Q. Why is upper epidermis of the leaf provided with a layer of cuticle?
Q. Why is varigatesd leaf used in the starch test?
Q. Why do we add leaf in the boiling water during starch test?
Answers
1. The upper surface is covered with a waxy, waterproof cuticle, which serves to reduce water loss from the leaf.
2. Variegated leaves have green parts (where the cells contain chlorophyll) and white parts (where there is no chlorophyll). Only the parts that were green become blue/black with iodine solution, showing the importance of chlorophyll in photosynthesis. The parts without chlorophyll do not photosynthesise, and so they do not make starch and the iodine does not change colour.
3. We boil the leaf in alcohol when we are checking it for starch to eradicate chlorophyll, which is the green pigment present in leaves. During the starch test, we observe the colour change of leaf from brown to blue when iodine is put on the leaf as iodine reacts with the starch present in the leaf.
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