TESTING FOR GERMS

[risa]

I really hope someone out there can help me. My son is in 3rd grade and this is his first real sciene fair project. Unfortunately it feels like mine. We chose to test objects i.e cellphone,money,doorknobs etc to see which has the most germs/bacteria on it. I had acquired the info when I recently attended school for my Esthetics license but can't find the directions anywhere. They used a gelatin. I need to access step by step instructions ASAP and I'm quite confused in the "variables" for a project like this. Thanks-desperate mom

[MelissaB]

Risa,

Try taking a look at the instructions on this Science Buddies project: https://www.sciencebuddies.org/mentorin ... ?from=Home. The gelatin you're thinking of is called agar, and that site will tell you how you can get agar plates.

As for variables, they can be things you can measure, or things that you want to know the difference between. So it looks like you've got one categorical variable (cellphone/money/doorknob) and one continuous variable (# bacteria on these items).

Let us know if you've got more question!

[risa]

We are still having trouble distinguishing how to label the variables. We need to have an Independent(manipulated),Dependent(responding),and Controlled variables. We also need to have measurements in metric form. How would you advice we use that in this instance since we were planning on counting colonies? Also, can we get more specific i.e what types of bacteria we are seeing, types of colonies etc.?

Thanks for the help! Anxiously awaiting your response.

[kmanies]

We are still having trouble distinguishing how to label the variables. We need to have an Independent(manipulated),Dependent(responding),and Controlled variables. We also need to have measurements in metric form. How would you advice we use that in this instance since we were planning on counting colonies? Also, can we get more specific i.e what types of bacteria we are seeing, types of colonies etc.?

Thanks for the help! Anxiously awaiting your response.

Hi there,

The responding/Dependent variable is easy = how many germs are there on a door. Since you're supposed to have a manipulated and control variable it means you need to have a question that you want to ask. YOu could do this in two ways:

First, you could compare doorknobs in general (control) to doorknobs that have a particular feature (manipulated) and see if the responding variable (number of germs) varies between the two.

I think this could be a fun thing for you and your child to come up with together. Where does your son think that there might be more germs? In places with lots of people versus a few ? In place that are considered dirty versus place considered clean?

Or you could take generic doorknobs (ones in your house that have been cleaned the same way) and then put different things on them. Again, choose things that he thinks might effect the growth of germs (light, food, moisture, etc.) You would have one of those things the same (as a control) and then a set of knobs that you would vary the condition you want to test (manipulated).

See what sort of question he's interested. For me this science stuff should be as much about asking a question the kids think is interesting and helping them figure out how to answer it, than what the question really is. Help guide him along in something he things is neat (or germy in this case).

Good luck!

[Sareena Avadhany]

Hi kmanies,

You had mentioned in your first post that you feel that you are doing the project, not your son. The whole point of doing a science project is to learn about science. Try to see if this project is what your son really wants to do, and if it is, he should really be doing all the work, and you should be guiding him. If it isn't, maybe he should do something else. Science Buddies provides excellent tools to facilitate the process of completing the steps of the scientific method.

I hope this helps.

Sincerely,
Sareena

[HeatherL]

Dear Risa,

I just wanted to follow up on your question about labeling your variables. The independent variable is the one YOU change. In your original example, it sounds as if your independent variable is the material (cellophane, doorknob, etc.). I like kmanies' idea about sticking with one material (doorknobs) and comparing them in different areas, too. Keep in mind that it's probably not the materials per se that have different amounts of bacteria, but really the amount of bacteria to which each thing was exposed. Depending on which way you go, your independent variable will be either the material (if you use different materials) or the location of your material (if, for example, you decide to test different doorknobs).

The dependent variable is the one you measure. In this case, it will be the number of bacterial colonies you count on your agar plates. (MelissaB gave you the link to the Science Buddies information about agar plates.) The number of colonies will be your metric. You probably won't be able to identify the different types of bacteria growing, but may be able to make some observations about the colonies (e.g., color).

Your control can be a very simple one. The purpose of a control is to account for variables that you are not able to manipulate, but that could affect your results. For this project, you can open an agar plate and then close it without swabbing anything on it. This will control for bacteria present in the air.

Once again, another variable that could affect your results is the amount of exposure to bacteria that each of your materials has. The makeup of the material may also affect things. It's best to only vary one variable. If you use different materials, do your best to keep them in the same conditions to "control" for exposure. Alternatively, you can control the makeup of the material by comparing only one (e.g., doorknobs) in different situations. Either experiment is an interesting way to go; it depends on what most interests your son!

Good luck, and feel free to post back with further questions.

Cheers,
Heather