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Autotrophs
Photosynthesis the most plausible form of organic self nutrition.(among the most ancient formation in the geological record are some showing signs that small amounts of free ovygen- the gaseous by product of photosynthesis- were present early in the history of the earth.) Many modern bacteria are photosynthetic, although they don't produce free oxygen; all modern blue-green algae are photosynthetic and produce free oxygen. Bacteria and blue-green algae are alon among living things in the simplicity of their cells. They have neither a membrance enclosed nucleus nor such specialized cellular organelles as mitochondoria. Their genetic material is diffused throughout the cell, and they are incapable of either mitosis(body cell division) or meiosis(germ-cell division). Both kinds of cell division require that genetic material be organized into chromosomers.