Osmolarity and Tonicity

osmosis

the movement of water across a membrane

osmosis occurs in response to

solute concentration gradients

osmolarity is “colligative” which means

it expresses the number of osmotically active particles, but says nothing about what particles are involved

water will move by osmosis, from a

less concentrated (hyposmotic) solution to a more concentrated (hyperosmotic) solution

isomotic

two solutions contain the same number of solute particles per unit volume

hyperosmotic

if solution A has a higher osmolarity (more concentrated) than solution B, we say that solution A is hyperosmotic to solution B

hyposmotic

solution C, with fewer osmoles per unit volume, is hyposmotic to solution A

tonicity

describes a solution and how that solution would affect cell volume if the cell were placed in the solution and allowed to come to equilibrium