Does it change anything if I say "Bu biyoloji bir laboratuvarı"? And I guess putting "Bunu" instead of "Bu" it's wrong
You can't put "bir" in between. If you have two nouns together (biyoloji & laboratuvar), and only the second one has received a suffix (laboratuvarı), you can't put anything in between.
And yes, you can't say "bunu" in this sentence. That's the subject: it has to be in the nominative (Dictionary) form.
Based on my personal experience, "lab" is used commonly at universities. Though, if you use it outside the context (talking with family, the elderly, small children, man on the street etc. :P), most people wouldn't even understand what you are referring to.
Yeah pretty much. I hear/say things like "labdayız" or "ders labda" almost on a daily basis at uni. :)