Instructional explanations are an important part of teaching, but there seems to be a contradiction: a teaching culture that is often dominated by fact-oriented and linear instructional explanations on the one hand and complex explanations including non-knowledge and uncertain knowledge from biologists on the other hand. The study addresses this contradiction and examines challenges of explaining complex biological phenomena in biology classes. Therefore, an online questionnaire was developed that includes three linear and three complex instructional explanations. Participants (students, student teachers, teachers and didacticans) rate the instructional explanations and state reasons in an open text field. The analysis shows that especially students, but also teacher students and teachers, prefer linear explanations. Didacticans were the least likely to rate along this trend. The participants stated different reasons, for example: While didacticans evaluate the explicit inclusion of non-knowledge positively with references to ‘nature of science’, for teachers it seems to contradict the goal of knowledge communication. Students don’t refer to non-knowledge, but rate complex explanations to be more vague. The findings are discussed in the context of the challenges associated with explaining and understanding complex phenomena. Additionally, reference is made to a fact-oriented teaching and learning culture. The implications concern the integration of non-knowledge and uncertain knowledge into biology teacher education. Furthermore, the concept of the ‘nature of science’—or, more specifically, the understanding of tentativeness—needs to be broadened.