All living organisms alive today are assumed to have evolved from some one-celled ancestor that lived about four billion years ago and has been called the Last Universal Common Ancestor or LUCA. LUCA has been extinct for a long time but evolutionary biologists have hypothesized as to what it was like. Given the characteristics of modern prokaryotic and eukaryotic organisms, what cellular characteristics would you suggest that LUCA had? What type of cellular respiration might LUCA have used? Why?

LUCA was an extremophile organism that likely lived in an area where seawater and magma meet on the ocean floor. LUCA lived in habitat with no oxygen and fed on hydrogen gas, the hydrothermal vents. LUCA had the characteristics of the anaerobic bacteria in the genus clostridium and the hydrogen gobbling archaea in the methanogens group.

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answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

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