Fifth Grade
Worksheets
The Cell Theory
In 1665, Robert Hooke used a microscope to look at a thin slice of cork. He saw tiny little shapes that looked like little rooms with walls around each of them. He named them cellulae. This Latin word means "little rooms."
Almost two hundred years passed by. Microscopes were improved. In 1838, Matthias Schleiden saw that all plants were made of cells. At almost the same time, Theodor Schwann saw that all animals were made of cells. In 1855, Rudolf Virchow determined that all cells came from other cells. These three things are the basis of the Cell Theory:
1. All living things are made of one or more cells.
2. Cells are the smallest unit of life.
3. All cells come from other cells.
