Do the aliens from the Alien franchise have cells as we know them?
I want to know as I assumed they didn't and just secreted a resinous exoskeletal system.
The chestburster then matures to an adult phase, shedding its skin and replacing its cells with polarized silicon.
Due to Horizontal gene transfer during the gestation period, the Alien also takes on some of the basic physical attributes of the host from which it was born, allowing the individual alien to adapt to the host's environment.
Both those facts imply that cells are involved.
According to Ash in the first Alien film, the facehugger alien does indeed have a cellular structure. When damaged, the cells are replaced/repaired with "polarized silicon" which strongly implies that the original cells are made of something other than silicon.
Ash: But I have confirmed that he's got an outer layer of protein polysaccharides. He has a funny habit of shedding his cells and replacing them with polarized silicon, which gives him a prolonged resistance to adverse environmental conditions.
There's no indication what the adult Xenomorphs are made of, but the scientists in the 'Aliens, Colonial Marines Technical Manual' hypothesise that they're actually a fluorine-based lifeform, rather than silicon-based. This would also explain the extremely strong molecular acid-for-blood since the acidity would break down any material the alien ingests, including organic materials and certain inorganic compounds such as glass and certain metals.
"It would work as a hydrofluoric/hydrochloric mix. The preferred concentration in the blood is KF. However, an embryo implanted in a human body would have access to a ready supply of HC1 from the host's stomach. It starts life with an HCl imbalance which could alter as it grows. Of course, it could take on additional chlorine and fluorine from its prey, or it could 'salt' it with sodium chloride or sodium fluoride."
"Sorry, this modal is just too elaborate for my tastes. I still don't buy it. Even with PTTE [Teflon] coated cell-membranes, wouldn't the body chemistry of a fluorine-based embryo be so hostile that it would just eat through the linings of the host's body?"