Phylogenetic analysis of Mg-tetrapyrrole biosynthesis genes reveals that anoxygenic photosynthetic processes became evident in primitive organisms like certain bacteria before the oxygenic variety in other organisms like cyanobacteria (Xiong and Bauer, 2002). Joint analyses of the pigment genes and reaction centers have yielded stronger evidence to this effect (Xiong and Bauer, 2002). At the time when photosynthesis became a rudimentary process for energy storage in arcane organisms cellular respiration was still to evolve and the energy release mechanism for utilizing the photosynthetic stored energy used processes that sourced their electrons from suppliers other water (Todar, Undated). Later, genetic transfer mechanisms between endosymbiotic bacteria, their closest living relatives being the proteobacteria, and their pre-eukaryotic cellular hosts inducted cell organelles like mitochondria and chloroplasts (Simpson et al, 2002) into the pre-eukaryotic system and cellular respiration became possible. Some time during the endosymbiotic processes there was gene transfer from the bacteria to the pre-eukarytic cells whereby the bacterial genome was reduced and much of the remaining genetic materials got encoded in the cellular nucleus while, locally, some of the bacterial genetic materials were encoded within the organelle, mitochondrion or otherwise, to form localized DNA entirely associated with organelle function (Chihade et al, 2000). While the induction of the mitochondria into the pre-eukaryotic cells to produce the eukaryotic system shall be dealt with later in the paper a short comparison by organisms will now be made of photosynthesis and cellular respiration processes.
The following table will be used to compare and contrast photosynthesis and cellular respiration in the species of euglenoids that have primitive plastids (Borza et al, 2005). Euglenoids are either autotrophs, photosynthetic with chlorophyll a and b chloroplasts, or heterotrophs with parasitic or absorptive nutrition. Some of them also have motile mechanisms like flagella or cilia. It is notable that euglenoids with plastids acquired them through secondary endosymbiosis and, thus, the plastids are not as developed as those of more evolutionary advanced species (Borza et al, 2005). It is also notable that euglenoids with plastids also use absorptive nutrition, absorbing organic matter from their environs, as supplementary dietary processes. Though they may be photosynthetic they can respire both aerobically and anaerobically (Hoffmeister et al, 2004). Anaerobically, these organisms store energy in the form of fatty acids (waxes) that are broken down when oxygen becomes available more plentifully (Hoffmeister et al, 2004). This makes these organisms so interesting. It is notable that both photosynthesis and cellular respiration in euglenoids with chloroplasts are still not fully understood (Hoffmeister et al, 2004; Lonergan and Sargent, 1979). Nevertheless, these processes have been simplistically compared and contrasted in the following table.
Chemical energy in sugars (anaerobic) and sugars/fatty acids