Xenomorph evolutionary pressures

[Galvatron]

ANY acid is "molecular acid". It's just a vague term.

Bear in mind Bishop was talking to Colonial Marines whose specialities include making things go boom as loud as possible
He's going to pitch the technobabble to a level they can understand

"Molecular acid" was first mentioned in Alien. To paraphrase, Dallas said the blood's corrosive properties reminded him molecular acid, not that it IS molecular acid.

[Kamakazie Sith]

Newt never was impregnated, her body was clean in Alien 3. However a neurotixin is required to keep the hosts quiet at pretty much all stages of implantation, from capture through to chest-burst.

Read the script. It was Newt. The queen embryo exited her dead body and entered Ripley by the mouth after the EEV crashed. Stupid, sure. But that's Alien 3.

Moreover, Ripley's tube wasn't even broken until after the fire started.

IIRC That didn't make it to the movie though. The opening credits show Ripley with the facehunger on her.

[Kamakazie Sith]

Nevermind, I was wrong. Sorry for doubting you Galvatron.

[Darth Nostril]

Wait, is it a sugar, or silica-compound? I love contradictory sources

Sorry for the really late post, took me ages to find the sodding book. (It was in a box in the roofspace above the garage.)
My recollection of what I read was more than slightly off.

"What do you think the stuff is?"' Dallas's gaze travelled from the tiny craters in the deck to the hole in the ceiling overhead. "I've never seen anything that could cut through hull alloy like that. Not with that kind of speed."
"I've never seen anything like it myself," the science officer confessed. "Certainly highly refined varieties of molecular acid are tremendously powerful, but they generally will act only on certain specific materials. They have restricted general applications.
On the other hand, this stuff appears to be a universal corrosive. We've already watched it demonstrate it's ability to eat through several very different substances with equal facility. Or indifference, if you prefer. Hull alloy, surgical gloves, the medical pallet, infirmary bedding; it went through all of them with equal ease."
"And that damned thing uses it for blood. One tough son-of-a-bitch little monster." Brett spoke of the hand-shaped alien with respect, despite his feeling toward it.
"We don't know for a fact it uses it for blood." Ash's mind was functionong overtime under the pressure of the situation.
"It might be a component of a seperate circulatory system, designed to lubricate the creature's insides. Or it might comprise part of a protective inner layer, a sort of liquid, defensive endothelium. It might be no more than the creature's counterpart of our own lymph fluid."
"Wonderful defensive mechanism, though," Dallas observed. "You don't dare kill it. "

"It's got an outer layer of what appears to be protein polysaccharides. At least, that's my best guess. Hard to tell without a piece for detailed analysis, and attempting to remove even a sample might cause it to drain fluid again. We can't risk it dissolving part of the autodoc."
"Not hardly," she said drily " Right now that machine's the only chance Kane's got."
"Exacly. What's more interesting than that is that it's constantly sloughing off cells within a secondary, internal dermis and replacing them with polarized organic silicates. It appears to have a double skin, with that acid flowing between the two layers. Also, the acid seems to be flowing under high pressure.
It's a good thing Dallas didn't cut too deeply with the knife or I think it would have sprayed the entire infirmary."
Ripley looked properly impressed.
"The silicate layer demonstrates a unique, very dense molecular structure under the scope. It might even be capable of resisting the laser. I know, I know," he said in response to her look of disbelief, "that sounds crazy. But this is the toughest chunk of organic material I've ever seen. The combination of the way those cells are aligned with what they're composed of adds up to something that defies all the rules of standard biology.
Those silicated cells, for example. They're metal bonded. The result is what gives the creature such resistance to adverse environmental conditions."

In the Aliens novelization there is no mention of the composition of the acid, just a discussion between Ripley and Bishop about the the origin of all the aliens required to infect all of the colonists