The document summarizes the history and key concepts of cell theory. It describes how Robert Hooke first observed "cells" using a compound microscope in 1665 and how Anton van Leeuwenhoek later observed pond water cells using a single lens microscope. It then outlines how Matthias Schleiden and Theodor Schwann established in the 1830s that plant and animal cells are the basic units of life. Rudolf Virchow later determined that new cells are produced from existing cells, establishing the three main concepts of cell theory - that all living things are composed of cells, cells are the basic functional units of life, and new cells arise from preexisting cells.
