Number of physical forces drives the water movement in plants.
Physical forces drive the transport of materials in plants over a range of distances : Imbibition Imbibition is the swelling of tissues, alive or dead, to several times their original volume through the absorption of water by surface attraction.
Substances, which are made up of cellulose or proteins are hydrophilic (strong affinity for water). They imbibe water or moisture and swell up. This swelling process is the initial step in the germination of seeds. Due to imbibitional pressure, seed coat ruptures. It is an important force in the ascent of sap.
Transport in plants
Diffusion : Diffusion is the movement of molecules or ions of a substance (solute or solvent, gas, liquid, or solid) from the region of their higher concentration to the region of their lower concentration when the two are in a direct contact. Think of it as a rebalancing. The molecules or ions are said to be moving along a diffusion gradient. If molecules or ions moving in the opposite direction are said to be moving against a diffusion gradient. Diffusion will continue until a state of equilibrium is reached. Rates of diffusion are affected by temperature and the density of the involved molecules among other things. In the leaves, water diffuses out via the stomata into the atmosphere.
Osmosis : Osmosis in plant cells is basically the diffusion of molecules through a semi–permeable or differentially permeable membrane from a region of higher solute concentration to a region of lower solute concentration. The application of pressure can prevent osmosis from occurring. Osmosis can be explained more precisely in terms of potentials. Osmotic potential is the minimum pressure required to prevent fluid from moving as a result of osmosis. Fluid will enter the cell via osmosis until the osmotic potential is balanced by the cell wall resistance to expansion. Any water gained by osmosis may help keep a plant cell rigid or turgid.
Turgor pressure : Turgor pressure develops against the cell walls as a result of water entering the cell's vacuole. This pressure is also referred to as the pressure potential. The osmotic potential and pressure potential combined make up the water potential of a plant cell. Water enters plant cells from the environment via osmosis. Water moves because the overall water potential in the soil is higher than the water potential in the roots and plant parts.