Materials Needed
Provide the following materials for each group of students:
4 plastic sandwich bags
masking tape or self-adhesive mailing label (to label each bag)
markers, pens, or pencils
waxed paper
a potato cut into four slices of roughly equal size
toothpicks
writing paper
Lesson Plan
Divide students into small groups (three or four students). Provide each group with four plastic bags. Each should have a label attached. The students should write on each label one of the following:
Bag 1: Handled by group members
Bag 2: Rubbed on surface of _____
Bag 3: Blown on by group members
Bag 4: Control
Cover part of each group's work area with waxed paper. Place the potato slices on the waxed paper. (NOTE: Handle the potato by the outer, skin-covered surface only. Do not touch the inside, exposed surface of the potato.) Tell students not to touch the potato yet.
Ask students in each group to pass around the first potato slice; each student should have an opportunity to thoroughly handle the slice. Then have a student put the slice in Bag 1.
Have students rub the second potato slice on a selected surface in the classroom (e.g., the floor, a countertop, the classroom sink) and fill in the blank on the bag to indicate the surface the potato was rubbed on. Then ask a student to put that slice in Bag 2.
Show students how to use a toothpick to handle the next potato slice. Tell students not to touch the potato or let it touch any surface. Have each student take a turn holding the toothpicked potato and blowing on it for about ten seconds. Ask a student to put that potato slice into Bag 3.
Finally, have a student use another (clean) toothpick to place the fourth slice in Bag 4. That slice is the control slice. It has not been touched, rubbed on any surface, or blown upon.
Ask students to record on paper what they have done. Have them predict which potato slice contains the most germs and the least germs. Then have each group gather its four bags and place them in a dark closet. Leave the potato slices in the closet for a week.
At the end of the week, ask students to record the results of the experiment, including answers to the following questions: Which potato slice had the most germs? Which had the least? Why might that be? Did you predict correctly? How is a control important in a scientific experiment?
Have students record their observations and write a statement that explains what this experiment taught them about germs. Follow up with this question: What does this experiment teach you about the importance of washing your hands regularly?
Variations: Invite the school nurse to participate in this activity and to help add to the discussion. Supplement the lesson with a children's book about germs.
Assessment
Evaluate students on their observations and discussion of the experiment's questions.
