Low and high resolution of an image

Electron microscopes (1930s) use beams of electrons, not light waves, to magnify objects up to 1 million times.

II. First sightings of cells– A. Robert Hooke

• 1. 1663, he observed slices of cork under a microscope. They looked like tiny rooms, so he called them “cells.”

– B. Anton van Leeuwenhoek• 1. First person to see living organisms under a

microscope (bacteria).

III. Cell Theory– A. 1838: Matthais Schleiden

concluded that all plants are made of cells.

– B. 1839: Theodor Schwann concluded that all animals are made of cells.

– C. 1855: Rudolf Virchow proposed that new cells are formed from existing cells.

– D. These observations, and others led to the development of the cell theory:

Cell Theory–1. All living things are made

of cells.

–2. Cells are the basic unit of structure and function in living things.

–3. All cells are produced from other cells.