Module 3 (The Development of Cell Theory)

• Cell is the basic unit of life.
• The discovery of cells was made possible by the development of the microscope in the 17th century.
• During the 1590's , two Dutch spectacle makers, Zacharias Janssen and his father Hans started experimenting with lenses. They put several lenses in a tube and made a very important discovery.
• The object near the end of the tube appeared to be greatly enlarged, much larger than any simple magnifying glass could achieve by itself. The Janssens observed that viewed objects in front of the tube appeared greatly enlarged, creating both the forerunner of the compound microscope and the telescope.
• In 1665, the English scientist Robert Hooke used a microscope to examine a thin slice of cork. Hooke describe it as consisting of "a great many little boxes." These "little boxes" reminded him of the cubicles or "cells" in which monk's lived, so he called them cells.
• The first man to witness a live cell under a microscope was a Dutch scientist named Anton van Leeuwenhoek.
• Anton van Leeuwenhoek in 1674 described Spirogyra and named the moving organisms animalcules, meaning "little animals." He was also the first scientist who observe and describe bacteria.
• In 1838, a German botanist named Matthias Schleiden showed that the development of all vegetable tissues comes from the activity of cells.
• Schleiden emphasized that structures and morphological features, not processes, give organic life its character.
• Schleiden also proved that a nucleated cell is the first element of the plant embryo.
• Theodor Schwann proposed that in animals too, every structural element is composed of cells and cell products.
• Schleiden and Schwann worked together and proposed the first two principles of cell theory.
• In 1855, German pathologist Rudolf Virchow published biogenic law and coined the phrase "omnis cellula e cellular" which means cells originate from cells.
• The three principles of cell theory are: all living things are made of cells, cells are the basic unit of life, cells come from pre-existing cells.