Osmotic Pressure and Osmotic Potential

Whenever a solution is separated from its pure solvent by a semipermeable membrane, the dissolved solute creates a real, measurable pressure in the solution called osmotic pressure (OP, symbol π) - specifically, the pressure that would have to be applied on the solution side to just prevent net water from entering it. Osmotic pressure for pure water itself is zero, and it rises as more solute is dissolved, so a strongly concentrated (hypertonic, low water potential) solution always has a higher osmotic pressure than a weakly concentrated (hypotonic, high water potential) one; osmotic pressure is always given as a positive number. Osmotic potential expresses this exact same solute effect but from a different angle - it is the ratio between the number of solute particles and solvent particles present, numerically identical in magnitude to osmotic pressure, but always written with a negative sign, since dissolving solute can only ever lower, never raise, a solution's water potential. So osmotic pressure and osmotic potential describe one and the same physical effect of dissolved solute, …