Imbibition: Have you ever experienced the swelling of wooden frames of doors or windows during rainy seasons? Or do the seeds swell when kept in water? Do you know why this happens? This happens because of a process called imbibition, which occurs in the plant cells.

In imbibition, the water molecules or any other liquid molecules are adsorbed by the solid particles of the substances that result in an enormous increase in the volume of the essence. Scroll down to learn about the conditions, factors, and imbibition’s importance.

What is Imbibition?

Imbibition is a phenomenon of adsorption of water or any other liquid by the solid particles of a substance without forming a solution. Imbibition is an exceptional type of diffusion, which occurs when water is absorbed by solids-colloids causing an increase in volume.

The solid particles which imbibe water or any other liquid are called imbibants, and the liquid which is imbibed is known as imbibate.

Imbibition Characteristics

Following are the characteristics of imbibition:

1. It is a particular type of diffusion in which water is absorbed by a substance’s solid particles (or colloids), resulting in an enormous increase in volume. E.g., if a dry piece of wood is placed in water, it swells up and increases in volume.
2. During imbibition, the water molecules get tightly adsorbed and become immobilised.
3. The absorbed water molecules lose most of their kinetic energy in the form of heat during imbibition, which is called heat of wetting (or heat of hydration).
4. The water potential or matric potential of imbibants is negative because water has maximum water potential, i.e., zero \(\left( 0 \right).\)
5. Steep water potential is created when a dry imbibants comes in contact with the water.
6. The imbibants hold the imbibate by an attractive force called adsorption.
7. The swelling imbibants develop a pressure called imbibants pressure. This is also called imbibitional pressure.
8. The imbibate is held between and over the surface of particles of the imbibant through a process of adsorption and capillarity.

Fig: The Process of Imbibition

Conditions Required for Imbibition

Following are the conditions necessary for imbibition:

1. A potential water gradient should occur between the imbibing (like a wooden piece) and the liquid being imbibed (e.g., water).
2. There should be some forces of attraction (or affinity) between imbibants and imbibed liquid for imbibition to occur.
3. Adsorption is the property of colloids, and hence the materials which have a high proportion of colloids are good imbibants, and for this reason, only wood is considered to be a good imbibants because it contains protein, cellulose and starch as colloidal substances.

Factors Affecting Imbibition

Following are the factors affecting imbibition:

1. Texture of imbibants: Looseness of imbibant shows more imbibition while compactness less. More colloidal material imbibes easily. For this reason, wood, which contains lignin, cellulose, etc., is a very good imbibant.
2. Temperature: Imbibition increases with the temperature rise. With the temperature rise, liquid viscosity generally decreases, so imbibition, inversely related to viscosity, increases.
3. Pressure: Imbibition decreases with the rise in pressure. If the imbibing substance is kept in a confined place, pressure develops due to increased volume. This pressure develops due to matric potential, which is denoted as \({{\rm{\psi }}_{\rm{m}}}.\)
4. pH of the medium: Imbibition either decreases or increases depending on the charge of the imbibant.
5. The affinity of the imbibant for the imbibant.

Imbibition in Plants

1. Imbibition in plant cells refers to the adsorption of water by hydrophilic-protoplasmic and cell wall constituents.
2. Imbibition causes swelling of seeds that results in the breaking of the seed coat or testa.
3. Imbibition forms the initial step in seed germination.
4. Imbibition helps in the movement of water into the ovules, which are ripening into seeds.
5. Imbibition is needed in the initial phases of water absorption by the roots.

Imbibition Pressure or Matric Potential

Imbibition pressure is the pressure developed by an imbibant when submerged in a pure imbibing liquid. It is also known as matrix potential \(\left( {{{\rm{\psi }}_{\rm{m}}}} \right).\) When water is in contact with solid or colloidal particles, adhesive intermolecular forces between the water and the solid is the matric potential (= matrix potential). Due to this pressure in plants, seedlings emerge out of the soil and establish themselves. This pressure can be of tremendous magnitude.

