“We are going to work in teams of three
of four students. You need to name your team. Each student will complete
the Lab Outline I am
handing out. Each team will complete the Bacteria
Everywhere Data Table. ”
“I would like you to try to test for
bacteria in as many different areas as possible. If you are going
to test hands and under fingernails
for bacteria, wash your hands after you have swabbed these areas.”
“Each team should talk quietly among
themselves and hypothesize which areas you might test that will
have the most bacteria. State
why. State how fast the bacteria will grow in the areas you are
selecting and why.”
“Now, I would like you to design an
experiment that will test your hypothesis.”
5. Ask each team:
“Are you ready to explain your hypothesis
to the class? If so, let us begin.”
6. Encourage the teams by saying:
“Please discuss the merits of each test
you are suggesting. I would like the teams to exchange helpful information
experiments of each team.”
After group discussion, give the teams time to revise their hypotheses
Show students how to swab a surface (on dry surfaces use a moist
swab) and inoculate a Petri dish (see page 9, Science and Our Food
Supply Investigating Food Safety from Farm to Table: Teacher's
Guide for High School Level Science Classrooms, Laboratory Procedures).
These procedures will be used throughout these two laboratory lessons.
Review with students the information related to the important rules
of lab safety, especially handling of bacteria in Petri dishes(see
page 8, Science and Our Food Supply Investigating Food Safety from
Farm to Table: Teacher's Guide for High School Level Science Classrooms,
10. Give instructions:
After giving each team three Petri dishes, provide the following
Label the dishes on the bottom (agar side).
- Divide the control dish
into thirds. Label the control plate: agar, wet swab, and dry
swab. Then swab the control plate.
- Divide and label the other
two dishes with the areas they want to test.
- Label the dishes
with the date, their team name, class, and hour to avoid mix-ups.
Label along the side, so you can see bacterial
growth in the center.
- For easy and fun identification, students
can swab the plates using their initials.