Experiment 1
Aim: To demostrate the action of ptyalin (saliva) on cooked starch.
Method: Some saliva is introduced into a test tube X and diluted with little amount of water.
Two test tubes are labelled E and F. To test tube E, cooked starch solution is introduced and saliva is added. To test-tube F, only starch solution is added and thus acts as a control.
The two test tubes E and F are then placed in water-bath maintained at the temperature of 37°C and stirred at every 1 minute interval.
After five minutes, one drop of solution from each test tube is put on a white tile with a glass rod. A drop of iodine solution is added to each drop on the white tile. Fehling solutions A and B are added to the contents of test-tubes E and F and heated.
Results
- A reddish brown colour is observed when one drop of iodine is added to one drop of solution in E.
- A blue-black colour is observed when one drop of iodine is added to one drop of solution from test-tube F.
- With Fehling solution A and B, the contents of test-tube E indicates brick-red colour while the test-tube F shows blue colour.
Conclusion
A reddish brown colour with iodine solution in test-tube E shows that cooked starch has been digested by ptyalin.
The brick-red precipitate with Fehling’s solutions A and B in test-tube E shows that cooked starch has been digested to simple sugar. The blue black colour with iodine solution in test-tube F shows that starch is not digested and the deep blue colour with Fehling’s solutions A and B shows that sugar is absent.
Experiment 2
Aim: To show the effect of high temperature and acid on enzymes.
Method: 3cm³ of starch solution is added to each of the four test-tubes labelled A,B,C and D. Some fresh saliva is added to test-tube A, the same volume of boiled saliva is added to test-tube B. To test-tube C, water of the same volume is added while test-tube D receives three drops of dilute hydrochloric acid. Testtube C thus provides control for other three.
The four test-tubes with their contents are placed in a beaker of warm water kept at approximate temperature of 37°C. They are left for about 30 minutes and are later tested for both starch and sugar.
Conclusion: The presence of sugar in the test-tube A shows that ptyalin in saliva has changed starch to sugar (maltose). The absence of sugar in test-tube B containing starch and boiled saliva indicates that an enzyme is denatured or destroyed when boiled. The absence of sugar in test-tube D indicates that ptyalin in saliva does not work in acid medium. The absence of sugar in test-tube C shows that water has no action on starch.