Detailly explain what happens to a cell when exposed to an hypotonic, hypertonic and isotonic solution

Alright Gobte, let's break down the effects of different solutions on cells. This all comes down to osmosis, the movement of water across a selectively permeable membrane.

The cell membrane is selectively permeable, meaning it allows water to pass through relatively freely but restricts the movement of many solutes. The direction of net water movement is always from an area of higher water concentration (lower solute concentration) to an area of lower water concentration (higher solute concentration).

Here's what happens in each type of solution:

1. Isotonic Solution

   • Definition: An isotonic solution has a solute concentration equal to that inside the cell.
   • Water Movement: There is no net movement of water across the cell membrane. Water molecules move in and out of the cell at equal rates.
   • Effect on Animal Cells: The cell maintains its normal shape and volume. For example, red blood cells in an isotonic solution (like 0.9% saline) remain disc-shaped.
   • Effect on Plant Cells: The cell is flaccid (limp). While the cell wall prevents bursting, the cell membrane is not pressed firmly against the wall, and the cell lacks turgor pressure.

2. Hypotonic Solution

   • Definition: A hypotonic solution has a solute concentration lower than that inside the cell. This means the water concentration outside the cell is higher than inside.
   • Water Movement: There is a net movement of water into the cell, moving down its concentration gradient.
   • Effect on Animal Cells: Water rushes into the cell, causing it to swell. Since animal cells lack a rigid cell wall, they can burst, a process called lysis (or hemolysis for red blood cells).
   • Effect on Plant Cells: Water enters the cell, and the cell swells. However, the rigid cell wall prevents the cell from bursting. The incoming water pushes the cell membrane against the cell wall, creating turgor pressure. This makes the cell turgid (firm), which is the normal and healthy state for most plant cells, providing structural support to the plant.

3. Hypertonic Solution

   • Definition: A hypertonic solution has a solute concentration higher than that inside the cell. This means the water concentration outside the cell is lower than inside.
   • Water Movement: There is a net movement of water out of the cell, moving down its concentration gradient.
   • Effect on Animal Cells: Water leaves the cell, causing it to shrink and shrivel. This process is called crenation. The cell loses volume and can no longer function properly.
   • Effect on Plant Cells: Water leaves the cell, causing the cell membrane to pull away from the cell wall. This process is called plasmolysis. The cell becomes flaccid and loses turgor pressure, leading to wilting in plants. If plasmolysis is severe and prolonged, the cell can die.

3 de faites, encore 2 aujourd'hui. Tu progresses.