The difference between two-dimensional and three-dimensional structures is the absence of z-axis in 2D structures, rendering them plane or flat figures. Three-dimensional structures have an extra Z-axis to add depth to their structures. For example, you can see and understand a cube or a prism that they are existing in three dimensions; length, breadth and height. Whereas, this is not the case for two-dimensional structures. They only have two allotted axes to define their measurements, that is, length and breadth.