In the extreme environments of deep-sea hydrothermal vents, the giant tube worm *Riftia pachyptila* relies entirely on a symbiotic relationship with chemolithoautotrophic bacteria housed in an organ called the trophosome. These bacteria oxidize hydrogen sulfide () from the vent fluid to produce organic molecules for the worm. Biologist Dr. Sunita Alvarez hypothesized that the metabolic rate of these endosymbiotic bacteria is primarily regulated by the availability of dissolved in the surrounding water rather than by fluctuations in the ambient water temperature. Alvarez and her team monitored several *Riftia pachyptila* colonies near a vent field in the East Pacific Rise, recording bacterial metabolic activity under varying environmental conditions.
Which choice, if true, would most directly support Alvarez's hypothesis?
- AColonies of *Riftia pachyptila* that were positioned farther from the main hydrothermal vent opening developed larger trophosomes than those positioned closer to the vent, allowing them to host a greater overall volume of bacteria.
- BBacterial metabolic rates fluctuated in direct correlation with hourly temperature shifts in the vent field, even when the concentration of dissolved in the surrounding water was artificially held constant.
- The metabolic rate of the endosymbiotic bacteria remained stable during a period of localized volcanic heating that raised the ambient water temperature by , but declined sharply when hydrothermal fluid flow decreased and reduced the local concentration of dissolved .Cevap
- DSymbiotic bacteria residing in shallow-water organisms likely depend on similar environmental triggers to regulate host metabolic rates, suggesting a shared evolutionary origin with deep-sea symbionts.