What does isotonic mean regarding cell environments?

Isotonic refers to a state where the concentration of solutes outside the cell is equal to the concentration of solutes inside the cell. This balance leads to no net movement of water across the cell membrane. When environments are isotonic, water molecules move in and out of the cell at equal rates, meaning that there is no overall change in the volume of the cell.

In an isotonic solution, the cell maintains its shape and function effectively, as cells neither swell due to excess water nor shrink from water loss. This is important for cellular health and the proper functioning of cells in various biological systems. Other options describe different conditions: a higher concentration of solutes would indicate a hypertonic environment, while a lower concentration of solutes would indicate a hypotonic environment, each leading to a different water movement scenario compared to isotonic conditions.