A larger organism does not necessarily have larger cells — and measuring specimens under a microscope makes that clear. Human cheek cells average about 70 microns, human vein cells about 47 microns, and spinal cord cells come in near 57 microns. Then consider the plants: Elodea, a common water plant, has cells averaging 242 microns, and wild algae cells average 174 microns. That means the smallest organism in the group has the largest cells. Body size simply does not predict cell size.

A microscope's lenses reveal details far too small for your eyes alone — including the actual size of individual cells. When you measure cells from different organisms under a microscope, the numbers are surprising. Human cheek cells average about 70 microns, while Elodea, a small water plant, has cells averaging 242 microns. That means the smallest organism in the group has the largest cells. No unaided eye can detect objects measured in microns, so without microscopy this finding would be invisible — and the assumption that body size predicts cell size would go unchallenged.