Turgor pressure

Turgor pressure is the force within the cell that pushes the plasma membrane against the cell wall. Turgor pressure is the force within the cell that pushes the plasma membrane against the cell wall. It is also called hydrostatic pressure, and defined as the pressure measured by a fluid, measured at a certain point within itself when at equilibrium. Generally, turgor pressure is caused by the osmotic flow of water and occurs in plants, fungi, and bacteria. The phenomenon is also observed in protists that have cell walls. This system is not seen in animal cells, seeing how the absence of a cell wall would cause the cell to lyse when under too much pressure. The pressure exerted by the osmotic flow of water is called turgidity. It is caused by the osmotic flow of water through a selectively permeable membrane. Osmotic flow of water through a semipermeable membrane is when the water travels from an area with a low-solute concentration, to one with a higher-solute concentration. In plants, this entails the water moving from the low concentration solute outside the cell, into the cell's vacuole. Osmosis is the process in which water flows from an area with a low solute concentration, to an adjacent area with a higher solute concentration until equilibrium between the two areas is reached. All cells are surrounded by a lipid bi-layer cell membrane which permits the flow of water in and out of the cell while also limiting the flow of solutes. In hypertonic solutions, water flows out of the cell which decreases the cell's volume. When in a hypotonic solution, water flows into the membrane and increases the cell's volume. When in an isotonic solution, water flows in and out of the cell at an equal rate. Turgidity is the point at which the cell's membrane pushes against the cell wall, which is when turgor pressure is high. When the cell membrane has low turgor pressure, it is flaccid. In plants, this is shown as wilted anatomical structures. This is more specifically known as plasmolysis. The volume and geometry of the cell affects the value of turgor pressure, and how it can have an effect on the cell wall's plasticity. Studies have shown how smaller cells experience a stronger elastic change when compared to larger cells. Turgor pressure also plays a key role in plant cell growth where the cell wall undergoes irreversible expansion due to the force of turgor pressure as well as structural changes in the cell wall that alter its extensibility. Turgor pressure within cells is regulated by osmosis and this also causes the cell wall to expand during growth. Along with size, rigidity of the cell is also caused by turgor pressure; a lower pressure results in a wilted cell or plant structure (i.e. leaf, stalk). One mechanism in plants that regulate turgor pressure is its semipermeable membrane, which only allows some solutes to travel in and out of the cell, which can also maintain a minimum amount of pressure. Other mechanisms include transpiration, which results in water loss and decreases turgidity in cells. Turgor pressure is also a large factor for nutrient transport throughout the plant. Cells of the same organism can have differing turgor pressures throughout the organism's structure. In higher plants, turgor pressure is responsible for apical growth of things such as root tips and pollen tubes. Transport proteins that pump solutes into the cell can be regulated by cell turgor pressure. Lower values allow for an increase in the pumping of solutes; which in turn increases osmotic pressure. This function is important as a plant response when under drought conditions (seeing as turgor pressure is maintained), and for cells which need to accumulate solutes (i.e. developing fruits).