* Isotonic: An isotonic solution has the same concentration of solutes (dissolved substances) as the cell's cytoplasm. This means the water potential (tendency for water to move) is equal inside and outside the cell.
* Equilibrium: Since the water potential is the same, there's no net movement of water across the cell membrane. The cell maintains its normal shape and volume.
* No change: The cell neither gains nor loses water, and its internal environment remains stable.
Think of it like this: Imagine a room with an equal number of people on each side of a door. The door is open, but no one moves because there's no reason to. The same applies to water movement in an isotonic solution.
In contrast to isotonic solutions:
* Hypotonic solution: Has a lower solute concentration than the cell. Water moves into the cell, causing it to swell and potentially burst (lysis).
* Hypertonic solution: Has a higher solute concentration than the cell. Water moves out of the cell, causing it to shrink (crenation).
