Mammalian & Plant Physiology

Experiment 3

Aim of the Experiment

To demonstrate plasmolysis in peels of Tradescantia or Rheo plant cell, Elodea plants or onion epidermal cells in hypotonic and hypertonic solutions using salt solution.

Principle:

Plasmolysis is the process of shrinkage or contraction of the protoplasm of a plant cell as a result of loss of water from the cell. Plasmolysis is one of the results of osmosis and occurs very rarely in nature, but it happens in some extreme conditions. We can induce plasmolysis in the laboratory by immersing living cell in a strong salt solution or sugar solution to lose water from the cell. Normally people use Rheo or Tradescantia plant epidermal cell for experiment because they have coloured cell sap which can be clearly visible.

The cell membrane is a semipermeable membrane that separates the interior of all cells from the surrounding environment. The semipermeable membrane allows some particles, ions, or water molecules across the membrane, but blocks others. Water molecules constantly move inside and outside the cell across cell membranes. This free flow of water has the very important consequence of enabling cells to absorb water.

Plasmolysis and deplasmolysis

When a plant cell is immersed in concentrated salt solution (hypertonic solution), water from the cell sap moves out due to exosmosis. Exosmosis is the passage of water from higher water concentration to lower water concentration through a semipermeable membrane.

When a plant cell is placed in concentrated salt solution, water concentration inside the cell is greater than that which is outside the cell. Therefore, water moves through the cell membrane into the surrounding medium. Ultimately the protoplasm separate from the cell wall and assumes spherical shape. It is called plasmolysis.

When a plasmolysed cell is placed in a hypotonic solution, (i.e., the solution having solute concentration lower than the cell sap), the water moves into the cell because of the higher concentration of water outside the cell than in the cell. The cell then swells to become turgid. It is called deplasmolysis.

If we place living cells in isotonic solution (i.e., both solutions have the same amount of solute concentration), there is no net flow of water towards the inside or outside. Here, the water moves in and out of the cell and is in equilibrium, so the cells are said to be flaccid.

Materials required:

Rhoeo leaf, glass leaf, cover slips, dropper, Sodium chloride 0.1%, needle, Microscope.

Procedure:

1. Take two glass slides and place them on the table.

2. Take a rhoeo leaf from the Petri dish.

3. Fold the leaf and tear it along the lower side of the leaf.

4. Using a forceps, pull out two small segments of thin transparent layer from the lower epidermis of the rhoeo leaf.

5. Place the epidermal peels on both glass slides.

6. Using a dropper, take some sodium chloride 0.1% solution from the beaker.

7. Put 1 to 2 drops of solution on one slide.

8. Using another dropper, take sodium chloride 5% solution from the beaker.

9. Put 1 to 2 drops of solution on the next slide.

10. Place a cover slip over the peel of both slides using a needle.

11. Place the slides one by one under the compound microscope.

12. Observe them under the microscope.

Observation:

After half an hour we can observe that cells in sodium chloride 0.1% solution appear turgid, while cells in the sodium chloride 5 % solution show plasmolysis.

Conclusion:

When plant cells are immersed in sodium chloride 5 % solution or concentrated salt solution, water moves through the cell membrane into the surrounding medium because the water concentration inside the cell is greater than that which is outside the cell. Ultimately the protoplasm causes shrinkage and assumes spherical shape. This is called plasmolysis. When a plant cell is immersed in sodium chloride 0.1% solution or dilute salt solution, the water moves into the cell because of the higher concentration of water outside the cell than inside the cell. The cell then swells and becomes turgid.

Questions

1) Why you don't require stain for visualization of plasmolyzed cell?

2) how can you recover the hypertonic and hypotonic cell?