McqMate
| Q. |
A potato tuber has been cut into two halves. A few drops of iodine solution are placed on the cut surface of one of the halves. What colour change will be noticed? |
| A. | From brown to blue-black |
| B. | From brown to orange-red |
| C. | From blue to pink |
| D. | From pink to blue-green |
| Answer» A. From brown to blue-black | |
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Explanation: Any form of starch (carbohydrate) turns blue-black when iodine solution is applied to it. This is because starch is composed of polymers of glucose. Long linear chains are amylose. Amylopectin is similar but contains a branch point about every 25th glucose or so. Amylose coils into a helical secondary structure resembling a tube with a hollow core. Certain molecules including fatty acids and iodine can lodge inside the core as already mentioned. The complex of iodine stuck insidethe amylose coil produces a characteristic blue- black colour. |
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