Cellular Osmosis and Tonicity Summary

Hypotonic Solution

A solution with a lower solute concentration (higher water concentration) than the inside of a cell, causing water to flow into the cell and making animal cells swell and gain mass.

Hypertonic Solution

A solution with a higher solute concentration (lower water concentration) than the inside of a cell, causing water to flow out of the cell and making cells shrink or shrivel and lose mass.

Isotonic Solution

A solution with equal solute and water concentrations inside and outside the cell, where water molecules move in dynamic equilibrium with no net change in cell volume.

Water Concentration Calculation

The percentage of water in a solution is equal to $100\text{\%}$ minus the percentage of solute (for example, a solution that is $75\text{\%}$ solute contains $25\text{\%}$ water).

Percent Mass Difference Formula

$\text{Percent Difference} = \frac{\text{Final Mass} - \text{Initial Mass}}{\text{Initial Mass}} \times 100$

Osmosis Behavior (20\% vs 50\% Solute)

If a cell with an interior solute concentration of $20\%$ is placed in a $50\%$ solute solution, water flows out of the cell into the hypertonic solution to equalize solute concentrations.

Beaker A (Bag of Water in Sugar Water)

Initial mass $20\,\text{g}$, final mass $16\,\text{g}$, mass difference $-4\,\text{g}$, resulting in a percent mass difference of $-20\%$.

Beaker B (Bag of Sugar Water in Water)

Initial mass $19\,\text{g}$, final mass $25\,\text{g}$, mass difference $+6\,\text{g}$, resulting in a percent mass difference of $+31.58\%$.