Case: Observe the image given below. There are two test tubes (i) and (ii). Test tube (i) contains a starch solution, while test tube (ii) contains starch solution and saliva. Both the test tubes are kept undisturbed for about 20 min. Later, dilute iodine solution (brown in colour) was added to both the test tubes.
We have two test tubes here, X and Y. X contains boiled rice and Y contains boiled rice that has been completely chewed on. Which one is more likely to turn blue-black on adding an iodine solution?

[0.8 Mark]

Test tube X

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Test tube Y

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Both X and Y

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None of them

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Solution

The correct option is A Test tube X
Rice contains starch. When we add an iodine solution to the test tube containing starch, iodine forms a starch-iodide complex. Due to this, the solution turns blue-black. In the test tube Y, there is boiled and chewed rice. It means that it contains saliva and starch. Saliva contains the enzyme salivary amylase which breaks down starch into simple sugar. Iodine cannot form a complex with sugar. So, there was no blue-black colour formed in test tube Y.

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Similar questions

Q. Case: Observe the image given below. There are two test tubes (i) and (ii). Test tube (i) contains a starch solution, while test tube (ii) contains starch solution and saliva. Both the test tubes are kept undisturbed for about 20 min. Later, dilute iodine solution (brown in colour) was added to both the test tubes.

Which among the following enzymes is present in saliva?

[0.8 Mark]

Option	Test tube (i)	Test tube (ii)
A.	Blue-black	Brown
B.	Brown	Blue-black
C.	Blue-black	Blue-black
D.	Brown	Brown

[0.8 Mark]

In which part of the alimentary canal does the digestion of food begin?

[0.8 Mark]

Question 20
Boojho took some grains of boiled rice in test tube ‘A’ and Paheli took boiled and chewed rice in test tube ‘B’. Both of them poured 1 - 2 drops of iodine solution into the test tube and observed the colour change. What colour change would they have observed? Give reasons for your answer.

Q. Boojho took some grains of boiled rice in test tube ‘A’ and Paheli took boiled and chewed rice in test tube ‘B’. Both of them poured 1 – 2 drops of iodine solution into the test tube and observed the colour change.
What colour change would they have observed? Give reasons for your answer.

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