Science Buddies: "Ask an Expert"

The project questions if homemade green cleaners are as effective as commercial cleaners in killing bacteria. The information sheet that was given for the log book section says the log book must show "data recorded for minimum of ten in each group (25 for people)". So.. I'm wondering about the 10 and what would be a good way to conduct this experiment. We were thinking maybe the following: 1. sample taken from bathroom door knob... have a control petri dish with bathroom door knob bacteria...10 petri dishes with same bacteria with all of them having the same green cleaner applied... and 10 petri dishes with same bacteria with all of them having the same commercial cleaner applied.... then 2. sample taken from kitchen sink.... repeat process except we would use a different green cleaner as in #1 but the same being used in all 10 trials of #2 and we would use a different commercial cleaner than in #1 but of course, the same commercial cleaner would be used in all 10 trials of #2..... then 3. bacteria from kitchen counter.. but again, with a different green cleaner (the 3rd one used so far) but of course it being used in all 10 petri dishes in this test... and a 3rd commercial cleaner but it being used in all 10 petri dishes... Would this be acceptable? Would we need to take bacteria from a 4th or even a 5th location with a 4th and 5th kind of green and commercial cleaner ? Just really confused on the best way to proceed. And apologies, I am many years removed from a classroom and know I haven't explained myself well at all.

Also, if a little handbook were included with the experiment that included tips on how to go green( recipes for homemade green cleaners for example) would each 'tip' or 'fact' need to be cited? Or could we just include sources in the bibliography?

Again, I apologize for my confusion and ignorance; I appreciate any advice you can give. And I have to say that this site is a godsend; there is so much really good info here. Thank you so very much.

You've explained yourself just fine! The way I interpret the requirement is that you would need a total of 20 doorknobs: each would be swiped first for a control, and then 10 would have one type of green cleaner applied and the other 10 would have a commercial cleaner applied. Then all 20 would be swiped again, to give you a sample size of 10 for each cleaner. If you wanted to test multiple types of green cleaners and commercial cleaners, you would need 10 doorknobs (or whatever you choose to study) for each one. You wouldn't necessarily need to only use doorknobs; you could use various locations around the house--but I would try to pair up locations, so you have one tap for each cleaner, one doorknob for each cleaner, etc.

Does that make more sense?

I personally would cite each tip and fact with a footnote or using parenthetical citation, but this really depends on your teacher's requirements. I suggest asking your teacher about how you should do citations.

Thank you so much for your quick response! When reading your answer, I realized I forgot to mention something quite important ... my son wants to work with zones of inhibition. So does this mean that he can use 10 doorknobs? For example: he would swipe knob #1 and then innoculate three prepared petri dishes. The first petri dish would be a control; the second petri dish would have a disc with a green cleaner; and the third petri dish would have a disc with a commercial cleaner. Next, he would move on to knobs 2 - 10, following the same procedure with all . Then if he wanted to try a different green and commercial cleaner, could he swab 10 different bathroom wall tiles (getting those close to sink, toilet and shower) and just follow the same 3 petri dish procedure with all 10 tiles?

Also, is it preferrable to prepare a dilute solution of bacteria to innoculate the plates as opposed to just swiping the knobs with a sterile cotton swab and then using that swab to run across the surface of the agar?

I really appreciate your help; everyone here is doing an awesome job!!

Ah-ha! Yes, exactly: when you do a zone of inhibition test you want to create more of a bacterial 'lawn', which means purchasing some bacteria and preparing that. Take a look at this Science Buddies project, which you should be able to adapt for your purposes: https://www.sciencebuddies.org/science- ... p014.shtml .

In this case, you would then prepare 10 control plates and 10 plates with discs of each cleaner you want to test. You could potentially put more than one disc in a plate and measure the zone of each disc...but technically it would be more 'correct' to do 10 different plates. Still, agar and plates and things can be expensive, so you'll have to make a decision about what you want to do.

If you have further questions, let us know, and you're very welcome!