The Setup
* Elodea: A common aquatic plant.
* Phenol Red: A pH indicator that turns yellow in acidic solutions and red in basic (alkaline) solutions.
The Experiment
1. Initial Observation: The phenol red solution will be a reddish color, indicating it's slightly basic.
2. Adding the Elodea Leaf: When you add the Elodea leaf to the phenol red solution, you'll observe a gradual change in color towards yellow. This is because the leaf will release carbon dioxide (CO2) into the water.
3. The Chemical Reaction: The CO2 dissolves in water to form carbonic acid (H2CO3), which is a weak acid. The acidic H2CO3 reacts with the phenol red, causing the indicator to change color from red to yellow.
The Science
* Photosynthesis: Elodea leaves, like other plants, perform photosynthesis. During photosynthesis, they absorb carbon dioxide and release oxygen. However, this process requires light.
* Respiration: In the absence of light, Elodea (and all living organisms) continue to respire. During respiration, they break down sugars (glucose) for energy. A byproduct of this process is carbon dioxide.
In the experiment, the Elodea leaf is in the dark, so it's predominantly carrying out respiration. This is why it releases CO2, which makes the solution more acidic and changes the phenol red's color.
Key Points
* This experiment demonstrates the process of cellular respiration.
* The color change of the phenol red solution is a visual indicator of the production of carbon dioxide.
* Elodea leaves can perform both photosynthesis and respiration, but the dominant process in darkness is respiration.
