A hypertonic environment for a cell is created when the solution outside of the cell is hypertonic in comparison to the cytoplasm of the cell. Such a hypertonic solution has more dissolved solute than the cytoplasm of the cell. For example, the fluid outside the cell has 5% solute and 95% water, while the cell has 1% solute and 99% water. In this situation, water is in higher concentration inside the cell and will move, by osmosis, to the outside in an attempt to equalize the concentrations. Water leaving the cell will cause shrinkage of the cell and a loss of mass. A cell shrunk in this manner is said to be crenated.

An isotonic environment for a cell is created when the solution outside of the cell is isotonic with the cytoplasm of the cell. An isotonic solution has the same concentration of dissolved solute as the cytoplasm of the cell. In this case, the fluid outside of the cell and the cytoplasm of the cell would both be 1% solute and 99% water. Water is found in equal concentrations both inside and outside of the cell. Although water will still move into and out of the cell, there is no net movement of water or change in cell volume.