer T cells track down and
destroy the bacteria, fungi, protozoan, or foreign
tissue that contains the antigen. Helper T cells
produce memory T cells. The memory T cells, like
the memory B cells, will cause a secondary
response if the same antigen enters the body
again. As the pathogenic cells are brought under
control, suppressor T cells release substances
that shut down the killer T cells. The process
of cell-mediated immunity is summarized in
Figure 40–10.
What is cell-mediated immunity?
Transplants Although killer T cells are
helpful in the immune system, they make the
acceptance of organ transplants difficult. Body
cells have marker proteins on their surfaces that
allow the immune system to recognize the cells.
If an organ was going to be transplanted into
your body, your immune system would recognize
the transported organ as foreign and attack it.
Your immune system damages and destroys the
transplanted organ. This process is known as
rejection. To prevent organ rejection, doctors
search for a donor whose cell markers are nearly
identical to the cell markers of the recipient.
Recipients must take drugs—usually for the rest
of their lives—to suppress the cell-mediated
immune response.
Figure 40–10 During the cell-mediated immune
response, T cells provide defense against abnormal
cells and pathogens inside living cells. The yellow
objects in the scanning electron micrograph are killer
T cells attacking a cancer cell. Comparing and
Contrasting How are humoral immunity and cellmediated immunity similar? How are they different?
HISTORY OF SCIENCE
Cells that eat cells
A significant step in understanding the immune
system came in 1883 with the work of Elie
Metchnikoff. The Russian biologist was researching the cause of inflammation in animals, using
sea star larvae as research subjects because they
have transparent bodies that allow for clear observation of internal processes. Wondering how the
organism’s cells would react to a foreign body,
1040
Chapter 40
Metchnikoff plucked a thorn from one of the
roses in his rose garden and plunged it into a
larva. A day later, he noticed the thorn was surrounded by a swarm of cells. Through further
study, he identified similar cells in humans, specifically the white blood cells in pus. He recognized
that these cells are able to digest foreign particles,
and he named the cells phagocytes, from the
Greek words meaning “to eat” and “cells.”
How does cell-mediated
immunity work?
Materials 3 red balloons; 3 yellow balloons; 3
light-blue balloons; red, purple, and light-blue
adhesive notes; toothpick
Procedure
1. Partially inflate and tie the balloons. The balloons
represent pathogens. The different colors represent
different surface antigens. Put the inflated balloons
on the table.
2. The adhesive notes represent antibodies that can
bind to antigens on the surface of a pathogen of
the same color. Use the adhesive notes to model
the binding of antibodies to antigens on
pathogens.
3. The toothpick represents a killer T cell. Use
the toothpick to burst any balloons marked by
adhesive notes.
Analyze and Conclude
1. Using Models How did you model the binding of
antibodies to matching antigens in step 2?
2. Using Models What signals a killer T cell to attack
a pathogen?
3. Using Models What do the yellow balloons and
purple adhesive notes represent in the model?
Acquired Immunity
More than 200 years ago, the English physician Edward Jenner
wondered if it might be possible to produce immunity against
one of the deadliest diseases of the day—smallpox. Jenner knew
that a mild disease called cowpox was often contracted by
milkmaids. Jenner observed that the milkmaids who contracted
cowpox developed an immunity to smallpox. Was there a way, he
wondered, to deliberately infect people with cowpox and thus
protect them from getting the more serious disease of smallpox?
To answer this question, Jenner took fluid from one of the
sores of a cowpox patient and put the fluid into a small cut that
he made on the arm of a young farm boy named Jamie Phipps. As
expected, Jamie developed a mild cowpox infection. Two months
later, Jenner performed a daring experiment. He injected Jamie
with fluid from a smallpox infection. Fortunately for Jamie, the
experiment was a success—the boy did not develop smallpox. His
cowpox infection had made him immune to smallpox.
Acquired Immunity
Use Community Resources
Have students contact a pediatrician’s
office or their local health department to obtain a schedule of
recommended vaccinations from
birth to adulthood. Then, have students create a poster to convey the
information in an eye-catching way.
If possible, arrange to have their
posters displayed at a location in the
community where families with
young children are likely to see them,
for example, at a public library or
preschool.
Active Immunity The injection of a weakened form of a
pathogen to produce immunity is known as a vaccination.
Vacca is the Latin word for “cow,” reflecting the history of
Jenner’s first vaccination experiment. Today, more than 20
serious human diseases can be prevented by vaccination. Like
early vaccines, modern vaccines stimulate the immune system
to create millions of plasma cells ready to produce specific types
of antibodies.
FACTS AND FIGURES
So many flu strains, so little time
Influenza, or flu, is caused by an airborne virus. It
occurs in periodic epidemics, which sometimes
have a high death toll. For example, a 1968 flu
epidemic killed almost 700,000 people worldwide
in just six weeks. Scientists have developed fairly
effective flu vaccines, but it takes at least six
months to prepare a vaccine once the particular
Objective Students will be able to
use a model to determine how cellmediated immunity works.
Skill Focus Using Models
Materials 3 red balloons; 3 yellow
balloons; 3 light-blue balloons; red,
purple, and light-blue adhesive
notes; toothpick
Time 15 minutes
Advance Prep To save time, you
can inflate the balloons before class.
Strategy You might want to have
students work in pairs on this lab. If
you do, make sure each student
individually answers the Analyze and
Conclude questions.
Expected Outcome Students
should break only the red and lightblue balloons.
Analyze and Conclude
1. The binding of antibodies to
matching antigens was modeled by
attaching colored adhesive notes to
balloons of the same color.
2. An antibody bound to an antigen
on the surface of a pathogen signals
a killer T cell to attack the pathogen.
3. In the model, the yellow balloons
represent pathogens for which there
are no antibodies, and the purple
adhesive notes represent antibodies
for which there are no pathogens.
strain of flu virus is isolated. Mutations occur frequently in the flu virus, and new strains appear
every couple of years, so scientists cannot predict
for certain which strain of flu virus will strike in a
given year. Therefore, a vaccine that is effective
against one year’s strain of flu virus may prove
useless against the next year’s strain.
Answers to . . .
Immunity in which killer
T cells destroy infected cells
Figure 40–10 Both are specific
defenses. In humoral immunity, B cells
produce antibodies against the
pathogen. In cell-mediated immunity,
killer T cells attack infected cells.
The Immune System and Disease
1041
The type of immunity produced by the body’s
reaction to a vaccine is known as active immunity.
Active immunity appears after exposure to an antigen, as a result of the immune response. Active
immunity may develop as a result of natural exposure
to an antigen (fighting an infection) or from deliberate
exposure to the antigen (through a vaccine).
40–2 (continued)
Build Science Skills
Inferring Ask: Why does passive
immunity last for only a few weeks
or months? (Passive immunity occurs
when antibodies are injected into the
blood or ingested in milk. Because antigens are not included with the
antibodies, the immune system does
not “learn” how to make the antibody.
