neither looks good for a science class like physiology, but if youve taken enough upper level bio courses and have done well, then I think pass might look better, as you can make it seem like you're taking an extra bio class just to learn more and be better prepared for dental school but don't necessarily want a grade in it, whereas a withdraw shows that you obviously was doing poorly in the class. But if you can get a B- or above in the class, then its most likely best to just take the letter grade.
