2. Read the given activity and answer the following questions. Take 1 ml starch solution (1%) in two test tubes (A and B). Add 1 ml saliva to test tube A and leave both test tubes undisturbed for 20-30 minutes Now add a few drops of dilute iodine solution to the test tubes.
(a) In which test tube do you observe a colour change?
(b) What does this indicate about the presence or absence of starch in the two test tubes?
(c) What does this tell us about the action of saliva on starch?
Answers
Answer:
(a) in test tube A colour changes to blue
Answer:
Activity to show action of saliva on starch
Procedure:
(i) 1 mL of 1% starch solution is taken in two test tubes and labelled as A and B.
(ii) 1 mL of saliva is added to test tube A. Nothing is added to test tube B (control).
(iii) The test tubes are left undisturbed in safe place and similar conditions for about 30 minutes.
(iv) After about 30 minutes, a few drops of dilute iodine solution is added to each test tube.
Observations:
(a) In test tube A there no change in iodine solution i.e., solution remain brownish that is the colour of iodine solution. It means that starch is not present.
(b) In test tube B, the solution turns blue black. It proves presence of starch.
Conclusion:
Saliva has enzyme which can digest starch and convert into other carbohydrate (sugars).
Conclusion
In test tube A the saliva acts on the starch and break them down. whereas in test tube B where no saliva is present the starch is not broken down.