Once the antibodies are destroyed, the
person is no longer immune.)
3 ASSESS
왖 Figure 40–11 Vaccines stimulate the immune system to produce
plasma cells. Applying Concepts
What type of immunity do vaccines
produce?
Evaluate Understanding
Have students make a concept map
entitled “Defenses Against Pathogens,”
using the following terms: nonspecific defenses, specific defenses,
humoral immunity, cell-mediated
immunity, first-line defenses, and
second-line defenses.
Reteach
Play a quiz game in which you read
definitions of the Vocabulary terms
and student contestants try to identify the terms from the definitions.
Passive Immunity In active immunity, the body
makes its own antibodies in response to an antigen.
The body can also be temporarily protected from
disease in another way. If antibodies produced by
other animals against a pathogen are injected into
the bloodstream, the antibodies produce a passive
immunity against the pathogen. Passive immunity lasts only a
short time because eventually the body destroys the foreign
antibodies.
Like active immunity, passive immunity can develop naturally or by deliberate exposure. One kind of natural immunity
occurs when antibodies produced by the mother are passed to
the fetus during development (across the placenta) or in early
infancy through breast milk. This immunity protects a child
against most infectious diseases for the first few months of its
life, or longer if the infant is breast-fed.
Sometimes, antibodies are administered to fight infection or
prevent disease. For example, travelers to certain regions of the
world are given vaccines before leaving home. These vaccines
may contain antibodies against tropical diseases, such as
malaria. People who have been bitten by rabid animals are
injected with antibodies that attack the rabies virus. This is
another example of passive immunization.
40–2 Section Assessment
Students should find that medical
professionals and public health
officials strongly support vaccinations because they prevent
epidemic outbreaks of disease and
prevent deaths. However, vaccinations cause side effects in a
number of people. For this reason,
some people do not think vaccinations should be mandatory. Assign
several students to represent each
viewpoint. Assign a moderator
and a timekeeper to ensure that
each side has the same amount of
time to present its views.
1.
Key Concept Describe the
body’s nonspecific defenses
against pathogens.
2.
Key Concept Describe the
function of the immune system.
3. How do interferons protect the
body against viruses?
4. How are antigens related to
antibodies?
5. Critical Thinking Comparing
and Contrasting How are
active and passive immunity
similar? How are they different?
Conducting a Debate
Getting vaccinated is much
safer than getting the disease
that the vaccine prevents.
However, like any drug, vaccines are capable of causing
serious problems. Interview
five people about their
thoughts on vaccinations. As
a class, arrange a debate that
addresses both the benefits
and risks of vaccinations.
40–2 Section Assessment
If your class subscribes to the iText,
use it to review the Key Concepts in
Section 40–2.
Answer to . . .
Figure 40–11 Active immunity
1042
Chapter 40
1. Unbroken skin is a barrier to pathogens. If
pathogens penetrate the skin, they cause an
inflammatory response. Pathogens that
enter through the mouth or nose are
trapped in mucus, or attacked by lysozyme,
digestive enzymes, and stomach acid.
Viruses trigger the production of interferons.
2. To protect the body against pathogens
3. Interferons inhibit the progress of viral infections, which may give specific defenses time
to respond.
4. An antigen is a substance on the surface of a
pathogen that triggers an immune response.
Antibodies are molecules that are custommade to bind to specific antigens.
5. They both provide antibodies against a specific pathogen. Active immunity is often permanent; passive immunity is temporary.
40–3 Immune System Disorders
Section 40–3
1 FOCUS
A
lthough the immune system defends the body from a wide
range of pathogens, sometimes disorders occur in the
immune system itself. There are three different types of disorders. These disorders include allergies, autoimmune diseases,
and immunodeficiency diseases.
Allergies
Objectives
Key Concepts
• What is an autoimmune
disease?
• How can AIDS be prevented?
Vocabulary
The most common overreactions of the immune system to
antigens are known as allergies. Common allergies include
those to pollen, dust, mold, and bee stings. Antigens that cause
allergic reactions are called allergens. Some common allergens
are shown in Figure 40 –12.
When allergy-causing antigens enter the body, they attach
themselves to mast cells. Mast cells are specialized immune
system cells that initiate the inflammatory response. The activated mast cells release chemicals known as histamines.
Histamines increase the flow of blood and fluids to the surrounding area. They also increase mucus production in the respiratory
system. The increased mucus production brings on the sneezing,
watery eyes, runny nose, and other irritations that make a
person with allergies so uncomfortable. If you have allergies, you
may have taken antihistamines. Antihistamines are drugs that
are used to counteract the effects of histamines.
allergy
histamine
asthma
40.3.1 State what happens when
the immune system overreacts.
40.3.2 Explain what an autoimmune disease is.
40.3.3 Describe how HIV is transmitted and affects the
immune system.
Reading Strategy:
Using Prior Knowledge
Do you or someone you know
have allergies? As you read this
section, use what you learn to
explain the causes and symptoms of allergies.
Vocabulary Preview
Suggest that students scan the section for the highlighted, boldface
Vocabulary terms and write a definition for each term based on the
information in the text.
Reading Strategy
Have students read the figure captions and find the terms allergens,
autoimmune disease, and retrovirus.
Challenge students to define the
terms based on the information in
the captions.
Figure 40–12 Common allergens include ragweed pollen, dust, and
dust mites. In the SEM of the dust ball, notice the insect parts, gray spider
webbing, and other dirt. Dust mites live in furniture, mattresses, and even
pillows. Inferring Why do you think it is recommended that people wash
their bed coverings in hot water?
2 INSTRUCT
Allergies
Build Science Skills
Ragweed Pollen (magnification: 770⫻)
Dust Ball (magnification: 760⫻)
Dust Mite (magnification: 900⫻)
SECTION RESOURCES
• Reading and Study Workbook A,
Section 40–3
Save
• Adapted Reading and Study Workbook
B,
e
Section 40–3
• Teaching Resources, Section Review 40–3
• Lesson Plans, Section 40–3
• iText, Section 40–3
• Transparencies Plus, Section 40–3
Tim
Technology:
r
Print:
Using Tables and Graphs Have
students design a simple allergy
questionnaire that includes questions
on whether the subject has allergies
and which allergens are known or
thought to be responsible. Then,
have each student administer the
questionnaire to at least five people,
such as family members and neighbors, and summarize the results in a
table that shows the number of people with allergies and the number
allergic to each allergen. Assign a few
students to pool the results for the
whole class, and use the data to create a bar graph showing the
proportion of the total sample
affected by the top three allergens.
Answer to . . .
Figure 40–12 To kill dust mites that
can cause allergies
The Immune System and Disease
1043
Asthma
40–3 (continued)
Asthma
Use Community Resources
Arrange to have a nurse, physician’s
assistant, or other medical professional visit the class. Ask the visitor to
explain the various causes of asthma
as well as the different types of medications used to treat asthma.
