Final answer:
When both the cell and the outside environment have equal concentrations of water and solute (50% each), the condition is isotonic, with no net water movement and cells maintaining normal function.
Step-by-step explanation:
When a cell has 50% water and 50% solute inside it, and the outside environment also has 50% water and 50% solute, the conditions are said to be isotonic. An isotonic solution means that the solute concentrations inside and outside the cell are approximately equal, resulting in no net movement of water across the cell membrane.
In living systems, when cells and their extracellular environments are isotonic, the concentration of water molecules is the same outside and inside the cells, and the cells maintain their normal shape and function. No net water movement ensures that the cells do not swell or shrink, which is critical for cell survival.