When a plant cell is placed in a concentrated salt solution, it undergoes plasmolysis, causing the cell to shrink as water moves out of the cell.
Plasmolysis Explained
Plasmolysis is the process where the protoplasm of a plant cell shrinks away from the cell wall due to water loss via osmosis. This occurs when the plant cell is surrounded by a hypertonic solution (a solution with a higher solute concentration, such as concentrated salt water) compared to the cell's interior.
The Process of Osmosis
Osmosis is the movement of water across a semi-permeable membrane from an area of high water potential (low solute concentration) to an area of low water potential (high solute concentration). In the case of a plant cell in concentrated salt solution:
- Higher Solute Concentration Outside: The concentrated salt solution has a higher solute concentration, therefore a lower water potential, than the plant cell's cytoplasm.
- Water Movement: Water moves out of the plant cell and into the surrounding salt solution down the water potential gradient.
- Protoplast Shrinkage: As water leaves the cell, the protoplast (the cell contents inside the plasma membrane) shrinks and pulls away from the rigid cell wall. This shrinkage is plasmolysis.
- Turgor Pressure Loss: Plasmolysis leads to a loss of turgor pressure (the pressure of the cell contents against the cell wall), causing the plant cell to become flaccid.
Why This Happens: Water Potential
Water potential is a measure of the relative tendency of water to move from one area to another. Water always moves from an area of higher water potential to an area of lower water potential. In the case of the plant cell in the salt solution, the salt solution has a lower water potential, causing the water to flow out of the cell.
Consequences of Plasmolysis
If a plant cell remains in a hypertonic solution for an extended period, plasmolysis can become irreversible, leading to cell damage and potentially cell death. This is why high salt concentrations in the soil can be harmful to plants.
