solve this question
Answers
Answer:
Testing a leaf for starch is the simplest photosynthesis lab. A positive test for starch in a leaf provides evidence that photosynthesis has occurred. The test for starch is a leaf is an is an extension of the Iodine Test for Starch.
Apparatus/Materials
bunsen burner, tripod stand, wire gauze(OR 90oC electric water bath OR hot plate)
250 cm3 beaker
boiling tube
anti- bumping granules
forceps
test tube holder
white tile
leaf to be tested (hibiscus leaves are excellent)
90% ethanol
iodine/potassium iodide solution
Procedure
The video above shows the steps in Testing a Leaf for the Presence of Starch. The Procedure outlined below is slightly different.
Remove a green leaf from a plant that has been exposed to sunlight for a few hours
Half-fill a 250cm3 beaker with water. Heat the water until it boils. Keep the water at boiling point.
Use the forceps to place the leaf in the boiling water. Boil for 2 minutes.
Turn off the Bunsen Burner. (If you are using a heat source without a naked flame - electric water bath or hot plate - this step is unnecessary.)
Place the boiled leaf in a boiling tube containing 90% ethanol.
Place the boiling tube in hot water and boil for 10 minutes or until the leaf decolourizes. ( It may be necessary to replace the ethanol)
Gently remove the leaf and wash with a fine trickle of cold tap water.
Spread the leaf evenly on a white tile.
Add a few drops of iodine/potassium iodide solution to the leaf and note any observations.
Observations/Results
The leaf was flaccid (soft) after being boiled in water
The ethanol changed from colorless to green
The leaf was brittle after being boiled in ethanol
The leaf become flaccid once more after being rinsed in cold water
After iodine solution was added...