TURGOR AND OSMOSIS IN ARTIFICIAL CELLS 



From the bulging of the membrane we infer that something passes through the mem- 

 brane faster in one direction than in the other — increasing or decreasing the internal 

 "pressure". In a living cell increased pressure results in a turgid, or swollen, condi- 

 tion, whereas reduced "pressure" results in a flaccid, or flabby, condition,:a5<seen in 

 wilted plants. By means of appropriate solutions and indicators we can demonstrate 

 the passing of dissolved food materials and gases into and out of such "cells" 



all. Cell walls and similar substances are therefore called "semipermeable". 

 Osmosis appears to be selective. As a result of the difference in the be- 

 havior of dissolved substances, osmosis will be greater in one direction than 

 in the opposite; and cells exposed to the same material surroundings may 

 not be affected in the same way. 



We can imitate the passage of materials into and out of cells by making 

 model cells of small widemouthed glass bottles, each closed with a bladder 

 membrane (see illustration above). By using appropriate solutions and indi- 

 cators, we can demonstrate the movement of dissolved food materials and 

 dissolved gases into and out of these "model cells". 



Osmosis and Turgor^ When a cell has absorbed water so that the mem- 

 brane is stretched, the cell is said to be turgid — that is, swollen. Turgid cells 

 in the tissue of a plant or animal make the structure stiff, whereas wilted 

 tissues are flabby — just as an empty meal sack is limp, whereas a full sack 

 will stand on its own bottom. Similarly, turgid tissues crack through easily, 

 as we see in the brittleness of celery or in the crispness of a juicy sausage. We 



If we nearly split off a thin layer 

 of a crisp rhubarb stalk and then 

 place it back, it no longer reaches 

 the full length. The shrinkage is 

 due to the loss of water. The 

 epidermal tissues are normally 

 turgid, but when water evapo- 

 rates from the cut surfaces each 

 cell collapses somewhat 



TURGIDITY AS SUPPORT 



^See No. 8, p. 95. 

 88 



