Cells gain water primarily due to a process called osmosis, driven by differences in solute concentration between the cell's cytoplasm and its surrounding environment.
Osmosis and Cellular Water Gain
Osmosis is the movement of water across a semi-permeable membrane from an area of low solute concentration (high water concentration) to an area of high solute concentration (low water concentration). This movement continues until equilibrium is reached.
Cellular Environments and Water Movement
The direction of water movement into or out of a cell is determined by the tonicity of the surrounding medium, which is a measure of relative solute concentration compared to the cell's cytoplasm:
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Hypotonic Medium: If the medium surrounding the cell has a lower solute concentration than the cell's cytoplasm, it is considered hypotonic. In this case, water will move into the cell through osmosis, causing the cell to swell. The reference states: If the medium is hypotonic relative to the cell cytoplasm, the cell will gain water through osmosis.
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Isotonic Medium: If the medium surrounding the cell has the same solute concentration as the cell's cytoplasm, it is considered isotonic. Here, there will be no net movement of water across the cell membrane, as the water flows in and out at equal rates. The reference states: If the medium is isotonic, there will be no net movement of water across the cell membrane.
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Hypertonic Medium: If the medium surrounding the cell has a higher solute concentration than the cell's cytoplasm, it is considered hypertonic. In this case, water will move out of the cell by osmosis, causing the cell to shrink. The reference states: If the medium is hypertonic relative to the cell cytoplasm, the cell will lose water by osmosis.
Summary Table of Cellular Environments
| Medium Type | Solute Concentration Relative to Cell | Water Movement | Cell Appearance |
|---|---|---|---|
| Hypotonic | Lower | In | Swells |
| Isotonic | Same | No net movement | Normal |
| Hypertonic | Higher | Out | Shrinks |
Practical Examples:
- Freshwater protists: Live in hypotonic environments, requiring special adaptations to expel excess water.
- Red blood cells: Must be maintained in an isotonic solution (saline) in clinical settings to prevent swelling or shrinking.
- Plant cells: Maintain turgor pressure (internal pressure due to water) through a hypotonic environment to stay rigid.
Key Takeaways:
- Cells gain water through osmosis.
- Water moves from areas of low solute concentration to areas of high solute concentration.
- The tonicity of the environment dictates the direction of water movement.
- Hypotonic solutions cause water to enter the cell, resulting in cell swelling.
- The cell membrane allows water to pass through based on the principles of osmosis.
