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Distension of a plant cell wall and membrane by the fluid contents.



the state of tension of cell membranes that is caused by the osmotic pressure of the intracellular fluid (P int), the osmotic pressure of the external solution (P ext), and the resilience of the cell membrane. In animal cells, except for the cells of some Coelenterata, this resilience is generally minimal. Most animal cells lack turgor and maintain their integrity only in isotonic or near-isotonic solutions; in these cells the difference between the P int and the P ext is less than 0.5–1.0 atm.

In living plant cells, the P int is always greater than the P ext, but the cell membrane does not rupture owing to the presence of a cellulose cell wall. The difference between the P int and the P ext in such plants as halophytes and fungi reaches 50–100 atm, but even then the cell wall’s reserve of strength amounts to 60–70 percent. In most plants the relative elongation of the cell membrane that results from turgor does not exceed 5–10 percent, and the turgor pressure is in the range of 5–10 atm. Turgor gives plant tissues resilience and strength. All stages of autolysis, fading, and aging are accompanied by a decline in turgor.