Question

The occurrence of blue-black colouration of starch test with chewed rice means

• A. Starch is present
• B. Starch is absent
• C. Iodine is present
• D. Iodine is absent

Answer 1

The correct option is A

Starch is present

The correct option is (A)

Explanation for the correct option:

1. Glucose in plants is stored as starch which is a complex carbohydrate.
2. Starch, when added with iodine solution, changes the color to blue-black.
3. A salivary amylase enzyme is present in the oral cavity, which causes starch breakdown into simple sugars.
4. When chewed food is tested for starch and shows a change in color to blue-black, it signifies that the action of salivary amylase was not complete, and starch is present in the chewed food.

Explanation for incorrect options:

Option (B)

1. The starch test is said to be negative if it does not detect the presence of starch.
2. The color of the iodine solution will not change, and it will remain red.
3. This signifies that starch was absent in the sample.

Option (C)

1. A starch test is used to confirm the presence of starch.
2. Iodine solution is required to confirm the presence of starch. In the presence of starch, the color of the iodine solution changes from red to blue-black.

Option (D)

1. Iodine solution is used to detect starch, and it will always be present in both negative and positive results.

The occurrence of blue-black coloration of chewed food means starch is present.