I was wondering, could the professional clarinetists use beginner clarinets and not touch professional ones?? other than sound quality, what does the professional clarinet offer??

stronger resisitance than beginner clarinet do.

I own both type and it`s a big difference in the resistance.

The professional wood clarinets also tend to have a more refined sound than the plastic beginner ones. But you can get a good sound out of both.

How about the keys?? are they different?

the keys are different too. you`ll have a much better feeling in pressing the keys of a professional model than a student one. You can play fast passages more freely and easy with a professional model. There are many other differences to be discussed too.

You can tell the difference once you have played the Buffet B12 (Student model) and the Buffet R13 (professional).

Well I never noticed any difference in the keywork when I was testing professional models this year.
One thing I did really notice (this is comparing an intermediate to a pro model) is the difference in the altissimo register. On my clarinet, anything above upper altissimo Bb (5 lines above the stave) is an effort. On the pro model that I tried, I got right up to the D (6 lines above the stave) with no trouble at all.