Students' difficulties interpreting diagrams remain a concern in science education. Research about improving diagram comprehension has included few studies of teachers' orchestration of language and gesture in explaining diagrams--and very few in senior high schools. Research with younger students and studies of research scientists' practice indicate the significance of the interaction of teachers' gesture and language in explaining visualisations. The strategic deployment of such teacher-focussed authoritative explanations has been observed in facilitating progression to more complex and symbolic representations in classroom work. However, the paucity of such research in senior high school leaves open the question of how these teachers use gesture and language in managing the challenges of explaining the intricate sub-microscopic and abstract visualisations senior high school students need to negotiate. In this paper, we outline existing studies of teachers' use of gesture and language to explain complex images in senior high school and investigate how it is managed by two biology teachers with images of different types and complexity representing the activity of certain cell components in the early phase of cell duplication. Implications are drawn for foci of further research including the role of a metalanguage describing different types of visualisations and their affordances.