The teaching of science is a complex process, involving the use of multiple modalities. This paper illustrates the potential of a multimodal semiotics discourse analysis framework to illuminate meaning-making possibilities during the teaching of a science concept. A multimodal semiotics analytical framework is developed and used to (1) analyze the semiotic and epistemological meanings communicated by multiple modalities during the teaching of a biology concept and (2) highlight features of semiotic modalities that extend meaning-making opportunities in science classrooms. The classroom discourse of a Grade 11 biology teacher was analyzed during the teaching of the concept chemosynthesis. Data were drawn from lesson transcripts, observational fieldnotes, and informal interviews with the teacher. The findings showed that the multimodal semiotics framework was useful at illustrating how semiotic and epistemological functions of modalities compounded meanings. Most significantly, an emergent multimodal framework relating semiotic functions and science learning outcomes emerged that has the potential to (1) act as a metacognitive tool for teachers to select, sequence, and scaffold modalities and (2) act as an analytical framework for educational researchers to analyze meaning making in science teaching and learning. (Contains 3 tables, 5 figures, and 4 footnotes.)