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The Hijacker -- How a Virus Spreads
Grades 9-10


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: #10 Viruses
Learning Objectives
Students will be able to:
Per class:
Per student:

Pre-Viewing 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 a cold 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 Viewing
Say, "Can anyone tell me what a hijacking is?" (A hijacker boards an airplane and takes it over by force.) Ask your students, "How does the hijacker get past security? How does he or she get the pilot to follow his or her 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 those steps."
Viewing Activities
BEGIN tape where the video shows an image of frolicking seals; the words "Viral infections" are written in the upper lefthand 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. Say, "Explain, step by step, the process occurring in the animation sequence."

(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 cell's 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 one 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 1 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 to 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 HIV 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."
Post-Viewing Activities
Say, "We've looked at how your body attacks most pathogens, and how it fails to attack when infected with AIDS. Now, let's 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?" (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 has body fluids, I would like you to share with one other person. 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 two to three 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 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 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 that shows the number of people who were infected at the end of rounds one, two, and three. Students should record this data in a table. Distribute one 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.

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, 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.)

Action Plan
Invite a physician from your city or county health department to speak about contagious diseases, and how epidemics are tracked within your area.

Take a virtual field trip to one or more of the following sites on the World Wide Web:

This site contains an interview with Dr. Frederick Murphy, a researcher of the Ebola virus. This Web site also has electron micrographs of this virus.

This site has beautiful electron micrographs of viruses, which may be viewed without downloading.

The World Wide Web server for the Institute for Molecular Virology at the University of Wisconsin, Madison, is a colorful, user-friendly site that has a wealth of information on viruses, including connections to other virology-related Web sites. Color images of many viruses may be viewed at this site, or larger versions may be downloaded.

For the most current statistics on the spread of the AIDS epidemic, visit the World Health Organization's Global Programme on AIDS.
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, by Richard Preston, 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.

Research past epidemics, such as bubonic plague, polio, and influenza epidemics. Compare the number of lives lost in these epidemics to the number of lives lost in different wars.

Master Teachers: Veronica Zonick and Edna Soulas

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