Question

A slice of bread gives a positive iodine test.However,if the slice is thoroughly chewed,the iodine test is negative.Explain by giving reasons.

Answer 1

Answer:

When you chew the bread saliva digests the starch present in it hence it gives negative test.

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Answer 2

Reason why a slice of bread after chewing gives negative iodine test:

The bread packed in the packet is composed of starch. Iodine gives blue color when it reacts with raw bread due to the presence of starch in it.

On the other hand, when we chew the bread, the starch present in the bread gets converted into glucose by the enzymatic activity of an enzyme called salivary amylase. It digests the starch present in the bread as we chew it. Due to the absence of starch in the chewed bread, the iodine test shows a negative result.