The ways in which students organize knowledge about entities, such as photons and electrons, (or their ontologies) influence their learning of quantum phenomena. In prior work, we have described different types of dynamic ontologies seen in collective student reasoning; here we extend this analysis to individual written responses to Modern Physics homework, exam, and survey questions about canonical quantum mechanics topics. We present a refined framework that describes unitary, parallel, and blended ontological structures, and then examine students' patterns of use of ontological structures across entities (e.g., photon or electron) and topic areas (double slit, Mach-Zehnder interferometer, and tunneling). Analysis of seven students' responses demonstrate their flexible use of ontologies in individual written work. Through this analysis, we raise questions for future studies about how the wording and framing of the prompts impacts students' ontological reasoning.