Origins of Life

1
Origins of Life

• Pages 21 -23

2
Spontaneous Generation

• This theory states that living things can be
  generated from non-living things
• For example worms from the hair left by a horse
• For example rotting meat produces maggots

3

• Why did people believe this? (page 22)
• Before refrigerators, people observed the maggots
  on the rotting meat
• It gave people an answer to a question
• Theory was believed for a few centuries

4
Biogenesis (NOW!)

• This theory states that living things can only
  come from other living things
• This is reproduction
• ALL LIFE FROM LIFE
• Scientists gradually started to accept this
  theory over the other

5
Three Scientists

• These three scientists were involved in the
  acceptance of the Biogenesis Theory
• Redi
• Spallanzani
• Pasteur

6
Francesco Redi

• 1625-1695
• Challenged spontaneous generation
• Challenged the idea that maggots came from
  rotting meat
• See page 22
• If spontaneous generation is possible, maggots
  would appear even when the jars are sealed

7

• 1st jar uncovered flies laid eggs on meat
  (maggots appeared)
• 2nd jar sealed no maggots (control)
• 3rd jar screen on jar laid eggs on screen,
  but eggs did not develop without the moisture of
  the meat (maggots)
• If maggots could come from meat than the
  maggots would be on ALL the meat
• Maggots from another source
• (Remember microscope not invented yet)

8
Lazaro Spallanzani

• 1729 1799 (not discussed in book)
• Italian biologist
• Looked into smaller organisms
• He boiled broth in glass bottles
• Why?
• To kill any organisms in the broth
• Sealed the bottles so air could not enter
• Broth stayed clear

9

• He opened the bottles and let air enter
• Organisms from the air entered and the broth
  began to spoil
• This observation supported Redis discoveries
• Yet people still not believing Biogenesis

10
Louis Pasteur

• Finally 100 years later
• 1822 1895
• French scientist
• See page 23
• Use beef broth and long neck flasks (curved thin
  open neck)
• Air could get in but dust got caught in the
  curved neck of the flask

11

• Nothing grew until the neck of the glass was
  broken off
• Why?
• Dust could enter with small organisms
• Broth got cloudy and bubbly, could see
  microorganisms under a microscope (bacteria)
• Shows that organisms could not appear in broth
  unless it came in contact with a living
  organism..Biogenesis was proved!