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Materials

The materials required for this science fair project:
- 5 agar petri dishes
- 5 disinfected swabs
- 1 bottle of disinfected water
- 1 marker pen

Procedure

1. For this science fair project, the independent variable is the locations the swabs are wiped to sample for germs. The dependent variable is the number of bacteria colonies that grown in each petri dish. This is determined by observing and counting the bacteria colony spots. The constants (control variables) are the room temperature, the amount of sunlight and the ingredients in the petri dishes.

2. The four petri dishes are stored in a refrigerator. The petri dishes are brought to room temperature before the start of the science experiment, by taking them out of the refrigerator and allowing them to attain room temperature. The petri dishes are labeled A, B, C, D and E.

3. The sterilized swab is first made damp using  sterilized water.  The swabs are rubbed in the  following  places and then rolled and rubbed in the petri dishes.

a. Rub the swab on  the handle of the shopping trolley and then roll it over the agar in petri dish A.

b. Rub the swab on  a computer keyboard and then roll it over the agar in petri dish B.

c. Rub the swab on the water cooler handle and then roll it over the agar in petri dish C.

d. Rub the swab on a lift button and then roll it over the agar in petri dish D.

e. Rub the swab on a door knob and then roll it over the agar in petri dish E.

4. The cover is closed and the 5 petri dishes are kept in a cool place for the bacteria to cultivate.

5. The number of  bacteria colonies  is counted after 5 days and recorded in the below table.

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Complexity level:
7
Project cost ($):
20
Time required:
1 day to prepare, 5 days for the science project experiment
Material availability:
Easily found
Safety concerns:

The bacteria should be destroyed before it is disposed of, by pouring bleach into the petri dish to kill all the bacteria before disposing of them in the trash. Alternatively, use a proper biohazard disposal bag.