Some crushed boiled rice is put in water in a test-tube and a few drops of dilute iodine solution are added to it. A blue-black colour is produced which shows the presence of X in rice. If, however, the crushed boiled rice and water are first warmed with saliva for some time and then dilute iodine solution in added, then no blue-black colour is produced. This shows that saliva converts X into product Y which does not produce blue-black colour with dilute iodine solution.
What does the above activity tell us about the role of saliva in the digestion of food?

Explanation

**Step-by-Step Solution:**

1. **Observation of Blue-Black Color:**
- When crushed boiled rice is mixed with water and dilute iodine solution is added, a blue-black color is produced. This indicates the presence of starch (X) in the rice, as iodine reacts with starch to produce this color.

2. **Effect of Saliva on Starch:**
- When the crushed boiled rice is warmed with saliva before adding the iodine solution, no blue-black color is produced. This indicates that the starch has been converted into another substance (Y) by the action of saliva.

3. **Role of Saliva:**
- Saliva contains an enzyme called amylase, which breaks down starch into simpler sugars. This process is known as digestion. The absence of the blue-black color after the addition of iodine indicates that the starch has been digested into simpler compounds that do not react with iodine.

4. **Conclusion:**
- The activity demonstrates that saliva plays a crucial role in the digestion of food by converting starch (X) into simpler sugars (Y), which do not produce a blue-black color with iodine. This shows that the digestive process begins in the mouth with the help of saliva.

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