The concept of energy serves biologists as a powerful analytical model to describe phenomena that occurs in the natural world. Due to the concept's relevance, educational standards of different countries identify energy as a core idea for the teaching and learning of biology and other science subjects. However, previous research on students' energy understanding has mostly focused on physics contexts. This cross-sectional study extends insight to the field by providing a systematic analysis of students' (N = 30, grades 5, 7, 9, 11) conceptions about energy in biological contexts. In order to connect the findings to previous research, the study analyses conceptions about four energy aspects that are regarded as central for understanding the concept in different disciplinary contexts, i.e. (1) energy forms/sources, (2) transfer/transformation, (3) degradation/dissipation and (4) energy conservation. The findings identify substantial changes in students' conceptions about energy between the different grade levels, but also highlight conceptions that students consistently employed across age groups. The results are discussed in the light of previous research on students' progressing energy understanding and the connection of their energy understanding across different disciplinary contexts. Lastly, the article provides implications for the further development of energy teaching in biological contexts.