Imbibition

Imbibition is a special kind of diffusion where water is diffused in by hydrophilic colloids, which otherwise do not dissolve in water. This results in an increase in the final volume. Imbibition in nature mostly relates to the movement of water. However, theoretically, any liquid can be imbibed. As per imbibition definition, the features of imbibition consists of two major players- the solid colloid substance called imbibants, and the liquid is called the imbibate. 

For imbibition to occur, the imbibant needs to be hydrophilic. Hydrophobic substances cannot imbibe. For example, proteinaceous substances can imbibe while starchy substances do not. Therefore, this can be considered as the reason why proteinaceous pea seeds swell up in the water, but starchy wheat seeds do not. 

Factors Affecting Imbibition

There are several factors affecting imbibition. Some of them are:

Water Potential: Imbibants must have very high negative water potential. The more negative is the water potential of any substance, the greater is its capacity to imbibe. Water is considered to have the highest water potential, equals to zero (0).

Water Potential Gradient: Water moves from a higher potential to a lower potential.  The drier the imbibant is, the steeper is the water potential gradient. The water potential gradient determines the rate of imbibition.

The Adsorption Capacity of the Imbibant:The adsorption capacity of the imbibant depends on its hydrophilicity. It is defined by the degree of attraction that the imbibant has for water molecules. It determines how much water can diffuse into the body and can be held by the imbibant molecules.

The Affinity Between Imbibant and Imbibate: The imbibant needs to have an affinity for the imbibate for imbibition to occur. If the imbibate molecules repel the molecule of the imbibant, imbibition will not occur.

The pH of the System: The pH of the system plays a crucial role in the process of imbibition. It determines the affinity of the imbibant for the imbibate.

The Temperature of the System: The temperature of the system determines the molecular spacing as well as the energy per molecule of any system. With an increase in temperature, the molecular spacing of the imbibant increases and thus increases the chances and extent of imbibition.

The Pressure of the System: Pressure also determines the molecular spacing of any system. Therefore the pressure of the system determines the imbibition rate. 

The Capacity of the Imbibant to Increase in Volume: The imbibant must have the capacity to increase in volume after the imbibition process. If the imbibant has a rigid outer layer, it reduces the ability to increase in volume, and as a result, the rate of imbibition decreases.

Heat of Wetting: Heat is produced during the process of imbibition. This heat is called the heat of wetting.

What Are The Conditions That Are Necessary For Imbibition To Occur?

There are three necessary conditions for imbibition to occur:

  • A water potential gradient must be created between the imbibant and the imbibate. The imbibate moves from a region of higher water potential gradient to a region of lower water potential gradient.

  • There should be some attraction and philicity between the imbibant and the imbibate.

  • An increase in temperature increases the rate of imbibition. 

Role Of Imbibition In Plants

Imbibition has important roles to play in the process of plant development.

  • Seed germination and initial stages of plant growth. Seed germination begins with the breaking of the seed coat. Water is imbibed when the seed coat is broken. After the seed coat is broken and the seedling grows, it needs to ascent through the soil above it. The growth of the seedling has a contribution from imbibition pressure developed within it.

  • Absorption of water by roots: roots are the main tissues required for collecting water from the soil. Water moves into the root hair by imbibition. Imbibition also plays a major part in the ascent of sap through the plant body.

  • The plant keeps its cells moist by transferring water from adjacent cells through imbibition.

Imbibition Pressure

When the imbibant is kept in a confined area, pressure increases with an increase in the imbibant volume. This pressure is known as imbibition pressure. It is also known as the matric potential since it develops due to the matric potential of the imbibing substance. It is denoted as  Ѱm and is measured in megapascals (MPa) or bars.

This imbibition pressure can be tremendous and can be used to split open a rock. For example, in ancient times, Egyptians used to put a dry stick in any crevices of the rock and used to apply water on the stick. The rock used to split open due to the constant imbibition pressure from the water.

Significance Of Imbibition In Nature

  • Imbibition helps in seed germination

  • Imbibition helps in water absorption by root hairs of plants

  • Imbibition helps to keep the cells moist.

Although imbibition is a form of diffusion, there are certain subtle differences between the two.

Difference Between Diffusion And Imbibition

Diffusion

Imbibition

Diffusion involves movement of any substance from a region of its higher concentration to a region of its lower concentration.

Imbibition is the movement of a solvent (mainly water) from a region of its higher concentration to a region of its lower concentration.

No adsorption is involved.

Adsorption is involved.

No change in volume

The volume of the imbibant increases.

No affinity is required.

Affinity must be present between the imbibant and the imbibate.

Little change in pressure.

An enormous increase in pressure.

No heat is liberated.

Heat is liberated.

The Diffusion of gases can also take place

Gas is not involved.

FAQ (Frequently Asked Questions)

1. What is Imbibition?

Imbibition is the movement of a solvent into a solute following a water potential gradient.

2. What is Imbibition Pressure?

The pressure developed in the imbibant due to imbibition is called imbibition pressure.

3. Give a Few Examples of Imbibition.

Seed coat rupturing during germination, the ascent of sap, absorption of water by root hairs are all examples of imbibition.

4. How is Imbibition Different from Diffusion?

Diffusion does not involve any affinity between the two systems. Imbibition requires affinity between the imbibate and the imbibant. Diffusion does not generate heat, pressure and does not involve changes in volume, but imbibition involves all these parameters. Diffusion can also take place between two gaseous systems. Imbibition does not involve any gaseous exchange.

5. How is Imbibition Different from Osmosis?

Imbibition can take place in both living and dead systems. Osmosis takes place between two living cells. Imbibition does not require a semi-permeable membrane. Osmosis takes place through a semi-permeable membrane.