They are difficult to classify in relation to plants or animals, but are usually considered to be more closely aligned to the plant kingdom than the animal kingdom. All bacteria are prototypes, meaning that they have a more simple cellular organization than plants and animals, which are eukaryotes.
Prokaryotes have no chromosomes.
Ferdinand Cohn published the first classification of bacteria in 1872, but subsequent attempts to impose some kind of taxonomic order on the huge range of bacteria have met with great difficulty. Bacteria are classified by their shape, size and response to certain chemical stains. Robert Koch, a student of Cohn's, was a pioneer in the field who worked with the bacteria which cause important diseases such as anthrax and tuberculosis. For these reasons they are extensively used in modern biochemical research. RB See also abiogenesis .