Abstract
This study advocates integrating the One Health approach into biology teacher education to address the current fragmentation of human, animal, and environmental health teaching across disciplines such as medicine, veterinary science, and ecology. Recognizing gaps in teacher training, particularly in didactic strategies for holistic instruction, the study presents the design of an instructional activity within the expanding One Health toolbox for biology educators. Using mitosis as a gateway topic, the activity situates cellular processes within an ecotoxicology scenario of herbicide contamination in a freshwater lagoon. Through inquiry, modeling, and argumentation, pre-service teachers investigate environmental, animal, and human health interconnections while reflecting on strategies for classroom integration. This design aims to strengthen biology teacher competencies (TeachComp) and contribute to reorienting teacher education towards sustainability, fostering eco-social awareness and interdisciplinary thinking essential for addressing contemporary health and environmental crises.