genome are produced without mitosis. Although binary fission is an asexual form of reproduction, genetic recombination does occur, providing a source for genetic diversity. In binary fission, the single, circular chromosome first replicates itself. Both the new and old copies of the chromosome are attached to the cell membrane. In between the two copies, at the mid-point of the cell, some new cell membrane is created. This new part of the membrane grows inward, cutting the cytoplasm and nucleiod in half to produce two new cells. Some bacteria can undergo binary fission as often as every twenty minutes.
Although some bacteria (those that contain chlorophyll a in membrane-bound vesicles, called chromatophores) are photosynthetic autotrophs, the majority of bacteria are heterotrophs. Most rely on aerobic respiration. Some, the obligate anaerobes, rely on fermentation solely and are killed by oxygen. Some, the facultative anaerobes, can carry out either fermentation or respiration depending on whether oxygen is present.
In their unicellular form, the Cyanophyta, or blue-green algae, are either rod- or sphere-shaped and can occur either singly or united by a gelatinous matrix into colonies. Blue-green algae can also exist as filamentous multicellular organisms,
where some division of labor among the cells exists but where the individual cells retain a great deal of independent functions. All blue-green algae are photosynthetic,
