Water Movement by Osmosis into or out of Cells
- If you placed a wet sponge on a dry table, water would move out of the sponge onto the table.
- But if you place it in a bowl of water, the sponge would absorb more water and swell.
- This movement of water, depending on the surroundings, is exactly how osmosis works
Definition
Osmosis
Osmosis is the passive movement of water molecules across a semi-permeable membrane from a region of lower solute concentration (hypotonic) to a region of higher solute concentration (hypertonic).
Osmosis Works For Three Main Reasons
- Semi-Permeable Membrane: Allows water to pass but restricts solutes.
- Concentration Gradient: Water moves to balance solute concentrations on both sides of the membrane.
- Net Movement: Water moves until equilibrium is reached, where concentrations are equal.
In animal cells, excessive water intake can cause the cell to burst (lyse) because they lack a cell wall for support.
NoteIn an isotonic environment, there is no net movement of water, but water molecules continue to move across the membrane.
Why Osmosis Matters
- Cell Survival: Osmosis regulates water balance, preventing cells from bursting or shrinking.
- Nutrient Uptake: Root cells absorb water from the soil through osmosis.
- Medical Applications: Isotonic solutions are used in IV drips to prevent damage to blood cells.
How does the concept of osmosis connect to broader ideas of balance and equilibrium in biology? Can you think of other systems where balance is critical?
