Turgor Pressure and Wall Pressure

When a plant cell is placed in pure water or any hypotonic solution, water enters the cell by endosmosis and presses the cell membrane outward against the surrounding, rigid cellulose cell wall - this outward hydrostatic pressure exerted by the membrane on the wall is called turgor pressure (TP). The wall is not simply passive - it resists this outward push with an equal and opposite counter-pressure directed back inward onto the cell membrane, and this reactive force is called wall pressure (WP). A cell becomes fully turgid only once these two opposing pressures are in balance, summarised as TP + WP = Turgid, and it is this turgidity that keeps herbaceous plant parts firm and upright. The physical importance of turgor pressure is not just structural bulk - rapid, localised changes in turgor pressure are also the direct mec …