Self-generated analogical models have emerged recently as alternatives to teacher-supplied analogies and seem to have good potential to promote deep learning and scientific thinking. However, studies of the ways and contexts in which students generate these models are still too limited to allow a fuller appraisal of these models' effectiveness in enhancing conceptual learning in science. This study explores how biology students aged 15-17 generated physical concrete models to represent their understanding of the respiration pathway after learning about it through a conventional flow diagram model. The analogies portrayed in students' self-generated models provide teachers with a supplementary channel to explore students' conceptual understandings of this complicated topic and allow students to reflect on ways in which the abstract pathway portrayed in textbooks actually makes sense to them.