Leaf starch test on a variegated leaf (one lacking green chlorophyll in some areas). The leaf on right has been tested for starch, a carbohydrate produced in photosynthesis. The test, with iodine, gives a dark blue colour in the presence of starch and a pale brown colour in its absence. Only the areas of the leaf that contain chlorophyll contain starch, showing that the pigment is essential for photosynthesis.
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