Textbooks can have a fundamental and positive effect on both learning and teaching. As such, in order to understand how students structure concepts in their minds, it is necessary to analyze the structure in which those concepts presented in textbooks are described. This study examined a network of concepts used in the domain of biotechnology in the Iranian 12th grade biology textbook and investigated the alignment of science concepts used in its sub-domains. The findings of this study suggest that too many concepts, as well as unconnected ones, were used in biotechnology domain, which led to a complicated conceptual network. Therefore, this paper recommends that the number of biology concepts described in the later text books in the biotechnology domain at Iranian high schools should be reduced in order to facilitate a better formation of connections between concepts and their descriptions.