Experiences

Destruction of starch by saliva

Roberto Checchi

Italy

Vocational School

Biology

Teaching in class, Laboratory, Online Learning

Direct

Teaching of scientific subjects often crashes with objective difficulties of the students who do not understand how these disciplines explain real-life events and/or situations. Moreover, the indispensable use of mathematical formulas and scientific laws misleads students to learn by memorizing rather than by understanding.
During our didactic activity, setting the path together with students (who suggested thematic paths found out on the internet), we have organised some courses in laboratory, integrated with ICT tools, for realising activities that lead the students to extrapolate the law, the formula or the graph from the practice into the laboratory. The students were very interested in this methodology because they had the possibility to build their own knowledge.
For instance, the enzymes are hard to understand for the students. But, thanks to their direct involvement, students have understood importance of the enzymes and have also deepened their knowledge about Food Chemistry.
Description of the experience: the saliva carries out its digestive properties through the enzymes, such as salivary lipase and amylase. The saliva starts to digest the starch producing simple sugars composed by two or more molecules of glucose.
Procedure: put in the beaker 100ml of water and a potato starch spoonful. Warm up the beaker on a burner until it boils. After it has lost heat, pour some tincture of iodine drops. The solution turn blue highlighting the high quantity of starch inside. In another beaker, put water and saliva. In a test tube, mix part of the mixture of the two beakers. Warm up till 37°C this test tub putting it in a beaker filled of water
Put the test tube in a beaker filled of water and warm up it in bain-marie till 37°C (like that of the human body). Reached this temperature, take off the test tube and observe it. The tracks of blue coloration are disappear because of the saliva has “digest” the starch, so the indicator does not signal its presence anymore.
Students have appreciated this didactic approach with much positive results also for their study motivation and for the improving of the self-awareness on their potentialities.