The most likely scenario for the emergence of eukaryotes is that they arose from a symbiosis in which the host was an archaeal cell and the symbiont was a bacterium. According to this theory, the bacterial symbiont subsequently gave rise to the mitochondria -- the intracellular organelles that are responsible for energy production in eukaryotic cells. One hypothesis proposes that the archaeal host was dependent on hydrogen for its metabolism, and that the precursor of the mitochondria produced it. This "hydrogen hypothesis" posits that the two partner cells presumably lived in an anoxic environment that was rich in hydrogen, and if they were separated from the hydrogen source they would have become more dependent on one another for survival potentially leading to an endosymbiotic event
Intentional Insights on 23 Dec 15You pass through the long security line at the United States Capitol building in Washington, DC. While the line of tourists streams forward into the Exhibition Hall, you turn right, and head to the Senate appointment desk. There, you sign in, get an ID badge, and are guided by a security officer to a large meeting room.
