Question

11. What do the dark areas of the leaf represent? 12. Why was the leaf boiled in ethanol?

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Answer 1

Answer:

From the observation and the alcohol treatment it is interpreted that the leaf is tested for the presence of starch in it.

Q11) Dark area represents the presence of starch in the leaf after addition of Iodine solution

Q12)Ethanol treatment makes the leaf to release green coloured chlorophyll,so that it is easy to identify the presence of starch upon addition of iodine solution.

Rationale:

Starch is produced in a plant with the help of photosynthesis process.In photosynthesis generally green plants utilise the energy from the  sunlight in presence of carbondioxide ,water and convert it a carbohydrate and release oxygen.Generally presence of starch is analysed with the help of iodine solution.

This leaf is a variegated leaf (has white and green color in the same leaf).Generally,these leaves are placed in a boiling tube containing ethanol(alcohol) then the tube is kept in a boiling water bath.Boling kills the cells in the leaf and stop further metabolism and ethanol removes the chlorophyll compound from the leaf by breaking cell membranes inorder to make starch granules in cytoplasm accessible to iodine solution.So when the iodine solution is added the cells uptake the solution and starch granules forms a complex with iodine.This leads to dark blue coloration in the leaf and the regions without starch (surrounding region ) remains colorless.

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