<P> Compartmentalization was necessary for chemical reactions to be more likely as well as to differentiate reactions with the external environment . For example, an early RNA replicator ribozyme may have replicated other replicator ribozymes of different RNA sequences if not kept separate . </P> <P> When amphiphiles like lipids are placed in water, the hydrophobic (water fearing) tails aggregate to form micelles and vesicles, with the hydrophilic (water loving) ends facing outwards . Primitive cells likely used self - assembling fatty - acid vesicles to separate chemical reactions and the environment . Because of their simplicity and ability to self - assemble in water, it's likely that these simple membranes predated other forms of early biological molecules . </P> <P> Prokaryotes lack membrane - bound organelles, such as mitochondria or a nucleus . Instead, most prokaryotes have an irregular region that contains DNA, known as the nucleoid . Most prokaryotes have a single, circular chromosome, which is in contrast to eukaryotes, which typically have linear chromosomes . Nutritionally, prokaryotes have the ability to utilize a wide range of organic and inorganic material for use in metabolism, including sulfur, cellulose, ammonia, or nitrite . Prokaryotes as a whole are ubiquitous in the environment and exist in extreme environments as well . </P> <P> Bacteria are one of the world's oldest forms of life, and are found virtually everywhere in nature . Many common bacteria have plasmids, which are short, circular, self - replicating DNA molecules that are separate from the bacteria chromosome . Plasmids can carry genes responsible for novel abilities, of current critical importance being antibiotic resistance . Bacteria predominantly reproduce asexually through a process called binary fission . However, about 80 different species can undergo a sexual process referred to as natural genetic transformation . Transformation is a bacterial process for transferring DNA from one cell to another, and is apparently an adaptation for repairing DNA damage in the recipient cell . In addition, plasmids can be exchanged through the use of a pilus in a process known as conjugation . </P>

Abundant and diverse organisms that lack membrane bound organelles