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350
Aristotle
Aristotle hypothesizes the spontaneous generation. -
Period: 350 to
Development of Cell Theory Timespan
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Zacharias and Hans Janssen
Zacharias and Hans Janssen invented the world's first compound microscope. While experimenting with several lenses in a tube, they discovered that nearby objects appeared greatly enlarged. -
Robert Hooke
Robert Hooke of England investigated a sliver of cork through a microscope. He notices what he calls cells or pores. He is the first person to use the word cellto describe microscopic structures. -
Fransesco Redi
An Italian physician, Francesco Redi, performed an experiment to see if rotting meat changed into flies. He discovered that only flies to could make more flies, thus disproving the theory of spontaneous generation. -
Anton Van Leeuwenhoek
Anton Van Leeuwenhoek, of Holland, used microscopes to view many things including pond organisms, bacteria and blood cells. He made careful sketches of what he observed. -
John Needham
John Needham discovered that soup that had been exposed to the air contained micro organisms. He theorized that a life force was present in all inorganic matter including air and oxygen that could cause spontaneous generation. -
C.F. Wolff
C.F. Wolff comes up with a generalised cell theory. He attempted to find common features between both the animal and plant cells and managed to observe that both cells had vesicles and granules. He formed the foundation for the germ layer theory. -
Lazzaro Spallanzani
Lazzaro Spallanzani, a biologist in Italy tried several variations on the experiments done by John Needham. He discovered that soup that was kept sealed did not contain the micro organisms that appeared in soup open to the air. He determined that micro organisms get into the soup from the air. -
Rene Dutrochet
Rene Dutrochet discovered that "the cell is the fundamental element in the structure of living bodies, forming both animals and plants through juxtaposition." -
Robert Brown
Robert Brown discovers the nucleus of the cell. He stresses its importance in fertilisation. -
Matthias Schleiden and Theodor Schwann
Matthias Schleiden and Theodor Schwann create cell theory. The theory states that all living things are made up of one or more cells. Schleiden publishes his cell theory applying it to plants, while Schwann publishes his applied to animals. Theodor Schwann discovers special cells that form a sheath around nerve axons. They are now called Schwann cells. He conducts experiments to help disprove spontaneous generation once and for all. -
Rudolf Virchow
Rudolf Virchow writes and publishes his theory that every cell stems from another cell. He theorizes that all forms of disease come from changes in normal cells. Robert Remak discovers a method to isolate the membrane of the cell and proves that it divides a cell. -
Louis Pasteur
Louis Pasteur repeated the soup experiment, determining that soup spoiled when exposed to air only if the air was not filtered or if the container had an opening allowing micro organisms to enter. He stated that flasks with long S shaped necks protected the soup because the micro organisms settled in the neck instead of the soup. -
Walther Fleming
Walther Fleming, a German biologist, uses dyes to stain cells. Upon examination of these cells, he finds rods that he calls chromosomes. -
Edouard van Beneden
Edouard van Beneden, a Belgian biologist, discovers that all members of the same species contain the same number of chromosomes. -
Water Stanborough Sutton
Water Stanborough Sutton, American biologist, demonstrates that chromosomes exist in structurally similar pairs. -
Water Sutton
Walter Sutton proves that egg and sperm cells only have one out of each set of chromosomes. -
Max Knoll and Ernst Ruska
Max Knoll and Ernst Ruska invented the electron microscope, which allows us to see cell organelles in greater detail. Transmission electron microscopes magnify the samples up to 1 million times, while scanning electron microscopes magnify the substance up to 200,000 times. We were able to see mitochondria because of electron microscopes. -
Cell Fractionation
Cell fractionation was introduced. This is when the cell contents are ground up and suspended in solution. Then the solution is centrifuged at different velocities to separate the cell organelles of different densities. The heavier organelles will need a lower velocity, whist the lighter organelles will need a greater velocity. The sediments at the bottom form into pellets which are analysed. We can find out the cell organelle’s composition and function this way. -
Modern Cell Theory
Modern Cell Theory contains 4 statements, in
addition to the original Cell Theory:
The cell contains hereditary information(DNA) which
is passed on from cell to cell during cell division.
All cells are basically the same in chemical
composition and metabolic activities.
All basic chemical & physiological functions are
carried out inside the cells.(movement, digestion,etc)
Cell activity depends on the activities of sub-cellular
structures within the cell(organelles, nucleus, plasma
membrane)