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Observation:

1. Iodine does not turn starch treated with saliva in test tube A into blue
colour. Only pale-yellow colour of iodine is observed.
2. Starch solution of test tube B turns blue.

Inference:

 Iodine solution reacts with starch to form blue-coloured product. The
reaction is almost immediate. This happens in test tube B.
 In test tube A, no such change occurs, indicating that its starch has been
broken down into simpler carbohydrates. This is possible by enzyme
contained in saliva.

Conclusion :

Saliva contains salivary amylase. It degrades starch into simple sugar. Iodine
does not act on the simple sugar. Hence solution treated with saliva is not
turned blue.

Lab Activity Work Sheet

1. In which test tube do you observe a colour change?
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2. What does this indicate about the presence or absence of starch in the two
test tubes?

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3. What does this tell us about the action of saliva on starch?

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4. What does saliva contain and what is role in digestion?
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