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Science Fair: The Plant Killer

The claim we want to test is if a plant can tell the difference between water that has been microwaved and water that has not been microwaved.

In 2006 a website and email forward emerged online with the claims that the author’s grand-daughter had performed a science fair project comparing the effects two kinds of water on common house plants. The comparison made was between two kinds of boiled water; stove top and microwave. And the conclusions drawn claimed a notable difference in the observed outcomes; Water that had been boiled on the stove top (then cooled) allowed for normal plant growth, while water that had been boiled in the microwave (then cooled) killed the plants. Critical thought alarms went off around the world: Prove it!

The urban legend website Snopes has the full details of the original claim, and the results of their own similar experiments.

Science Fair Projects?

The idea of a skeptical science fair project is redundant. Truly winning projects are both scientifically sound and teach kids to think critically about predicting, planning, methodology, and evidence. The skep/dad blog science fair projects are meant to be starting points in skeptical, do-at-home experimentation that could (with the proper, careful guidance) form the foundations of a winning science fair project for kids. I don’t claim to have invented any of these projects. Rather, I’m taking the step of compiling them for use by parents looking for ideas for their kids. As such, I’ve chosen these projects on a small number of criteria:

Ultimately, success in any science fair will be decided on how well the experiment is planned, executed, and reported. I don’t guarantee anything! But, as with any project, if you perform this one for yourself please do post a comment with the results (or a link to your own page with your results) for others to see.

The Problem with Plant-Killing Water

The skeptic will easily realize why the claim as detailed above is tough to swallow; Kids may need a little help from you as a parent to draw the same conclusions. Brian at Skeptoid gets to the heart of the problem:

This whole paranoid suggestion is based on the presumption that a microwave oven somehow changes or poisons water. If true, wouldn’t you be able to perform some kind of a test on water, and see if it has ever been microwaved? Water is H2O, whether it’s ever been microwaved or not.

So, the claim we want to test is if a plant can tell the difference between water that has been microwaved and water that has not been microwaved.

The Science Fair Project

My own belief about science fair projects: Kids should do the work; Parents should keep their hands off as much as possible, take three steps back, and (1) answer questions when asked (2) encourage logical thinking and (3) foot the bill. With that in mind:

Step 1: Do the background research. I’ve provided some links below, but please do more searching. Plan the experiment by figuring out a place to conduct it, the types of plants to use (and learn about those plants), how water will be boiled and what kind of container it will be in, a schedule, and anything else that might be important or influence the outcome.

Here is some reference material to get you started — and as always, parents should check these first for content they deem appropriate:

Part of the plan should include what kind or measurements are to be recorded — and how often. Some suggestions that I have are the height (or weight — though it is a little trickier) of the plant, the number of leaves, the color or other appearance features, and the general health of the plant. Figure out if photographs be taken. Also measurements of the temperature, sunlight, amount of water, and other important external factors should be kept track, so plan how this will be accomplished and what tools are needed.

Step 2: Make an educated prediction. Of course, if you are a skep/dad too, you will have let your child do much of the background research (as I mentioned above) and will not have told her the ‘answer’ that you might, by this point in my description, expect. Let her make a prediction about what she thinks will happen and write it down in the log book. Of course, encourage her to make predictions and observations all through the experiment; That is how good scientists operate. By now you should have long since started a log book, and your predictions and observations go there.

Step 3: Obtain the plants to be to tested, and get them in identical sets. This is important. An “identical set” of plants consists of (at least) two plants for each value of the variable you are hoping to test. What does that mean? In this experiment we are going to test one variable: the kind of boiled water. That variable has two values: water boiled with (1) a microwave and (2) a stove. So, we have one variable with two values which means we need four plants. The plants should be identical in every way you can possibly think of; They should be the same size, species, and of relatively similar health. They should come from the same nursery, sold on the same shelf, on the same day. You should transport them in the same vehicle. If you are going to re-pot them, they should go into identical containers, and use soil from the same source.

Keep track of all this information. It may not seem important, but will impress any judge that the experimenters knows as much information about the plants as possible: it’s all part of the Methods, after all.

Note: Young scientists should try to always (in the case of a science fair project) do things in multiples of two (at the very least) which is why I’ve stressed the importance of “identical sets” — it is not exactly bullet-proof science, but it is economical and much easier to keep track of fewer plants. That said, if experimenters have the time and resources, do more.

Step 4: Conduct the experiment as planned. I’m not going to elaborate on that. From here on in it’s up to the experimenter and the plan she set out in step one. Follow the schedule, record observations, and keep track of anything that might be important.

Step 5: Perform an analysis using a critical thinking approach as a guide. In other words, look at the evidence and answer some important questions:

An analysis need not be an essay, particularly in a science fair project. Use graphs and charts, tables and photographs.

How to Make it Better

You could conduct the experiment exactly as above, but if you have the time and resources to improve it — expand it — and make it even better, here are some tips:

More Plants - If resources and time are not a problem for your family, get more plants. Set up a tray with six, ten, or even twenty plants, half for each kind of water.

More Variables - For example, different plants or the same plants under different conditions (lighting, different rooms in your house, outdoor versus indoor) results in more data — but always a use complete “identical set” of plants under each change. In other words, if the experiment above is going to be repeated for a different room in the house, an additional four plants are needed.

More Values - This experiment makes use of water from the same source under different boiling conditions, but it would be easy to add more conditions: try comparing unboiled water, use tap water (boiled both ways) versus rain water (boiled both ways), et cetera. Be careful that you are not adding anything to the water as this is an entirely different experiment.

Remember, the skep/dad blog science fair projects are meant to be starting points in skeptical at-home experimentation that could (with the proper, careful guidance) form the foundations of a winning project for kids. Good luck!

The SkepDad Blog is meant to casually reflect on questions surrounding parenting and raising kids to become critical thinkers by asking questions and examining parenting ideas with a skeptical eye for facts and science. Each article is one dad's personal opinion, backed (where relevant) by literature and published research, or otherwise based on personal experiences and insights. SkepDad welcomes balanced discussion, comments, and ideas.

January 7, 2008 by Brad
Filed as: Science Fair Projects

Popularity: 21%

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