R.H. Whittaker had proposed a five kingdom system of biological classification in 1969. It is based on complexity of cell structure, body organization and mode of nutrition. The kingdom Monera includes all prokaryotes. They are basically unicellular with peptidoglycan in cell wall. Naked circular DNA is coiled to form nucleoid without association with histones, ribosomes are 70S, thylakoids are present in photoautotrophs but other membrane bound organelles are absent. These are heterotrophic, phototrophic or chemotrophic in their mode of nutrition. The bluegreen algae, nitrogen fixing bacteria and methanogenic archaebacteria are all unicellular prokaryotes so they are included in the Kingdom Monera.