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In this lesson and its extension the students will have an opportunity to learn how an infectious disease such as AIDS may be quickly transmitted throughout a population. Video has been chosen to help students understand the basic structure and function of viruses. Some background as to the structure of cells and how the DNA and RNA molecules function is necessary to the understanding of this activity. Students will develop an understanding of how viruses and retroviruses differ in their use of DNA and RNA. The students will conduct a simulated transmission of an infectious disease and mathematically determine the number of possible infected individuals based on the data they collect.
ITV Series
Our Human Body #10: Viruses

Teens Talk Aids #1: Teens Talk Aids
Learning Objectives
Students will be able to:
Transmission of Diseases:
one of each of the following per student:

Pre-Viewing Activities
Have the students brainstorm and come up with as many diseases as they can that are caused by viruses. Ask the students to compare the size of viruses to bacteria or other cells with which they may be familiar. Go over the unit micrometer with the students and be sure they understand this unit of measurement.
Focus Viewing
The focus for viewing is a specific responsibility or task(s) that the students are responsible for doing while viewing the video, or after seeing video, to focus and engage students' viewing attention. In this first segment of the video I would like to divide the class into three sections. The first section will be responsible for answering the question "What is a virus"? The second group will answer the question "How do we know what viruses look like'? and the third section will answer the question, "How big is a large virus"?

Viewing Activities
BEGIN the video Our Human Body #10 Viruses with the title showing on the screen. PAUSE when SciFax along with the question "How big is a large virus" appears on the screen. Have the students respond to the questions they were responsible for in the focus for viewing section. Note to the Teacher: the video may not have provided sufficient information to answer all the questions at this point. Therefore, the focus for viewing should continue.) Also at this time go over the unit micrometer(micron). Make sure each student understands this unit. The question in the video indicates that 75,000 large viruses would be one inch in height. Have the students convert this to micrometers and therefore have a better understanding of the unit and the small size of viruses. RESUME the video and PAUSE when the two word heading viral infection appears on the screen. Answer the remaining questions from the first section. Also the students should be able to respond to the following questions at this point. How do viruses reproduce? Why do some scientists feel that viruses should not be considered living? What is a host? Why are all viruses parasites? RESUME the video and STOP when the SciFax question appears on the screen. "More than 350,000 AIDS cases were reported between 1981 and 1991." How many recovered? Also check the students knowledge of the following questions. What is an antibody? Why is medicine often ineffective against viral infections? What is the role that viruses may play in genetic engineering? Why is it not important that a virus kill the cell?


This focus for viewing is for a different video Teens Talk AIDS. The video is approximately 30 minutes in length, but I have chosen to use only about 4 minutes of the tape. This video is to develop the mind set that an infectious disease can happen to anyone, Also this segment will help prepare the students for the post viewing activities. To give the students a specific responsibility while viewing divide the class into two groups. Have the first group be able to list three specific questions the person at the testing center asked the test subject when he came in to get tested for HIV. Have the second group of students be able to list two precautions the tester gave to the test subject after he told him he had tested negative for the HIV virus.

Note to the Teacher: Some of the responses that group number one should provide are: How many different sex partners have you had? Have you been using condoms? Have you had sex with a male? Have you had sex with a prostitute? Responses from the second group should include: Take as many precautions as you can, such as wearing condoms, or do not share needles. Abstinence was not mentioned. This would be a teacher preference as to whether you want to discuss this aspect.


BEGIN the video Teens Talk Aids #1 when the girl in the pink top responds "I don't have that attitude that it can't happen to me." This is approximately 8 minutes into the video. PAUSE when the young man is shaking hands after being tested for AIDS. Have the students react to this portion of the video. FAST FORWARD to the portion where the young man is making a return visit to the testing center. RESUME play at this point and STOP when he is ready to leave the testing center. Again have the students respond to his actions when he found out he did not test HIV positive.
Post-Viewing Activities
At this point the students should have a good concept of what a virus is and how it is transmitted. Review with the students what is meant by the terms communicable and transmission. You may also wish to review the terms base and indicator at this time, if your students are not familiar with those terms. This activity is designed to show students how they could give or get a communicable disease from someone. You may choose to use any communicable disease you wish.

