Why is the green leaf boiled with water in test of starch
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This procedure kills a leaf, disrupts the cell membranes and softens the cuticle and cell walls. This makes it possible to extract the chlorophyll with hot ethanol and also allows the iodine solution to penetrate the cells and react with any starch present.
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During the test of starch in plants, the green leaf is boiled in water because:
- Plants contain chlorophyll which is a green pigment that enables photosynthesis process. To test starch we use iodine solution. Iodine solution can changes its color from blue to black in presence of starch. However the green pigment makes it difficult for iodine to penetrate the epidermis.
- Most plants have a cuticle layer that is made of waxy substances and is impermeable to substances and protects the leaf. The presence of the cuticle layer does not allow iodine solution to enter the cell and stain it.
- Hence the green leaf is boiled in water to denature the cuticle layer and remove chlorophyll pigment. This will allow entry of iodine solution in the leaf and proper visibility of color change.
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