<span>the part of science that deals with microorganisms</span>
Absorbing prokaryotic cells. This theory is called the endosymbiotic theory.
The early prokaryotic cells that were absorbed likely evolved into mitochondria and chloroplasts, membrane-bound organelles with their own DNA in single chromosomes and their own ribosomes.
Some individuals are more likely to survive and reproduce than others because they are fit and easily adapting. This idea is called 'survival of the fittest'.
The answer would be mouth and stomach
