Membranes of Valonia ventricosa : Apparent Absence of Water-Filled Pores

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Abstract
Osmotic and diffusional permeabilities to water have been measured in internally perfused cells of Valonia ventricosa . The osmotic and diffusional permeability coefficients for the protoplast are identical, 2.4 × 10 -4 centimeter per second. Thus, both osmotic and diffusional flows can occur by the same mechanism, that is, by diffusion; and there is no need to postulate the existence of water-filled pores in the membranes of this cell. Supporting evidence for this conclusion is the absence of solvent-solute interactions, that is, "solvent drag," for water, urea, and methanol crossing the protoplast of Valonia .