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No Trick More Enlightening: Making Every Demonstration an Experiment

By Thomas M. Zinnen, PhD

Food is fundamental to many aspects of culture and religion. You can also use food to communicate basic ideas about science because classical and modern biotechnologies are so commonplace in food production. Food is familiar, accessible, inexpensive and safe; and therefore it's a great topic to use in helping develop inquiry skills in students--no matter what their age.

I often open biotechnology workshops with a familiar activity: shaking cream into butter. Fill a plastic canister half full with cream, snap on a lid, and have some unlucky participant shake it like crazy for a few minutes. Meanwhile, ask the other people a series of questions: Is this hands-on? active? concrete? kinetic? When the cream has turned to butter, ask: Have we proven that shaking is essential? Have we done an experiment?

Most answer "yes" to all six. And therein lies a core challenge for teachers and scientists who work with students: how to convince them that not all demonstrations are experiments.

Control, Kontrollieren & Compare

"There is no trick more infuriating," wrote Sinclair Lewis in Arrowsmith, his 1925 book on the scientific enterprise, than "the trick of using the word 'control' in reference to the person or animal or chemical left untreated during an experiment, as a standard for comparison." Infuriating, that is, to people who fail to include such comparisons in their research. Lewis, who won the 1930 Nobel Prize in Literature largely on the strength of Arrowsmith, created the fictional Professor Gottlieb who "always snorted 'Where was your control? How many cases did you have under identical conditions, and how many of them did not get the treatment?'"

While most students take the English word "control" to mean "to precisely regulate," I wonder if the German verb "kontrollieren" meaning "to check, to supervise, to examine" as well as "to control" isn't closer to the meaning intended by experimenters.

Gottlieb's demand for a fair comparison is still a question that separates experimental science from other ways of knowing. In many types of classrooms students are judged by their answer to the question, "What do you know?" If you're a practicing scientist working with students in a lab, you could do them a favor by emphasizing an additional question: "How do you know that?" Demonstrations may show what you know, but experiments show how you know it.

Bench scientists tend to be skeptical. They seem to be from Missouri, with "Show Me" punched on their state of mind. That's a valuable if undervalued mindset to impart to students. Look at the butter activity: have we really proven that shaking is essential? One definition of "to prove" is to "to test". Have we really tested that shaking is essential?

This skepticism generates creativity. How many other possible explanations can the participants list? Was it perhaps the temperature from the hand, the effect of exposure to light or to air or to plastic? Maybe the cream would have set spontaneously, without shaking, had we just let it sit. So how do we test those ideas?

Creativity generates competing ideas, and ingenuity finds ways to test the competing ideas. The simple, but not obvious, answer is to do an experiment: take two identical canisters, both half full of cream, and put one in each hand. Shake one, but not the other. The second is the control, the one "left untreated during an experiment, as a standard for comparison." If any of the other factors (temperature, air, light, etc.) is sufficient, then the cream in both canisters should turn to butter. But if only the cream in the shaken canister turns, while the cream in the other remains unchanged, you have tested and found that shaking is essential.

The Number 2: Make Every Demonstration an Experiment

One way to underscore the crucial nature of comparison is to ask a series of questions: How many hands do you have? And what can you do because you have two hands? You can contemplate not just one item, but you can simultaneously compare two things. What's the Roman numeral for 2? II, two parallel lines. The difference between a demonstration (or a protocol or a recipe) and an experiment is the difference between I and II. In a recipe, you just follow one line of instructions. In an experiment, you do two things in parallel, two things that differ by only one factor, so any difference in result can be attributed to the difference in treatment.

According to Protocol: Extracting DNA

Passing off demonstrations as experiments can confuse students. A common activity of biotechnology workshops is extracting DNA from onion or from calf thymus (the butcher's "sweetbreads"). While often referred to as an "experiment" it's really just a demonstration. Grind some tissue, add some detergent, spin and save the liquid, add some cold ethanol, and the student gets some slimy stuff--it's DNA!

Well, maybe. The student so far has followed a protocol, and really can't conclude anything about the slime. Now is the time for skepticism: How do I know this contains some DNA? Might it also contain carbohydrate? protein? What experiments can I do to test these ideas?

From Slime to Chyme: An Enzyme Example

The first product of recombinant DNA technology in the US food supply was a chymosin (rennet) produced by Pfizer Dairy Ingredients using a genetically engineered bacterium and introduced in 1990 under the tradename CHY-MAX. Chymosin is a protein enzyme found in the slime of stomachs of calves ("chyme" means stomach slime in ancient Greek). The enzyme coagulates milk and is used in cheesemaking to form curds.

You can use chymosin from any source to introduce students to a product of industrial biotechnology. You'll have a choice: do a demo by adding some chymosin to warm milk and watch it coagulate, and then you can explain what happened. Or have the students do an experiment by adding some chymosin to one vessel of warm milk and none to a second vessel, and have them analyze the results.

One approach sets you up as the authority. The other tells the students that their investigations, their careful comparisons, their experiments, are valid ways to know. This is the difference between "knowing" and "knowing how"--the difference between knowing just the conclusions, and knowing how people can design experiments that generate the evidence that test the ideas.


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