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 development
of 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 and
zoologist 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