Difference Between Osmosis and Reverse Osmosis

The main difference between osmosis and reverse osmosis is that the osmosis is the diffusion of water molecules from high to a lower water potential across a semipermeable membrane whereas the reverse osmosis is the diffusion of water molecules across a semipermeable membrane against the potential gradient. Furthermore, osmosis is a natural process while reverse osmosis is an artificial process.

Osmosis and reverse osmosis are two methods of water movement through a semipermeable membrane. The semipermeable membrane can be a type of biological or synthetic, polymeric membrane, which allows only certain molecules or ions to pass through it by diffusion.

Key Areas Covered

1. What is Osmosis
     – Definition, Facts, Applications
2. What is Reverse Osmosis
     – Definition, Facts, Applications
3. What are the Similarities Between Osmosis and Reverse Osmosis
     – Outline of Common Features
4. What is the Difference Between Osmosis and Reverse Osmosis
     – Comparison of Key Differences

Key Terms

Direction of Flow, Endosmosis, Exosmosis, Osmosis, Reverse Osmosis, Semipermeable Membrane, Water Purification

What is Osmosis

Osmosis is the movement of water molecules through a potential gradient. It occurs through a semipermeable membrane, which is mainly the plasma membrane of the cell. Water molecules move from a higher to a lower water potential until the water potential of either side of the semipermeable membrane becomes equal. The two main types of osmosis that can occur in the cell are endosmosis and exosmosis.

• Endosmosis occurs when cells are placed in a hypotonic solution, which has a higher water potential when compared to the cytosol. Sometimes, the cells can burst open due to the filling with too much water.
• Exosmosis occurs when cells are placed in a hypertonic solution, which has a lower water potential when compared to the cytosol. Cells become shrunk with the loss of water.
  

  Figure 1: Different Types of Water Movements

Applications of Osmosis

1. The opening of the stomata, which involves the gas exchange in plants
2. Absorption of water from the soil by roots
3. The effect on freshwater and saltwater fish when they are put into water with different salt concentrations

What is Reverse Osmosis

Reverse osmosis (RO) is the opposite of osmosis, which occurs against the water potential. It is done by increasing the pressure of the concentrated side or the side with the lower water potential. This will keep most of the salts in the concentrated side while moving water molecules to the side with the high water potential. Hence, the applied pressure overcomes the osmotic pressure of the system.

Applications of Reverse Osmosis

1. Water purification systems that produce desalinated water use water from natural sources, which carry contaminants. These contaminants do not pass through the RO membrane, which is semipermeable. Hence, demineralized, desalinated or deionized water can be obtained through reverse osmosis. This process is also known as ultrafiltration.
   

   Figure 2: Membrane Used in Reverse Osmosis

2. Bacteria in the intestine that cause cholera make the intestine unable to absorb water. This is done by reversing the normal flow of osmosis. It may cause severe dehydration and sometimes death.

Similarities Between Osmosis and Reverse Osmosis

• Osmosis and reverse osmosis are two methods of water movement through a semipermeable membrane.
• Both processes have their own applications.

Difference Between Osmosis and Reverse Osmosis

Definition

Osmosis refers to a process by which water molecules of a solvent tend to pass through a semipermeable membrane from a less concentrated solution into a more concentrated one while reverse osmosis refers to a process by which water molecules of a solvent passes through a semipermeable membrane in the direction opposite to that of natural osmosis when subjected to a hydrostatic pressure greater than the osmotic pressure.

Movement

The osmosis occurs through a potential gradient while reverse osmosis occurs against the potential gradient.

Natural/Artificial

Osmosis is a natural process while reverse osmosis is an artificial process.

Applications

Absorption of water from the soil by roots and opening the stomata occurs due to osmosis while reverse osmosis is used in the water purification systems.

Conclusion

The osmosis is a natural process of water movement through a potential gradient of water while the reverse osmosis is an artificial process in which the movement of water occurs against the potential gradient of water. Therefore, the main difference between osmosis and reverse osmosis is the direction of the water flow.

Reference:

1. “Osmosis – Definition and Examples.” Biology Dictionary, Biology Dictionary, 29 Apr. 2017, Available Here
2. “What Is Reverse Osmosis?” Puretec Industrial Water :: Ultrapure Water Solutions, Puretec Industrial Water, Available Here

Image Courtesy:

1. “Osmosis Diffusion Ultrafiltration and Dialysis” By ColnKurtz – Own work (CC BY-SA 4.0) via Commons Wikimedia 
2. “Reverse osmosis membrane coil” By David Shankbone – Own work (CC BY 3.0) via Commons Wikimedia