Cells are the basic unit of structure and organization in organisms.
Plants have cells!!
Those look like a thousand little cells, so I shall call them cells.
Animals have cells!!
All cells come from preexisting cells.
Zacharias Janssen was the first man to develop the microscope, which was in the early 1600s. Antony van Leeuwenhoek heard about the microscope and went out to create his own. Antony was the first one to see cells in bacteria.
Antony van Leeuwenhoek
Robert Hooke, Antony's friend, receive letters from Antony about cells and brought the discovery to public. Matthias Schleiden was another scientist who studied plants, and Theodore Schwann, who studied animals, discovered how all organisms had cells.
Through a collaboration, Schleiden and Schwann built on the idea that all cells came from preexisting cells. From there on, many other scientists continued the cell theory.