The diatoms interact with the outer environment through the siliceous walls of a frustule. Because of that the surface area of the frustule determines the ability of diatoms to absorb and excrete material resources. Such as unicellular organisms exchange matter only through the pores in their cell wall, to find relationships between characteristics of material fluxes and surface area of microorganism cover that is penetrable for substance, it is necessary to estimate the total surface area of

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... res or a porosity-relative area of pores perforated frustule. In the paper we describe a method of estimating the porosity of a diatom valve using SEM images. The method is tested on SEM images of the valves of centric diatom Minidiscus vodyanitskiyi recently described from the Sea of Azov. The results show that the valves porosity is less than 5 % of the total valves area. This value is consistent with the relative perforation of land plants leaves, which is less than 3%. We hypothesize that such value of diatom valves porosity is usual for many other diatom species. To verify this hypothesis additional researches are necessary.