Hi Alan,
OCA is now a prerequisite for OCP if you are not taking an upgrade exam. This is new for the SE 7 certifications, and was not the case for SE 6.
I usually find the chart on this page helpful:
http://education.oracle.com/pls/web_prod-plq-dad/db_pages.getpage?page_id=458&get_params=p_track_id:JSE7Prog
-Bob