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2016-03-07T15:11:40+05:30

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By conducting iodine test we can study the presence of starch in leaves Remove a green leaf from a plant that has been exposed to sunlight for a few hoursHalf-fill a 250cm3 beaker with water. Heat the water until it boils. Keep the water at boiling point.Use the forceps to place the leaf in the boiling water. Boil for 2 minutes.Turn off the Bunsen Burner. (If you are using a heat source without a naked flame - electric water bath or hot plate - this step is unnecessary.)Place the boiled leaf in a boiling tube containing 90% ethanol.Place the boiling tube in hot water and boil for 10 minutes or until the leaf decolourizes.    ( It may be necessary to replace the ethanol)Gently remove the leaf and wash with a fine trickle of cold tap water.Spread the leaf evenly on a white tile.Add a few drops of iodine/potassium iodide solution to the leaf and note any observations.The leaf was flaccid (soft) after being boiled in waterThe ethanol changed from colorless to greenThe leaf was brittle after being boiled in ethanolThe leaf become flaccid once more after being rinsed in cold waterAfter iodine solution was added
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2016-03-07T15:12:17+05:30

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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 stops its chemical reactions)
2. heat it in boiling ethanol for a few minutes (this removes most of its colour.
3.wash with water and spread onto a white tile
4. add iodine solution from a dropping pipette
after a few minutes the parts of leaf that contain starch turn blue black.

Note that ethanol is heated using a hot water bath. Ethanol boils at 78°C, so a tube of it boils when placed in a beaker of hot water. This is safer than using a Bunsen burner because ethanol is flammable.

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