In this paper I report on the sociological and educational particulars of "The Biodiscovery Space" exhibition of the Life Museum of the Oswaldo Cruz Foundation in Rio de Janeiro, Brazil, using Basil Bernstein's framework of pedagogic discourse and recontextualization. Data for analysis was obtained from interviews with the exhibition developers, field observations of museum visitors and analysis of exhibition documents. Using the ideas of power, classification and framework, among others, I analyzed the recontextualization process of the production of expositive discourse. Thus, working with Bernstein's idea of classification, I explain the relationship between the discourses of the science of biology, history of science, museology, education, and communication in order to produce an expositive discourse. I also make explicit how agents of the Official Recontextualization Field of the Museum and the Pedagogic Recontextualization Field "....of the Museum determine partly the final expositive discourse of an exhibition". Using the idea of a pedagogic discourse framework, I discuss how the constraints imposed by objects and texts in exhibitions help to create a specific manner of visitor interaction with these elements, "even if they have some autonomy". Considerations about the audience and the intended process of acquisition are presented, when I discuss the control strategies of the exhibition. I propose that the Biodiscovery Space exhibit has a visible pedagogy. Finally, using the collected data I discuss the power tensions created in the production of expositive discourse showing how distributive, recontextualization and evaluation rules work in the context of exhibitions. The study of the dynamics in forming the expositive discourse using Bernstein's framework reveals the individuals and institutions, the selection criteria, the negotiations and the power relations involved. It has the potential to assist both educators and researchers in the museum education field, as well as designers to understand the teaching and learning processes that occur during a visit and to establish relevant criteria to evaluate quality to best produce exhibitions in science museums.