An extremely salt-tolerant group of these organisms performs photosynthesis using retinal instead of chlorophyll. For 10 points each:
[10e] Name this domain of prokaryotic (pro-carry-AH-tik) microbes that are contrasted with bacteria.
ANSWER: archaea (ar-KEE-uh) [or archaeans; or haloarchaea]
[10h] Those haloarchaea (ha-lo-ar-KEE-uh) transport protons across their membrane using a "microbial" form of this retinal-containing protein, which is given a nickname referencing its violet color.
ANSWER: rhodopsin [or microbial rhodopsin or bacteriorhodopsin; prompt on visual purple]
[10m] Unrelated "purple bacteria" can perform photosynthesis using this molecule as an electron donor, instead of water. Giant tube worms harbor symbiotic bacteria that metabolize this molecule.
ANSWER: hydrogen sulfide [or H2S; or sulfide]
<June Yin , Science - Biology - Cell/Molecular>