Question

how will you test a leaf for a starch mention an​

Answer 1

Answer:

Iodine solution is used to test leaves for the presence of starch. You need to:

1)Heat a plant leaf in boiling water for 30 seconds (this kills the leaf, stopping any chemical reactions)

2)Add the leaf to boiling ethanol in a water bath for a few minutes (the boiling ethanol dissolves the chlorophyll and removes the green colour from the leaf - it turns white so it is easy to see the change in colour)

3)Wash with water to rehydrate and soften the leaf and spread onto a white tile

4)Add iodine solution from a dropping pipette

After a few minutes, the parts of the leaf that contain starch turn the iodine from brown to blue/black

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Answer 2

Answer:

To test a leaf for starch:

1. First, take a leaf from a healthy plant that has been exposed to sunlight for a few hours prior to the experiment.

2. Then, place the leaf in a beaker with some ethanol and boil it until most of the green colour of the leaf has dissolved into the water. This is done in order to remove the chlorophyll from the leaf and allow us to see the presence of starch better.

3. Rinse the leaf in water and place it on a plate.

4. Add a few drops of iodine solution on the leaf and wait for a few seconds. The spots of iodine (which were originally brown in colour) will change to blue-black colour, thus indicating the presence of starch.

(If the plant from which the leaf was kept in shade for a few days before the experiment was conducted, there would be no change in the colour of iodine, thus indicating that there is no starch present.)

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