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Exposure of Baby food and the degree of contaminationFeatured science projectScience project video

Materials

The materials required for this experiment:

  • 9 petri dishes prepared with blood agar
  • 3 bottles of chicken baby food
  • 3 bottles of pumpkin baby food
  • 3 bottles of apple baby food
  • A refrigerator
  • 9 sterile cotton buds
  • 1 permanent marker pen

Procedure

  1. For this experiment, the independent variable is the type of baby food (chicken vs. pumpkin vs. apple) and the amount of time the food is left out the refrigerator. The dependent variable is the rate of growth of the bacteria colony. This is determined by measuring the size of the colony using a ruler. The constants (control variables) are the room temperature, the brand of each type of baby food, the amount of sunlight exposure and the ingredients used in the preparation of 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 normalize at room temperature.
  3. The 3 bottles from each type of baby food are labeled A, B and C
    - Chicken A
    - Chicken B
    - Chicken C
    - Pumpkin A
    - Pumpkin B
    - Pumpkin C
    - Apple A
    - Apple B
    - Apple C
     
  4. The 3 types of bottles marked A are opened briefly, then covered/closed. Following this, the bottles are immediately stored in the refrigerator for 24 hours.
  5. The 3 bottles marked B are opened and kept out of the refrigerator for 30 minutes before replacing the cap. Following this, the bottles are immediately stored in the refrigerator for 24 hours.
  6. The 3 bottles marked C are opened and kept out of the refrigerator for 30 minutes before replacing the cap and it is then left out of the refrigerator for another 24 hours.
  7. After the 24 hour incubation period, mark the Petri dishes according to the list provided in step 3.
  8. Remove the petri dish lids and using sterile cotton buds, take a small swab sample from each bottle (from at least 3 different spots within the bottle) and place it in the center of the relevant Petri dish (i.e. chicken sample from bottle A will be placed in petri dish marked Chicken A). A new cotton bud must be used to collect the swab from each bottle.
  9. Replace the petri dish lid and store the Petri dishes in a cool, shaded place.
  10. The diameter of the bacteria colony is measured after 3 days and recorded in the below table.

 

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Complexity level:
5
Project cost ($):
20
Time required:
1 day to prepare, 3 days for experiment
Material availability:
Easily found
Safety concerns:

The bacteria should be destroyed before it is disposed of. Pour some bleach into the petri dish to kill all the bacteria before disposing in the trash.