Digestion in a test tube!

Yasmin Jayathirtha

In the biology classroom, the most common experiments are the food tests. To check the presence of starch, the iodine test is done. For protein, a biuret test is done, and for reducing sugar, the Benedict’s test is routinely used. The tests for biochemicals are useful, but can we use them to study and illustrate processes? Some of the problems with these types of experiments are the complexity of the chemicals, processes that are completely dependent on the organization in an organism and the difficulty of working with living organisms. But we could consider those that can be replicated in test tubes.

fig-1 For example, what experiments can illustrate digestion? Starch digestion is the easiest to study, since it starts in the mouth and the enzyme is available just a spitting distance away.

So, let us consider digestion in a test tube!

  • Starch solution 1 per cent
  • Salivary amylase (get the students to rinse their mouth out with water and spit into a beaker. A few will feel repelled but it is good to have a mix of the amylase, since there may be individual differences.)
  • Test tubes
  • Boiling tubes
  • Droppers
  • Petri dishes
  • Avalakki
  • Iodine solution (I2 in KI solution)


  1. Ask the students to rinse their mouths out with water and put some Avalakki in their mouth. Let the food sit in the mouth and note the taste. Chew about 50-60 times and note the taste of the mush. What change in taste do they notice?
  2. Take about 10 cm3 of starch solution in a boiling tube and add two drops of iodine solution. Add 2 cm3 of saliva solution. Keep overnight.
  3. In separate petri dishes, take solid maida paste and cotton. Add about 1 cm3 of saliva to both and keep overnight.
  4. Take 3 test tubes and add 5 cm3 of starch solution to each. To the first, add 2 cm3 of saliva, to the second add 2 cm3 of water and to the third add 2 cm3 of boiled saliva. Make sure that the test tubes are appropriately labelled.

The author works with Centre for Learning, Bengaluru. She can be reached at yasmin.cfl@gmail.com.

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