The ability of an extracellular solution to make water move into or out of a cell by osmosis is known as its tonicity. A solution’s tonicity is related to its osmolarity, which is the total concentration of all solutes in the solution. A solution with low osmolarity has fewer solute particles per liter of solution, while a solution with high osmolarity has more solute particles per liter of solution. When solutions of different osmolarities are separated by a membrane permeable to water, but not to solute, water will move from the side with lower osmolarity to the side with higher osmolarity.
Three terms—hypotonic, isotonic, and hypertonic—are used to compare the osmolarity of a cell to the osmolarity of the extracellular fluid around it.
Note: When we use these terms, we are considering only solutes that cannot cross the membrane.
If the extracellular fluid has lower osmolarity than the fluid inside the cell, it’s said to be hypotonic—hypomeans less than—to the cell, and the net flow of water will be into the cell.
In the reverse case, if the extracellular fluid has a higher osmolarity than the cell’s cytoplasm, it’s said to be hypertonic—hypermeans greater than—to the cell, and water will move out of the cell to the region of higher solute concentration.
In an isotonicsolution—iso means the same—the extracellular fluid has the same osmolarity as the cell, and there will be no net movement of water into or out of the cell.
Define the following terms:
Now use the following terms to identify the solutions below as either Isotonic, Hypertonic, and/or Hypotonic.
Describe what would happen to the animal and plant cell if placed in each of the solutions below. (Refer to your textbook and PowerPoint slides for assistance with this question.)
What would be the difference between the way animal and plant cell react in each of the solutions? (Refer to your textbook and PowerPoint slides for assistance with this question.)