Materials:
* Spirogyra filament: Obtain a fresh sample from a pond or aquarium.
* Microscope: A compound light microscope with a slide and coverslip.
* Slides and coverslips: Clean glass slides and coverslips.
* Concentrated salt solution (NaCl): Prepare a solution of about 5-10% salt in water.
* Water: Distilled water for rinsing.
* Dropper: For transferring solutions.
* Forceps: For handling the Spirogyra filament.
* Petri dish: For holding the Spirogyra filament.
Procedure:
1. Prepare the Spirogyra:
- Using forceps, carefully remove a small filament of Spirogyra from the pond water or aquarium.
- Place the filament on a clean slide and add a drop of distilled water to cover it.
- Gently place a coverslip over the filament, avoiding air bubbles.
2. Observe the Normal Spirogyra:
- Examine the Spirogyra filament under the microscope. You should see the characteristic spiral chloroplasts within the cells.
- Note the appearance of the cytoplasm and the cell wall. The cytoplasm should fill the cell, and the chloroplasts should be close to the cell wall.
3. Introduce the Salt Solution:
- Carefully lift a corner of the coverslip to allow a small drop of the concentrated salt solution to flow under the coverslip.
- Let the solution diffuse into the water for a few minutes.
4. Observe Plasmolysis:
- Observe the Spirogyra under the microscope. You should see the following changes:
- The cytoplasm will shrink away from the cell wall. This is because the salt solution has a higher solute concentration than the cell's internal environment, causing water to move out of the cell by osmosis.
- The chloroplasts will appear more concentrated in the center of the cell. This is due to the shrinking cytoplasm.
- The cell wall will remain intact. This is because the cell wall is rigid and does not shrink like the cytoplasm.
5. Rehydration (Optional):
- If you want to see the Spirogyra cells recover, you can carefully lift the coverslip again and replace the salt solution with distilled water.
- Observe the cells again after a few minutes. The cells should gradually rehydrate, and the cytoplasm will expand back to its original shape.
Safety Precautions:
* Wash your hands thoroughly with soap and water after handling Spirogyra and any solutions.
* Use a compound light microscope with caution, especially when handling slides and coverslips.
Note: This experiment helps demonstrate the concept of osmosis and the importance of water movement in biological systems.
