This really depends. Are we talking about “hard” science fiction (where the science is the main driver of the story, like much of Star Trek where attempts are made to explain the fictional science) or “soft” science fiction (like Dune, where the science is not really explained, more assumed, and serves as the background for the film)? I’d argue Alien falls into the former because the biology of the xenomorph is the major focus of the story.
This really depends. Are we talking about “hard” science fiction (where the science is the main driver of the story, like much of Star Trek where attempts are made to explain the fictional science) or “soft” science fiction (like Dune, where the science is not really explained, more assumed, and serves as the background for the film)? I’d argue Alien falls into the former because the biology of the xenomorph is the major focus of the story.