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It’s Catching!
MOD EL
ACTIVIT Y OVERVIEW
IN
SUMMARY
Students model the spread of an infectious disease by exchanging “saliva.” They use
a “disease indicator” to find out if (and when) they were infected. The class results are
used to discuss the pattern of infectious-disease spread and to lay a foundation for preventive measures.
KEY CONCEPTS AND PROCESS SKILLS
1.
Graphing data can reveal patterns that are not apparent from data tables.
2.
Creating models is one way to understand and communicate scientific
information.
3.
Diseases can be caused by infectious agents, genes, environmental factors,
lifestyle, or a combination of these causes.
4.
Infectious diseases can spread rapidly through a population.
5.
Data can be analyzed to determine trends and/or patterns. Analyzing trends in
how a disease spreads can suggest ways of preventing its further spread.
KEY VOCABULARY
evidence
infectious
trade-offs
Teacher’s Guide
C-1
Activity 30 • It’s Catching
MATERIALS AND ADVANCE PREPARATION
For the teacher
*
1
transparency of Student Sheet 30.1, “Tracking the Disease”
1
Transparency 30.1, “Predicting Infectious Disease Spread”
1
Transparency 30.2, “Procedure for ‘Saliva’ Exchange”
1
Transparency 30.3, “Location of Initial Infection”
1
overhead projector
*
distilled water
8
*
Place Cards
tape, transparent or holder for Place Cards
1
*
bottle of sodium carbonate solution
graph paper (optional)
For each group of four students
1
dropper bottle labeled “Disease Indicator” (containing phenolphthalein
solution)
For each pair of students
1
9-oz. plastic cup containing “saliva” (see below)
For each student
*
1
SEPUP tray
1
dropper
1
Student Sheet 30.1, “Tracking the Disease”
1
sheet of graph paper
For the Extension
additional copies of Student Sheet 30.1
*Not supplied in kit
Without telling the class, prepare two different “saliva” solutions, one containing
only distilled water and one containing sodium carbonate solution. (Differences in pH
of tap water can affect results. For this reason, either use distilled water or check the
reaction of tap water with the “Disease Indicator” in advance. The “Disease Indicator”
is phenolphthalein solution, which turns pink in a basic solution, such as sodium carbonate. In this model, a pink color indicates the presence of disease.)
Assuming a class size of 32 and students working in pairs, only two student pairs should
receive cups containing sodium carbonate solution. (If you have much smaller class
C-2
Science and Life Issues
It’s Catching • Activity 30
sizes, provide the sodium carbonate solution to just one pair of students.) The remaining student groups should receive cups containing only distilled water. Students should
not be made aware of differences between the solutions during the simulation. For this
reason, it is advised that the “saliva” cups be filled in advance and all labeled the same.
The cups containing sodium carbonate can be prepared by adding about 40 drops of
the sodium carbonate solution to a half-full cup of distilled water. Set up two demonstration trays to model how to do an exchange (see Transparency 30.2, “Procedure for
‘Saliva’ Exchange”).
Tape the Place Cards in different locations around the classroom. Laminate them first,
if desired.
To increase the population size for this simulation, consider combining classes with
another teacher. Be sure to review the Procedure in advance and check that you have
enough SEPUP trays to do this. Continue to provide sodium carbonate solution to
only two pairs of students. You can then conduct the simulation for more “days.”
TEACHING SUMMARY
Getting Started
1.
The class discusses the meaning of the term infectious.
2.
The class predicts how an infectious disease might spread over time
(Transparency 30.1).
Doing the Activity
3.
Students decide where they will go to “exchange saliva.”
4.
Model how to conduct a “saliva” exchange and guide the class through the
model of saliva exchange.
5.
Students model getting tested and then share and graph results.
Follow-Up
6.
The class analyzes trends in class data (Analysis Question 1).
7.
Students complete Analysis Questions 2–5.
