The endosymbiotic theory states that chloroplasts and mitochondria evolved as a result
a. a prokaryotic cell engulfing a bacterial cell.
b. a eukaryotic cell engulfing a bacterial cell.
c. a bacterial cell engulfing a prokaryotic cell.
d. a bacterial cell engulfing a eukaryotic cell.

According to the endosymbiotic theory, the cellular organelles were prokaryotic cells. The Prokaryotic cells were englulfed by a different bigger prokaryotic cell. So, the correct answer is A. The engulfed cell was not completely digested, and the two cells started to mutually benefit each other, resulting into the formation of eukaryotes.

If you remove all the lions from the savanna it will lead to a increase of gazelle and a increase of cheetahs becasue of no competition