Q. Can a book that's on reserve be borrowed for the entire semester?

No, you would not be able to borrow the book for an entire semester. 

Reserve materials are books, articles or other items that professors have assigned to an entire class.  The library's copy or the professor's personal copy is then placed at the Circulation Desk "On Reserve" for the class.  So that the material can be available to all the class members, reserve materials get very short circulation periods.  Most items are limited to use only within the library on a one-hour or three-hour loan.  Some items can go out of the building on a one-day or three-day loan.