Simple organisms that lack a distinct nuclear membrane and other organelles. Many structural systems are different between procaryotes and eucaryotes including the DNA arrangement, composition of membranes, the respiratory chain, the photosynthetic apparatus, ribosome size, the presence or lack of cytoplasmic streaming, the cell wall, flagella, the mode of sexual reproduction, and the presence or lack of vacuoles. Some representative procaryotes are the bacteria and bluegreen algae.