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What’s Living in My Mouth?

From: “Lets [sic] Get Defensive: A Unit Studying the bodies [sic] defensive mechanisms”.
By Jaret Schug and Jeff Baier

Modified by: Kirstin Bittel and Rachel Hughes



Time: 3 class periods
Preparation Time: None
Materials:

1 protocol sheet
1 square of paraffin wax
1 sterile tube for saliva collection
1 blood agar plate
2 sterile cotton swabs
1 wax pencil
1 conclusion sheet
1 copy of article – Bacteria: Friend or Foe

Abstract
Student groups are presented with an opportunity to see bacteria alive and feeding inside the human mouth. This lesson serves as the engagement piece in a larger learning cycle about human immunity: how the body naturally defends itself from pathogens.

Objectives
Students will be able to:

i. Articulate in written and oral formats that bacteria can be found living everywhere.
ii. Explain in written and oral formats why the immune system is necessary.

National Science Education Standard:
Content Standard C – Life Science
BIOLOGICAL EVOLUTION
• The great diversity of organisms is the result of more than 3.5 billion years of evolution that has filled every available niche with life forms.

THE INTERDEPENDENCE OF ORGANISMS
• Organisms both cooperate and compete in ecosystems. The interrelationships and interdependencies of these organisms may generate ecosystems that are stable for hundreds or thousands of years.

THE BEHAVIOR OF ORGANISMS
• Like other aspects of an organism's biology, behaviors have evolved through natural selection. Behaviors often have an adaptive logic when viewed in terms of evolutionary principles.



Teacher Background
Numerous varieties of bacteria are known to call the oral cavity home. Two of the most common inhabitants are lactobacillus acidophilus and streptococcus mutans. Both bacteria play a role in cavity formation in humans. These bacteria break down sugar into lactic acid that eats away the tooth enamel. Streptococcus mutans is the initiator while actinomyces viscosus, another variety of bacteria, colonizes later and is important in generating acid by-products, which de-mineralize the enamel. Once the enamel has been demineralized, bacteria can enter the dentin of the tooth, which protects the nerve endings from exposure.

SAFETY WARNING: AS STUDENTS ARE WORKING WITH SALIVA, A BODILY FLUID, IT IS IMPERATIVE THAT YOU IMPRESS ON STUDENTS THE IMPORTANCE OF NOT TOUCHING ANYONE ELSE’S FLUIDS OR MATERIALS AS THEY ARE CONSIDERED BIOHAZARDS!


Related and Resource Websites
Let’s Get Defensive
http://www.aai.org/committees/education/defensive.pdf

Pre-Lab Preparation
Prepare one agar plate with no bacteria. Use this sterile plate as a baseline with your class in the event that bacteria are growing in places within the room.


Activity

DAY ONE
1. As students enter the room, have the following question written on the board. “What kingdom of life (Bacteria, Archaea and Eukarya) is represented almost everywhere in the world?” Allow students a few minutes or so to record their ideas individually. Once students have identified the correct answer as “bacteria” ask them if they believe that bacteria can live inside our mouths.

2. Tell students that today they will complete a lab to determine if bacteria do indeed live inside their mouths.

3. Distribute the protocol sheets to students and ask them to read them over. Have them copy information into their lab books.
(Depending upon your budgetary constraints you may choose to make copies of the protocols for students to keep in their lab books so they do not have to copy the information.)

4. Ask students if they have any questions at this time.

5. Inform students that in order to keep the experiment safe they CANNOT SHARE MATERIALS as this lab makes use of bodily fluids. Also students CANNOT WORK WITH ANOTHER STUDENT’S SALIVA. These are important safety issues that need to be addressed before allowing students to complete the lab.

6. Discuss with students the importance of taking samples from different parts of the room and accurately describing that location in their science notebooks.

7. Allow students time to follow the protocol and complete the investigation.

8. Have students bring their plates to be incubated.

9. Once all the plates have been placed in the incubator, have students predict what they believe will appear in the agar plates. What, if anything, will grow on the saliva side of the plate? What, if anything, will grow on the room side of the plate?

10. Ask the students to share what they already know about bacteria. What are they? Where can they live? What do they do? What niche do they fill?

DAY TWO
1. As students enter the room, have the following question written on the board: Are bacteria friend or foe? Allow students a few minutes or so to record their ideas individually.

2. Distribute the article titled, ‘Bacteria Friend or Foe?’ and have students read it. Ask students if they agree with the article. Are bacteria more helpful than harmful?

DAY THREE
1. Have students collect their agar plates.

2. Ask students to look over their results. What do they notice about the two sides of the plate? Are they similar? Different? What does that tell them? Give students about 10 minutes to sketch their results and record their observations and inferences on a T-chart in their lab books. [A conclusion sheet has been included if your students are not comfortable writing their own conclusions. We advise against using the conclusion sheet if possible, as having students write their own conclusion encourages higher order thinking.]

3. Next, have students meet in groups to compare notes. What do they notice on the two sides of the plates? What do the plates have in common? What is different? Where did they collect room samples from?

Closure

Bring the class together to discuss the results. Ask students, “Does bacteria live in the human mouth? What about the room? Does it live there? In which locations? How do you think it got there? Are all of the bacteria in our bodies and in the room bad? “

Ask students what questions they have at this time. Allow students to hypothesize answers. Clarify that while you are accepting student ideas, and answers to questions, that does not mean the answers are necessarily correct and that over the next week or so, they will be investigating how the human body fights off the bacteria that make us ill.

Embedded Assessment

1. Students’ ability to analyze experimental results and text can be assessed by their written and verbal responses.

2. Students’ ability to draw a conclusion about the role of both bacteria and the immune system can be drawn in both class discussion and in a written conclusion.

3. Students’ ability to recognize bacteria as a group of organisms within the diversity of life that has evolved in such a manner that they may have roles in each others’ life history can be assessed in class discussion.

Homework

Have students write a conclusion in the laboratory notebook. What did they learn? How does this information impact students and their daily lives? What questions do they have as a result of the investigation/discussion?

Embedded Assessment

 

 


PULSE is a project of the Community Outreach and Education Program of the Southwest Environmental Health Sciences Center and is funded by:


an
NIH/NCRR award #16260-01A1
The Community Outreach and Education Program is part of the Southwest Environmental Health Sciences Center: an NIEHS Award

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Supported by NIEHS grant # ES06694


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Last update: November 10, 2009
  Page Content: Rachel Hughes
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