 |
| Activities and Experiments |
|
| To study the action of pepsin on proteins |
| |
| Boil egg white in distilled water till a cloudy suspension is obtained. Cool it and divide the mixture into five equal portions in separate test-tubes. Label them A to E. |
| |
| Add different substances to each of the five tubes as shown in the table below and explain the observations: |
| |
 |
| |
 |
| |
| To study the digestive action of saliva on starch |
| |
| Rinse mouth 2 to 3 times to remove any food particles and collect saliva in three test-tubes labelled A, B and C. To B add half the quantity of 2% starch solution. To C add boiled saliva. Leave them for 5 minutes. |
| |
| At the end of five minutes, |
| |
| a) Addition of iodine to A gives no blue colour. Why? |
| |
| The action of salivary enzymes on starch converts it to sugar. Since there is no starch in the test-tube, There is no blue colour. |
| |
| b) Addition of Benedict's reagent to B gives red precipitate. Why? |
| |
| Benedict's reagent gives red colour precipitate with sugar. In B also the salivary enzyme has converted starch to sugar and the latter gives the red precipitate. |
| |
| c) Additon of iodine to one portion gives blue colour and addition of Benedict's reagent to the other portion does not produce any red precipitate. Why? |
| |
| C contained boiled saliva. Heating denatures the enzyme present in saliva. Hence there is no action on the starch. The solution therefore gives blue-black colour with iodine. Since sugar has not been formed, there is no red precipitate with Benedict's solution. |
| |
