EXPERIMENT 10.1 Objective. To study the action of salivary amylase on starch.

                           EXPERIMENT 10.1

Objective. To study the action of salivary amylase on starch.

REQUIREMENTS

Test tubes, test tube stands, pipettes, beakers, cotton, funnel, water bath, spirit lamp or burner, measuring cylinder, starch, sodium chloride, distilled water, iodine solution, iodide, etc.

PREPARATIONS

1. 1% Starch solution. To 10 ml of distilled water add 1 g of soluble starch to make it into a thick paste. Boil 90 ml of distilled water and to it add 10 ml of the starch paste already prepared, gradually by stirring. Leave the solution overnight and then filter to get 1% starch solution.

2.1% NaCl solution. Dissolve 1 g NaCl in 100 ml of distilled water.

3.Collection of saliva. Make a thin film of cotton and dip it into water. Drain off the water of the cotton and spread it over the mouth of funnel in such a way that it acts as filter. Keep the funnel over a clean test tube.Now chew a piece of rubber and pour the incoming saliva into the funnel. Filtered saliva will collect in the test tube. Take 1 ml of saliva and add 19 ml of water to get 1: 20 dilution of the enzyme.

PROCEDURE

1.Prepare series of test tubes having 1 ml of iodine solution in each. Make two sets of iodine tubes and keep them in separate stands.

2.To a test tube add 5 ml of 1% starch solution and 1 ml of 1% NaCl. Label it as experimental tube. To another test tube add 5 ml of 1% starch solution and 1 ml of 1% NaCl. Label it as control tube. Now put both these test tubes in a water bath maintained at 37°C approximately for about 10 minutes so that they also aquire the same temperature (In summer a beaker filled with water can be used for this purpose).

3. To the experimental tube add 1 ml of dilute enzyme and to the control tube add 1 ml of water. With the help of dropper, take a drop from each of these test tubes and pour it into two separate tubes, containing iodine (from two series of iodine tubes-one for experimental and other for control). Note the time of adding as zero minute reading.

4.After an interval of 2 minutes, again take a drop from each experimental and control tubes and pour to the iodine tubes. Note the change in colour of iodine. Keep on repeating after an interval of every 2 minutes till the colour of iodine does not change. Note that iodine for control tube always gives blue colour.

5.Note the total time taken for the experimental tube till it does not give any colour with iodine. This is known as achromic point (i.e., no blue colour with iodine solution).

6. Compare the series of experimental iodine tube with the control iodine tube.

7.Perform Benedict's test for both the experimental and the control tubes. Only the experimental tube will develop orange colour on heating.

OBSERVATIONS

RESULT

It takes......minutes for 1 ml of diluted enzyme (1: 20 dilution) to digest completely 5 ml of 1% starch solution to the achromic point (end point).

At achromic point experimental tube shows a positive Benedict's test indicating the presence of simple sugars and absence of starch.

EXPLANATION

The enzyme salivary amylase present in saliva acts on starch and convert it into maltose (a disaccharide).Starch gives blue colour with iodine.

In the experimental tube, we have starch and enzyme both. NaCl acts as an activator of the enzyme. The enzyme gradually acts on starch and convert it into maltose. Starch keeps on giving blue colour with iodine till it is completely digested into maltose. At this point no blue colour is formed. This is the end point or achromic point.In the control tube, we have only starch and NaCl. Instead of enzyme, 1 ml of water has been added. There-

fore, in this tube starch is not digested to maltose. Hence, blue colour keeps coming with iodine solution.

PRECAUTIONS

1.Filter the saliva through a wet cotton film and not through a filter paper.

2.All the weighing and measuring should be done very accurately.

3.Maintain uniform temperature of the water for both, throughout the experiment.

4.While measuring saliva, there should be no air bubbles.

5.All the glasswares used must be thoroughly cleaned and dried.