What is the Difference Between Imbibition and Osmosis

The main difference between imbibition and osmosis is that imbibition is the absorption of water by a solid substance without forming a solution whereas osmosis is the movement of water molecules from a higher water concentration to a lower water concentration through a semipermeable membrane. Furthermore, imbibition requires colloidal and hydrophilic substances, while osmosis requires solutes. Moreover, the absorption of water by seeds or dry wood is an example of imbibition, while the two types of osmosis are endosmosis and exosmosis. 

Imbibition and osmosis are two types of movements of water molecules. Generally, they are natural processes that occur in the environment. 

Key Areas Covered 

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

Key Terms 

Colloids, Endosmosis, Exosmosis, Imbibition, Osmosis, Semipermeable Membrane

What is Imbibition 

Imbibition is the uptake or absorption of water by a solid substance without forming a solution. Here, the solid substance that absorbs water is known as the imbibant. However, it does not dissolve in water. Also, the solvent which is going to be absorbed is known as imbibate. Generally, imbibition is also a type of diffusion while the colloids in the imbibant enormously increase the volume. Moreover, to absorb water, these colloids have to be hydrophilic. The water potential of imbibant is negative, while imbibate has the highest water potential. 

Figure 1: Seed Germination Steps
Water Imbibition (II), The Uptake of Water, Results in Rupture of Seed Coat (III), The Imbibition of the Seed Coat Results in Emergence of the Radicle (IV) and the Plumule (V), the Cotyledons Get Unfolded (VI)

Furthermore, imbibition plays an important role in plants. It is the initial step of seed germination. Generally, the seed coat is the first structure of the seed which undergoes imbibition first, and it is followed by the embryo and other parts of the seed. On the other hand, the initial absorption of water by roots occurs in the form of imbibition of water by cell walls of the root hair cells. Furthermore, water moves into the ovules through imbibition.  

What is Osmosis 

Osmosis is the net movement of water molecules from a lower solute concentration to a higher solute concentration through a semipermeable membrane in a spontaneous manner. Osmosis is an important process that occurs through biological membranes such as cell membranes. Generally, these membranes are impermeable to large and polar molecules such as proteins and carbohydrates. Also, they are impermeable to ions. However, they are permeable to non-polar molecules such as lipids and small molecules such as oxygen, carbon dioxide, nitric oxide, etc. Water molecules diffuse through the cell membrane via aquaporins.

Figure 2: Osmosis

Moreover, there are two types of osmosis: endosmosis and exosmosis. Endosmosis is the movement of water into the cell. Usually, it occurs when a cell is placed in a hypotonic solution. However, the excess filling of water into the cell may break open the cell wall. Exosmosis is the movement of water out of the cell when placed in a hypertonic solution. Excess leakage of water from the cell may shrink the cell. 

Similarities Between Imbibition and Osmosis 

• Imbibition and osmosis are two types of movements of water. 
• Both occur in nature. 

Difference Between Imbibition and Osmosis 

Definition 

Imbibition refers to the absorption of one substance by another, in particular, the uptake of water by a plant or seed while osmosis refers to the process by which molecules of a solvent tend to pass through a semipermeable membrane from a less concentrated solution into a more concentrated one. 

Significance 

Moreover, imbibition is the absorption of water from a solid substance without forming a solution while osmosis is the movement of water from a higher water potential to a lower water potential through a semipermeable membrane. 

Semipermeable Membrane 

Moreover, imbibition does not require a semipermeable membrane while osmosis requires a semipermeable membrane. 

Involvement of Solutions 

A single solution with water requires imbibition, while osmosis requires two solutions with different water potentials. 

Formation of a Solution 

Imbibition does not form a solution while osmosis forms a solution with a lower solute concentration. 

Particles or Solutes 

Furthermore, imbibition requires colloidal and hydrophilic substances, while osmosis requires solutes. 

Generation of Pressure 

Imbibition develops relatively high pressure (1000 atm) while osmosis develops relatively low pressure (100 atm).  

Generation of Heat 

While imbibition does not generate heat, osmosis does not generate heat. 

Reversibility 

In addition to these, imbibition is an irreversible process, while osmosis is a reversible process. 

Types 

Absorption of water by seeds or dry wood is an example of imbibition, while the two types of osmosis are endosmosis and exosmosis. 

Conclusion 

Imbibition is the absorption of water from a solid substance without forming a solution. Therefore, it only requires a single solution with water and colloidal substances. However, it does not occur through a semipermeable membrane. In contrast, osmosis is the movement of water molecules from a higher to a lower water potential through a semipermeable membrane. Therefore, it requires the presence of two solutions with two different water potentials. Ultimately, it gives rise to a solution with a higher water potential than the initial solution. Hence, imbibition and osmosis is the type of water movement. 

References:

1. “Osmosis.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 19 Sept. 2017, Available Here
2. “Imbibition – Difference Between Imbibition And Diffusion.” BYJUS, Byju’s, 6 Sept. 2019, Available Here.

Image Courtesy:

1. “Seed Germination” By Noahjgagne – Own work (CC BY-SA 4.0) via Commons Wikimedia   
2. “0307 Osmosis” By OpenStax (CC BY 4.0) via Commons Wikimedia