Answer:
From The School of Biomedical Sciences Wiki. Complementary base pairing is the phenomenon where in DNA guanine always hydrogen bonds to cytosine and adenine always binds to thymine. The bond between guanine and cytosine shares three hydrogen bonds compared to the A-T bond which always shares two hydrogen bonds.
Im not 100% sure but the best answer I can give is Prokaryotes because they came to be around the time oxygen did as well.
They are found in the body
Answer: population
hope this helped