No Trick More Enlightening: Making
Every Demonstration an Experiment
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
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
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
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
The Number 2: Make Every Demonstration an
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
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
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.