For a 4th grade science fair project how do you test which antibacterial hand soap kills the most bacteria?

Answer 1

You wold need to use bacteria that can easily be seen with a microscope, perhaps you could just use easily visible paramecium, and extrapolate that data for the use against other microorganisms, like bacteria. Get some paramecium, you can buy them online, then use a dissecting microscope for large paramecium, or a light microscope if you are using the smaller kind, to count out a certain number a place them in a teat tube. Place appropriate amounts of food in each tube, perhaps a single kernel of corn would be good, and let it sit for a couple of days. Every day, you should take a sample count of the paramecium present. To do this, shake the tube, or comtainer, or whatever, so that the paramecia that are bunched up near the corn will be spread out (by the way, the paramecia arent eating the corn, but the bacteria that grok on the corn). Then, take a plastic dropper and take out a cerain amount of water, perhaps a quarter of a mililiter, mL. Place it in a small dish and look at it under the microscope, and attempt to count up the number of living paramecium inside. Paramecium dart around constatly, so if it isnt moving, that means its dead. Then, extrapolate the number of paramecia in that sample of water for the amount of water in the entire sample. For instance, if the entire test tube held 10 mL of water, and I took out 0.5 mL of water, and I counted 5 living paramecium therein, then I would multiple the number of paramecium, 5, by 20, since there are 20 portions of 0.5 mL of water in the test tube. When you are done, put the water and the paramecium back in the test tube. Try to get all the paramecium back in, but its okay if a little water is left in the dish. Now for the part where you test different types of handsoap, only proceed this far if it appears that after two or three days that the paramecium arent all just dying. If that is the case, look at your setup and see if you are doing anything wrong. By the way, if the number of paramecium get so big that you cant count it, then take a single drop of water, count the larameciumin it, or even in a quarter of a drop if neccessary, and then extrapolate that for the number of drops of water in each mL, then the number of mL in the sample space (the test tube, for instance). Now, choose perhaps three different kinds of antibacterial handsoap, and devise jow much you shuld add so that the paramecia wont just die from swimming in soap, but will die frok the antibacterial properties of it. Perhaps tou could add eough that the water within the test tube becomes a 1% mixture of hand soap. I should have said this at the beginning, but you want to have a faurly karge number of test ibes for each different griup. Id say, if you have three types of handsoap, use 10 test tubes for each type of hand soap, and have 10 ,ore that dont have any handsoap, sothat you can see if it really is the handsoap that is affecting the paramedia, and not just a lack of food or something. Also, make sure that the child makes a hypothesis first and a prediction, before they start the experiment. To test the data, use excdl and perform t tests on the average numbers of paramecium per group. If you need more information, by all means contact me, I am a bilogy major, and I do these things every week. Its actually pretty fun, playing with paramecium.