Disease Transfer: Difference between revisions

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== Age ==
{| class="wikitable" style="color:black; background-color:#ddd; margin-left: auto; float:right"
| [[Biology]], [[Math]]:
| Disease Transfer, Exponential Growth
|-
| Grade Range:
| [[Middle School]], [[High School]]
|-
| Format:
| [[Hands-on]]
|}


Elementary School, Middle School, High School
This is a simple demonstration that gets two messages across: How easily diseases can be transferred, and why the number of people sick grows so quickly. This demonstration also can help students make connections between different subjects, in this case seeing the connection between math and biology.
 
== Format ==
 
Stage/Hands-on (requires a group of about 15-40 students)


== Materials ==
== Materials ==


    Paper cups (one for each student)
* Dixie Cups (One per student)
    DI water (~30 mL per cup, needs to be neutral!)
* Water
    NaOH solution (0.3 molar)
* Eyedropper with Phenolphthalein
    Phenolphthalein indicator solution & eyedropper
* 0.3M NaOH Solution
* 10mL Graduated Cylinder
* 100mL Beaker


== Safety Precautions ==
== Safety Precautions ==


Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience. Make sure students do not try to drink from their cups, even dilute NaOH should not be swallowed! Also try to minimize expose to skin.
Please read the Liquid Chemical section of the [[Demonstration Safety]] page before performing this demonstration.
 
[http://www.sciencelab.com/msds.php?msdsId=9927755: .3M Sodium Hydroxide MSDS]
 
[http://www.sciencelab.com/msds.php?msdsId=9926477: Phenolphthalein MSDS]
 
== Preparation ==
 
Note that this demonstration will not work well for very small or very large groups. An audience of about 15-40 students should work well.
 
Prepare the NaOH and indicator solutions beforehand.
 
Pour ~30 mL of water into each cup, enough for every student to have one.


== Demonstration ==
== Demonstration ==


Give each student a cup with water. Randomly pick about one tenth (1/10) of all the students. Add about 5 mL of the NaOH solution to those selected students' cups.
;Preparation:
 
* Fill the dixie cups about 1/3 with water. Select a tenth of the cups (rounded up) and add 5mL of the NaOH solution to them. To do so, first pour the NaOH into the beaker, then measure 5mL using the graduated cylinder. Be sure to select the cups at random!
Instruct all the students to each find three other students share their water with. To share the water, instruct them to first pour one cup of water into the other cup, then pour half that mixture back into the first cup.
;Presentation:
 
# Have students all pick a cup of water, and make sure to remind them that they should NOT drink from them. Some of these cups are contaminated with a mysterious disease! Be sure to state how many of the cups are contaminated.
Once every student has mixed their water with three other students, go around and add a few drops of the indicator to each cup. Compare the number of students that started out with a basic solution to the number of students that ended up with one.
# Explain that students will be mixing their water cups with the others around them. Each student will end up mixing four times, and shouldn't mix more than once with the same person. To mix waters, one of the students should pour their cup fully into the other student's cup. Then, that student should pour water back into the first student's cup until they are equal.
 
#* Ask the students to all choose one person next to them, shake hands, and mix their water with them.  
== What to Say ==
#* Have students now choose someone they have to walk to, shake hands, and mix their water again.
 
#* Have students now choose someone nearby that they haven't mixed water with, shake hands, and mix their water again.
This demonstration can easily be adapted for younger and older audiences. Younger audiences may be more interested in the concept of basic hygiene - how hand washing and bathing can prevent them from getting sick. Older audiences may be interested in the spread of sexually transmitted diseases.
#* Have students choose someone they know that they haven't mixed water with, shake hands, and mix their water again.
 
# After students have finished, have them all sit in their seats or in a row. Let them know that you are now going to check who caught the mysterious illness by using your indicator. Walk along and put 3-4 drops of the indicator in each cup, and have students gently swirl their cups to see if a color change happens.
A sample script for young audiences:
# After noting how many students have a color change, remind them of how few of them were originally infected. How did it spread so quickly?
 
== Why This Works ==
I bet every single one of you hears your parents tell you to wash your hands every day. You all do it, too, right? That's good - do you know why they tell you to wash your hands?
 
That's right, because if you don't wash your hands, you can introduce harmful germs to your body and get sick. But how big of a threat are these germs really?
 
In fact, there is a very serious danger of catching a cold or another disease from bacteria or viruses that you might find on a doorhandle, a computer keyboard, your friend's hands, or even in the air you breathe. Washing your hands to kill these germs really does help keep you healthy.  
 
