1. respect from whom? your choice of major should be based on how much it interests you, whether you're good at it, and whether you think it'll provide you with something to do after graduation.
2. no. by the time you've already said the word "bioengineering," you've probably already garnered the respect of your listener (unless he/she considers his/her major to be superior to yours), if that's what you were trying to ask.
3. well, it depends on what kind of graduate program you're going for. they don't care so much about the specifics of the major as they do your qualifications, how good you are at research, your letters of rec, and to a lesser extent, your grades and GRE scores.
don't pick your major with the sole intention of impressing other people.