Biology » The Excretory System » Osmoregulation and Osmotic Balance

Summarizing Osmoregulation and Osmotic Balance


Solute concentrations across a semi-permeable membranes influence the movement of water and solutes across the membrane. It is the number of solute molecules and not the molecular size that is important in osmosis. Osmoregulation and osmotic balance are important bodily functions, resulting in water and salt balance. Not all solutes can pass through a semi-permeable membrane. Osmosis is the movement of water across the membrane.

Osmosis occurs to equalize the number of solute molecules across a semi-permeable membrane by the movement of water to the side of higher solute concentration. Facilitated diffusion utilizes protein channels to move solute molecules from areas of higher to lower concentration while active transport mechanisms are required to move solutes against concentration gradients. Osmolarity is measured in units of milliequivalents or milliosmoles, both of which take into consideration the number of solute particles and the charge on them. Fish that live in fresh water or saltwater adapt by being osmoregulators or osmoconformers.



solute that breaks down into ions when dissolved in water


number of moles of solute per kilogram of solvent


number of moles of solute per liter of solution


gram equivalent of the molecular weight of a substance


solute that does not break down into ions when dissolved in water


organism that changes its tonicity based on its environment


mechanism by which water and solute concentrations are maintained at desired levels


organism that maintains its tonicity irrespective of its environment

osmotic balance

balance of the amount of water and salt input and output to and from a biological system without disturbing the desired osmotic pressure and solute concentration in every compartment

osmotic pressure

pressure exerted on a membrane to equalize solute concentration on either side

semi-permeable membrane

membrane that allows only certain solutes to pass through

Got questions about this content? Get access to an AI-Powered Study Help/Tutor you can chat with as you learn! Continue Learning With Ulearngo

[Attributions and Licenses]

This is a lesson from the tutorial, The Excretory System and you are encouraged to log in or register, so that you can track your progress.

Log In

Share Thoughts