The 5 Kingdoms in biology provide categories for all living things. They are: Plants Animals Bacteria Fungi Prokaryotes Viruses have to have a host cell (or an 'invaded' cell) to survive, so scientists don't class them as a living organism. Viruses are different from all bacteria.
A bacteria cell differs structurally from plant and animal cells because of its small size. A bacteria cell has flagella outside of the cell to help it move. A bacteria cell does not contain organelles. Only the chromosome and sometimes ribosomes are visible in a bacteria cell.