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Bacteria and Cleanliness. Question: Among the insides of a toilet, dishcloth, sink, and a refrigerator handle, what is the cleanest?

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Pooja Mehta 4th period IB Biology 1-3-2010 Cleanliness Background: Bacteria are microorganisms that grow everywhere. We can collect and grow them in specially prepared Petri dishes. Blood agar or tryptic soy agar with 5% sheep's blood is an excellent medium for supplying bacteria with nutrients and an environment in which we can see them grow. Sterile powdered agar with nutrients can be mixed with water, heated and then poured into empty Petri dishes or ready-to-use dishes can be purchased. The indigestible agar is a gelatin-like substance with a semi solid surface on which the bacteria can grow while they consume the added nutrients (like sheep's blood). In fact, this is why gelatin itself does not make a good growing medium. Some bacteria can digest gelatin, which is a protein derived from animal tissue. This destroys the growing surface in the Petri plate making it unsuitable as a bacteria growth medium. CAUTION: Most bacteria collected in the environment will not be harmful. However, once they multiply into millions of colonies in a Petri dish they become more of a hazard. Be sure to protect open cuts with rubber gloves and never ingest or breathe in growing bacteria. Keep growing Petri dishes taped closed until your experiment is done. Then you should safely destroy the fuzzy bacteria colonies using bleach. Question: Among the insides of a toilet, dishcloth, sink, and a refrigerator handle, what is the cleanest? ...read more.


13. Before disposing of dishes in the trash the bacteria should be destroyed. Pour a small amount of household bleach over the colonies while holding dish over sink. CAUTION-do not allow bleach to touch your skin, eyes or clothes. It will burn! Data Table: Number of Bacteria Colonies in Petri Dish 1 Number of Bacteria Colonies in Petri Dish 2 Number of Bacteria Colonies in Petri Dish 3 Average Number of Bacteria Colonies in all 3 Petri Dishes Inside of a Toilet 175 colonies 195 colonies 180 colonies 183 1/3 colonies Dishcloth 268 colonies 254 colonies 271 colonies 264 1/3 colonies Sink 153 colonies 248 colonies 187 colonies 196 colonies Refrigerator Handle 200 colonies 198 colonies 202 colonies 200 colonies The positive control (the spit) did produce 264 bacteria colonies, and the negative control (nothing inside the Petri dish) produced 0 bacteria colonies, thus showing my experiment was properly conducted. Since the negative control yielded zero bacteria colonies, the number of bacteria colonies initially counted is the true number of bacteria colonies present. If the negative control did produce some colonies, we would have to subtract this number from the colonies counted upon experimentation. The uncertainty, which was derived from the standard deviations of each of the four areas tested, is as follows: Inside of a Toilet: � 10.4083 bacteria colonies Dishcloth: � 9.0738 bacteria colonies Sink: � 48.1352 bacteria colonies Refrigerator Handle: � 2 bacteria colonies The spread of data is due to the different areas of the four items I tested. ...read more.


Procedural errors were kept to a minimum, and the equipment in addition to the time management were suitable for this experiment. The time to collect all the bacteria took seven minutes, and the choice of equipment, as stated above, avoided any possible errors with judgment. Furthermore, the chosen process was the most appropriate for this experiment and thusly eliminated any possible errors involved with the procedures. Though this experiment yielded results that are credible and are of good quality, there are multiple methods that I could have taken to improve this experiment. A weakness in this experiment that multiple trials were not conducted. Although I did have three different Petri dishes for each of the four independent variables, I simply tested the four variables out of one common household. To have a better comprehension of the data, I should have ventured out to test other households. This weakness is very significant, and could have dramatically altered the results, possibly inviting a couple of outliers, and a change in the order of cleanest to the dirtiest. Another weakness in this experiment, also highly significant as the last one, was the fact that I only tested four areas that were concentrated in either the kitchen or the bathroom. To retrieve a better representation of a common living area and to overall improve the experiment, I should have extended the experiment to other areas such as the living room, study room, garage, the attic, and the master bedroom. Spreading out the areas I would have tested could have too altered the results severely. ?? ?? ?? ?? 1 ...read more.

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