What is the key feature of a hypotonic solution?

A hypotonic solution is characterized by having a lower concentration of solutes compared to the inside of a cell. This key feature leads to the fundamental behavior of cells when they are placed in such a solution. Because water moves from areas of lower solute concentration to areas of higher solute concentration, when a cell is placed in a hypotonic solution, water flows into the cell. This influx of water can cause the cell to swell and potentially burst, a phenomenon known as osmotic lysis.

In contrast, solutions described in the other options do not exhibit the same effects on cells. For example, a hypertonic solution has a higher solute concentration outside the cell, which would draw water out of the cell, causing it to shrink. An isotonic solution has equal solute concentrations inside and outside the cell, which would result in no net movement of water. Moreover, a solution causing cells to become inactive does not specifically refer to the osmotic characteristics of hypotonic solutions, as inactivity can arise from various other factors unrelated to osmotic pressure. Thus, the defining characteristic of a hypotonic solution is its lower solute concentration relative to the intracellular environment, leading to the movement of water into the cell.