Cell

Robert Hooke did not discover cells in the biological sense—he discovered the walls of dead plant cells and gave them a name. Looking at thin slices of cork through his microscope in 1665, Hooke saw a honeycomb pattern of empty chambers that reminded him of monks' cells in a monastery. He called them "cells" and published detailed drawings in his Micrographia.

Hooke was looking at the cellulose walls of cells that had died and dried long ago. The living contents—cytoplasm, nucleus, organelles—had vanished. Cork is specifically designed to have empty, air-filled cells; that's what makes it useful for bottle stoppers. Hooke saw architecture, not biology.

But the term stuck. Antoni van Leeuwenhoek, using superior lenses of his own making, observed living single-celled organisms in the 1670s—he called them "animalcules." The connection between Hooke's structural observation and Leeuwenhoek's living creatures was not immediately apparent. The synthesis into cell theory would take another 170 years.

Matthias Schleiden (for plants, 1838) and Theodor Schwann (for animals, 1839) established that all living things are composed of cells. Rudolf Virchow added in 1855 that all cells come from preexisting cells—"omnis cellula e cellula." These three principles constitute classical cell theory, the foundation of modern biology.

The microscope made cell discovery possible, but the concept required theoretical development. Hooke saw cells; understanding them required chemistry, physics, and decades of observation. The compound microscope of the 1620s enabled Hooke's observation in 1665; cell theory emerged in the 1830s. Two centuries separated the instrument from the insight.

Hooke's naming was accidentally profound. "Cell" captured something essential about life's organization—discrete, bounded, repeating units. The metaphor of the monastery cell, chosen for visual similarity, turned out to describe functional reality: cells are indeed compartments where life's chemistry occurs in protected isolation.