(a) With the help of an activity, explain the action of saliva on the food we eat. (b) Why is bile juice important in the process of digestion?

Take $\displaystyle 1$ ml $\displaystyle 1$% starch solution in two test tubes A and B.

Add $\displaystyle 1$ ml saliva in test tube A and leave both test tubes undisturbed for $\displaystyle 20$-$\displaystyle 30$ minutes. Now add a few drops of iodine to both the test tubes.

The colour of iodine does not change in the test tube A as starch is converted to sugar by enzymes present in saliva.

The colour of iodine changes to blue-black in test tube B because it contains only starch solution.

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(b) ($\displaystyle 1$) Bile changes the acidic medium of food to alkaline medium so that the pancreatic enzymes can act on it.

(2) It also emulsifies fats. / Breaks down the large fat globules into smaller particles.