An examination of diatom area: volume ratios and their influence on estimates of plasma volume

Abstract

Measurements of diatom surface area (A) and cell volume (V) from laboratory studies, natural populations and model solids show, predictably, that discoid cells possess lower A/V ratios than tubular or ellipsoid cells of an equivalent cell volume. Estimates of plasma volume based on microscopical measurements must exhibit a similar pattern with respect to cell morphology: any estimate of plasma volume for a discoid species will contain less plasma volume per unit cell volume, than tubular or ellipsoid species. To examine whether or not a constant or variable cytoplasm thickness influences estimates of plasma volume, a comparison is made between estimates of diatom plasma volumes assuming that cytoplasm thickness is either a constant (1μm) or a variable function of cell A/V ratios. The limited number of morphometric observations from the literature show that there is insufficient data to choose between the assumption that diatom cytoplasm is constant or variable; this is most evident in larger diatoms. Future studies are needed to compare morphometric estimates of plasma volume with cell constituents to determine if a relationship exists.