The aim of this article is to understand biology teachers’ challenges with laboratory work in the light of tensions between the different cultures, or discourses, in biology teacher education. The data material in this study consists of a survey with 314 responses from biology teachers as well as a group interview. Our findings suggest that teachers struggle to transform the knowledge and experience from their pure biology education into their practice in the laboratory. Concepts from a scientific discourse, such as ‘hypothesis’ and ‘report’, are therefore integrated into traditional teacher-directed laboratory tasks where the results are given in advance. We argue that this contributes to a misleading image of science. One of the major challenges for teachers, we argue, is to design appropriate contexts for addressing aspects of nature of science in the laboratory. However, many biology teachers report that they lack knowledge about teaching methods in the laboratory.