This activity complements the animated short video Seeing the Invisible. Students explore concepts related to relative size and scale using cards of cells and microorganisms.

Students begin by reviewing metric units and how to convert between them. They then apply that knowledge to building scale models of different microorganisms and cells first visualized by 17th-century scientist Antonie van Leeuwenhoek. Finally, they use the models to compare relative sizes of the cells and organisms.

The activity is adapted from an activity originally developed by Project Neuron.