(Now pick 1/10th of the audience - if it's a class of 30, pick 3 students)
 
 
Today we're going to see just how quickly a disease can spread. We're going to give you all a cup of water - this water represents your own body. Now, you three special volunteers are actually not so lucky - you're going to start off with a disease. Right now I'm adding a special chemical to your water that represents the virus in your body that is causing this disease.
 
Unfortunately, this chemical is clear and you can't see it in the water, so no one else knows you have the disease. That means, if you give the disease to your friend, someone who meets your friend will have no idea that they're coming into contact with the disease.
 
So, everyone in the class needs to find a partner and they are going to mix their water with that partner. Just pour both of your volumes of water together into one cup, and then pour half that water back into the other cup. Then I want you to find another, different person to do the same thing with, and then another. In total, you need to share your water with three different people!
 
While you guys are mixing your water, think about what this activity represents. Sharing your water is like bringing your body into contact with this other person - this could mean shaking hands with them, touching something after they have touched it, or even just breathing the same air they are breathing.
 
Ok, now I am a doctor. I am going to go around and test you all for the disease. I'm going to add a chemical to your water that will turn pink if you have the disease.
 
At first, only three people had that disease. Do you think you have the disease now? Did you come into contact with one of those three people? How many of your classmates do you think have the disease? Do you think it's twice as many people? Do you think it's three times as many people?
 
Ok, let's count. Wow, X many people have the disease now! Isn't it amazing quickly it spread? Think of how many people you interact with during the school day - if one person brings a germ to school, it could easily find its way into nearly anyone else in your school. But, you can stop those germs! Washing your hands is a great way to kill those germs and prevent the spread of diseases such as the flu or colds.
 
You should also offer a very brief explanation of the acid/base chemistry that is helping to illustrate this demonstration (see below).
 
== Why It Is ==
 
This is really a demonstration of exponential growth which we are applying to one real-life example, the spread of diseases. Every time you have the audience mix their water, a disease-carrier turns into two disease carriers. In other words,
 
[Disease carriers] = [Initial disease carriers] x 2
 
So how many students would you expect to catch the disease by the end of the demonstration?
 
[Disease carriers] = [Initial disease carriers] x 2 x 2 x 2


Eight times as many students as you started with may end up with the disease, although slightly fewer will probably catch it because sometimes two disease-carriers will mix water with each other, in which case no one new gets the disease.
Diseases can transfer from host to host in a variety of ways. Coughing and sneezing are common ways for disease to spread, and other diseases can survive on surfaces like counters and doors. Something as simple as shaking hands with someone could be enough to transfer the illness from one person to another, and then that person becomes a new host to spread the disease.


In general,
To track how quickly a disease spreads, we can look at how many were original carriers, and how many became hosts. (''Note: for the following section, this will assume a class of 30 students.'')
{| class="wikitable" style="color:black; background-color:#ddd; text-align: left; margin-right: 20"
| Rounds
| Total Infected
|-
| 0 (Start)
| 3
|-
| 1
| ~6
|-
| 2
| ~11
|-
| 3
| ~19
|-
| 4
| ~27
|}


[% disease carriers] = [Disease carriers] / [Total population] = [Initial disease carriers] / [Total population] * 2^N = 2^N / 10
This sample data collection shows how quickly our disease can spread from one host to another. As more trials were performed, the number of people infected increased faster and faster. This is because with each new trial, there were even more people infected than before, with the rate of growth accelerating. This means that the rate at which a disease spreads is ''Exponential'', or grows faster as time goes on.


where N is the number of times you mix the water. The factor of 2 ^ N is where the phrase "exponential growth" comes from.
For tracking the spread of disease, you can use a simple "Pint-size"<!--PUNPUNPUNPUNPUNPUNPUNPUNPUNPUN--> calculation:
{| class="wikitable" style="color:black; background-color:#ddd; text-align: left; margin-right: auto"
|+ Exponential Growth
| '''P ≈ i''' * 2<sup>''N''</sup> '''/ T'''
|-
| '''P''': Percentage infected
|-
| '''i''': Initial # infected
|-
| ''N'': Number of Trials performed
|-
| '''T''': Total # of people
|}
This equation is a way to approximate how many will be infected by the end of each trial, and in general it will be quite accurate. There will be some small differences from the actual results, since the equation doesn't account for anyone who is infected mixing with another infected individual. However, it still shows us how the spread of diseases, like the common cold or flu, can be predicted using math.


The phenolphthalein indicator is just an acid/base indicator. Water is neutral, so the phenolphthalein does not change color. Students that carry some NaOH in their water will have a basic (high pH) solution, so the indicator will turn pink.


