As students enter the room, have the following question
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
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?
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.
the article titled, ‘Bacteria Friend
or Foe?’ and have students read it. Ask students
if they agree with the article. Are bacteria more helpful
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?
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
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.
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?