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