Different strokes with starch

Jyotsna Vijapurkar, Aakanksha Sawant, Swapnaja Patil

The starch test is an easy-to-do test, commonly included in school textbooks (generally from grades 6 through 9). All one has to do is add a few drops of iodine to test if something contains starch; if it does, it turns blue. This test is usually done on potatoes or rice or cereal flours. Even if the books say that students can use any food item for the test, the figure alongside this activity often depicts the test being done on a potato. Doing the test this way, with predictable outcomes, is rather dull and boring, and indeed barely even a test in the real sense! More importantly, opportunities for a host of elements of a scientific inquiry are missed – exploring, generating questions, guessing what the answers might be, figuring out how to find answers to new questions that may arise, and perhaps doing further tests to answer those questions. How can these elements be included in this experiment? By simply presenting it in a slightly different way, and including items other than potato and rice which, as students have already been taught, are sources of starch. Here we share how we have been doing this test with groups of teachers, to demonstrate the power of a well conducted experiment.

Making it truly investigative, i.e., doing the experiment to find out the answer
brinjal-cross-section We begin by asking teachers about the various carbohydrates they have had for a recent meal and jot them down on the board, marking those that they think contain starch (all carbohydrates are not starch!). We then add some more items, ones that the class may not be sure about (and neither were we, until we did the experiment). Our list includes bananas (ripe) and plantains (raw); brinjals; sugar; pulse and cereal flours; boiled eggs. So we start by asking for a guess of which contain starch, which don’t, keeping count of the ‘ayes’ and ‘nays’ on the board next to each item. Everyone has to make a guess, or explicitly state they are not sure. Now the whole class is eager to find out the result of the test.

Often, as they attempt a prediction, the reasoning serves to bring out alternate conceptions that they may harbour. A lively discussion ensues as other participants and observers also get involved in trying to solve the ‘puzzle’.

The authors are at the Homi Bhabha Center for Science Education, Tata Institute of Fundamental Research, Mumbai. They can be reached at jvijapurkar@gmail.com, aakankshasawant1992@gmail.com, swapnajapatil17@gmail.com.

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