INTEGRATIONS
Mathematics
Students calculate the percent of people infected out of the class total at the end of each
“day.” This activity also emphasizes predicting and analyzing trends of graphed data.
Teacher’s Guide
C-3
Activity 30 • It’s Catching
BACKGROUND INFORMATION
Causes of Disease
Table 1: Examples of diseases caused by different factors:
Cause
Disease
Genes
cystic fibrosis, sickle cell anemia, hemophilia, childhood diabetes
Infectious Agents
(Germs)
colds, flu, pinkeye, food poisoning, malaria, plague, chicken
pox, Ebola, AIDS, leprosy, polio, sexually transmitted diseases
such as syphilis and chlamydia
Environment
radiation sickness, leukemia associated with radiation exposure, poisoning
Lifestyle
certain forms of cancer (such as lung cancer from smoking)
Combination
of factors
asthma, certain forms of cancer, heart disease, adult onset
diabetes
Spread of Infectious Diseases
Statistics compiled from large closed populations (which have no interactions with
other populations) during an epidemic of an infectious disease show a bell-shaped
curve of the number of infected people over time. Epidemics initially spread slowly;
they accelerate as more and more people become infected. This results in an exponential increase in infections until almost all susceptible people in a population have
contracted the disease. This activity models only what would happen up to this point
in the spread of an infectious disease and does not simulate recovery. In a closed population, the rate of new cases declines once all people have been exposed.
The speed with which an infectious disease spreads will be affected by the infectiousness of the disease, the density and frequency of susceptible people, and the behavior of the susceptible people. The height of the plateau will be affected by how many
susceptible people there are. The number of susceptible people is related to the number who have not been vaccinated or have not been exposed to the infectious disease
before (such as when a new disease enters a population or when many individuals
have been born since the last epidemic of the disease).
REFERENCES
Mausner, J.S. and S. Kramer. Mausner and Bahn Epidemiology–An Introductory Text.
Philadelphia: W.B. Saunders Co., 1985.
C-4
Science and Life Issues
It’s Catching • Activity 30
TEACHING SUGGESTIONS
GETTING STARTED
1.
exchange can happen in a variety of ways, such as
sharing drinks, touching a contaminated surface
and placing hands in the mouth, breathing infected droplets, kissing, sexual contact, etc. This activi-
The class discusses the meaning of the
ty models the spread of a highly infectious disease,
term infectious.
such as a cold or the flu, that can be spread through
Begin to discuss the meaning of the term infectious
by asking, What are the different ways in which
casual contact.
2.
The class predicts how an infectious
diseases are caused? Review the idea that diseases
disease might spread over time
can be caused by different factors, including infec-
(Transparency 30.1).
tious agents, genes, environment, lifestyle, or a
combination of these causes. This idea will be further discussed in the next activity.
Ask the class, How quickly could an infectious disease spread through a population? Students may
mention a variety of factors that could influence
Write the term infectious on an overhead projector
the rate of infection, such as incubation period,
or on the board and ask students to provide defini-
mode of transmission, etc. Help students predict
tions or explanations of the term. Students are like-
what might happen to the number of infected peo-
ly to propose that infectious diseases are those that
ple over time. Use Transparency 30.1, “Predicting
are spread from person to person. Raise the issue of
Infectious Disease Spread” or a blank graph (on the
diseases transmitted by other organisms, such as
board or overhead) with an x-axis of time and a y-
insect-borne diseases: Would students categorize
axis of incidence of disease (or number of infected
them as infectious? Scientists typically do. Other
people) to enable students to predict what would
student responses may generate some discussion.
happen to the number of cases of infectious disease
For example, does the type of contact (direct vs.
in a population over time. (If using the Transparen-
indirect) affect whether a disease is considered
cy, ask students to select the graph they favor and
infectious? Infectious diseases can be transmitted
explain their reasoning.) Discuss their predictions:
by either direct or indirect contact. However, some
Would you expect the number of people infected
infectious diseases may be transmitted only
over time to increase, decrease, or stay the same?
