Leaf test of starch
4. Ethyl alcohol
6. Test tube
- After 4 green leaves were collected, 2 of them were put into the beaker of 150 mL of water boiling over the bunsen burner and tripod.
- After 2 minutes, the leaves were taken out from the beaker and were put into the test tube of ethanol. The test tube was then put in the warm beaker used in step 1.
- After some time, the leaves were taken out from the ethanol test tube. They were then laid down on a white paper along with 2 other fresh leaves.
- Iodine was dropped onto each of the leaves on the paper using the pipette. The color change of the iodine drops on the leaves and the soaked iodine on the paper were then observed
- Why do we boil the leaves? - When the leaves are boiled, the cell walls are weakened and broken, allowing the organelles including the chloroplast out, stopping all the reactions from taking place inside the leaves.
- What is the leaf texture like after boiling? - The leaf becomes softer, smoother, and appear less green.
- Why do we use ethanol on the lead after boiling? - We use ethanol on the leaf to extract the chlorophyll out.
- What is the color of the water after boiling the leaf? Why? Why did some people get pink brown water? - The color of the water appeared pink brown after boiling because the leaves are relatively small and thin relative to the leaves of other groups. The boiling time is therefore too long for the leaves and substances other than chlorophyll are extracted as well.
- When you test for starch with the iodine, why did the paper turn black? - After the iodine is dropped onto the boiled leaves, the iodine turned black because the starch test is positive. When the iodine soaks the white paper, it then turned the paper black.
- What happened to the iodine test on the unboiled leaf? Why? - The iodine didn't turn black for the unboiled leaves because the chlorophyll and the starch is not extracted out of the cell.