What are the differences between tonicity and osmolarity?

Question

Accepted Answer

Basis of differentiation

Tonicity

Osmolarity

Definition

Is the measurement of the osmotic pressure difference between two solutions separated by a semipermeable membrane assessed by comparing their water potentials

The concentration of all osmotically active particles in a solution, expressed as the number of osmoles (or milliosmoles) of solute per liter of solution

Types of solutions

Isotonic, hypertonic, and hypotonic solutions

Hypersomotic, isosmotic, and hypoosmotic solutions

Type of solute

It quantifies the concentration of solutes that cannot cross a semipermeable barrier

It measures the combined concentration of solutes that can and cannot pass through a semipermeable membrane

Relative to

Relative to the solute concentration inside a cell

Is an absolute measure of solute concentration and independent of any specific cellular environment

Basis of differentiation	Tonicity	Osmolarity
Definition	Is the measurement of the osmotic pressure difference between two solutions separated by a semipermeable membrane assessed by comparing their water potentials	The concentration of all osmotically active particles in a solution, expressed as the number of osmoles (or milliosmoles) of solute per liter of solution
Types of solutions	Isotonic, hypertonic, and hypotonic solutions	Hypersomotic, isosmotic, and hypoosmotic solutions
Type of solute	It quantifies the concentration of solutes that cannot cross a semipermeable barrier	It measures the combined concentration of solutes that can and cannot pass through a semipermeable membrane
Relative to	Relative to the solute concentration inside a cell	Is an absolute measure of solute concentration and independent of any specific cellular environment

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