Encourage students to ask any questions they might have.
Autoimmune
Diseases
Make Connections
Health Science Point out that there
are many autoimmune diseases in
addition to those listed in the text.
Another relatively common example
is systemic lupus erythematosus
(SLE). In this disease, the immune
system attacks normal connective tissue, and this leads to inflammation
and pain in the joints, among other
symptoms.
왔 Figure 40–13
When the
immune system makes a mistake
and attacks the body’s own cells,
it produces an autoimmune
disease. Multiple sclerosis is one
example of an autoimmune disease
in which axons in the optic nerve,
brain, or spinal cord are affected.
Symptoms of multiple sclerosis
include problems with balance and
motor coordination.
Some allergic reactions can create a dangerous condition called
asthma. Asthma is a chronic respiratory disease in which the
air passages become narrower than normal. This narrowing of
the air passages causes wheezing, coughing, and difficulty in
breathing. Many factors, including both heredity and environment, play a role in the onset of the symptoms of asthma.
Asthma is a leading cause of serious illness among children,
and can be a life-threatening disease. If treatment is not started
early enough or if medications are not taken properly, asthma
can lead to permanent damage or destruction of lung tissue.
Asthma attacks can be triggered by respiratory infections,
exercise, emotional stress, and certain medications. Other
triggers include cold air, pollen, dust, tobacco smoke, pollution,
molds, and pet dander.
There is no cure for asthma; however, people who have
asthma can sometimes control the condition. If the attacks are
caused by an allergy, a series of tests can identify what substances cause the problem. Medications are sometimes used to
relieve the symptoms of asthma. Often, these medications relax
the smooth muscles around the airways, making breathing easier.
What happens in the lungs during an asthma attack?
Autoimmune Diseases
The immune system could not defend your body against a host
of invading pathogens unless it was able to distinguish those
pathogens from the cells and tissues that are part of your body.
In other words, the immune system usually has the ability to
distinguish “self” from “nonself.”
When the immune
system makes a mistake and attacks the body’s own cells,
it produces an autoimmune disease. In an autoimmune
disease, the immune system produces “antiself” antibodies.
Some examples of autoimmune diseases include Type I
diabetes, rheumatoid arthritis, myasthenia gravis, and multiple
sclerosis (MS). In Type I diabetes, antibodies attack the
insulin-producing cells of the pancreas. In rheumatoid arthritis,
antibodies attack connective tissues around the joints. In myasthenia gravis, antibodies attack neuromuscular junctions.
Multiple sclerosis is an autoimmune disease in which antibodies
destroy the functions of the neurons in the brain and spinal cord.
Some autoimmune diseases are treated with medications
that alleviate specific symptoms. For example, people who have
Type I diabetes can be given insulin injections. Other autoimmune diseases are treated with medications that suppress the
immune response. However, these medications also affect the
normal immune response against pathogens, so this type of
therapy is not used often or is carefully monitored. As
researchers find out more about autoimmune diseases, they
hope to develop more effective treatments.
SUPPORT FOR ENGLISH LANGUAGE LEARNERS
Vocabulary: Word Analysis
Beginning Write disease and antibiotic on the
board. Then, rewrite each word as a separate
prefix and base, i.e., dis- and ease, and antiand biotic. Explain that the two prefixes, disand anti-, can have similar meanings; they can
mean “against,” or “opposing.” Explain that
ease can mean “comfort” or “wellness,” and
that disease is the opposite of comfort or wellness. Similarly, biotic comes from a word
1044
Chapter 40
meaning “life,” and an antibiotic acts against
harmful living things, specifically bacteria.
Discuss other words with these prefixes, such
as disagree, discomfort, and antifreeze.
Intermediate After the beginning-level activity,
have the students form a collaborative writing
group to write sentences using each term.
Have a volunteer from the group read the
sentences.
AIDS, an
Immunodeficiency
Disease
AIDS, an Immunodeficiency Disease
Another type of immune system disorder is immunodeficiency
disease. In one type of immunodeficiency disease, the immune
system fails to develop normally. A second type of immunodeficiency disease is AIDS. AIDS results from a viral infection that
destroys helper T cells. As the number of helper T cells declines,
the normal immune response breaks down.
During the late 1970s, some physicians in Europe and the
United States were bewildered. Some of their patients were
dying from infections produced by microorganisms that didn’t
normally cause disease. Previously healthy people began to
suffer from unusual illnesses such as Pneumocystis carinii
(a kind of pneumonia), Kaposi’s sarcoma (a rare form of skin
cancer), and severe fungal infections of the mouth and throat.
Normally, such infections are prevented by the immune system.
Individual doctors realized that the symptoms were a signal that
the immune systems of their patients had been weakened.
Some doctors recognized that these illnesses were actually
symptoms of a new disease. Doctors in Los Angeles suggested
the name AIDS—for acquired immune deficiency syndrome. As
more cases appeared, researchers realized that this “syndrome”
was actually an infectious disease caused by a pathogen that
was unknown to the scientific community.
The Virus That Causes AIDS In 1983, researchers identified
the cause of AIDS—a virus that they named HIV for human
immunodeficiency virus. HIV is a retrovirus—a virus that carries
its genetic information in RNA, rather than DNA. HIV turned out
to be a deadly and efficient virus for two reasons. First, HIV
evades the defenses of the immune system. Second, HIV attacks
key cells in the immune system, destroying the body’s defenses
and leaving the body with no protection against other pathogens.
Among HIV’s main targets are the helper T cells. When the
HIV virus attacks a helper T cell, it attaches to receptor molecules on the cell membrane. This allows the virus to enter the
cell, as shown in Figure 40 –14. Once the viral core is inside the
cell, it forces the host cell to make DNA copies of the virus’s
RNA. Some of those copies insert themselves into host cell DNA
and stay there permanently. Other copies remain in the cytoplasm. The viral DNA may remain inactive in the host cell for
varying periods of time. When activated, it directs the production of viral RNA and proteins that are assembled into new
virus particles. These viruses eventually leave the infected cell
and infect new cells. The immune system produces antibodies
for HIV. Unfortunately, these antibodies are not effective in
stopping the progression of the disease.
Despite the production of antibodies, HIV destroys everincreasing numbers of T cells, crippling the immune system. By
counting the number of the helper T cells, the progression of
HIV infection can be monitored. The fewer helper T cells, the
more advanced the disease.
Address Misconceptions
(magnification: about 5000⫻)
왖 Figure 40–14 HIV is an example
of a retrovirus, which contains RNA as
its genetic material. Retroviruses get
their name because their genetic
information is first copied backward
from RNA to DNA. Interpreting
Graphics In the micrograph, what
type of blood cell are the red HIV
particles attacking?