through direct contact (such as impetigo—a bacte-
Students may bring up the idea that different dis-
rial skin disease) or through the exchange of bodily
eases may yield different patterns over time, or they
fluids (such as AIDS).
may suggest a trend not shown on the transparency. Use the blank graph axes on the Transparency to
This activity models the spread of a disease that is
record and discuss other possibilities. Allow stu-
infectious, meaning that it can be passed from one
dents to disagree; inform students that they will be
person to another. Tell students that they will be
collecting evidence about this issue from an in-class
modeling an infectious disease, such as the flu or a
simulation.
cold, that is spread by the exchange of saliva. Saliva
Teacher’s Guide
C-5
Activity 30 • It’s Catching
DOING THE ACTIVIT Y
3.
Students decide where they will go to
“exchange saliva.”
that follow. Consider having students thoroughly
rinse and dry their trays before beginning the activity, as well as after the activity. It is also helpful to
collect the large “saliva” cups immediately after stu-
Hand out Student Sheet 30.1, “Tracking the Dis-
dents have taken their samples. This prevents con-
ease.” Point out the Place Cards around the room.
tamination of these cups from one class period to
Before beginning the exchanges, students must
the next.
decide where they will go each “day,” choosing
from the places on the Place Cards, such as the
shopping mall, a fast food restaurant, and a movie
theater. Students should record their choices in
Table 1, “My Movements,” on Student Sheet 30.1.
n Teacher’s Note: You can conduct this activity in
two ways. In one way, students can consult with
one another and move as a group, visiting various
locations with their friends. Another option is for
students to decide independently where to go.
Infection rates tend to be higher when students
associate randomly, especially if they are instructed
4.
Model how to conduct a “saliva” exchange
and guide the class through the model of
saliva exchange.
n Teacher’s Note: During Part Two of the Procedure,
students simulate disease spread by transferring
“saliva” in fluid exchanges at three different
“places” around the classroom. Students perform
successive exchanges while retaining a portion of
each exchange. It is highly recommended that you verbally guide students through Steps 5–8. The directions
provided in the Student Book provide an additional resource.
not to exchange again with the same students. If
you have time, conduct the activity both ways and
Use laboratory materials or Transparency 30.2,
discuss why random association increases the num-
“Procedure for ‘Saliva’ Exchange,” to show students
ber of people infected. (In a closed population, such
how to conduct the activity. Model a “saliva”
as when students move together in groups, every-
exchange with another student to demonstrate. For
one within the group eventually becomes infected
each exchange, a student removes liquid from his
but is unlikely to infect others not in their group.)
or her tray and places it in the tray of another stu-
If you can conduct the activity only one time,
dent. The second student takes an equal amount of
encourage students to decide independently where
liquid from that same cup (which now has signifi-
they will go (without consulting other students).
cantly more solution) and places it back into the
first student’s cup. Both students should now have
After students have completed column one of Table
1, provide them with the saliva solutions. They can
then complete Steps 2–4 of the Procedure.
n Teacher’s Note: Be sure that students have completely washed out the SEPUP trays between class
periods. Residual sodium carbonate solution in the
trays can lead to false results for the class periods
C-6
Science and Life Issues
an amount of solution equal to that with which
they started; the only difference is that the solutions of the two students have been partially mixed.
Contamination can seriously interfere with the
effectiveness of this simulation. Caution students
to be very careful not to contaminate their samples
It’s Catching • Activity 30
and to avoid touching their dropper to any surfaces
5.
or liquids except during exchanges. One common
mistake students make is to mix solutions in the
wrong cups (working backward).
Guide students through Part Two of the Procedure:
1.
Turn the lights off and on to indicate the
start of Day 1.
2.
Students go to the place they selected for
Day 1. The Place Card states the number
Students model getting tested and then
share and graph results.
