lafayette1234,
Only engineers need to take five courses a semester to graduate in four years. As a B.S. Biology major, you'd only need to take four each semester (unless you felt like taking five...I wouldn't recommend it).
Click on this link to view a curriculum planning sheet created by the Biology department at Lafayette:
http://ww2.lafayette.edu/~biology/planBS.html. Notice that you'll have adequate opportunities to take electives, and can take upper-level Biology courses in any order.
- Justin