The search for and verification of fossils of small, single-celled microorganisms and subcellular microbial structures is warranted. This heavily salified rosette structure has been regarded as a bacterium by some, but current evidence suggests that it is non-cellular. Introduction Prokaryotic cells show a tremendous range in size. However, such large cell sizes are a rarity in the prokaryotic world. Certain physical constraints dictate the minimum size of an organism.
All cells have a cell membrane, cytoplasm, ribosomes, and nuclear material.
Cell membranes are about 8 to 10 nm thick, and sufficient DNA, ribosomes, and enzymes are needed for cells to metabolize and reproduce. The cell size of many bacterial species is variable, being influenced by growth conditions. Actively growing cells of bacteria are typically larger than senescent cells, and starving cells may be very small indeed. In fact, it is possible that starving cells may turn over so much of their cell matter that they are no longer able to reproduce, and therefore persist in the environment as nanocarcasses less than 0.2 m in size. Also, the effects of physical parameters may be very important in determining cell sizes.