1. Testing a leaf for starch.

2. AIM
To test a leaf and to proove the presence of starch.

3. Submerge a leaf in boiling water for one minute
Submerge a leaf in boiling water for one minute. This kills the leaf since it destroys membranes.
Safety: Wear eye protection

4. ⏎ TURN OFF BUNSEN BURNER!
Safety: ethanol is flammable
TURN OFF BUNSEN BURNER!
Put the leaf into a test tube of ethanol for 10 minutes.
A hot bath of ethanol decolorizes
the leaf by washing out the chlorophyll. If the leaf is not decolorized, you cannot see the blue-black stain that results from the iodine reacting with the starch. ⏎

5. ⏎ Wash the leaf in cold water.
This needed to remove the ethanol and rehydrates the leaf which softens it ans makes it easier to spread out.

6. The brownish area is were the aluminium was placed
Spread the leaf out flat on a petri dish then add some drops of iodine solution. ⏎
Iodine solution is needed to see starch is present in a substance. If it’s present it would turn blue black. If no starch is present then it remains as light brown.

7. Conclusion
Starch is produced by leaves during Photosynthesis, therefore if the leaf has not been exposed to light then it will not contain starch, and so when tested the Iodine will stay Yellow/Brown. Consequently if the leaf has been left in the light Photosynthesis will have taken place and when tested the Iodine will go Blue/Black showing that Starch is present.