Point out that the terms HIV infection
and AIDS are often used interchangeably. Explain that a person with an
HIV infection may or may not have
symptoms of the disease AIDS. In
fact, an infected person may have no
idea that he or she is even infected.
Add that a person is diagnosed with
AIDS only after the HIV infection has
caused immune system damage leading to specific unusual infections,
such as fungal infections in the
mouth and rare forms of skin cancer.
The clinical definition of AIDS
includes a helper T cell count of
200/mm3 of blood or lower.
Build Science Skills
Applying Concepts Check students’ comprehension of the way HIV
causes disease. Ask: How does HIV
“trick” helper T cells into making
new copies of HIV? (HIV forces host T
cells to make DNA copies of viral RNA.
The DNA, in turn, directs the production of new viral RNA and proteins that
are assembled into new virus particles.)
Ask: How does HIV enter the central nervous system? (By hiding
inside certain blood cells)
Make Connections
Health Science Emphasize the
point that the symptoms of AIDS are
not caused directly by HIV but rather
by the damage HIV does to the
immune system. Explain that similar
symptoms are produced by other
causes of immune system damage or
dysfunction, including immunosuppressant drugs, which are given to
people who have organ transplants.
Answer to . . .
Smooth muscle contractions reduce the size of air passageways in the lungs and make breathing
very difficult.
Figure 40–14 White blood cell
The Immune System and Disease
1045
40–3 (continued)
Make Connections
Health Science Explain that HIV
infections can be detected with a
blood test for the presence of antibodies to HIV. A positive test
indicates that the antibodies are
present, and a negative test indicates
that the antibodies are not present.
Ask: What do you think a false negative result indicates? (That
antibodies are present but not detected
by the test) Point out that someone
who was very recently infected with
HIV might have a false negative
result because the immune system
has not yet produced enough antibodies to be detected in the blood.
Use Community Resources
Invite a professional who works with
people with AIDS to speak to the
class about the medical, emotional,
and financial consequences of living
with AIDS. Possible speakers might
include a public-health nurse, home
healthcare provider, or social worker.
Urge students to ask questions at the
end of the presentation.
FIGURE 40–15 HIV Infection
HIV travels through the bloodstream, where it binds to receptors on helper T cells. Once inside the cell, the virus
directs the cell to produce many new viruses. These new viruses are quickly released back into the bloodstream,
where they travel to new cells and destroy them.
1 Virus attaches to host cell membrane by
recognizing specific molecules on the cell surface.
Capsid
Viral
RNA
Envelope
Reverse
transcriptase
enzyme
Protein
coat
5 Viral mRNA
directs the host
cell to assemble
viral proteins.
1
Cytoplasm
Nucleus
cell membrane and
viral RNA enters the
cell.
3 Reverse transcriptase
uses viral RNA as a
template to make viral
DNA.
6 Capsids are
mRNA
2 Viral coat fuses with
5
DNA
3
2
6
4
assembled
around the viral
proteins and
RNA. The new
viruses bud off
from the host
cell membrane.
RNA
4 Viral DNA enters nucleus and
attaches to host chromosome.
There it may remain dormant or
begin directing the synthesis of
viral mRNA and RNA.
As the number of helper T cells decreases, the body becomes
more and more susceptible to other diseases. The diseases that
attack a person with a weakened immune system are called
opportunistic diseases.
Transmission of HIV Although HIV is a deadly disease, it is
not easily transmitted. It is not transmitted through casual
contact. HIV can only be transmitted through the exchange of
blood, semen, vaginal secretions, or breast milk.
There are four main ways that HIV can be transmitted:
• through any form of sexual intercourse with an infected person;
• through shared needles or syringes that are contaminated
with the blood of an infected person;
• through contact with blood or blood products of an infected
person; and
• from an infected mother to child, either during pregnancy,
during birth, or during breast-feeding.
FACTS AND FIGURES
HIV and helper T cells
Two types of HIV virus are known: HIV–1 and
HIV–2. In both types, each viral particle consists
of a protein core that surrounds its RNA and
several copies of the enzyme reverse transcriptase. When the virus attaches to a helper T cell,
the protein core becomes wrapped in a lipid
envelope derived from the T cell’s plasma membrane. The virus progresses from the surface of
the T cell to the cell interior. Once the virus is
1046
Chapter 40
inside the T cell, the reverse transcriptase uses
the viral RNA as a template for making DNA.
This DNA is then inserted into a chromosome of
the helper T cell. When the helper T cell is activated, it transcribes the HIV DNA along with
portions of its own DNA, thus inadvertently producing copies of viral RNA. The viral RNA is
translated into viral proteins, which assemble to
form new viruses that go on to infect and
destroy more helper T cells.
Preventing HIV Infection Fortunately you can choose
behaviors that will help you reduce your risk of becoming
infected with HIV.
The only no-risk behavior with
respect to HIV and AIDS is abstinence. Within a committed
sexual relationship such as marriage, sexual fidelity between
two uninfected partners presents the least risk of becoming
infected with HIV.
Avoiding drug use is also important for reducing the risk of
HIV infection. People who share contaminated needles to inject
themselves with drugs are at a high risk for contracting HIV.
People who have sex with drug abusers are also at high risk.
Before 1985, HIV was transmitted to some hemophiliacs and
surgical patients through transfusions of infected blood or blood
products. Such cases have been nearly eliminated by screening
the blood supply for HIV antibodies and by discouraging potentially infected individuals from donating blood.
Science News provides students
with the most current information
on infectious diseases and the
immune system.
For: Articles on infectious
diseases and the immune
system
Visit: PHSchool.com
Web Code: cbe-0400
3 ASSESS
Evaluate Understanding
Have students write a concise,
informative paragraph correctly using
each of the Vocabulary terms.
Can AIDS Be Cured? At present, there is no cure for AIDS.
However, progress has been made in developing drugs that
make it possible to survive HIV infection for years. Unfortunately, HIV mutates and evolves very rapidly. For this reason, the
virus has been able to evolve into many different strains that
are resistant to virtually all drugs used against them. Because
HIV evolves so rapidly, no one has developed a vaccine that
offers protection for any length of time.
At present, the only way to control the virus is to use expensive multidrug and multivitamin “cocktails” that fight the virus
in several ways. Thanks to these drugs, more HIV-infected
people are now living with HIV rather than dying from it.
Unfortunately, the knowledge that HIV can be treated
(though not cured) has given people the idea that HIV infection
is not as serious as it was a decade ago. In one year, more than
5 million people around the world became infected with HIV,
including roughly 800,000 people under the age of 15. That
same year, more than 3 million people around the world died of
AIDS, bringing the total number of deaths worldwide to more
than 20 million people.
Reteach
On the chalkboard or an overhead
transparency, make a concept map
with the following terms: immune
system disorders, allergies, autoimmune diseases, and AIDS. Call
on students to describe or give an
example of each type of disorder
listed in the concept map.
