Hello
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
thankyou
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.
Both methods mentioned by your teacher and the BBC website are correct, and they aim to achieve the same result - removing chlorophyll from the leaf so that the presence of starch can be easily detected. However, there is a slight difference in the process.
The method described by the BBC website involves using a warm bath of alcohol to remove chlorophyll. Here's the step-by-step explanation:
1. Start by adding the leaf into boiling water. This step is common in both methods and helps to stop further cell activity.
2. Transfer the leaf into a warm bath of ethanol (alcohol). The alcohol dissolves the chlorophyll, making the leaf lose its green color and turn white. The purpose of ethanol is to aid in the removal of chlorophyll for easier observation of the color change.
3. Soften the leaf by dipping it into hot water. This step is common in both methods. Hot water helps to make the leaf more pliable and easier to spread out for testing.
4. Spread the softened leaf on a flat white tile or surface.
5. Add 2-3 drops of iodine onto the leaf. If starch is present, it will react with iodine and turn blue-black, indicating the presence of starch.
On the other hand, your teacher's method skips the ethanol step and relies on hot water alone for removing chlorophyll. Here's an explanation of the steps:
1. Add the leaf into boiling water, which halts cell activity and allows substances to move into the cell more easily.
2. Transfer the leaf into a boiling water bath in a tube filled with ethanol (alcohol). The purpose of the boiling water bath is to warm the ethanol and aid in the chlorophyll removal process. The leaf becomes white and crispy/stiff due to the chlorophyll dissolution.
3. Soften the leaf by dipping it in hot water. This step is similar to the previous method, where hot water is used to make the leaf more pliable.
4. Spread the softened leaf on a flat white tile or surface.
5. Add iodine onto the leaf to test for starch. If starch is present, it will react with the iodine and turn blue-black.
In summary, both methods will work to determine the presence of starch in a leaf. The key difference is that the BBC website suggests using a warm bath of ethanol to remove chlorophyll, while your teacher's method relies on boiling water for the same purpose.