Background: Photomicrographs are major biological representations which help students understand more about the structures of cells and tissues. Owing to their abstract nature, students often rely on representations in textbooks to develop their understanding of photomicrographs. Purpose: This study investigated how students with low, medium and high competence for visualizing photomicrographs integrated textbook representations into their understanding of visual aid. Sample: Twelve 14-15 year-old students who were studying biology in a UK secondary school participated in this study. Design and methods: We carried out semi-structured interviews with these students. A modified model of integration of text and picture was used to interpret students' verbal response and their drawing. An innovative discourse analysis approach, Epistemic Network Analysis, was used to analyse the connections between codes which were informed by the model. Results: Compared to students with high competence, students with low and medium levels of competence did not necessarily understand the structure-behaviour-function relationship of the textual representation, or notice the visual elements in the diagrams. Hence, they could not transfer their understanding of textbook representations into that of the photomicrograph. Conclusion: This study suggests that the modified model of integration of text and picture can potentially reveal how students with different levels of visualization competence access information from textual and pictorial information. Equally importantly, the study argues for using epistemic network analysis as a tool to examine how students integrate textbook representations.