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THE HIJACKER--HOW A VIRUS SPREADS
MASTER TEACHER Veronica Zonick
GRADES 9-10
OVERVIEW
This lesson provides students with an understanding of how
viruses attack the body, and how the body's immune system defends the body from
attack. Additionally, this lesson simulates how any infectious disease
travels through a population, and how scientists trace the progress of epidemics
such as AIDS. The use of video and the simulation of an epidemic are
intended to address the learning styles of both visual- and
tactile/kinesthetic-oriented students. Students will establish,
through deductive reasoning, which student was the initial carrier of the
simulated disease, and how this disease spread throughout the classroom
population. This analysis will be aided by use of a graphic
organizer. The progression of this simulated epidemic will be linked to a
real-life situation, the AIDS pandemic.
ITV SERIES
Our Human Body from Science Source: Viruses
LEARNING OBJECTIVES
Students will be able to:
* describe how the body's immune system attacks invaders.
* explain the breakdown of the immune system in the disease AIDS
* simulate the transmission of a viral infection.
* track the progress of a viral infection.
* graph the rate of infection in a population, using data
collected in class.
* extrapolate from a graph to predict the future growth of an
epidemic.
MATERIALS
(Per class)
Overhead projector
screen
transparency markers
Transparency "Tracking an Epidemic"
(Before class begins, fill out this transparency with
the names of each student--see sheet at end
of
lesson)
Transparency "Progress of an Epidemic"
Transparency "New Cases of AIDS From
1979 to 1995"
1 disposable plastic transfer pipet
distilled water
1% Phenolpthalein solution (acid/base indicator)
1 M NaOH stock solution (dissolve 4 g of NaOH in
100 mL water)
0.1 M NaOH stock solution (dilute 1mL of 1 M NaOH
in a total volume of 10 mL distilled
water)
test tube containing distilled water
1 or more test tube racks to hold class set of test tubes
1 plastic dishwashing pan, labeled "I was not
infected"
1 plastic dishwashing pan, labeled "I was
infected"
(Per student)
1 numbered test tube containing distilled water or 0.1
M NaOH (for a class of 25 students, prepare 24 test
tubes of distilled water, and 1 test tube of
0.1 M
NaOH)
disposable 7 mL plastic transfer pipet (available from
biological supply companies)
1 pair of safety glasses/goggles
pen or pencil
handout "The hijacker"
1 sheet graph paper
1 sheet notebook paper
VOCABULARY
pathogen
immune system
antibody
virus
acquired immune deficiency syndrome
PREVIEWING ACTIVITIES
Ask your students to turn to the person next to them and shake
hands. Then, tell the students, "Every time you shake a
person's hand you expose yourself to disease!" Elicit discussion leading to
the fact that our body's immune system is the body's defense mechanism, by
asking questions such as, "How does your body protect itself? If
there are germs, or pathogens all around us, why aren't we sick all of the
time?" Say, "It makes sense to understand how our
body fights disease, successfully and unsuccessfully, and how diseases as common
as the flu, or as deadly as AIDS spread through populations. With this
information, we can prevent exposure to disease, remain healthy, and
possibly, find a cure or vaccine. Then, hopefully, we can save
lives."
FOCUS FOR VIEWING
Say, "Can anyone tell me what a hijacking
is?" Elicit from the students that a hijacker boards an airplane, and
takes it over by force. Ask your students, "How does he get
past security? How does he get the pilot to follow his orders? Are
the people on board safe?" Distribute a sheet of notebook paper to each
student. Tell your students, "You are going to watch a video that
shows how one type of pathogen invades and hijacks the cells of your body, and
how your body's immune system launches a counterattack." To give
students a specific responsibility while viewing, say, "Look for the things
that a virus does when it hijacks your body, and write down these steps."
VIEWING ACTIVITIES
Begin tape where the video shows an image of frolicking
seals; the words "Viral infections" is written in the upper left
hand corner of the screen. Audio is "Viruses are specialized in
attacking certain cells or bacteria." To allow students an
opportunity to record the sequence of events in a viral "hijacking," pause
the tape at the end of the computer animation sequence of viral invasion,
replication, and cell death. Video is blue spiked viral particles being
released from yellow hepatic cells. Audio is "...since the cell
no longer functions correctly." To check comprehension of the
sequence of events that occurs during a viral invasion, rewind tape to
the beginning of this animation sequence. Video is blue spiked ball moving
within a blood vessel. Audio is "...they can undergo attack by many
different kinds of viruses." Mute the sound. This will
give students the opportunity to focus on the animation sequence.
Use the frame advance (or slow) option to move through the tape
slowly. Ask the students to explain, step by step, the process occurring
in the animation sequence. Elicit the following responses from the
students: 1. Virus travels through the body until it locates a
target cell. 2. Virus secures to the cell membrane. 3.
Virus injects instructions into the cell. 4. These instructions
alter the cells metabolism. 5. The cell begins to produce many
copies of the virus. 6. These viruses are released from the
cell. 7. Viruses attack and often destroy other target cells. Pause
the tape to allow students to finish recording their answers. Video is
blue spiked viral particles being released from yellow hepatic cells.
