8. Alien
I know what you're thinking; how can Ridley Scott's Alien have an even remote sense of attention-to-detail when it's clearly rooted in fantasy? Well, you're wrong; even discounting the realistic implementation of suspended animation to keep the occupants of the Nostromo alive, it's the depiction of the Xenomorph that's unexpectedly authentic in its depiction of a creature's life cycle. We see the Xeno begin life as an egg, before hatching as a facehugger, and then bursting from the chest of whichever host it has attached itself to, beginning life as the form of which it is best recognised. Though many sci-fi films will introduce an alien with physiology that's "just because", the Xeno's life cycle matches that of countless parasites and insects found in nature, making the creature's behaviour seem all that more realistic and believable in spite of its uncharacteristic appearance. Of course, it's absurd that the Xeno can grow so big so fast, but if one can suspend their disbelief for this portion - given that it occurs largely to move the plot forward quicker - then the biological aspects of the creature are clearly well-studied.