posted by Blossom


My question which is making me totaly confused is that my teacher has given me the test for starch slightly different to what the bbc website had gave

The bbc website says :

First of all you add the leaf into boiling water in order to kill it. Then you put it in a warm bath of alchol that removes the chrorphyll which is the green colour. Then you dip it into water to soften it and then pyut it in a white tile and add 2-3 drops of iodine, if starch is present than it will turn blue-black.

For my tracher's explanation

it was :

1- Drops leaf in boiling water
This stops all further cell activity and allows substances to mive into the cell easily.

2- Put the leaf into a boiling water bath in a tube filled with ethanol. This removes the chlorophyll so you can see the colour change more easily. The leaf goes white and goes crrispy/stiff.

3- It is soften by dipping the leaf in hot water.

4- Add iodine to test after spreading leaf on a flat white tile.

Do I add ethanol or alchol to take off the colour I am totaly confused can anyone tell me please which is the right cause my sats are comin


Both are right. YOu have a water boiling bath. Put your leaf into a test tube filled with ethanol. Now dip the tube of ethanol into the hot water. The ethanol is warmed by the water, and the ethanol dissolves the cholorphyl. This is a better method for removing than the BBC site: ethanol will dissolve much better than just hot water. However, if you choose to skip the ethanol, just dip the leaf in hot water, enough should come out to see the iodine reaction.

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