Explain the colour of the leaf when iodine solution is added to it in the end.How can we test for starch in a leaf? 1. Remove a green leaf from a plant that has been exposed to sunlight for a few...

Explain the colour of the leaf when iodine solution is added to it in the end.

How can we test for starch in a leaf?

1. Remove a green leaf from a plant that has been exposed to sunlight for a few hours

2. Immediately put the leaf in boling water for two minutes

3. Put the boiled leaf in a boiling tube containing some alcohol or ethanol.Place the boiling tube in a beaker containing some hot water.

4. What is the colour of the alcohol

a) before the leave is put in;and 

b) ten minutes after the leaf is put in?

5. what is the colur of the leave after 10 minutes?

6.What has the alcohol done to the leaf?

7. The Leaf is now brittle. Gently remove the leave and put it back into hot water.This softens the leaf and makes it more permeable to iodine solution.

8. Remove the leaf and spread it evenly on a white tile. Add a few drops onto the leaf. Explain your observation.

Asked on by chisko12

1 Answer | Add Yours

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pacorz | High School Teacher | (Level 3) Educator

Posted on

Starch is created in leaves and other plant tissues when the plant does photosynthesis. The process of photosynthesis captures light energy and uses it to make glucose, a simple sugar. Then the glucose is converted into starch, a more complex carbohydrate, which can be used to store the energy for later.

In your experiment, you took a leaf that had been allowed to do photosynthesis, you boiled it to kill it and remove the waxy cuticle, then placed it in alcohol to remove the chlorophyll and other plant pigments.

Once the pigments have been removed, the leaf is treated with iodine solution. Iodine is an indicator chemical for starch; when the two come in contact, the starch turns a very dark color.

If the leaf in your experiment turned dark, then you would conclude that there was starch stored in the cells, and that that starch was the end product of photosynthesis. If you repeated this experiment with leaves that had been kept in the dark, there would be much less starch.

Sources:

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