It looks like the transition to the redesigned AP Bio test had none of the problems seen in Physics this year:
Course (year)…Total Tests…5’s (%)…5’s (#)…Failed (%)…Failed (#)…Avg Score
Bio Old (2012)…191,773…19.7%…37,813…49.0%…94,041…2.73
Bio New (2013)…162,381…12.7%…20,580…44.5%…72,183…2.77
While total test takers and number of 5’s dropped substantially, the failure rate actually dropped and the average score rose.
So merely having to deal with a redesigned curriculum, isn’t enough to explain the Physics 1 numbers this year.