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Independent Science Project
Transcript of Independent Science Project
Which disinfectant is the most effective in preventing bacterial growth?
.6 Petri dishes (must be disinfected)
I believe that the most effective disinfectant will be bleach because most disinfectants simply wipe away the germs while bleach completely eradicates them. A certain chemical in bleach, hypochlorite, disables the key protein in bacteria, cutting off its supply of nutrients, and killing it. The hypochlorite ion destroys the lipids in the cell walls and then destroys the enzymes.
.None of the samples grew bacteria but all of them grew mold.
.I should have used a more controlled environment. Mold spores tend to increase in numbers as the temperature rises in spring. I also should have checked the surface I cleaned for any signs of mold in case any was growing. One way to create more of a controlled environment would be to put bell jars over top of the petri dishes to prevent other substances coming in contact with the agar.
. The mold was affected by the disinfectants because certain dishes grew less mold then others the dish with no disinfectant grew the most.
My hypothesis was not supported by the experiment because I thought that bleach would work as the best disinfectant because of its hypochloric acid that kills the bacteria's enzymes, but no bacteria grew, the agar grew only mold. In a period of nine days I grew no bacteria though I noticed that the disinfectants affected the mold growth. I believe that the disinfectant originally destroyed some of the bacteria but mold was growing on the surface I took samples from so it went into the agar with the bacteria. I think that the mold growing was a type of bread mold, penicillin, a mold typically used in a medicine made to fight bacterial infections. The mold actually releases a chemical called Penicillin that kills bacteria by damaging its cell wall. Once the mold began to grow, the bacteria surrounding it would die. The reason the bleach grew mold was because it may kill both bacteria and mold but only on nonporous surfaces. The surface I cleaned was a type of plastic which is porous and bleach cannot penetrate a porous surface. I think the salt must have scrubbed into the pores scraping the mold off the surface.
The Independent Variable:
The Dependent Variable:
The amount of bacteria grown
It will be measured in Millimeters.
The Controlled Variables:
Are the size of the petri dish, the temperature in the room, the amount of sunlight in the room, the type of agar used, the amount of time we left it in the dish, and the surface we take the sample from.
.An unclean surface
.A measuring cup
1. Gather materials
2. Take a small handful of agar and cut it into short pieces with the scissors.
3. Put them into the grinder and blend them. When blended into a fine powder stop.
4. Get one cup of lukewarm water and pour it into the small pot. Turn on the stove and place the pot on its surface.
5. When the water begins to boil add two tablespoons to it and wait until it dissolves.
6. Then turn off the stove and gently pour equal amounts of agar into the six petri dishes, just enough to coat the bottom, and wait for it to cool.
7. Once cooled divide the bottom of each petri dish into three parts label them trial 1, 2, and 3.
8. Now take a piece of tape and put it on the lid of the petri dish label them Original Sample, Cinnamon Sample, Salt Sample, Lemon Juice Sample, Bleach Sample, and Alcohol Sample.
9. First take a sampling of the original unclean surface and using a Q- tip wipe it onto each section of the appropriate petri dish in a z pattern
10. Take a cotton ball and dab it into the bleach. Gently scrub the ball on the unclean surface for 30 seconds. Take a Q- tip and swipe it against the scrubbed area rub it along each section of the appropriate petri dish in a z pattern
11. Repeat step ten four more times using the other disinfectants and their labeled petri dishes.
12. Lastly find a safe place with little change in light and no large fluctuations in temperature to keep the petri dishes. Wait five days before measuring so that the bacteria has a chance to begin to grow. Check every three days so that there will be a notable difference. Record the data found by taking pictures through the microscope.
Data Tables and Charts
First row: Original Sample
Second row: Bleach Sample
Third row: Salt Sample