| Complexity level: | 5 |
| Project cost ($): | 20 |
| Time required: | 1 day to prepare, 5 days for experiment |
| Material availability: | Easily found |
| Safety concerns: | The bacteria should be destroyed before disposal. Pour some bleach into the petri dishes to kill all the bacteria before disposing them in the trash. |
Hypothesis
Overview
Scientific Terms
Materials
Procedure
1. For this experiment, the independent variable is the composition of the test specimen. The dependent variable is the growth of the bacteria colony. This is determined by measuring the size of the growth using a ruler. The constants (control variables) are the room temperature, the amount of sunlight and the ingredients in the petri dish agar.
2. The petri dish prepared with the blood agar must be stored in a refrigerator. Before the start of the experiment, remove the petri dish from the refrigerator to allow it to reach room temperature.
3. Three test specimens are made and labeled as described below:
4. Specimen A - 100 ml of milk is measured using the measuring cup and poured into test tube A. With the marker pen, label this test tube A
5. Specimen B - 100 ml of milk is measured using the measuring cup and poured into test tube B. With the marker pen, label this test tube B. Using a toothpick, add a small amount of E. Coli specimen to test tube B. Shake the test tube to mix the specimen thoroughly.
6. Specimen C - 100 ml of milk is measured using the measuring cup and poured into test tube C. With the marker pen, label this test tube C Using a toothpick, add a small amount of E. Coli specimen to test tube C. Next, add the extracted garlic juice to test tube C. The test tube is shaken to mix the specimen.
7. The specimens in test tubes A, B and C are allowed to incubate for 2 hours.
8. Mark the 3 petri dishes - A, B and C. Remove the lid and using the syringe, extract 10 ml of the sample mixture from test tube A and place it in the center of petri dish A.
9. Use a new syringe to extract a 10 ml sample from test tube B and place it in dish B and repeat for test tube C/dish C.
10. Replace the petri dish lids and store the petri dishes in a cool and shaded place.
11. The diameter of the E. Coli colony is measured everyday for 5 days and recorded in the table below.
Results
The results show that test tube B with the milk and E. Coli specimen had the largest colony of bacterial growth whereas test tube C with milk, the E Coli specimen and garlic extract did not show any signs of bacterial growth. Test tube A showed some small signs of bacterial growth probably due tocontamination during the incubation period.
Use the graph below to plot the results in the above table.
