Examining the effect of temperature on bacteria
Materials required for the science fair project:
- 15 agar Petri dishes
- 15 disinfected swabs
- 1 bottle of disinfected water
- 15 test tubes and a rack
- 1 measuring cylinder
- 50 ml E Coil bacteria culture
- 50 ml Streptococcus bacteria culture
- 50 ml Bacillus bacteria culture
- 1 Marker pen
- 5 beakers
- 2 hot plates
- 3 thermometers
- 1 bag of ice
- 1 bag of dry ice
- 1 clock
1. The independent variables in this science fair project are the temperature and species of bacteria - E Coli, Streptococcus or Bacillus. The dependent variable is the size of bacteria growth after five days, which is determined by measuring the size of bacterial growth with a ruler. The constants (control variables) are the temperature of the room, amount of sunlight, and agar preparation of the Petri dishes.
2. Store the 15 Petri dishes prepared using the agar in a refrigerator. Before the start of the experiment, take the 15 Petri dishes out of the refrigerator and allow them to warm up to room temperature.
3. Divide the 15 Petri dishes and 15 test tubes into three groups of five. Each group will contain five test tubes and five Petri dishes. Use the marker pen to label each group according to the species of bacteria that will be cultivated in it E Coli, Streptococcus or Bacillus. Next, label each of the five test tubes and Petri dishes within each group as -78 degrees Celsius, 0 degrees Celsius, 25 degrees Celsius, 60 degrees Celsius or 100 degrees Celsius.
4. Transfer 10 ml of the E Coli, Streptococcus and Bacillus bacteria culture into each of the five test tubes according to the labels made earlier.
5. Fill three beakers with water. Leave one beaker to warm up to the room temperature of 25 degrees Celsius, and place the other two beakers on two hot plates. Adjust the temperature of one hot plate to 60 degrees Celsius, and the other to 100 degrees Celsius. Next, fill the remaining two beakers are with ice cubes (0 degrees Celsius) and dry ice (-78 degrees Celsius).
6. Place three test tubes, one from each group (E Coli, Streptococcus and Bacillus), into the beakers according to the temperature markings made earlier. Leave the test tubes in their respective beaker for two hours.
7. After two hours, rinse the swab with disinfected water and dip it into the first test tube. Open the cover of the corresponding Petri dish, the one that has the same label as the test tube, and swab gently on the Petri dish. Close the cover closed and keep the Petri dish in a cool, shaded are for five days, allowing the bacteria to incubate. Repeat the procedure for the remaining 14 Petri dishes.
8. After five days, use a ruler to measure the size of the bacteria colony and record the measurements in the table given below.
Always follow laboratory safety guidelines and always practice sterile technique when handling microbes. Never have any food or drink at your workstation and always thoroughly wash your hands with disinfectant soap or alcohol before leaving your workstation. Always dispose of used material in a biohazard bag. If none are available, the bacteria should be destroyed with bleach before being disposed of