Development of the Cell Theory

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Development of the Cell Theory

• Abiogenesis
• Vs
• Biogenesis

2
Abiogenesis

• The theory states that non-living things can be
  spontaneously changed into living things.
• Also referred to as the theory of spontaneous
  generation.
• Developed by Aristotle the ancient Greek
  philosopher.

3
Francesco Redi

• An Italian doctor tried to disprove this theory
  of abiogenesis.
• Left 4 jars of rotting meat open to the air,
  after a while found maggots on the meat and flies
  hovering in the air.

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Redi Continued

• He repeated the same thing again but covered 2 of
  the jars with a lid. The result, No maggots on
  the meat that was covered. Concluded that flies
  came from flies not rotting meat , thus
  disproving Aristotles theory of Abiogenesis.

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Hold On !

• The supporters of Abiogenesis said the covered
  jars were different from the controlled jars, no
  fresh air circulated around the meat. They
  claimed that the air was the Active Ingredient
  that caused spontaneous generation

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Redis Final Try

• He put a fine mesh wire over the jars so air
  could circulate, result NO maggots. Proved
  rotting meat cant be changed into flies.
• However, critics said that the mesh was too fine
  to let this Active Ingredient into the jars. So
  abiogenesis was NOT yet disproved!

7
John Needham

• The meat broth was teaming with microbes that
  made it look cloudy.
• He heated it for a short time until the meat
  broth was clear.

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Needham Continued

• After a few days, microbes were present. He
  concluded that microbes came from non-living
  things thus supporting Abiogenesis.
• Two big problems, he used a cork seal to allow
  air to circulate but it allowed microbes to
  enter. Secondly, he heated the broth for a short
  time and didnt destroy all the microbes. POOR
  SCIENCE !

9
Lazzaro Spallanzani

• He performed Needhams experiment but melted the
  glass at the top of the flask to seal it and then
  heated it for a long time.

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Spallanzani Continued

• The result showed no microbes present.
• However, critics claimed once again that the
  Active Ingredient in the air was not allowed to
  enter the flask. So Abiogenesis was not yet
  disproved!

11
Louis Pasteur To The Rescue
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Pasteur

• Pasteur heated an open flask containing microbe
  filled meat broth for a long time killing all the
  microbes.

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Pasteur

• He then let it sit for a few days and it was
  teaming with microbes.
• He hypothesized that the microbes must have
  entered from the air.

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Abiogenesis is Dead!

• Pasteur developed a special swan-necked flask
  designed to trap the microbes from the air but
  still let the Active Ingredient enter the
  flask.
• The result of this second experiment showed no
  microbes in the broth thus disproving Abiogenesis
  and proving Biogenesis which states that only
  life can produce life!

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Contributors To The Cell Theory

• Van Leeuwenhoek built a microscope that allowed
  him to see these Tiny Beasts in pond H2O.
• Hooke examined cork under a microscope and saw
  tiny chambers he called Cells because they
  looked like the tiny chambers where monks slept.
• Brown first to discover a Nucleus inside a
  cell.
• Schleiden discovered all plants consist of
  cells.
• Schwann discovered all animals consist of
  cells.
• Virchow stated that cells came from only other
  living cells.

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The Cell Theory

• 1.All living things are composed of cells.
• 2.Cells are the basic units of structure and
  function in living things.
• 3.New cells are produced from existing cells.