== Real Life Examples ==
== Additional Information ==


The spread of disease and other exponential growth processes, including population growth and investment interest.
* This can be turned into a detective game! Have the students record who they mixed their water with during each trial. After all the trials and finding out who is now infected, have the students work together and compile their data. By comparing who mixed water with whom, and with careful evaluation, students can learn to determine which individual(s) had to be the initial carrier(s)! For this type of game, it is suggested that the number of carriers be decreased to simplify the detection work.
* This demonstration pairs well with the [[Towers of Hanoi]] and the [[Chlorine The Bacteria Killer]] demonstrations

Latest revision as of 16:41, 19 August 2016

Biology, Math: Disease Transfer, Exponential Growth
Grade Range: Middle School, High School
Format: Hands-on

This is a simple demonstration that gets two messages across: How easily diseases can be transferred, and why the number of people sick grows so quickly. This demonstration also can help students make connections between different subjects, in this case seeing the connection between math and biology.

Materials

  • Dixie Cups (One per student)
  • Water
  • Eyedropper with Phenolphthalein
  • 0.3M NaOH Solution
  • 10mL Graduated Cylinder
  • 100mL Beaker

Safety Precautions

Please read the Liquid Chemical section of the Demonstration Safety page before performing this demonstration.

Demonstration

Preparation
  • Fill the dixie cups about 1/3 with water. Select a tenth of the cups (rounded up) and add 5mL of the NaOH solution to them. To do so, first pour the NaOH into the beaker, then measure 5mL using the graduated cylinder. Be sure to select the cups at random!
Presentation
  1. Have students all pick a cup of water, and make sure to remind them that they should NOT drink from them. Some of these cups are contaminated with a mysterious disease! Be sure to state how many of the cups are contaminated.
  2. Explain that students will be mixing their water cups with the others around them. Each student will end up mixing four times, and shouldn't mix more than once with the same person. To mix waters, one of the students should pour their cup fully into the other student's cup. Then, that student should pour water back into the first student's cup until they are equal.
    • Ask the students to all choose one person next to them, shake hands, and mix their water with them.
    • Have students now choose someone they have to walk to, shake hands, and mix their water again.
    • Have students now choose someone nearby that they haven't mixed water with, shake hands, and mix their water again.
    • Have students choose someone they know that they haven't mixed water with, shake hands, and mix their water again.
  3. After students have finished, have them all sit in their seats or in a row. Let them know that you are now going to check who caught the mysterious illness by using your indicator. Walk along and put 3-4 drops of the indicator in each cup, and have students gently swirl their cups to see if a color change happens.
  4. After noting how many students have a color change, remind them of how few of them were originally infected. How did it spread so quickly?

Why This Works

Diseases can transfer from host to host in a variety of ways. Coughing and sneezing are common ways for disease to spread, and other diseases can survive on surfaces like counters and doors. Something as simple as shaking hands with someone could be enough to transfer the illness from one person to another, and then that person becomes a new host to spread the disease.

To track how quickly a disease spreads, we can look at how many were original carriers, and how many became hosts. (Note: for the following section, this will assume a class of 30 students.)

Rounds Total Infected
0 (Start) 3
1 ~6
2 ~11
3 ~19
4 ~27

This sample data collection shows how quickly our disease can spread from one host to another. As more trials were performed, the number of people infected increased faster and faster. This is because with each new trial, there were even more people infected than before, with the rate of growth accelerating. This means that the rate at which a disease spreads is Exponential, or grows faster as time goes on.

For tracking the spread of disease, you can use a simple "Pint-size" calculation:

Exponential Growth
P ≈ i * 2N / T
P: Percentage infected
i: Initial # infected
N: Number of Trials performed
T: Total # of people

This equation is a way to approximate how many will be infected by the end of each trial, and in general it will be quite accurate. There will be some small differences from the actual results, since the equation doesn't account for anyone who is infected mixing with another infected individual. However, it still shows us how the spread of diseases, like the common cold or flu, can be predicted using math.


Additional Information

  • This can be turned into a detective game! Have the students record who they mixed their water with during each trial. After all the trials and finding out who is now infected, have the students work together and compile their data. By comparing who mixed water with whom, and with careful evaluation, students can learn to determine which individual(s) had to be the initial carrier(s)! For this type of game, it is suggested that the number of carriers be decreased to simplify the detection work.
  • This demonstration pairs well with the Towers of Hanoi and the Chlorine The Bacteria Killer demonstrations
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