Final answer:
An isotonic solution is where water movement into and out of a cell is balanced, causing no change in cell size. Hypotonic and hypertonic solutions can cause cells to swell or shrink, respectively.
Step-by-step explanation:
When water goes back and forth into and out of the cell, and the cell stays the same size, the cell is in an isotonic solution. This means that the concentration of solutes outside the cell is equal to the concentration inside the cell, resulting in no net movement of water into or out of the cell. However, water molecules will continue to move in both directions across the cell membrane.In comparison, a hypotonic solution has a lower concentration of solutes outside the cell compared to inside, leading to a net influx of water into the cell, potentially causing it to swell. Conversely, in a hypertonic solution, the environment outside the cell has a higher concentration of solutes, causing water to leave the cell, which may lead to cell shrinkage.