Testing a leaf for starch

你需要知道的

• Boil the leaf in water for about 20 seconds to kill it, stopping its reactions and softening it.
• Turn off the flame, then warm the leaf in ethanol in a hot-water bath to remove the chlorophyll, because ethanol is highly flammable.
• Rinse the brittle leaf in warm water to soften it, then spread it on a white tile.
• Add iodine solution: areas with starch turn blue-black, while areas without starch stay orange-brown.
• In a variegated leaf only the parts that were green turn blue-black, which is evidence that chlorophyll is needed for photosynthesis.

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