What is easier biology or anatomy and physiology?
Anatomy and physiology is biology, so it's a hard question to answer directly. As far as having a general biological science background prior to starting A&P, most universities either highly recommend it or require it. So, with that, it stands to reason that A&P may possess challenges not seen in a general biology sequence.
In my opinion, general major's level biology (usually 200-level) is significantly easier. Much of what you learn in this series is further explored in A&P and detailed beyond the scope of the general biology sequence.