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In biology, turgor pressure or turgidity is the pressure of the cell contents against the cell wall, in plant cells, determined by the water content of the vacuole, resulting from osmotic pressure. i.e. the hydrostatic pressure produced by a solution in a space divided by a semipermeable membrane due to a differential in the concentration of solute. Turgid plant cells contain more water than flaccid cells and exert a greater osmotic pressure on its cell walls.
When a cell is in a hypotonic environment, water flows across the cell membrane into the cell, causing it to expand due to osmotic pressure. In plant cells, water enters the cell until the inside and outside water potential is equal, however, the cell wall prevents the cell from bursting, resulting in pressure on the cell wall from within.
The pressure of each cell wall against its neighbour results in stiffness that allows the plant to stay upright. Cells not adapted to hypotonic environments will burst due to the inflow of water if they have no strong membrane or cell wall.
Turgor pressure is not only important in terms of plant rigidity, but also of key importance in microbial growth.
Campbell, N. A., Reece, J. B. Biology: Sixth Edition; Benjamin Cummings: New York, NY, 2002; Vol. 1.