The aim of this Graduation Thesis is the nanostructural characterization of cell surface of lightly silicified marine diatom Cylindrotheca closterium exposed to increased cadmium concentration, using atomic force microscopy (AFM). C. closterium growth dynamics was monitored with optical microscope at selected cadmium concentrations in the range 1–1000 μg/L. Morphological changes on the cell surface of C. closterium exposed to cadmium (500 μg/L and 1000 μg/L) were characterized with AFM. The consequences of increased cadmium concentrations in C. closterium cultures were inhibition of growth and reduction of specific growth rates and number of cell divisions per day, also changes in the surface of the frustules were observed in the form of single spherical particles and their aggregates on certain parts of the cell. The most expressed changes were observed on more silicified parts of the cell, girdle band and around the raphe on fibulae of the cells that grew at cadmium concentration 1000 μg/L, while a smaller number of particles were located on the valves. These changes are likely to be due to the impact of cadmium on the silicon dioxide deposition mechanism, which results in the appearance of irregular structures on certain, more silicified, parts of the frustules. These results contribute to a better understanding of the impact of heavy metal cadmium on the growth dynamics and the morphological characteristics of the marine diatom C. closterium at the nanometric scale. Although, the results apply directly to Cylindrotheca closterium, they also form the basis for further investigation of the impact of heavy metals on the nanostructural properties of other phytoplankton species.