Why do we boil the leaf in alcohol when we are testing it for starch?

A green leaf is bleached before carrying out a starch test by boiling the leaves in alcohol. It breaks the cell wall of the leaf and removes the chlorophyll present in the leaves. Chlorophyll is removed so that the leaf can absorb iodine solution and turn into a blue-black color. Thus, we can properly identify the starch present in the leaf.

Extra information:

The iodine test can determine whether or not leaves contain starch (carbohydrate).

Here are the procedures for determining whether or not leaves contain starch:

Step 1: Collect a green leaf from a plant that has been in direct sunlight for at least a few hours.

Step 2: Half-fill a beaker with water and bring it to a boil.

Step 3: Place the leaf in a pot of boiling water and let it sit there for a few minutes to soften the cell wall.

Step 4: Boil the leaf in alcohol to extract the chlorophyll.

Step 5: Immerse the leaf in hot water to loosen its cells.

Step 6: Next, test the leaf for starch by dropping a few drops of iodine solution onto it.

A blue-black hue develops on the leaf once iodine is added, indicating the presence of starch in the sample.


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