62 



ELECTROLYTES IN BIOLOGICAL SYSTEMS 



of potassium and the secretion of sodium, that these mechanisms are inde- 

 pendent of each other, and that they are energized by the metaboHc degrada- 

 tion of carbohydrate (fig. 21). 



Any comparison between Ulva and Valonia must take cognizance of the 

 morphological differences between the cells of the two organisms. In the rela- 

 tively small cells of Ulva the cytoplasmic mass is large relative to the amount 

 of fluid in the vacuole, while in Valonia cells the opposite situation pertains, 

 i.e. by far the greater portion of the mass is vacuole with the cytoplasm con- 

 tributing only a very small part. There are three obvious consequences of 

 these relationships which must be considered in comparing the two forms. First, 

 in Ulva one analyzes largely the cytoplasmic fluid, while in Valonia the cyto- 

 plasm contributes little to whole-cell analyses. Secondly, in Valonia the major 

 fraction of the analyzed ions has passed through two living membranes. Finally, 



RADIANT L 



ENERGY I 



STORED CARBOHYDRATES 



3-PHOSPHOGLYCERALDEHYDE 



3-PHOSPHOGLYCERIC ACID 



PHENYLURETHANE 

 DNC 



PHENYLURETHANE 

 DNC 



ENERGY- 

 . UTILIZING , 



No+ ^.MECH ANISMS ^j\<^ "'"'^ 



fu^ 



CELL 



"MEMBRANE" 



DIFFUSION ^ M«17 ^K"^ 'DIFFUSION 



Fig. 21. Diagrammatic representation of the interpretation of the data presented above. 



the ratio of total exterior surface to total mass is much greater in Ulva than in 

 Valonia. These last two factors are important in kinetic studies and may prob- 

 ably be at least partly responsible for the rather sluggish responses of Valonia 

 to metabolic inhibitors contrasted with the more rapid responses in Ulva. 

 There also exists the possibility that the Valonia membranes are less permeable 

 to ions of sodium and potassium than is the Ulva membrane. 



Regardless of the diflFerences in the time scales, the striking feature of this 

 comparison is the similarity of the two organisms as regards sodium and potas- 

 sium movements in response to inhibition by iodoacetate and phenyl urethane. 

 Although the data presented do not serve to separate the mechanisms regu- 

 lating potassium and sodium in Valonia, since the organism behaves in other 

 respects so much like Ulva, where separate mechanisms must be postulated, it 

 is probable that independent potassium- and sodium-regulating mechanisms 

 do exist in Valonia as well. 



