Movement of water in living cells is important. If the number of water molecules will move from an area where water molecules per unit volume are greater to an area where they are less. Such movements explains why plants in moist soil are erect and turgid while those in dry soil are limp and droopy. In animal cells, the surrounding fluids has tge same concentration of dissolved substances as those in the cells.
In plant cells, when water enters the plasma membrane, the vacoule, which contains mostly water and dissolved substances, expands. Expansion pushes the cell wall outwards. But since the cell wall is rigid it is made up mostly cellulose and lignin it counteracts the outward pressure of the expanded vacoule. Thus, only so much water can enter the cell. The cell becomes a turgid. A plant that has turgid cells has erect stems. Its leavees are attached to its nodes firmly.
When molecules of dissolved substances around the cell are greater in number, the water molecules move out from the vacoules. The vacoules then shrink pulling the cytoplasm away from the cell wall. This conditon is called plasmolysis. The cell then is similar to a flat tire. It loses its turgidity or turgor.
Too much exposure to sunlight and strong wind contributes to loss of turgor in plants. Water is lost in the leaves, stem and flowers. When the plants lose water to the surroundings faster than they can get water from the soil, their stems become limp and their leaves droop.
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