Imbibition Importance in Plant Life

It is believed that imbibition plays an important role in plant physiology, apart from seed germination. Sachs proposed the imbibitional theory in \(1878.\). According to this theory, the upward movement of water (i.e., the ascent of sap) in the stem is due to the force of imbibition. But this theory was rejected because it is evident that a large quantity of water moves through the lumen of xylem vessels, which can be checked by artificially blocking the lumen with gelatin or oil (the plant will show wilting).

Significance of Imbibition

Following are the significance of imbibition:

1. Imbibition plays an important role in the absorption and retention of water.
2. The absorption of water by young cells is mostly through imbibition. The germinating seeds absorb water through imbibition.
3. Breaking the seed coat in germinating seeds is due to greater imbibitional swelling of the seed kernel (starch and protein) compared to seed coverings (cellulose).
4. Seedling can come out of the soil due to the development of imbibition pressure.
5. Jamming of the wooden frames during rainy seasons is caused by swelling of wood due to imbibition.
6. Fruits of many plants develop matric potential in addition to their osmotic potential to maintain the inflow of water even under water scarcity conditions.
7. Imbibition is dominant in the initial stage of water absorption by the roots.

Difference Between Imbibition and Osmosis

IMBIBITION	OSMOSIS
In Imbibition, the water molecules are adsorbed to the surface of hydrophilic colloids (like cellulose, starch, protein, polypeptides, etc.)	In Osmosis, the water molecules move from their higher potential to their lower potential through a semipermeable membrane.
The semipermeable membrane is not required.	A semipermeable membrane is required.
Heat is released during imbibition, which is called heat of wetting.	Heat is not released during the process of osmosis.

Difference Between Imbibition and Diffusion

IMBIBITION	DIFFUSION
It is the process in which a solid substance’s absorption of solvent or water takes place.	It is the movement of substances from the region of their higher concentration to the region of their lower concentration.
It always results in the release of heat called heat of wetting or heat of hydration.	It does not involve any release of heat.
The water or any other liquid molecules are adsorbed to the surface of hydrophilic colloids.	The diffusing particles or molecules are distributed uniformly throughout the available space.
It develops a very high pressure.	It develops less pressure comparatively.

Summary

Imbibition is one of the most important physiological phenomena in plants. This process involves the imbibate and imbibant. This is a surface phenomenon and does not involve forming a solution. This is vital, as seeds swell during germination due to imbibition. During imbibition, the water molecules get tightly adsorbed and become immobilised. The absorbed water molecules lose most of their kinetic energy in the form of heat during imbibition, which is called heat of wetting (or heat of hydration).

FAQs Related to Imbibition

Q.1. What is the significance of imbibition?
Ans: The significance of imbibition is as follows:
a. This is one of the essential processes during seed germination.
b. Seedlings can come out of the soil due to the development of imbibition pressure.
c. Imbibition plays a vital role in absorbing and retaining water.
d. Absorption of water by the root and aerial parts are also attributed to this process.

Q.2. What is imbibition theory?
Ans: Imbibition theory was proposed by Sachs in \(1878.\). According to this theory, the upward movement of water in the stem is due to the force of imbibition.

Q.3. What is imbibition?
Ans: Imbibition is a phenomenon of adsorption of water or any other liquid by the solid particles of a substance without forming a solution.

Q.4. What is the difference between imbibition and diffusion?
Ans: The difference between imbibition and diffusion is discussed in the tabulated form below:

IMBIBITION	DIFFUSION
It is the process in which a solid substance’s absorption of solvent or water takes place.	It is the movement of substances from the region of their higher concentration to the region of their lower concentration.
It always results in the release of heat called heat of wetting or heat of hydration.	It does not involve any release of heat.
The water or any other liquid molecules are adsorbed to the surface of hydrophilic colloids.	The diffusing particles or molecules are distributed uniformly throughout the available space.
It develops a very high pressure.	It develops less pressure comparatively.

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