Plant Physiology - Musienko, M. M. 2001

Chemical and molecular composition, structure, and functions of the plant cell
Swelling

When considering Water uptake by a Cell, it should be noted that along with osmotic forces, swelling forces are also present. Swelling refers to the absorption of liquid or vapor by a macromolecular substance, accompanied by an increase in volume. This phenomenon is driven by colloidal and capillary effects.

In the protoplasm, swelling is primarily colloidal in nature, driven by the capacity of hydrophilic colloids to attract water molecules. The water potential of The Cell becomes more negative due to the Presence of water-binding organic substances. The swelling force is denoted as the "matric potential," which is always negative (-ψ_matric). Consequently, the WATER POTENTIAL OF the cell protoplasm in this case comprises:

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Interestingly, in certain plant Organs—such as seeds—water uptake occurs exclusively via swelling. Water penetrates the cell during swelling through diffusion. A distinct parallelism exists between osmosis and swelling, where osmotic pressure corresponds to swelling pressure.

Swelling can generate pressures of several hundred atmospheres. The Hydration state of the protoplasm is critical for The rate of overall METABOLISM, as the hydration of protoplasmic Proteins is essential for maintaining the ultrastructure and functional activity of Organelles.

In The Cell wall, both capillary effects (water accumulation between microfibrils and in the intermicellar spaces) and colloidal effects (hydration of Polysaccharides, particularly hemicelluloses) can be observed:

In the vacuole, swelling substances are generally absent; therefore:

An equilibrium is rapidly established among the protoplasm, cell wall, and vacuole following any change in water content:

Water may also enter the cell via electro-osmosis, driven by electrical potential differences across the membrane, or through fluid uptake via pinocytosis. Pinocytosis is the inward invagination of The Plasma Membrane, resulting in the engulfment of extracellular fluid droplets.