Answer: We boil the leaf in alcohol when we are testing it for starch to remove the green pigment chlorophyll present in it. We need to observe the color change from brown to blue when iodine is put on the leaf for the starch test.

Explanation:

Starch is a white, powdery substance consisting of glucose which is used by plants as food. The presence of starch in leaves is evidenced enough of the process of photosynthesis being carried out in leaves as the formation of starch necessitates photosynthesis.

Answer:

To soften the protective structure of leaf.

Explanation:

Reason :-

Iodine solution is used to test leaves for the presence of starch. So, we need heat the leaf again over water bath because it softens the protective structure of leaf, and disrupts the cell membranes to let the chlorophyll out and iodine solution in.

Also, it stops the leaf for form any other chemical reactions.