This study aimed to describe preservice and experienced secondary biology teachers' global and specific subject matter structures (SMSs) and elucidate the relationship between these structures and teaching experience. Teachers' global and specific SMSs respectively designate their conceptions and/or organization of their disciplines and of specific topics within those disciplines. Two preservice and two experienced secondary biology teachers were chosen to participate in the study. Participants were administered two open-ended questionnaires and were individually interviewed to assess their conceptions of biology and photosynthesis. The data were qualitatively analyzed through several rounds of category generation, confirmation, and modification. Teachers' global SMSs fell on a continuum from poorly articulated to well integrated and thematically organized. Contrary to global SMSs, specific SMSs separated the participants into their preservice and experienced groups. Unlike their preservice counterparts, the experienced teachers did not emphasize the details of photosynthesis and viewed the process as part of larger biological processes and systems. Analyses indicated that teaching experience and attention to student needs explained these latter differences. The present results indicate that the role of teaching experience in developing teachers' pedagogical content knowledge (PCK) should be emphasized and incorporated into theorizing the construct of PCK.