Starch in Leaves (Photosynthesis)
Investigate a fundamental principle of biology: that plants produce starch during photosynthesis. This simulation guides you through the process of destarching a leaf and testing it for the presence of starch using iodine.
Help & Instructions
â–¼- Start the Simulation: Click 'Run Experiment' to simulate a leaf being tested for starch.
- Observe the Results: Watch the step-by-step process and the final color change.
- Quiz Challenge: Answer questions about the procedure and the principles behind it.
- Understand the procedure for testing a leaf for starch.
- Explain the role of each step (e.g., boiling in water, alcohol).
- Connect the presence of starch to the process of photosynthesis.
- Identify positive and negative results of the iodine test on a leaf.
Starch Test on a Leaf Simulation
A healthy leaf is exposed to sunlight for several hours. We will now test it for starch.
Quiz Challenge: Starch Test Principles
What is the purpose of boiling the leaf in water at the beginning of the experiment?
This classic experiment is designed to show that photosynthesis produces starch. By boiling a leaf first in water and then in alcohol, we kill the leaf and remove the green chlorophyll pigment. This makes the leaf's final color change from the iodine test easily visible. The iodine solution turns the parts of the leaf that contain starch dark blue-black.
The Procedure Explained
The leaf is boiled in water to **kill the cells** and make them permeable. This allows the iodine solution to enter the cells and react with any starch that may be present.
The leaf is then placed in a test tube with ethanol and heated in a water bath. This step **removes the chlorophyll**, turning the leaf white. The chlorophyll must be removed so that the color change from the iodine test can be seen clearly.
The now colorless leaf is rinsed and placed on a white tile. A few drops of iodine solution are added. If starch is present, the leaf will turn **dark blue or black**, a positive result. If no starch is present, the leaf remains brownish-yellow, a negative result.
