Students can sometimes struggle to comprehend key concepts linked to very small structures that they can't see with the naked eye. Understanding the 3-dimensional aspects of cells, is one of these concepts. Cells are very small. There are many reasons for this and one of the key reasons is explained by an understanding of the relationship between cell surface area (where exchange of materials between the inside and the outside of the cell takes place) and the interior volume of the cell (which is where many of these materials are used/produced). The resource provided here is effectively a worksheet that guides students through using small blocks (centimetre blocks in this case but we have also run it with sugar cubes and other blocks such as Lego would work too) to represent single-celled organisms of various sizes and also multi-cellular organisms of varying sizes. The worksheet then asks the students to sketch a simple graph to visualise the relationship between cell surface area and volume - the cell surface area:volume ratio.