Question

The correct sequence of starch test in leaf should be

(I) Removal of black paper strips, boiling in water, testing with iodine solution.

(ii) Removal of black paper strips, boiling in alcohol over water bath, washing the boiled leaf, testing with iodine solution.

(iii) Removal of black paper strips, boiling in iodine solution, washing with water.

• A. (i)
• B. (ii)
• C. (iii)
• D. (i), (ii), (iii)

Answer 1

The correct option is B

(ii)

The correct option is (B)

Explanation for the correct option

1. Starch is a complex polysaccharide that is formed by the polymerization of glucose units.
2. In the presence of starch, the iodine solution changes its color from orange to blue-black. This test is called the starch test.
3. To do the starch test in the plant leaf, the performer should first remove the strips from the leaf, then boil the leaf in alcohol using a water bath, followed by washing and adding iodine solution.

Explanation for incorrect options

Option (A)

1. A starch test is a step-wise procedure to detect the presence of starch.
2. Alteration of steps will lead to false results.
3. Directly boiling the leaf after removing the strips will damage the leaf and lead to complete starch loss from the cells.
4. This will result in a negative test for starch.

Option (C)

1. A starch test is a step-wise procedure to detect the presence of starch.
2. Alteration of steps will lead to false results.
3. Direct boiling of a leaf with iodine will not lead to observable results.
4. The leaf should first boil in alcohol to remove its green pigment and then add the iodine to see the color change.

Option (D)

1. A starch test is a step-wise procedure to detect the presence of starch.
2. Alteration of steps will lead to false results.
3. Thus, one should follow the set protocol as performing more than one procedure will lead to a false result.

Option (B) is the correct sequence.