In biology, a solution is hypertonic compared to a cell if it has a higher solute concentration than the inside of that cell, and those solutes can't easily cross the cell membrane. This difference in concentration causes water to move out of the cell, potentially leading to cell shrinkage.
Understanding Hypertonicity
Here’s a breakdown of what makes a solution hypertonic and its implications:
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Solute Concentration: Hypertonic solutions have a greater amount of dissolved substances (solutes) per unit volume compared to the cell's interior.
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Membrane Permeability: Critically, the solutes contributing to the hypertonicity cannot freely pass through the cell membrane. If they could, the concentrations would equalize.
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Water Movement (Osmosis): Due to the higher solute concentration outside the cell, water will move out of the cell and into the surrounding solution by osmosis, which is the movement of water across a semipermeable membrane from an area of high water concentration (low solute concentration) to an area of low water concentration (high solute concentration).
Implications for Cells
The movement of water out of the cell due to a hypertonic environment can have several effects:
- Cell Shrinkage: The cell loses water and shrinks. In animal cells, this is called crenation.
- Plasmolysis (in Plant Cells): In plant cells, the cell membrane pulls away from the cell wall.
- Dehydration: In organisms, exposure to a hypertonic environment can lead to dehydration as cells lose water to the surroundings.
Example
Imagine a red blood cell placed in a solution with a very high concentration of salt. Because salt cannot easily cross the red blood cell membrane, the solution is hypertonic. Water will move out of the red blood cell into the salty solution, causing the cell to shrink.
Hypertonic vs. Hypotonic vs. Isotonic
To fully understand hypertonic, it's helpful to compare it to the other tonicity states:
| Term | Solute Concentration (Compared to Cell) | Water Movement | Effect on Cell |
|---|---|---|---|
| Hypertonic | Higher | Out of the cell | Shrinkage (crenation) |
| Hypotonic | Lower | Into the cell | Swelling, possibly burst |
| Isotonic | Equal | No net movement | No change |
