Plant Cells Are Default Turgid in Hypotonic Environments
- In healthy plants, turgor pressure is the default because they are in a hypotonic environment where water enters the cell, creating pressure against the rigid cell wall.
- This wall plays a crucial role in how cells respond to water movement, particularly in hypotonic and hypertonic environments.
Recall what hypotonic and hypertonic means.
Turgor Pressure in a Hypotonic Medium Maintains Cell Shape and Rigidity
- When a plant cell is placed in a hypotonic solution (e.g., pure water), water moves into the cell by osmosis.
- This influx of water causes the vacuole to expand, pushing the cytoplasm against the cell wall.
- The cell wall resists this pressure, preventing the cell from bursting.
Definition
Turgor Pressure
Turgor pressure is the pressure exerted by the cell contents against the cell wall.
- Think of a balloon inside a box.
- As you inflate the balloon, it presses against the walls of the box.
- The box doesn’t expand, but the pressure inside keeps the balloon firm.
- Similarly, the cell wall prevents the plant cell from bursting while the turgor pressure keeps it firm.
Why is Turgor Pressure Important?
- Structural Support: Turgor pressure helps non-woody plants stand upright. Without it, plants would wilt.
- Growth: Turgor pressure stretches the cell wall, enabling cell growth.
- Functional Processes: It aids in opening and closing stomata, which are essential for gas exchange and transpiration.
- Remember that the default state of plant cells differs from that of animal cells.
- In plant cells, turgor pressure is the default state, maintained in a hypotonic environment.
- In contrast, animal cells default to an isotonic environment to maintain balance and stability, as they lack a cell wall to support turgor pressure.
Plasmolysis in a Hypertonic Medium
- When a plant cell is placed in a hypertonic solution (e.g., concentrated saltwater), water moves out of the cell by osmosis.
- This causes the vacuole to shrink, and the cytoplasm pulls away from the cell wall.
- This process is called plasmolysis.
Notice how the cell is shrivelled but the plant wall firm and rigid.
What Happens During Plasmolysis?
- The cell loses water, causing the vacuole to shrink.
- The plasma membrane detaches from the cell wall.
- The cell becomes flaccid, and the plant wilts.
Plasmolysis is often irreversible and can lead to cell death if the cell is not rehydrated.
Why Does Plasmolysis Occur?
- In a hypertonic solution, the water potential outside the cell is lower than inside.
- Water moves out to balance the solute concentrations, causing the cell to lose water and shrink.
Comparing Turgor Pressure and Plasmolysis
| Feature | Turgor Pressure | Plasmolysis |
|---|---|---|
| Environment | Hypotonic | Hypertonic |
| Water movement | Water moves into the cell | Water moves out of the cell |
| Effect on Cell | Cell becomes turgid and firm | Cell becomes flaccid and shrinks |
| Outcome | Supports plant structure and growth | Can lead to wilting and cell death |
- In what ways does the regulation of water in plant cells reflect the broader idea of equilibrium in nature?
- Can turgor pressure be viewed as a metaphor for resilience in ecosystems?
