1.7 Starch

Introduction

Materials
-Bunsen burner
-tripod stand
-wire gauze
-250 cm3 beaker
-boiling tube
-forceps
-test tube holder
-leaf to be tested
-90% ethanol
-iodine/potassium iodine solution


Objectives 
1. Identify the presence of the starch in leaves.
2.Relate the presence of starch with photosyntesis.
3.Identify the presence of starch in some food.


Procedure
1.Remove a green leaf from a plant that has been exposed tosunlight for a few hours.
2.Half-fill a 250cm3 beaker with water. Heat the water until it boils. Keep the water at boiling point.
3.Use the forceps to place the leaf in the boiling water. Boil for 2 minutes.
4.Turn offthe Bunsen Burner.
5.Place the boiling leaf in a boiling tube containing 90% ethanol.
5.Place the boiling tube in hot water and boil for10 minutes or until the leaf decolourizes. (It may benecessary to replace the ethanol)
6.Gently remove the leaf and wash with a fine trickle of cold tap water.
7.Spread the leaf evenly on a white tile.
Add a few drops of iodine/potassium iodiene solution to the leaf and note any observations.


Observations
we can see thet in the

Questions
1.Which is the origin of the starch that you can see in the leaf? From the glucose that was synthesized the starch, photosynthesis.
2.Complete this reaction: And write the name of this process. 
CO2+H2O------>C6H12O6+O2
3.Explain the significance of boiling the leaf in water. Lose the turgent conditions
4.Explain the significance of boiling the leaf in ethanol. To lose the color (chlorophyll dissapears)

5.Explain the significance of rinsing the leaf in water. Because the lugol isn't soluble with ethanol