In the school curriculum of the 8th class in biology there istheme of digestion. Upon completion of the work on this topic, it should become clear to each student that the food begins to be processed from the very moment that it only enters the oral cavity. And the first in the processing of food is the process of grinding food with teeth and the effect of saliva enzymes on the food that has entered into the mouth.
Why do doctors recommend chewing not onlysolid, but also soft, semi-liquid food? It is for the enzymes to be able to make the primary processing of food, to split it into components.
The effect of saliva on starch is calledenzymatic hydrolysis. Since the starch itself is an inert substance, this reaction occurs under the influence of heat and a catalyst. At the moment, he is an enzyme amylase, which is in human saliva. It is he that breaks down starch into smaller components, in particular, dextrins.
Everyone feels this process about the debtchewing starchy foods, for example, bread. After a while, you can feel a sweetish taste in your mouth, which indicates that hydrolysis of starch has begun, and it gradually breaks down into carbohydrates. One of the most important carbohydrates for the human body is glucose.
When oxidized in every cell of the humanthe body formed water and carbon dioxide. Also, this reaction is accompanied by the release of energy, so necessary for the functioning of all organs. Excess glucose, obtained by hydrolysis of starch, turns into a nutrient glycogen, which is deposited "in reserve" in the liver.
In order to visually demonstrate this to children, it is proposed to do a laboratory work "The effect of saliva on starch."
The biology lesson on which the teacher plans to conduct a laboratory work "The effect of saliva on starch" is recommended to begin with a front-line survey. Students are offered the following questions:
During this survey, the mainsaliva functions in the digestive system. And at the end of the frontal conversation, the teacher sets a goal for the children in the laboratory: to find out experimentally the effect of saliva on starch, and to note the conditions under which the salivary enzymes are active.
For conducting laboratory work it is necessaryoffer students cut pieces of the size of a square decimeter starched gauze, a cotton swab, a bowl, an aqueous solution of pharmacy iodine. The solution can be suggested to the guys to do on their own, dropping a few drops of iodine into the water. The liquid must have the color of strong tea. Although to save time, it is perfectly permissible to give the children a ready-made solution. The process of preparing it for adolescents will not give any training effect for finding answers to questions on the topic "The action of saliva on starch."
Cotton bud should be moistened with saliva and written ona piece of starched gauze with a letter. Then a piece of starched gauze should be slightly warmed in the hands - this activates the work of enzymes that begin to affect starch. Then the piece of gauze, processed in this way, must be lowered into iodine water.
The place where the saliva was applied will remainwhite, and the rest of the area will turn blue. That is, on a blue background a white letter will be drawn. Why did this happen? Saliva managed to decompose the starch into its constituent parts, partially turning into glucose. Iodine has no effect on glucose, therefore the letter written with saliva does not turn blue.
After the experiment, the guys in the notebookrecord the course of laboratory work "The action of saliva on starch. Conclusion". You can offer specific questions that will help to draw the necessary conclusions from this experience.