Distribute the Disease Indicator bottles and show
students how to add drops of the Disease Indicator
without touching the “saliva” samples. To prevent
contamination, students should be sure to keep the
bottle cap away from any liquid (one method is to
always hold the cap and replace it directly onto the
bottle) and to re-cap the Disease Indicator bottle
immediately after use.
of people with whom the student should
exchange 10 drops of solution in Cup B.
Have students complete Steps 9 and 10 and record
If the student is the only person at the
their results in Table 1 of Student Sheet 30.1.
place, no exchange takes place.
3.
Each student should transfer half the
solution from Cup B to Cup C of his or
her SEPUP tray (Step 5(c) of the
Procedure).
4.
Turn the lights off and on to indicate the
start of Day 2.
5.
Students go to the place they selected for
Collect class results on an overhead projector, using
a transparency of Student Sheet 30.1. Students can
then enter the total number of people infected each
day in Table 2, “Class Results,” and calculate the
percent infected. You may need to remind students
how to calculate percent of people infected (number of people infected divided by the total number
of students in the class, multiplied by 100).
Day 2. The Place Card states the number
of people with whom the student should
FOLLOW-UP
exchange 10 drops of solution in Cup C.
If the student is the only person at the
place, no exchange takes place.
6.
7.
8.
6.
The class analyzes trends in class data
(Analysis Question 1).
Each student should transfer half the
Discuss how the percent of people infected
solution from Cup C to Cup D of his or
increased over time. Eventually, one-half to almost
her SEPUP tray (Step 7 of the Procedure).
all of the students will have become infected,
Turn the lights off and on to indicate the
depending on whether they associated randomly or
start of Day 3.
moved together in groups.
Students go to the place they selected for
Day 3. The Place Card states the number
of people with whom the student should
exchange 10 drops of solution in Cup D.
If the student is the only person at the
place, no exchange takes place.
Analysis Question 1 provides an opportunity to
review or teach how to interpret a graph. Alternatively, you may wish to use the graph and Analysis
Question 1(a) for assessment. The “Organizing
Data” element of the D ESIGNING
AND
C ONDUCTING
Teacher’s Guide
C-7
Activity 30 • It’s Catching
I NVESTIGATIONS (DCI) variable can be used to score
population, the number of people infected begins
student graphs while Question 1(a) can be scored
to plateau. As everyone infected either dies from the
using the “Analyzing and Interpreting Data” ele-
disease or recovers, the number of infected people
ment (of the same variable).
declines until it reaches zero. Since the class model
Use the graphs on Transparency 30.1 to compare
the graph of class results to students’ initial predic-
does not simulate death or recovery, class results
will not show this decline.
tions about the results of this activity. Three of the
Ask students to imagine that they could catch an
graphs on Transparency 30.1 could potentially
infectious, non-fatal disease only from someone
model the class data, which is limited to the first few
with whom they lived. Have them think of a time
days of initial disease spread. The linearly increasing
when a member of their family had a severe cold,
graph (top right corner), the increasing/plateau
pinkeye, or the flu. Ask, What do you predict would
graph (middle right), and the left side of the bell-
happen to the number of people infected over one
shaped curve graph (bottom left) are all possible
day? Over one week? Over one month? The number
based on the limited amount of class data (see Sug-
of people infected over time would increase and
gested Answer to Analysis Question 1 in this Activ-
then flatten out (as all members of the family
ity). In fact, the most common graph of infectious
become exposed to the disease). Ask, Does everyone
disease epidemics of closed populations resembles a
in a family catch an infection if someone in the
bell curve. Initially, an exponentially increasing
home is infected? From their own experiences, stu-
number of people are infected. Since typically some
dents may offer that some people do not get sick at
natural immunity to the disease exists within the
all. Once every member of the family has been
exposed to the disease, the number of new cases
reaches zero. (The exception to this prediction is in
Sample Class Results
living situations in which the population of people
16
living together rotates, such as in prisons, army barracks, or, ironically, hospitals.) Students can now
Number of Infected Students
14
begin to consider one of the limitations of the
12
model: unlike in real life, everyone who was
exposed to the disease was infected.
