What is Osmosis? Definition and Meaning of Osmosis

Definition and Meaning of Osmosis – With the purpose of equalizing the concentration levels of solutes, Osmosis is a process in which a solvent (commonly in the form of water) goes through a semipermeable membrane from a lowly concentrated solution to a higher one. Since it is the exact opposite of how diffusion works, it requires a certain degree of force which is provided by the interaction between the solvent and the membrane. Osmosis is essential for biological activities including the regular transport of water entering and leaving a cell.

Factors affecting osmosis

  • Osmotic Pressure – It is the required force that prohibits the flow of a solvent through the semipermeable membrane. Osmotic Pressure may also refer to a solution’s tendency to take in a solvent by the means of osmosis. This property is dependent on a solute’s concentration and not on its identity.
  • Osmotic Gradient – It refers to the difference between the concentration levels of two solutions parted by a semipermeable membrane. Osmotic gradient is utilized to compare the degree of concentration of a dissolved solute and how it will respond when put under the process of osmosis.


1. Hypotonic Solution – With “hypo” translating to “low,” a hypotonic solution has an overall solute concentration lower than the environment outside of it. Under the process of osmosis, it is bound to gain water which can cause it to swell up or burst. The stable cell walls of plants, fungi, and bacteria prevents such bursting. On the other hand, animal cells which lack this protective layer control the process of osmosis through an ion transport.

2. Hypertonic Solution– “Hyper” means “high,” thus a hypertonic solution is defined as one that obtains an overall solute concentration level higher than its external environment. When undergoing osmosis, its water level decrease. This causes a cell to either shrivel up or shrink in size.

3. Isotonic Solution– This kind features a concentration of solute which is equal to that of its environment. Osmosis would then involve an equal inflow and outflow of water, thus creating no net movement through the semipermeable membrane. In this scenario, the size of a cell will remain constant and will neither swell up or shrink. Application of isotonic solution principles include its use when needing intravenous injection to enter a patient’s blood stream.

Variations of Osmosis

  • Reverse Osmosis – It is generally characterised as a process of separating a solution’s solvent and solute. Reverse osmosis involves the application of pressure to push a solvent to pass through a semipermeable membrane, with the solute left on one side and the pure solvent transported to the other. External pressure is applied to oppose the natural osmotic pressure that prevents such process to happen. This method is often use when purifying potable water.
  • Forward Osmosis – Similar to reverse osmosis, forward osmosis is also used to part an unwanted solute from a solvent. However, they differ on the utilized force to induce such process. In this variant, a “draw” solution with a higher osmotic pressure as compared to a “feed solution” is maximized to create an outflow of water through a semipermeable membrane.