To address your questions step by step:
1. Pulling on the Plunger and Bubbles
When she pulls on the plunger in the context of a leaf disc experiment (often a demonstration of photosynthesis), the pressure decreases, and this causes any dissolved gases (primarily oxygen) that are trapped within the leaf discs to be released, forming bubbles. These leaf discs are often used to demonstrate the concept of photosynthesis because they can sink or float based on the production of oxygen.
2. Why Do the Bubbles Start to Sink?
Initially, the leaf discs may sink because they are denser than the surrounding water when the gases inside them have been removed through the vacuum created by pulling the plunger. As photosynthesis occurs when the leaf discs are exposed to light, oxygen will be produced as a byproduct. This oxygen collects within the leaf discs, reducing their density and causing them to become buoyant, which will make them rise to the surface. If they start to sink, it suggests that the leaf discs are still filled with water (and the air spaces have not yet been recharged with oxygen).
3. What Happens After Leaf Discs Are Exposed to Light for 5 Minutes?
After being exposed to light for about 5 minutes, the process of photosynthesis will begin to take place. Photosynthesis is the process by which plants, using sunlight, convert carbon dioxide (CO₂) and water (H₂O) into glucose (C₆H₁₂O₆) and oxygen (O₂).
In this experiment, if the leaf discs have chlorophyll and are healthy, they will start converting light energy into chemical energy. As a result, they will produce oxygen gas as a byproduct, which will fill the air spaces within the leaf discs. This increase in buoyancy due to the oxygen production will cause them to rise to the surface of the water.
Summary
- Pulling the plunger creates a vacuum that causes gas bubbles to escape from the leaf discs.
- The leaf discs may initially sink because they are waterlogged but can rise when oxygen is produced during photosynthesis.
- After about 5 minutes of light exposure, photosynthesis begins, leading to the production of oxygen, causing the discs to start floating as they become less dense.