VirusesWatch this thread
They have a structure, but not a cell structure, because viruses *don't have cells. Cells, such as muscle cells or bacterial cells, have to have organelles (like cytoplasm or a nucleus), but viruses have almost nothing. All they have is a protein shell, some appendages attached to that cell, and a strand or two of DNA or RNA. They don't respire, they don't need any nutrition, they don't have a metabolism or need to excrete - nothing. That's why they aren't cells, and why some scientists don't even count them as living organisms.