As a retrovirus, HIV transcribes
DNA from an RNA template,
which is the opposite of how most
other viruses replicate.
40–3 Section Assessment
Key Concept What
happens in an autoimmune
disease?
2.
Key Concept Describe the
various ways HIV is transmitted
from person to person.
3. What are the two main types of
immune system disorders?
1.
4. Why is it difficult for a person
with HIV to fight off infections?
5. Critical Thinking Applying
Concepts In treating asthma,
the first thing many physicians
do is ask patients to list times and
places they have experienced
asthmatic reactions. Why do you
think doctors do this?
If your class subscribes to the iText,
use it to review the Key Concepts in
Section 40–3.
Viral Replication
Compare the process of HIV
replication with that of other
viruses. You may wish to
review Figure 40–14 as well
as Chapter 19.
40–3 Section Assessment
1. In an autoimmune disease, the immune system attacks the body’s own cells.
2. Answers should include the four bulleted
items on page 1046.
3. Autoimmune diseases, and immunodeficiency
diseases
4. HIV kills off most of the helper T cells, which
greatly reduces the immune system’s
response to infection.
5. Doctors ask asthmatic patients where and
when their asthmatic reactions occur in
order to identify the antigens that trigger
the asthma attacks.
The Immune System and Disease
1047
Slowing a Worldwide Epidemic
Have students role-play a conference
about the issues. Assign students to
play the following roles: representative of an American pharmaceutical
company that manufactures anti-HIV
drugs; minister of health of an African
country; president of the World
Health Organization; and an expert
consultant on AIDS-prevention education. Students should research the
issues and then take one of the viewpoints presented in the feature. In
their role-playing, students should
present logical arguments, based on
their research, in support of the viewpoint they have chosen.
A
IDS is a threat on every continent in the
world, but nowhere has its effect been more
devastating than in Africa. Thirty million of the
world’s 42 million people infected with HIV live in
Africa. In some African countries, the HIV-infection
rate is as high as one in three people. Leaders from
around the world disagree on how the AIDS epidemic should be handled. Some argue that generic
drugs should be made available. Others argue that
the focus should be on AIDS prevention and education. Still others think that some money needs to
be spent on the millions of AIDS orphans.
The Viewpoints
Make Drugs More Affordable
Research and Decide
1. Students should list the options in
this feature as well as any additional
options they find through their
research.
2. Answers will vary depending on
how individuals choose to allocate
the money. Student answers should
include appropriate reasons and
explanations for their choices.
AIDS workers in Africa believe that more affordable drugs should be the top priority. HIV-infected
people in Africa do not have access to the advanced
medicines that people have in the United States. In
Africa, the use of antiviral drugs is not common.
Although the antiviral drugs do not cure AIDS,
they help prolong life as long as they are taken on
a regular basis. To increase access to these drugs,
activists are looking for generic drugs, which would
be lower in cost. Large pharmaceutical companies,
however, don’t like this idea because they say that
generic drugs violate the companies’ patents on
such antiviral drugs.
Spend Money for Prevention
Students can research the AIDS
epidemic on the site developed by
authors Ken Miller and Joe Levine.
Many people in HIV-infected populations do not
have basic knowledge about AIDS, including how
HIV is spread. Thus, what is needed is an intensive
program of public health education to stop the
spread of the virus. If prevention programs including education and counseling were available, the
incidence of new HIV infections could be reduced.
HIV-infection rate—that the number of orphans
could increase about 150 percent over the next ten
years. Because of this growing problem, a number
of people feel that some of the money used to fight
AIDS should be given to care for these orphans.
Research and Decide
1. Analyzing the Viewpoints To make an
informed decision, learn more about this issue
by consulting library or Internet resources.
Then, list the key arguments for each of the
viewpoints.
2. Forming Your Opinion Given limited resources to fight HIV, how would you decide the
allocation of those resources? Would you spend
all of the money on one area, or would you split
it up among the different areas? What are the
reasons for your decision?
Spend Money on AIDS Orphans
More than 11 million children have lost parents to
AIDS. Orphanages are overflowing with children
who have no one to look after them. It is expected
in Ethiopia—the country with the fastest-growing
For: Links from the authors
Visit: PHSchool.com
Web Code: cbe-0403
BACKGROUND
Putting HIV and AIDS in context
No one knows why HIV appeared suddenly in the
late 1970s, although most scientists believe it
originated in Africa. It could have been a virus in
monkeys that mutated and infected humans, but
it has never been isolated from any animal source.
In the United States and Europe, HIV has been
transmitted most often among male homosexuals
and intravenous drug users. In Africa, it has been
1048
Chapter 40
transmitted almost solely among heterosexuals.
Heterosexual transmission is also on the rise in
Latin America. Besides education and treatment,
a third way to possibly slow the AIDS epidemic is
through vaccination. Scientists have been working for years on a vaccine to prevent HIV
infection, but developing a vaccine has been difficult because HIV mutates rapidly. Nonetheless, a
vaccine may be available in the near future.
40–4 The Environment and Your Health
Section 40–4
1 FOCUS
Objectives
S
taying healthy involves more than the battles against
pathogens. You interact constantly with both living and
nonliving parts of your environment. Aspects of your environment that are important to health include the buildings in
which you live, the people with whom you share those spaces,
the air you breathe, the water you drink, and the food you eat.
Factors that have the potential to affect health in a negative
way are called risk factors. A risk factor is anything that
increases the chance of disease or injury. Both heredity (the
genes you carry) and environmental factors can affect your
health.
Environmental factors that can affect your
health include air and water quality, poisonous wastes in
landfills, and exposure to solar radiation.
Air Quality
The air you breathe comes into very close contact with your
delicate lung tissue and blood. It shouldn’t be surprising, therefore, that the quality of the air is very important to your health.
But what is meant by “air quality”? Air quality refers to the
number and concentrations of various gases present, as well as
the nature and amount of tiny particles suspended in the air.
Gases that are important to air quality include carbon monoxide
and ozone. Particles in the air include dust, pollen, or particulates produced by cars and trucks or the burning of coal. If the
concentration of these impurities gets too high, they can become
risk factors for various health problems.
Key Concepts
• What environmental factors
affect your health?
• How can you maintain your
health?
40.4.1 Identify environmental factors that affect your health.
40.4.2 Describe how you can maintain your health.
Vocabulary
risk factor
tumor
carcinogen
Vocabulary Preview
Reading Strategy:
Hypothesizing Before you
read, hypothesize about how
the environment can affect your
health. As you read, list evidence
that supports or rejects your
hypothesis.
Call students’ attention to the section
Vocabulary. Point out that risk factors
sometimes, but not always, involve
risky behaviors. Call on students to
give examples of both types of risk
factors. (Possible examples include
smoking cigarettes and sex or gender.)