10
7.
8
Students complete Analysis Question 2–5.
Analysis Questions 2 and 3 explore the idea that
6
knowing patterns of disease spread can suggests
ways of preventing it. Analysis Question 2 focuses
4
on what the individual could do to prevent catch-
2
ing a disease, while Question 3 focuses on what a
community could do. Students may need guidance
0
0
2
1
Time
C-8
Science and Life Issues
3
on how to respond to these questions. Use Trans-
It’s Catching • Activity 30
parency 30.3, “Location of Initial Infection,” to
environmental causes: for example, the case of a
summarize where individuals become infected. For
toxin that is found only at the movie theater. Stu-
example, ask students to raise their hands if they
dents going to the place with the environmental
caught the disease at the fast food restaurant on Day
factor could exchange “germs” with a cup of saliva
1. Count the number of students and record that
set up at that place.
value. Repeat this step for each place (or event) on
Day 1. Stop and discuss what someone who knew
SUGGESTED ANSWERS
this information might do to prevent catching the
TO ANALYSIS QUESTIONS
disease. For example, if you knew that someone at
the fast food restaurant had the infectious disease,
1.
Use your graph of the class results to answer the following questions:
you might avoid going to the restaurant. You could
also try to take preventive measures (such as getting
a. What happened to the number of people
a vaccine, if available) or being careful about wash-
infected with the disease over time?
ing your hands. Raise the issue that some of these
DCI
aid
The number of people infected over time
actions have trade-offs. For example, by avoiding a
increased; in most classroom simulations, the
particular restaurant, you give up the opportunity
graph is most likely to appear to be a linearly
to eat at that place.
increasing line (such as the one shown on the
Discuss Analysis Questions 4 and 5 as a class to rein-
top right corner of Transparency 30.1). In many
force the concept of modeling as a tool with both
cases, the graph of the number of people infect-
strengths and weaknesses. Follow up Question 5 by
ed over time in a large population will approxi-
asking, What would you expect the number of cases
mate an exponential curve. However, the pop-
over time to look like for a genetic disease? In fact,
ulation size of a single class is not large enough
the incidence of genetic diseases is fairly constant
to reveal such a curve.
over time (refer to the graph on the middle left of
b. How does this compare to your initial prediction?
Transparency 30.1), though the rate of a genetic dis-
Explain.
ease may decrease in a population where the disease
is lethal before reproductive age. As prenatal genet-
Responses to this question will depend on stu-
ic testing becomes more widely available, the inci-
dents’ initial predictions. Some students may
dence of some genetic diseases may drop if individ-
have predicted that the number of people
uals choose to terminate these pregnancies.
infected would eventually plateau, and perhaps
even decline. In a closed population (where
The incidence of diseases caused by environment or
there is no interaction with other populations),
lifestyle will vary widely. The more people exposed
this is typically what happens (see Background
to a toxin, the greater the incidence of disease (such
Information in this Teacher’s Guide). This sim-
as with smoking). But the incidence is unlikely to
ulation is not set up to show this.
spread in the exponential fashion of an infectious
disease. You may wish to ask students how the activity could be modified to model a disease that has
2.
Think about how the infectious disease was
spread from person to person in your com-
Teacher’s Guide
C-9
Activity 30 • It’s Catching
munity. If you were trying to avoid catching the dis-
nesses, and could result in negative economic
ease, what could you do? Use evidence from this
consequences for the community. Instituting a
activity to support your answer.
public awareness campaign could be expensive
and might not reach the target population.
Depending on the patterns of data collected in
Some people in the population might not have
class, students may suggest staying at home or
access to vaccines or medications, even if they
avoiding certain places (or events). These state-
were available, and this could result in contin-
ments should be supported by evidence. For
ued spread of the disease. Isolating individuals
example, if many infected people attended the
may be unethical if it is against their will.
movie theater each day, that might be a place a
person would avoid. Students may also point
4.
