Question

In the Coleus leaf, different colored regions are seen (green and yellow). What is the relationship between starch storage and photosynthesis in a variegated leaf as indicated by the addition of iodine?

Answer 1

Iodine is used to test presence of carbohydrate in a substance.The plant perform photosynthesis and the resulting substance is stored as starch in them.

Also as indicated, variegated leaf has a green part and a non-green part. The green part contains chlorophyll, but the non - green (yellow) part don't contains chlorophyll in them. The chlorophyll of the green part of variegated leaf can absorb light and perform photosynthesis. As a result starch is produced by these chlorophylls and remain stored their ( green part). But the yellow part of the variegated leaf don't have chlorophylls, so they can't perform photosynthesis ans starch is not stored in that region.

So when iodine test is done on the variegated leaf, the greenish part of the leaf turns to blue - black indicating the presence of starch there and also the carrying out of photosynthesis process there. But no change is found in the yellow part of the leaf on iodine test and conclude absence of starch or absence of photosynthesis in that region.

In a single sentence we can conclude that, starch storage and photosynthesis is found only at green part of the variegated leaf and these are absent in the yellow part of the variegated leaf.