Reading Strategy
왔Figure 40–16
Poor air
quality can affect your health. Smog
is a mixture of chemicals that appears
in the atmosphere as a gray-brown
haze. Smog is particularly dangerous
for people with respiratory conditions.
Carbon Monoxide Carbon monoxide (CO) is an odorless
gas produced when certain compounds are burned. Carbon
monoxide is found in automobile exhaust and cigarette smoke.
Carbon monoxide also can be produced by the furnace of a
heating system or by space heaters that burn fuel.
Recall that hemoglobin in red blood cells usually helps carry
oxygen to the cells of your body. If you inhale carbon monoxide,
that gas binds to hemoglobin, preventing it from carrying
oxygen. As a result, the body does not receive the oxygen it
needs. Overexposure to carbon monoxide can be fatal.
Ozone Ozone (O3), a highly reactive form of oxygen, is another
gas found in the air that is a potential risk factor when it occurs
at ground level. Ozone is produced by vehicle exhaust and
factory emissions. When the air is stagnant, ozone accumulates.
When ozone levels are high, you should limit your time outdoors
as much as possible, especially if you have a respiratory condition such as asthma, bronchitis, or emphysema.
Challenge students to predict what
each of the terms means before they
look for them in the section. Have
visual learners preview the section by
studying the figures and reading the
captions.
2 INSTRUCT
Build Science Skills
Applying Concepts Challenge students to identify ways that plants,
animals, and other people in their
environment might affect their health.
(Possible answers: Plants and plant pollens may cause allergies; animals are
vectors of Lyme disease and other illnesses; and people may behave violently
and injure or even kill other people.)
Air Quality
Make Connections
SECTION RESOURCES
• Teaching Resources, Section Review 40–4,
Enrichment
Save
• Reading and Study Workbook A,
e
Section 40–4
• Adapted Reading and Study Workbook B,
Section 40–4
• Biotechnology Manual, Lab 13
• Lesson Plans, Section 40–4
• iText, Section 40–4
• Transparencies Plus, Section 40–4
Tim
Technology:
r
Print:
Health Science Point out that carbon
monoxide is a relatively common danger in the home. It is especially
dangerous because it is odorless and
colorless. As a result, people may
breathe it in and succumb to its effects
without ever realizing they are in danger. Explain that one of the best ways
to prevent carbon monoxide poisoning is by using carbon monoxide
detectors in the home. You might
want to bring a carbon monoxide
detector to class and explain how it
works.
The Immune System and Disease
1049
Airborne Particulates Airborne particulates of many
different kinds can also be risk factors. Tiny dust mites, pollen,
mold spores, and animal dander can trigger allergic reactions
that can lead to respiratory problems or make existing health
problems worse. Some potential sources of airborne particulates
that can be found indoors are shown in Figure 40 –17.
Another type of particulate that can cause serious harm is
the metal lead. Lead can poison the liver, kidneys, and nervous
system. Lead poisoning in babies and young children can also
result in slow mental development.
Lead became a serious problem because for many years it
was added to gasoline to improve the performance of engines.
When that gas was burned, tiny particulates of lead were
released into the air. People inhaled lead particulates as they
breathed. Many more lead particulates were washed into rivers
and streams. When research revealed the health problems that
resulted, leaded gasoline was phased out and replaced with
unleaded gasoline. Within a few years, levels of lead in surface
waters dropped dramatically.
Another particulate that can be carried in air is asbestos,
which was commonly used for insulation. Asbestos can fragment
into tiny fibers that are small enough to remain suspended in
air for some time. When inhaled repeatedly, asbestos fibers can
cause lung cancer.
40–4 (continued)
Make Connections
Health Science Tell students that
some particulates known to cause
human diseases are found in high
concentrations in the air in certain
occupations. Describe the example
of coal dust. It causes a deadly lung
disease called “black lung” in longterm coal miners. Also, describe the
example of hemp fibers. They can
cause a lung disease referred to as
“brown lung” in people who work
with hemp.
Water Quality
Use Community Resources
Arrange for students to visit a water
treatment plant to see how water is
processed to make it safe for human
use in their community. After the
visit, have students make a diagram
showing the sequence of steps
through which water passes in the
treatment plant. Ask: What is
removed from water in each phase
of treatment? (Students should name
the particulate matter, biological pollutants, and other pollutants that are
removed from water during the phases
of treatment.)
Water Quality
왔 Figure 40–17 Air pollution can
occur indoors as well as outdoors.
Indoor air pollutants include fumes
and vapors given off by carpets,
paints, and household cleaning
products.
Water, like air, can carry biological and chemical pollution.
Biological pollutants in water, such as human and animal
wastes, can contain bacteria or viruses that can cause cramps,
vomiting, diarrhea, or diseases such as hepatitis or cholera.
Some chemical pollutants can cause organ damage. Others
interfere with the development of organs and tissues, causing
birth defects. Still others can damage DNA, causing normal cells
to become cancerous.
Certain types
of fresh paint
Tobacco
smoke
Smoky
fireplace
Some glues in
some brands
of plywood
Solvents from
some types of
new synthetic
carpet
Carbon monoxide
(if furnace is not
properly vented)
Pesticides
Asbestos
(in some older
homes)
Radon
Inclusion/Special Needs
On the board or an overhead transparency, work
with at-risk students to create a concept map that
incorporates the headings and subheadings in the
section. After the concept map is completed, have
students add examples to it. For example, under
radiation, they could add UV radiation, X-rays, or
radon. Tell students to copy the completed concept map into their class notebook and use it as a
study guide.
1050
Chapter 40
Less Proficient Readers
Guide students who need extra help in organizing
the material in the section. Have them draw a line
down the middle of a sheet of paper. Then, as
they read, have them fill in the left side of the
paper with a list of environmental factors that
adversely affect health. They should fill in the right
side of the paper with a list of steps they can take
to maintain their health. Advise them to save the
paper as a study guide.
Bioterrorism
왗 Figure 40–18 Many cities and
towns have sewage-treatment plants
that process household waste water.
In huge outdoor tanks, water is
treated with chemicals and microorganisms and then aerated.
Applying Concepts What is the
role of microorganisms in treating
waste water?
Build Science Skills
Drawing Conclusions Point out
that methods of bioterrorism are also
often referred to as “weapons of
mass destruction.” Ask: Why are
infectious diseases, such as smallpox and anthrax, potentially so
deadly? (Because they can be fatal
and, being infectious, can easily infect
huge numbers of people)
Fortunately, regulations requiring proper treatment of
residential and industrial sewage, for example, have led to
significant decreases in the amount of sewage-related bacteria in
drinking-water supplies across the nation. In the United States,
for example, public water systems supply clean, safe drinking
water to cities and many towns. Providing safe drinking water
has probably been the single most important factor in nearly
doubling human life expectancy over the last century or so.
Bioterrorism
In recent years, bioterrorism has become a new health threat.
