I was wondering about the rules of conduct if I happen to steal all of the questions from ResearchGate and put them on here? They are good questions related to biology but are there any legal issues with taking something that might be deemed the property of ResearchGate?
I do not think - in general - it is a good idea.
Legal issues aside (I am not going to say anything about that, as I am not an expert), I would ask for permission. You are way more likely to get a yes after asking for permission than to have a yes after having being "caught" by them and asked to remove stolen content.
Artificially inflating the site with duplicate questions will be fairly lame in my opinion. Let the site's users come up with new questions, if they have them. If we have to resort to copying questions from ResearchGate then let's just tell the users of BiologySE to go on ResearchGate, it will save us some typing.
Not being the original writer of the question you will not be able to give extra details on it. Often extra information is needed to reply to a question, and not being possible to give that will just create a big number of question with no answer or with poor quality answer. Personally I prefer less questions with good quality replies.
I'm with nico, I wouldn't copy and paste anything, or even reproduce anything with any degree of similarity, without explicitly checking their TOS and Copyrights/Permissions.
I think the best thing to do is keep an eye out for topics that haven't gotten much exposure here on the site and new research protocols that are up and coming. That way, we can get some good search terms for Bio.SE, so that we can be right in line with sites discussing "cutting edge" research (see Cutting edge research).