We present an activity that models the teaching of content knowledge that transfers to many areas of the life sciences and simultaneously targets growth in cognitive development. The activity provides students with concrete objects and thinking expenences that facilitate an understanding of how surface area, in the context of biological systems, is a critical and common factor in life-supporting functions. Alveolus structure and gas exchange in the lungs, nephron structure and water retention in the kidneys, villus structure and nutrient absorption in the small intestine, and root-hair structure and nutrient absorption in plants are all biological examples in which surface area plays a key role in living things. In addition, this activity incorporates components that engage students in thinking about proportional reasoning, as many students lack the proportional thinking skills needed to fully understand this structure/function relationship or to transfer the relationship to a new, but related, situation.