An isotonic solution is one that has a similar osmolarity, or solute concentration, as another solution. If the two solutions are isolated by a semipermeable layer, water will flow equally into the two solutions. The impact is zero water flow between the two solutions, though water is moving both ways. In science, there are some cells that must be kept in an isotonic answer to support their growth.
Many cells, which do not have a cell wall to offer support against the impacts of water and pressure, depend on the outside environment to keep up their shape. The body maintains the pH and osmolarity of its fluids to deliver isotonic solutions to wash their cells in. This solution can convey supplements and water in amounts that are equivalent to that inside the cell.