In 1665, Robert Hooke published Micrographia, a book filled with drawings and descriptions of the organisms he viewed under the recently invented microscope. The invention of the microscope led to the discovery of the cell by Hooke. While looking at cork, Hooke observed box-shaped structures, which he called “cells” as they reminded him of the cells, or rooms, in monasteries. This discovery led to the development of the classical cell theory.

The classical cell theory was proposed by Theodor Schwann in 1839. There are three parts to this theory. The first part states that all organisms are made of cells. The second part states that cells are the basic units of life. These parts were based on a conclusion made by Schwann and Matthias Schleiden in 1838, after comparing their observations of plant and animal cells. The third part, which asserts that cells come from preexisting cells that have multiplied, was described by Rudolf Virchow in 1858, when he stated omnis cellula e cellula (all cells come from cells).

Since the formation of classical cell theory, technology has improved, allowing for more detailed observations that have led to new discoveries about cells. These findings led to the formation of the modern cell theory, which has three main additions: first, that DNA is passed between cells during cell division; second, that the cells of all organisms within a similar species are mostly the same, both structurally and chemically; and finally, that energy flow occurs within cells.

Cell Theory

English scientist Robert Hooke published Micrographia in 1665. In it, he illustrated the smallest complete parts of an organism, which he called cells.

classical cell theory

theory that all organisms are made of cells, which are the basic structural units of life.


(deoxyribonucleic acid) molecule in every living organism that contains specific genetic information on that organism.


instrument used to view very small objects by making them appear larger.

modern cell theory

theory that cells are the basic structural, functional, and organizational units of both single-celled and multicellular organisms; cells divide and pass on hereditary information; and energy flows within cells.


place of residence and worship for a community of religious followers, usually called monks.


living or once-living thing.


group of similar organisms that can reproduce with each other.