ong answer... Iodine is a common general stain used in thin-layer chromatography. However the Iodine test is used to test for the presence of Starch. Iodine solution — iodine dissolved in an aqueous solution of potassium iodide — reacts with starch producing a blue black color.
This reaction is the result of the formation of polyiodide chains from the reaction of starch and iodine. The amylose, or straight chain portion of starch, forms helices where iodine molecules assemble, forming a dark blue/black color. The amylopectin, or branched portion of starch, forms much shorter helices and iodine molecules are unable to assemble, leading the color to be of an orange/yellow hue. As starch is broken down or hydrolyzed into smaller carbohydrate units, the blue-black color is not produced. Therefore, this test can determine completion of hydrolysis when a color change does not occur.
Iodine solution will also react with glycogen, although the color produced is browner and much less intense.
Chloroplasts are structures that enable the plant cells to make sugars through photosynthesis. Animal cells do not have chloroplasts and cannot make their own food.
The carbohydrates are the compounds which provide energy to living cells. They are compounds of carbon, hydrogen and oxygen with a ratio of two hydrogens for every oxygen atom. The carbohydrates we use as foods have their origin in the photosynthesis of plants. They take the form of sugars, starches, and cellulose.
Plants produce all three - however, not being like warm blooded animals, cannot store this sugar in a crystaline form (cellulose) within the cells vacule, so convert it to a helix form, starch for storage. It is this storage sugar you stain with Iodine..Source(s):bio teacher
