Biology Lab – Standards 10a

Dreaded Red   

Purpose: Why is it important for doctors to understand the transmission route of a disease?

State Standards: 10a

Organisms have a variety of mechanisms to combat disease.
As a basis for understanding the human immune response:
10a . Students know the role of the skin in providing nonspecific defenses against infection.  

Background: You have probably experienced a cold or flu and know what it is like to be sniffing and sneezing. When a person sneezes, viruses and bacteria can be spread on the aerosol droplets of the sneeze. The rapid spread of diseases, known as epidemics, is of great concern to public health officials. In this activity, you will simulate the transmission of disease in this classroom.

One year during Spring Break you and your friends decided to go on a cruise across the Atlantic Ocean. (Someone won the lottery!!!!!) One of the spots that you are looking forward to is Africa.

Once you and your friends arrived in Africa, you decided to grab a bite to eat while your friends go out sight seeing. About four to five hours after you ate, you and your friends got back on the boat to head to your next destinations. You start feeling a little sick to your stomach and a little light headed, but you assume that it is from all of the excitement from being on the trip. Later that night, you and your friends hang out at parties on the boat, sharing drinks, food, etc.

By this time you are feeling very ill, you now have a temperature, a severe headache, extreme abdominal pain, and are spending a good deal of time in the restroom.

About 35 of you are on this trip, and once the parties are over, all of your friends come down with the same symptoms you started with. These are all symptoms of Amoebic Dysentery, a disease that is caused by parasitic amoebas that eat away at the intestinal wall, you get them from contaminated food or water. This disease causes bloody diarrhea, or dreaded red.

Materials: small plastic cups, 1% phenolphthalein solution, dilute sodium hydroxide, solution safety goggles

CAUTION: Sodium hydroxide solution is toxic by ingestion. Avoid contact with body tissues, damage occurs quickly. Very dangerous to the eyes.


1. Your teacher will give you a cup containing a clear solution.

2. When instructed, you will find a person that will switch fluids with you. Simply pour the contents of your cup into their cup and repeat this process until the fluids have mixed (two or three times). Make sure you each have close to equal amounts when you are finished mixing.

3. Return to your seat and record the name of the person you switched fluids with in your data section.

4. Repeat steps #2 and #3 two more times when instructed by your teacher. Make sure to keep an accurate list of people you switch with. The correct order of the list is critical for your class to solve the origin of the disease.

5. Your teacher will now place a drop of phenolphthalein indicator solution in your cup. If your solution turns pink/red, then you have contracted dreaded red. If your solution remains clear, then you have not contracted the disease.

6. The infected people must place their names on the board along with the three people that they switched fluid with. The order of the list must be correct!

7. The class should be able to work through the order of transmission to determine which individual(s) were infected and are responsible for the spread of dreaded red.


Data Table 1: Contacts made in each round



Person contacted


Round 1


Round 2


Round 3




Data Table 2: Infected Individuals in Class



Names of infected people


Contacts of each infected person


Round 1


Round 2


Round 3


































1. Who started the outbreak of dreaded red in your class? (Narrow it down to two people)