Bioterrorism is the intentional use of biological agents to disable or kill individuals. Bioterrorism can involve the intentional
release of infectious agents—viruses (such as smallpox) or
bacteria (such as anthrax)—or the spread of toxic compounds
(such as botulinus toxin) extracted from living organisms.
Some forms of bioterrorism pose risks in part because
research and public health measures have been so successful in
the past. For example, worldwide vaccination programs eliminated smallpox around the world years ago. As a result, almost
no one has been vaccinated against the virus for decades. Thus,
the release of smallpox virus could cause serious problems.
Other forms of bioterrorism involve treating pathogens to
maximize their ability to infect and cause disease. Anthrax is a
disease that is common in cattle-ranching areas, but it is usually present in a form that either is not easily transmitted or is
not life-threatening. The spores of anthrax bacteria, however,
can be treated to make them light and fine enough to be spread
through the air and inhaled—which produces a possibly fatal
infection. Medical, research, and military establishments are
still in the process of performing research and evaluating the
best ways to minimize the risks of bioterrorism.
FACTS AND FIGURES
Not just anthrax and smallpox
Media attention has made the public aware of the
potential threat of bioterrorism with the smallpox
virus and anthrax bacterium. However, other
pathogens are also potential agents of bioterrorism, including the bacterium that causes
tularemia and the virus that causes hemorrhagic
fever. Both have been studied in germ warfare
laboratories for decades. In addition, the hemorrhagic fever virus has been weaponized by the
United States and Russia, and the tularemia bacterium may already have been used as a weapon
by the former Soviet Union in World War II. Both
pathogens are normally found in nonhuman animal populations. When introduced to human
populations, they cause potentially fatal, flulike illnesses. Aerosol dispersal could result in hundreds
of thousands of people being infected and thousands of lives being lost.
Answer to . . .
Figure 40–18 Microorganisms break
down complex compounds in waste
water to produce simpler ones. The
process produces water, carbon dioxide,
nitrogen gas, and compounds that can
be used as fertilizer.
The Immune System and Disease
1051
40–4 (continued)
Cancer
Cancer
N STA
Make Connections
Environmental Science Explain
how destruction of the ozone layer in
Earth’s atmosphere has increased the
amount of ultraviolet radiation to
which people are potentially
exposed. Ask: How is this likely to
affect rates of skin cancer? (The
rates are likely to increase.) Add that
skin cancer rates have in fact
increased since the late 1900s.
For: Links on cancer
cells
Visit: www.SciLinks.org
Web Code: cbn-0404
Demonstration
Point out that tumors can often be
detected by physical exam or X-ray
but determining whether a tumor is
cancerous usually requires a biopsy.
Explain that a biopsy is the surgical
removal of a small mass of tissue of a
tumor so it can be examined under a
microscope for evidence of cancer.
Use a microprojector and show students slides of normal and cancerous
cells. Alternatively, you can show students pictures of normal and
cancerous cells from histology textbooks or Internet sites. Ask: How do
the normal and cancerous cells
appear to differ? (Cancer cells are
often small, mitotically active cells with
little sign of cell differentiation.)
왔 Figure 40–19 The body recognizes cancer cells as foreign and tries
to destroy them. In this colorenhanced SEM, a killer T cell (orange)
is attacking a cancer cell (purple).
NS TA
Download a worksheet
on cancer for students to complete,
and find additional teacher support
from NSTA SciLinks.
(magnification: about 3000⫻)
1052
Chapter 40
Cancer is a life-threatening disease in which cells multiply
uncontrollably and destroy healthy tissue. Cancer is a unique
disease because the cells that cause it are not foreign cells but
rather the body’s own cells. This fact has made cancer difficult
to treat and to understand.
All forms of cancer are ultimately caused by harmful mutations in genes that control cell growth and development.
Sometimes, cancer arises almost entirely because some factor in
the environment damages DNA. An increased likelihood of
developing some cancers can be inherited.
Cancers begin when something goes wrong with the controls
that normally regulate cell growth and reproduction. A single
cell or a group of cells begin to grow and divide uncontrollably,
often resulting in the formation of a mass of growing tissue
known as a tumor. However, not all tumors are cancerous.
Some tumors are benign, or noncancerous. A benign tumor does
not spread to surrounding healthy tissue or to other parts of the
body. Cancerous tumors, on the other hand, are malignant,
which means that they can invade and destroy surrounding
healthy tissue.
As the cancer cells spread, they absorb the nutrients needed
by other cells, block nerve connections, and prevent the organs
they invade from functioning properly. Soon, the delicate balances that exist in the body are disrupted, and life-threatening
illness results.
Causes of Cancer Cancers are caused by defects in the
genes that regulate cell growth and division. There are several
sources of such defects. They may be inherited, be caused
by viruses, or may result from mutations in DNA that
occur spontaneously or are produced by chemicals or
radiation.
Chemical compounds cause cancer by triggering
mutations in the DNA of normal cells. Chemical compounds that are known to cause cancer are called
carcinogens. Some carcinogens are produced in nature.
One of these, aflatoxin, is produced by molds that grow
on peanuts. Others, such as chloroform and benzene, are
synthetic compounds. Some of the most powerful chemical carcinogens are found in tobacco smoke. In the United
States, cigarette smoking is responsible for nearly half
the cancers that occur.
Most forms of radiation—including sunlight, X-rays,
and nuclear radiation—cause cancer by producing
mutations in DNA. If mutations occur in genes that
control cell growth, a normal cell may be transformed
into a cancer cell. Most cases of skin cancer, for example,
are caused by the ultraviolet radiation in sunlight. For
this reason, it is important to avoid prolonged exposure
to the sun.
Cancer Mortality
Cancer is a disease that is easier to treat if it is
detected early. There are also things you can do to
decrease your risk of cancer, such as eating a diet high
in fruits, vegetables, and fiber; staying out of the sun;
and not smoking. The data in the table show the
5-year mortality rates of five different types of cancer
since 1950. Use the data to answer the questions.
1. Using Tables and Graphs Construct a line
graph of the data in the table.
2. Using Tables and Graphs Which type of cancer
has shown the greatest increase in mortality rate?
3. Inferring What can you infer about the use of
tobacco in men over the last 50 years? In women?
4. Predicting Given the trend in melanoma cancer
deaths over the past 50 years, predict the incidence
in 1995–1998 in both men and women.
5. Inferring Why do you think the incidence of
death from breast cancer has stayed relatively
stable over the last 50 years?
Cancer Mortality Rates (per 100,000 people)
Lung
Colon
Melanoma
Breast
Prostate
Year
Male
Female
Male
Female
Male
Female
Female
Male
1950–54
25.51
4.98
16.94
18.49
1.20
0.92
26.42
20.85
1960–64
42.15
6.39
17.86
17.48
1.67
1.19
26.22
19.78
1970–74
60.79
12.80
19.49
16.43
2.18
1.40
26.92
20.05
1980–84
71.30
23.33
21.22
15.52
2.95
1.64
26.90
21.29
1990–94
71.71
33.43
18.79
12.85
3.49
1.69
26.19
24.37
1995–98
68.00
34.30
20.50
14.10
?
