Concept:The iodine (
I2) test is the standard method used to detect starch in a leaf.
Starch reacts with iodine to produce a blue-black colour.
Explanation:The leaf is parboiled in hot water to soften it, then decolorized in alcohol to remove chlorophyll so the leaf appears pale or colourless.
Drops of iodine solution are now added to the treated leaf.
Areas containing starch turn blue-black, while parts without starch remain brown, which is the natural colour of the iodine solution.
A blue-black result therefore proves that starch is present in that region of the leaf.
Failure to produce a blue-black colour indicates that starch is absent.
Because this colour change is specific to starch, the entire apparatus in the diagram is set up to determine whether starch is present in the leaf.
This experiment is often used to confirm that green leaves manufacture starch during photosynthesis.
Answer:B. Starch
