Yadu conducted an experiment to test his idea. He took two test tubes, A and B, and added a pinch of rice flour to the test tubes, half-filled with water and stirred them properly. To test tube B, he added a few drops of saliva. He left the two test tubes for 35–45 min. After that, he added iodine solution into both the test tubes. What do you think he wants to test?
Yadu wants to test whether saliva breaks down starch present in rice flour into simpler sugars.
In test tube A (without saliva), the iodine solution will turn blue-black, indicating the presence of starch.
In test tube B (with saliva), the iodine solution will show no colour change or a lighter blue-black colour because the saliva has broken down the starch into simple sugars over 35–45 minutes.
This experiment demonstrates the digestive action of saliva on starch.
Explanation
The chapter describes a similar experiment (Activity 9.1) showing that saliva contains digestive juices that break down starch into sugars. Rice flour contains starch. When iodine is added to starch, it gives a blue-black colour. If saliva has acted on the starch and broken it down into sugars, the iodine will not produce the blue-black colour. Yadu's experiment tests this digestive action of saliva on starch over time.
Solution Steps
Yadu wants to test whether saliva breaks down starch present in rice flour into simpler sugars.
In test tube A (without saliva), iodine solution turns blue-black, indicating the presence of starch.
In test tube B (with saliva), iodine shows no colour change because saliva breaks down starch into simple sugars over 35–45 minutes.
The experiment demonstrates the digestive action of saliva on starch.