?
24.20
23.70
You may wish to point out to students that breast cancer can occur in
males, although it is very rare. Also
point out that the values are for 5year time spans, except the last row,
which is only four years.
Answers
1. Check students’ line graphs to
make sure that they have plotted the
data correctly.
2. Lung cancer for both men and
women
3. Tobacco use in both sexes has
increased dramatically.
4. Accept all logical responses. Male
rate may be around 4.0; female rate
may be around 1.8–1.9.
5. Self-exams have helped in early
detection of cancers, increasing the
rate of survival. Also, there are a variety of treatments available to breast
cancer patients.
Radon is another source of radiation. Radon is a radioactive
gas that is found naturally in some rocks and that sometimes
leaks into the foundations of buildings. If your home is located
in an area where radon is present, it can be tested for the
presence of radon.
Treating Cancer As with other diseases, prevention is the
best defense. The best way to fight cancer is by protecting your
DNA from agents that cause cancer. For example, you can
dramatically reduce your risk of developing lung cancer by not
smoking. In addition, regular exercise and a balanced diet with
plenty of fruits and vegetables can help to lower your cancer risk.
Physicians also stress that if a cancer is detected early the
chances of treating it successfully may be as high as 90 percent.
Regular checkups and tests are an important preventive measure. Recommended tests depend on a person’s age, gender, and
family history. Self-examinations for skin, breast, or testicular
cancer are also helpful when combined with regular checkups.
Your doctor can give you instructions for performing these selfexaminations.
FACTS AND FIGURES
Radon and cancer
The invisible, odorless, radioactive gas radon is
released through the decay of uranium in soil
and rocks. When uranium decays, it emits tiny
radioactive particles that can damage the cells
lining the lungs, and long-term exposure can
lead to lung cancer. Radon’s link with lung cancer was first discovered when scientists
discovered that underground uranium miners
died of lung cancer at far-higher-than-expected
rates. Although everyone breathes in some
radon every day, it is usually at very low levels
that have little if any health risks. However,
radon can reach dangerously high levels in wellinsulated homes and other buildings. As a
result, it is estimated to be responsible for about
10 percent of annual lung cancer cases in the
United States, making radon second only to cigarette smoking as a cause of lung cancer.
The Immune System and Disease
1053
40–4 (continued)
Maintaining Health
Maintaining Health
To keep your immune system working efficiently, you can
practice behaviors that reduce your exposure to pathogens and
maintain overall good health.
Healthful behaviors
include eating a healthful diet, getting plenty of exercise
and rest, abstaining from harmful activities, and having
regular checkups.
Build Science Skills
Applying Concepts Ask students
to think of at least one specific way
that they can maintain their health
for each of the four general ways that
are presented in the section: healthful diet, exercise and rest, abstaining
from harmful activities, and regular
checkups. (Possible ways include
avoiding high-fat foods; working out
three or more times a week; saying no
to drugs, alcohol, and sex; and getting
regular checkups.)
Healthful Diet Food provides the nutrients and energy your
cells need to function properly. To help all your body systems
work at their best, it is important to eat a balanced diet that
provides essential nutrients. Eating foods that are low in saturated fat and cholesterol may help prevent obesity. Eating plenty
of fruits, vegetables, and whole grains will also help protect you
from certain cancers, especially colon and rectal cancers.
Make Connections
Health Science Review some of the
regular screening tests recommended
for most adults, including testicular
and breast self-exams, mammograms, Pap smears, and
colonoscopies. Discuss the role of
screening in early detection and successful treatment of the
diseases.
왖
Figure 40–20
Getting
regular exercise is one way to
maintain your health. You should try
to get a minimum of 30 minutes of
aerobic exercise each day.
3 ASSESS
Evaluate Understanding
Exercise and Rest Regular exercise helps move blood throughout the body and maintains cardiovascular fitness. Exercise also
helps maintain an appropriate body weight, which helps prevent
certain kinds of heart disease. Adequate rest is important for
keeping your body functioning well. For most people, adequate rest
means getting about eight hours of sleep each night.
Abstaining From Harmful Activities Drugs, including
alcohol and tobacco products, can have harmful effects on the
body. Many types of drugs, including alcohol, can slow or suppress the immune system. Smoking and tobacco products also
cause a variety of respiratory conditions as well as certain
cancers, including cancers of the lung, mouth, and throat.
Some diseases can be spread through sexual contact with an
infected person. These sexually transmitted diseases (STDs)
include HIV, chlamydia, and gonorrhea. The only way to absolutely
prevent exposure to sexually transmitted diseases is to abstain
from all sexual activity.
Regular Checkups It usually is easier to treat a disease if it
is discovered early. You can perform regular self-examinations
for skin cancer, breast cancer, and testicular cancer. By getting
regular checkups, you can help maintain your health.
Ask students to make a concept map
of environmental factors that affect
health.
Reteach
Using the chalkboard or an overhead
transparency, work with students to
make an outline of the section by
writing the section headings and
subheadings as outline topics and
subtopics and calling on students to
fill in important details.
Cells would be most vulnerable to
damage from radiation during the
S phase of the cell cycle, when
DNA is being replicated. Cancer
cells would be especially vulnerable
to radiation because cancer is characterized by rapid cell division.
If your class subscribes to the iText,
use it to review the Key Concepts in
Section 40–4.
1054
Chapter 40
40–4 Section Assessment
1.
Key Concept Describe the
environmental factors that affect
your health.
2.
Key Concept Name three
things you can do to maintain
your health.
3. List some of the causes of cancer.
4. Why are regular medical checkups and self-examinations
important?
5. Critical Thinking Classifying
Should cancer be considered an
infectious disease? Explain your
answer.
The Cell Cycle
Recall the cell cycle from
Section 10–2. In which phase
do you think cells would be
most vulnerable to damage
from radiation? Explain your
choice. What characteristic of
cancer cells might make them
especially vulnerable?
40– 4 Section Assessment
1. Students should describe air and water
quality, poisonous wastes in landfills, and
exposure to solar radiation.
2. Any three of the following: eating a healthful
diet, getting enough exercise and rest,
abstaining from harmful activities, and having regular checkups
3. Cancers are caused by defects in the genes
that regulate cell growth and division. These
defects may be inherited or caused by
viruses, or they may result from mutations
in DNA produced by radiation or chemicals.
4. Regular medical checkups and selfexaminations are important for detecting
problems early so that there is a better
chance of treating them successfully.
5. Most cases of cancer are not infectious.
However, cancer-causing viruses can be
passed from person to person.