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?