Water Potential and Osmosis Basics
Think of water potential as the "pressure" water molecules create, measured in kPa. Pure water has a water potential of 0kPa—this is your baseline. When you add solutes (like salt or sugar), the water potential drops below zero.
Osmosis is simply water's natural tendency to move from areas of high water potential to low water potential through a selectively permeable membrane. The brilliant thing is that it's completely passive—no energy required from the cell!
Here's where it gets interesting for living cells. In animal cells placed in a dilute solution, water rushes in and the cell might burst (cytolysis). Put that same cell in a concentrated solution and it shrivels up (crenation) as water leaves.
Quick Tip: Remember that water always moves towards where there's more "stuff" dissolved—it's trying to dilute concentrated areas.
Plant cells behave differently thanks to their rigid cell walls. In dilute solutions, they become turgid (firm and swollen) but won't burst. In concentrated solutions, they become plasmolysed as the cell membrane pulls away from the cell wall.
