Should I explain some transcript peculiarities in secondaries?

I posted before about taking a more difficult intro to physics sequence that was mandatory Pass Fail at my school, and people said that that would be okay, but now I'm working on secondaries and wondering if I should explain it and other things about my transcript that may be a little weird to people not at my school. Context: I'm a traditional applicant at a pretty well-known school. However, I have 20 P/F credit hours on my AMCAS grid (and 103 graded credit hours). My school encourages... Should I explain some transcript peculiarities in secondaries?
Source: Student Doctor Network - Category: Universities & Medical Training Authors: Tags: Pre-Medical - MD Source Type: forums