Cells and Viruses

Cells are the smallest structural component of all known living organisms capable of self-maintenance and reproduction. Although cells vary greatly in their appearance or size, their structure is basically similar. Even the plant and animal cells show a significant degree of similarity in their overall organization. There are two types of cells: eukaryotic and prokaryotic. The main difference between them is the method of genetic material storage: in eukaryotic cells — in an isolated nucleus, in prokaryotic cells — directly in the cytoplasm (there is no nucleus). Prokaryotic cells are usually independent (unicellular), while eukaryotic cells are often found in multicellular organisms.