Prokaryotes lack nuclear membrane enclosing the genetic material, so they are placed under a separate kingdom Monera. The organisms that are placed in this kingdom are bacteria, archaebacteria, cyanobacteria, mycoplasma, actinomycetes and rickettsia. Prokaryotes are covered by cell wall with an exception of mycoplasma and cell membrane. They lack membrane bound organelles but have ribosomes (amembranous organelle)