I have to make an art portfolio to transfer schools, I am a graphic design major. So far I have 6 observational drawings but I don’t think they are superb because that is not my forte. But I must have observational drawings. I also have other work ranging from business cards, menus, magazine covers, flyers, resumes, and a package redesign. I think my graphics are better than my sketches because that is my major.
Perhaps you can find examples of accepted portfolios on line. Try conceptart.org for example. They have a lot of forums for schools and types of art–many people post portfolios there.
I think it depends what schools you are applying to. Different schools look for different things. I think the observational drawings in your case, because you are a graphic designer, are not what the portfolio reviewers are going to be looking closely at. Its probably just to make sure you have the basics of drawing down so you can communicate your ideas to your professor and classmates, see how you approach elements of design in your drawings, etc. I assume this because my cousin was also a graphic design major and wasn’t all that great at observational drawing. But just to make sure, I would do what gouf78 said and try to look for other examples.
Transfer portfolios should showcase the work completed to date - especially if you already completed some courses within your discipline, graphic design, which supports transfer of credits and allows the admissions representative to place you in the appropriate classes.