Cell Theory and Types of Cells

The cell is the fundamental unit of life. Every organism, from a single-celled bacterium to a blue whale, is built from one or more cells, and understanding the cell is the starting point for all of biology. This lesson introduces the cell theory, the reasoning and evidence behind it, and the major categories of cells that biologists recognize.

The origins and statements of cell theory

Cell theory emerged in the seventeenth to nineteenth centuries as microscopes improved. Robert Hooke first described "cells" in cork in 1665, and Antonie van Leeuwenhoek observed living single-celled organisms shortly after. By the 1830s and 1840s, Matthias Schleiden and Theodor Schwann proposed that plants and animals are composed of cells, and Rudolf Virchow added the crucial idea that cells arise only fro