Experimental Investigation - To test a leaf for starch
Activity: Pluck a leaf from a plant which has been exposed to sunlight.
2. Boil it for about 5 minutes in water to softer it.
3. Place it in a test tube containing alcohol.
4. Place the test tube in a beaker of water and warm the water gently until the alcohol begins to boil.
(caution: Do not allow the water in the beaker to boil).
5. The alcohol will dissolve the chlorophyll and the leaf will lose its green colour.
6. Wash the leaf in warm water to remove the alcohol.
7. Now spread the leaf out flat on a white tile and pour iodine solution on it.
8. Remove the leaf from the iodine and wash it with water.
9. Hold it up against the light.
10. You will observe that parts of the leaf become blue - black.
11. These parts of the leaf have starch in them.
The simplest method of testing whether photosynthesis has taken place is to find out if starch is present in a leaf.
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