Audio is "...since the cell no longer functions correctly."
Ask the students, "How will your body defend
itself from this attack?" To give students a specific responsibility
while viewing, say, " Look for the molecule that the body produces
and sketch it." Resume tape. Pause video with
visual of orange cell producing Y-shaped antibodies so that students may sketch
an antibody molecule.
Fast forward tape. During this time, ask
students to hypothesize what would happen if you had no immune system. To
give students a specific responsibility while viewing, say, "Watch the
video to find out what part of the immune system is missing when a person has
acquired immune deficiency syndrome." Begin tape with
visual of black monolith, engraved with the word "AIDS"; audio
is, "AIDS, or acquired immune deficiency syndrome, is one recent viral
infection that is causing alarm all over the world." To give
students the opportunity to record their responses, pause tape where
video shows a virus multiplying rapidly. Audio is, "The AIDS virus
can remain dormant for several years before it becomes active." Rewind
tape to the beginning of this second animation sequence. Video is the
image of 3 body cells and one virus particle. Audio is "Once
infection has taken place." Mute the sound. Use
the frame advance option to move slowly through this animation sequence.
Ask the students to explain how this sequence is similar and different from the
first animation sequence. Resume tape. Pause tape at
image of the words, "SCI FAX: More than 350,000 cases of AIDS
were reported from 1981 to 1991. How many survived?" Audio is
the sound of a computer printer. Ask students to guess the answer to that
question. Resume tape. Stop tape at the image of
the answer "none." Ask the students, "Is this information
correct? Are there any survivors of AIDS?" Elicit
discussion pertaining to the recent reports of several people who do not have
symptoms of AIDS who have been infected with the AIDS virus for over 12 years.
Additionally, in the past year, one infant who was born HIV+ is now HIV-.
Say, "Later, we will be looking at how the AIDS epidemic has changed
over time."
POSTVIEWING ACTIVITIES
Say, "We've looked at how your body attacks most
pathogens, and how it fails to attack when infected with AIDS. Now lets
examine how any pathogen can spread from person to person. At the
beginning of class I said that when you shake hands with someone, you are
exposed to many pathogens. Why do you think that is?" Elicit
from students the response that when a person has a cold, and sneezes or rubs
his nose with his hand, any virus in that person's mucus ends up on his hand.
When you shake hands, the virus is transferred to your hand, and if you rub your
eyes, you may become infected. Say, "Mucus, saliva, and blood
are examples of body fluids. Any virus or bacteria in your body can
be spread if you share your body fluids. Today we are going to demonstrate
this."
"We are going to use liquids to represent our body
fluids. Each of you will get a test tube containing either pure water, or
a mystery chemical." Remind students that they need to wear safety
glasses, since they do not know the identity of the liquid in their test tube.
Distribute the handout, "The Hijacker," and one disposable transfer
pipet to each student. Allow each student to select a numbered test tube.
Say, "Now that each of you have body fluids, I would
like you to share with one other person." Say,
"Choose someone that you do not know too well. When I say,
"go," find your partner. Ask your partner to tell you something new
about herself. Write down this information and your partner's name on your
handout. Then trade 10 drops of body fluids." Demonstrate how
to transfer 10 drops of liquid. Say, "When I say, 'stop,'
return to your seat." If there are an odd number of students, say
"One of you will be my partner." Give the signal to begin, and
allow 2 to 3 minutes for this first trade. Give the signal to stop and
tell students the following, "Now you have shared body fluids with
one person. Before you find a second partner, be sure to do the following:
Hold up your test tube and transfer pipet, and ask the students to squeeze the
bulb on the pipet to return all liquid to the test tube." (It is
critical that students complete this task exactly as directed, to avoid
confusing results.) Give the signal to begin the second trade of body
fluids, asking students to choose someone from the other side of the room. (This
is to ensure that small groups of students do not interact with each other only)
Repeat this procedure for a third trade.
Say, "All of us should have traded our body fluids
with 3 people. At the beginning of this demo, one person was infected.
Let's find out how many people are infected now." Ask for three
student volunteers. Say, "We are going to add an indicator dye to
each sample of body fluids. If you are infected, you will see a dramatic
color change. Be sure to write down the color of your solution." Ask
the first volunteer to add two or three drops of phenolpthalein to each test
tube, using a clean transfer pipet. Do not touch the pipet to the liquid
in the test tube. Ask the second and third volunteers to collect the test
tubes and transfer pipets after a color change is noted. Uninfected
samples should be collected in the dishwashing pan labeled "I
was not infected." (These pipets and test tubes are clean and may be
reused.) Infected samples should be collected in the dishwashing pan
labeled "I was infected." (These pipets should be discarded.
Test tubes must be washed thoroughly before reuse, to avoid false positive
results.)
After all samples have been tested and collected, project the
transparency, "Tracking an epidemic" Ask students,
"How many of you were infected? Would you like to know who infected
you?" Ask the students to raise their hands if they were infected.
