Some scientists think that complex eukaryotic cells formed from the union of two separate prokaryotic cells. The engulfing of one prokaryotic cell by another is a plausible explanation of why

Prokaryote - CreationWiki, the encyclopedia of creation science

a
organelles in a eukaryotic cell work cooperatively.
b
eukaryotic cells don't share any similarities with prokaryotic cells.
c
eukaryotic cells lack the defense mechanisms of prokaryotic cells.
d
organelles in a eukaryotic cell would attack other cells.

The correct answer is a) organelles in a eukaryotic cell work cooperatively. The theory of endosymbiosis suggests that complex eukaryotic cells formed when one prokaryotic cell engulfed another, leading to a symbiotic relationship where the two cells worked together and eventually evolved into a single, more complex cell with specialized organelles that work cooperatively. This process explains why organelles in a eukaryotic cell function together in a coordinated manner.