Scientists discovered that endosymbiotic bacteria living inside tubeworms are capable of using two fundamentally different means to generate organic carbon. The first is the Calvin Cycle (above), in which carbon molecules from CO2 are fixed into glucose (C6H12O2. The Calvin cycle works when there is plenty of oxygen around, but requires substantially more energy than the other method the bacteria use: the rTCA cycle (below). (Courtesy of Thinkquest.org)[back]
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