How are osmolarity and tonicity related in a hyperosmotic solution that is also hypertonic?

In a hyperosmotic solution that is also hypertonic, osmolarity refers to the total concentration of solute particles in the solution, while tonicity describes the effect that this solution has on the volume of cells immersed in it.

When a solution is hyperosmotic, it has a higher concentration of solute particles than the cytoplasm of the cells. Hypertonicity means that the solution can cause cells to lose water, leading to cell shrinkage as water moves out of the cells to balance the solute concentrations. In this scenario, the osmolarity of the hyperosmotic solution is indeed higher than the tonicity, which considers only the non-permeable solutes that cannot cross the cell membrane.

Therefore, although osmolarity encompasses all solute particles, tonicity only considers those that cannot permeate the cell membrane and affect its volume. This distinction is what confirms that in a hyperosmotic and hypertonic situation, osmolarity is higher than tonicity.