Note this on the overhead by marking an asterisk next to the names of the
infected.
Say, "How can we find out who infected whom?"
Individuals may immediately give reasons why he or she could not have been the
original carrier. Direct these student responses by saying, "In
real life, scientists track epidemics in a very organized way. It helps to
chart the order that people interacted with each other, and to eliminate people,
one by one. Let's figure out the order first." Ask the infected
students to list in order their first, second, and third partner. Record this
data on the transparency, "Tracking an epidemic."
After all infected students have provided data, say,
"Now we need to begin eliminating people. If a person was not the
original carrier of the disease, he or she might have interacted with people who
did not become infected. Can anyone look at this data and find a partner
of an infected person who did NOT become infected?" If this person
was not the original carrier, he or she can be eliminated. Cross this person off
the list. Ask the students, "But who infected this person? It
must be someone he or she interacted with. "Point out these partners on the
transparency. Check one of these potential carriers next. Did that
person exchange fluids with someone who did not become infected? If so, he
or she is not the original carrier. Work backwards until you find a two
people who infected each other.
At this point say, "We have narrowed things down
as far as we can. How can we figure out who started the epidemic?"
Explain that in real life, the time that a person became ill is often used to
figure this out, but sometimes it is impossible to determine who started an
epidemic. In this demonstration, students may be able to infer the
original carrier by observing the color of the solutions. The original
carrier should have the most concentrated base solution. The darkest pink
sample contains the most sodium hydroxide, and is the original carrier. If
necessary, reveal the identity of the original carrier by giving the number of
the test tube which contained the sodium hydroxide solution.
Ask students to use the data on the transparency,
"Tracking an epidemic," to create a table which shows the number of
people that were infected at the end of round one, two and three. Students
should record this data in the table provided in the "Hijacker"
handout. Distribute 1 sheet of graph paper to each student. Ask the
students to create a line graph to show this information in visual form.
Allow time for the students to complete this assigned task. Ask students
to predict what would have happened if a fourth, fifth or sixth round of
infection had occurred. Ask students to use their graphs to extrapolate
these further rounds of infection. Invite a student to fill in the
transparency "Progress of an epidemic," using his or her data.
Ask this student to explain to the class what this graph means.
Ask students to predict how many rounds of infections would
be needed to infect the entire class. (At the end of the first cycle, a total of
two students are infected. At the end of the second cycle, a four students
are infected. At the end of the third cycle, up to eight are infected.
At the end of the fourth cycle, up to 16 are infected. At the end of the
fifth cycle up to 32 are infected. This assumes that infected persons
always exchange with uninfected. It will take more cycles if students
exchange body fluids randomly.)
Direct students to the data table, "Death from
AIDS", (in the Hijacker handout) and ask students to draw a second
graph showing this information. Elicit from students the fact that like
the simulated epidemic done in class, AIDS grew exponentially in the time
period shown. Ask students to extrapolate the growth of AIDS from 1991 to
the present. Show the transparency, "New Cases of AIDS, from
1979 to 1995." Ask the students to hypothesize why the number of new
cases of AIDS has declined. Reasonable answers may include: drug
therapy, education and prevention efforts.
EXTENSIONS
English
Have interested students write a story about a viral hijacking
from the point of view of the virus, or the point of view of the body.
Reserve time for the students to present these stories to the class.
Read the book The Hot Zone, which tells about recent
efforts to identify new viruses such as Ebola, and track the spread of
epidemics.
Computer Science/Art
Use multimedia software such as Hyperstudio or Digital Chisel to
create an interactive tutorial on virus structure and function.
History
Research past epidemics, such as the plague, polio and influenza
epidemics. Compare the number of lives lost in these epidemics to the
number of lives lost in different wars.
DATA SHEET: The Hijacker
Name ___________________
Period ___________________
Test Tube # _______
Name of Classmate
New FactDiscussed
1. __________________ 1. __________________
2. __________________ 2. __________________
3. __________________ 3. __________________
Circle the color of your test tube of liquid:
Clear
Light Pink
Bright Pink
Record data about the number of people infected after each
round in the following table:
| Round |
Number of Infected Persons |
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Data Sheet-The Hijacker(page 2)
Use the information in the following table to create a graph
showing the number of new cases of AIDS from the year 1979 to the year 1989
| YEAR |
NEW CASES OF AIDS |
| 1979 |
2 |
| 1980 |
203 |
| 1981 |
343 |
| 1982 |
1330 |
| 1983 |
3678 |
| 1984 |
7521 |
| 1985 |
14847 |
| 1986 |
29493 |
| 1987 |
61530 |
| 1988 |
87494 |
| 1989 |
112839 |
TRACKING AN EPIDEMIC
| NAME |
PARTNER 1 |
PARTNER 2 |
PARTNER 3 |
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Progress of an Epidemic 
ROUND
NEW CASES OF AIDS, FROM 1979 TO 1995
YEAR
The source of the data in this graph
is the World Health Organization's statistics on AIDS reports received through
December 15, 1995.
Updated: April 01, 2008
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