What are the strengths and weaknesses of
out that the Place Cards themselves directed
this model for the spread of infectious dis-
students to exchange with more or fewer peo-
eases?
ple; students may cite the Place Cards as evi-
3.
dence against going to a particular place, such
Strengths of this model include the way it pro-
as the shopping mall, where the number of
vides data on how quickly an infectious disease
exchanges was high to represent close contact.
can spread through a community and how it
demonstrates that people are more likely to be
a. Imagine that you are the director of the health
exposed at certain events and when in contact
department in the town where this disease is
with more people. Weaknesses include the fact
spreading. It is your job to help prevent people from
that each infected person continued to infect
getting sick. Explain what you would recommend
every other person with whom they had con-
to try to prevent more people from getting infected.
tact, i.e. there is no incubation period and no
Answers may include closing down or discour-
one stops being infectious. In addition, the
aging people from visiting certain places or
number of people in a class is much smaller
attending certain events, instituting a public
than the number of people in a population
awareness campaign, or encouraging other pre-
exposed to most infectious diseases.
ventive measures, such as vaccines or medications (if available). If the people who were
infected could easily be identified, a health
director might also suggest isolating those individuals from the general population. (The issue
of quarantine will be further investigated in
Activities 33 and 34.)
b. What are the trade-offs of your recommendations?
5.
Could you use this activity to model how
diseases that are not infectious are spread?
Explain.
This activity could not model non-infectious
diseases because non-infectious diseases are not
spread from person to person (as was modeled
in this activity). Refer students to the Introduction to the activity where they considered the
Closing down or discouraging people from vis-
causes of diseases. Again, emphasize that this
iting certain places or attending certain events
activity modeled a particular scenario of an
could affect the profitability of specific busi-
infectious disease.
C-10
Science and Life Issues
Name
Date
Tracking the Disease
There are many places in your community. In this activity, you may go to any of
the places or events listed below:
Fast food restaurant
Home
Football game
Movie theater
Music store
School dance
Shopping mall
Video arcade
Table 1: My Movements
Times
Cup
Initial (Day 0)
A
Day 1
B
Day 2
C
Day 3
D
Place
Do you have the disease?
Your Desk
Table 2: Class Results
©2006 The Regents of the University of California
Times
Number of People Infected
Percent of People Infected
Initial
(Day O)
Day 1
Day 2
Day 3
Science and Life Issues Student Sheet 30.1
C-11
Number of
infected people
Number of
infected people
©2006 The Regents of the University of California
Number of
infected people
Number of
infected people
Number of
infected people
Number of
infected people
Predicting Infectious Disease Spread
Time
Time
Science and Life Issues Transparancy 30.1
Time
Time
Time
Time
C-13
Procedure for “Saliva” Exchange
Day 1
1 Exchange 10 drops with another person.
SEP
Y
TRA
UP
C
B
A
1
2
5
4
3
E
D
6
7
8
9
2 Move 1/2 of the solution into Cup C.
Day 2
3 Exchange 10 drops with another person.
Y
TRA
UP
SEP
C
B
A
1
2
5
4
3
E
D
6
7
8
9
4 Move 1/2 of the solution into Cup D.
©2006 The Regents of the University of California
Day 3
5 Exchange 10 drops with another person.
Y
TRA
UP
SEP
C
B
A
1
2
Science and Life Issues Transparency 30.2
3
4
5
E
D
6
7
8
9
C-15
Location of Initial Infection
PLACE
DAY 1
DAY 2
DAY 3
Total number infected
at each place (or event)
Fast food restaurant
Football game
Home
Movie theater
Music store
School dance
Shopping mall
©2006 The Regents of the University of California
Video arcade
Science and Life Issues Transparency 30.3
C-17