Development of the

Cell Theory

Big Question

• Where do living things come from?

1600s. Ideas of the time

• For centuries, people accepted the prevailing explanation for the sudden appearance of some organisms (flies, maggots, mice, bees)

• Scholars of the day gave a name to their accepted theory: spontaneous generation

1590. Zacharias & Hans Janseen (DUTCH)

• Credit for the first compound (more than one lens) microscope is usually given to Zacharias Jansen, of Middleburg, Holland, around the year 1595.

• HUGE impact on developmentof the theory could see small stuffs

1655. Robert Hooke (ENGLISH)

• Using a microscope, looks at a thin slice of cork.

• Calls the spaces in the cork “Cells” first person to use the word to describe these microscopic structures

1688. Francesco Redi (ITALIAN)

• Performed an experiment to see if rotting meat changed into flies; hypothesis of spontaneous generation was not supported.

1674. Anton van Leevwenhoek (DUTCH)

• Developed his own microscope & looked at pond samples identified simple microorganisms (bacteria & protozoa) which he called “animacules”

• Also looked at blood samples from plants and animals to see cells.

150-200 Year Gap???

• Between the Hooke/Leuwenhoek discoveries and the mid 19th century, very little cell advancements were made.

• This is due to the widely accepted, traditional belief in Spontaneous Generation.

1838. Matthias Schleiden (GERMAN)

• Looked at numerous plant samples under a microscope, concludes all plants are made of cells.

• Has dinner with colleague andzoologist Theodor Schwann…

1839. Theodor Schwann(GERMAN)

• After looking at numerous animal samples, concludes all animals are made of cells.

• Publishes “Microscope Investigations on the Accordance in the Structure of Growth of Plants and Animals,” which stated first statement of the cell theory:– ALL LIVING THINGS ARE MADE OF CELLS

1855. Rudolph Virchow (GERMAN)

• Extends work of Schleiden & Schwann by proposing that all living cells must rise from pre-exisiting cells.

• RADICAL idea (spontaneous generation still widely accepted)

1858. CELL THEORY

• The 3 Basic Components of the Cell Theory were now complete:1. All organisms are composed of one or more cells.

(Schleiden & Schwann)(1838-39)2. The cell is the basic unit of life in all living things.

(Schleiden & Schwann)(1838-39)3. All cells are produced by the division of preexisting cells.

(Virchow)(1858)• Cell Theory is accepted by scientific community, but

skepticism exists due to belief in spontaneous generation

Modern Cell Theory

• Adds 4 more statements:1. Cells contains hereditary information which is passed

from cell to cell during cell division. (The first cell is the exception because it could not have come from a previously existing cell)

2. All cells are basically the same in chemical composition.3. All energy flow (metabolism & biochemistry) of life

occurs within cells. 4. Cell activity depends on the activities of sub-cellular

structures within the cell(organelles, nucleus, plasma membrane)

1864. Louis Pasteur (FRENCH)

• Set out to denounce the ideas of spontaneous generation; is successful

How is the Cell Theory Used Today?

• The basic discovered truths about cells, listed in the Cell Theory, are the basis for things such as:– Disease/Health/Medical Research and Cures(AIDS, Cancer,

Vaccines, Cloning, Stem Cell Research, etc.)

1970. Lynn Marguilis (AMERICAN)

• Proposes the idea that certain organelles (chloroplasts & mitochondria) were once free living cells themselves ENDOSYMBIOTIC THEORY is added