Unlike most hydrothermal vent fauna that graze on free-living bacterioplankton, the giant tubeworm Riftia pachyptila lacks a functional digestive tract at maturity. Instead, it relies exclusively on sulfur-oxidizing chemoautotrophic bacteria housed within an internal vascularized organ, the trophosome. To sustain these endosymbionts, the tubeworm utilizes specialized extracellular hemoglobin capable of simultaneously binding both hydrogen sulfide and dissolved oxygen with high affinity—an adaptation that prevents sulfide from poisoning oxygen-binding sites. Because the bacterial metabolic pathway requires oxygen to oxidize hydrogen sulfide into usable chemical energy, Riftia must position its branchial plume in the turbulent interface where hot, anoxic, sulfide-rich hydrothermal discharge mixes with cold, oxygenated seawater. When localized fluid dynamics temporarily shift this mixing zone entirely beyond the reach of the plume, the tubeworm's production of organic carbon halts immediately, even though ambient sulfide or oxygen may remain individually available.
Based on the passage, which of the following statements are logically supported? Select all that apply.
- A mature specimen of the tubeworm cannot sustain organic carbon synthesis if it is exposed solely to an environment containing dissolved oxygen without hydrogen sulfide.Answer
- BJuvenile tubeworms ingest free-living bacterioplankton through external mouthparts prior to developing a functional trophosome.
- The tubeworm's specialized hemoglobin possesses a biochemical mechanism that enables simultaneous transport of toxic sulfide without inhibiting its capacity to carry oxygen.Answer
- DMost marine invertebrates living in non-vent environments possess alternative mechanisms to prevent hydrogen sulfide from binding to their respiratory proteins.
- EThe trophosome contains sufficient stored nutrient reserves to maintain ongoing chemoautotrophic synthesis during prolonged absences of hydrothermal fluid mixing.