[求助]生化phD毕业后想转JD?新手求教！

your OPT is an authorization form from USCIS

Warning: I am not an immigration attorney, the above sentence only represent my opinion. Please consult your lawyer on this matter.

what is OPT?

Does it mean that I have to obtain the Green Card before I take the patent bar exam?

NO, OPT is the temp status that allows you to work in the US after you graduate and before you transfer from F1 to H1B. This stage is way before you getting your green card.