Note to the teacher: a good base solution to use is a weak sodium hydroxide solution. Mix 4 grams of sodium hydroxide pellets with 1000 mL of water. A weak solution of other bases such as household ammonia will also work. Try to choose something which is odorless, when in a dilute solution. You need as many stock solutions as you have students in the classroom. Number each of the containers to keep track of the "infected" one. To prepare a 1% phenolphthalein solution, dissolve 1 g of phenolphthalein in 99 mL of distilled water.( If phenolphthalein is not available, some laxative pills contain this substance and a solution can be made from them). Each student needs their own dropper. Water works well for the neutral pH solution. However, I would suggest testing the water first. Some parts of the country have many minerals in the water, so do not assume it is neutral. Have all students use the same dropper for the indicator, so the indicator itself will not be "infected". The activity has minimal safety risks involved. However, if safety glasses and laboratory aprons are available, it would be recommended they be used. If students spill any of the liquid on their skin, have them rinse it off with water, immediately. After completion of the activity, rinse the tubes and droppers with a weak acid, such as vinegar. A base residue will cause the tubes to turn pink the next time you use them, before you want them to!


1. On your data table is a place for you to write your hypothesis, do so at this time, before obtaining your solution.

2. Obtain a numbered bottle of solution. Record the bottle number on you data sheet. Most solutions are neutral, and students having such solutions will represent healthy persons in the model. Someone in the class will be given a bottle containing a dilute base. This person will represent the infected person.

3. Use your dropper to transfer two droppersful of your solution into your test tube.

4. When your teacher gives you the signal, begin the first round of transfers. Choose a classmate at random. Fill your dropper from your test tube, and have your chosen classmate do the same. Then each of you transfer the dropperful into the other one's test tube. Record the name of the student on your data sheet. Trade with only one student per trial.

5. When you teacher gives the signal, carry out a second round of transfers, choosing a different classmate.

6. Record the name of the second round classmate on your data sheet.

7. For the third round choose still another classmate.

8. Your teacher will now place two drops of phenolphthalein indicator into your test tube. Record the color of the solution. Note: the neutral solution will remain colorless, but the basic solution will turn pink.

9. On your data sheet list the names of all the students who are "infected" (who have pink solutions).

10. Obtain from the "infected" students the names of all their contacts, by round, and record their names.

11. To deduce the identity of the first "infected" students, cross off the names of the uninfected students from the data table. This should allow you to narrow down the infected students from the first round to two students. Those two students should obtain a sample from the stock solution with the same number, and test it with phenolphthalein.

12. Use this information to infer who must have transmitted the disease to whom.

13. On your data table design a chart with student names and arrows to show the transition route from one round to the next.
Action Plan
Have a health professional speak to the class about infectious diseases.

Have a research scientist speak to the class, on the difficulties of using medicine to treat viral infections.

Science: Have students research the number of people "infected" with AIDS each of the past ten years, and prepare a graph. Also determine per unit of time, such as per minute, how many people are infected.
Art: Have students make a three-dimensional model of a virus. Social Studies and Geography: Have students color code various regions of the world and representative numbers of AIDS infection.

Science: Research why viruses may be helpful in genetic engineering.

Math: The unit to measure the size of a virus in usually micrometers. Do some calculations to show students understand the relationship between meters, centimeters, millimeters and micrometers.

Speech and Debate: Discuss: If you were the leader of your country, where would you rank finding a cure for AIDS among all other national concerns?

Health: Discuss the prevention of sexually transmitted diseases(STD).

Science: Use the video Discovering Great Minds of Science "Viruses" by Robert C. Gallo. Pangea Digital Pictures, 2246 Camino Ramon, San Ramon, CA 94563

Science: Use Laser Disk Series, "The Living Textbook" by Addison-Wesley Publishing Company.

Master Teachers: Dennis Reule and Cindy Yocum

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