Isotonic, hypotonic, and hypertonic are terms used to describe the relative concentrations of solutes in solutions and their effects on cells:

1. Isotonic Solution: An isotonic solution is one in which the concentration of solutes is equal inside and outside the cell or across a semipermeable membrane. In an isotonic solution, there is no net movement of water across the membrane, and the cell maintains its normal shape and size. The osmotic pressure inside the cell is balanced by the osmotic pressure outside the cell. Isotonic solutions are typically used in medical applications, such as intravenous fluids and eye drops, to maintain proper fluid balance.
2. Hypotonic Solution: A hypotonic solution has a lower concentration of solutes compared to the cell or the surrounding medium. When a cell is placed in a hypotonic solution, water moves into the cell by osmosis, causing the cell to swell and potentially burst. This is because the osmotic pressure inside the cell is higher than the osmotic pressure outside the cell. Hypotonic solutions are used to provide hydration and to replenish fluids in cases of dehydration.
3. Hypertonic Solution: A hypertonic solution has a higher concentration of solutes compared to the cell or the surrounding medium. When a cell is placed in a hypertonic solution, water moves out of the cell by osmosis, causing the cell to shrink or undergo plasmolysis. This occurs because the osmotic pressure outside the cell is higher than the osmotic pressure inside the cell. Hypertonic solutions are used to draw out excess fluid from swollen tissues, such as in certain wound dressings or in the treatment of edema.

It’s important to note that the terms isotonic, hypotonic, and hypertonic are relative and depend on the specific context or reference point. For example, a solution may be hypertonic compared to one cell type but isotonic compared to another. The effects of these solutions on cells and organisms can vary depending on their osmotic characteristics and the specific cell or tissue involved.