1. Department of Biotechnology
Cell theory

2. Discoveries Which Led To Cell Theory
The Cell Theory was developed from three German scientist's discoveries. They are Matthias Schleiden, Theodor Schwann, and RudolphVirchow. In 1838 the German Botanist Matthias Schleiden discovered that all plants were composed of cells. Then only a year later a German zoologist, Theodor Schwann, discovered that all animals were composed of cells. Later in 1855 a German physician named Rudolph Virchow was doing experiments with diseases when he found that all cells come from other existing cells. Cells of course were discovered much earlier. The first person to see a cell was Robert Hooke. He used a very primitive microscope, but when he was looking at cork cells under the microscope he saw cells for the first time. The shape of the cells reminded him of the monk monasteries and so he dubbed them "cells." The first person to see living cells was Van Leeuwenhoek, a microscope builder.

3. The Cell Theory Timeline
Year of Discovery
Scientist
Contribution
1595
Hans and Zacharias Janssen
produced the first compound microscope by combining two convex lenses within a tube
1665
Robert Hooke
discovered the cellular composition of cork and introduced the word cell to science
1674
Anton van Leeuwenhoek
improved magnification of microscopes by polishing lenses
1676
"animacules" were discovered
1683
discovered bacteria from a sample of saliva from his mouth
1838
Matthias Schleiden
discovered the plants were made up of cells
1839
Theodor Schwann
discovered that animals were made up of cells
1855
Rudolph Virchow
stated that all living things come from other living things

4. two of the three tenets of cell theory were postulated.
All living organisms are composed of one or more cells
The cell is the most basic unit of life
 In 1855, Rudolf Virchow added the third tenet to cell theory. In Latin, this tenet states Omnis cellula e cellula. This translated to:
All cells arise only from pre-existing cells

5. Modern interpretation
The generally accepted parts of modern cell theory include:
All known living things are made up of one or more cells
All living cells arise from pre-existing cells by division.
The cell is the fundamental unit of structure and function in all living organisms.
The activity of an organism depends on the total activity of independent cells.
Energy flow (metabolism and biochemistry) occurs within cells.
Cells contain DNA which is found specifically in the chromosome and RNA found in the cell nucleus and cytoplasm.
All cells are basically the same in chemical composition in organisms of similar species

6. The modern version of the cell theory
The modern version of the cell theory includes the ideas that:
Energy flow occurs within cells.
Heredity information (DNA) is passed on from cell to cell.
All cells have the same basic chemical composition

7. Exceptions
1. Viruses are considered alive by some, yet they are not made up of cells. Viruses have many features of life, but by definition of the cell theory, they are not alive.
2. The first cell did not originate from a pre- existing cell. There was no exact first cell since the definition of cell is imprecise.
3. Mitochondria and chloroplasts have their own genetic material, and reproduce independently from the rest of the cell

8. Reference /www.cliffsnotes.com www.saylor.org www.preceden.com