The most important factors regarding osmolarity of plant cells are solute concentration and hydrostatic pressure. Osmosis is a spontaneous process that is driven by a potential energy called water potential. The water potential is the sum of two energy potentials: the solute potential and the pressure potential, as explained by Dr. Koning in his Plant Physiology lecture notes.Continue Reading
The solute potential is the energy caused by dissolved substances. An area with high solute concentration has a decreased water potential which causes water to enter the area. The pressure potential is the energy caused by hydrostatic pressure. Increasing pressure in an area will increase water potential and cause water to leave that area, according to Dr. Koning.
Water and minerals enter plants through the roots and move up the plants through conducting tubes called xylem. Excess water is removed from plants through evaporation from the leaves. Osmosis is the driving force behind water movement through the plant, where water moves from areas of lower solute concentration to areas of higher solute concentration. Plant cells have a rigid cell wall which prevents them from swelling and causes turgor pressure when there is an osmotic influx of water. Potassium and chloride channels in the cell membrane open and close causing solute concentration of the cytosol to change. These changes result in the opening and closing of pores in the leaves (called stomata), which allows water to be evaporated or retained by the plant, according to Molecular Biology, 4th ed., Section 15.8.Learn more about Botany