Understanding diffusion of water into and out of the cell through osmosis is fundamental to the learning and teaching of biology. Although this process is thought of as occurring directly across the lipid bilayer, the majority of water transport is actually mediated by specialised transmembrane water-channels called aquaporins. This study investigated a total of 175 Taiwanese and Swedish students' conceptions of water transport across the cell membrane, and at what level of biological organisation students represented such knowledge. A free response instrument was employed to generate students' written and diagrammatic responses. Analysis of the data resulted in the emergence of four distinct categorisations of students' conceptions. Corresponding analysis of students' diagrams revealed varying levels of scale for representing and expressing water transport conceptions. The results revealed that many students lacked an awareness of the role of specialised water channels in water transport and thought that the majority of water molecules traversed the hydrophobic membrane through direct diffusion. Our findings suggest that teaching the topic of diffusion and osmosis be aligned with current scientific discovery. (Contains 4 figures and 1 table.)