Transcript Spontaneous Generation PowerPoint

Spontaneous Generation
Unit 3
What is Spontaneous Generation?
Who was the first person to come
up with the idea of Spontaneous
Generation?
Aristotle
Aristotle (384-322 BC)
• First person to propose the
theory of spontaneous
generation
• Spontaneous generation – the
idea that living things can arise
from nonliving matter
• Spontaneous generation is also
known as abiogenesis
• The idea of spontaneous
generation lasted for almost
2000 years!
• For centuries, people based their beliefs on their
interpretations of what they saw going on in the
world around them without testing their ideas
• They didn’t use the scientific method to arrive at
answers to their questions
• Their conclusions were based on untested
observations
Disproving Spontaneous Generation
Francesco Redi (1668)
• In 1668, Francesco
Redi, an Italian
physician, did an
experiment with flies
and wide mouth jars
containing meat
Redi’s Findings
• Redi used open & closed
flasks which contained meat.
• Hypothesis: If you leave meat
sitting out uncovered, then
flies will lay their eggs on the
meat.
• He observed the flasks to see
in which one(s) maggots
would develop.
Evidence against spontaneous
generation:
1. Unsealed – maggots on meat
2. Sealed – no maggots on meat
3. Gauze – few maggots on gauze, none on meat
Redi’s Findings
• He found that if a flask was closed with a lid so
adult flies could not get in, no maggots
developed on the rotting meat within.
• In a flask without a lid, maggots soon were
seen in the meat because adult flies had laid
eggs and more adult flies soon appeared.
Did Redi Disprove Spontaneous
Generation?
• The results of Redi’s experiment disproved the
idea of spontaneous generation for larger
organisms (such as flies, mice, bees, etc.)
• But people still thought microscopic
organisms like algae or bacteria could arise
through spontaneous generation.
Anton van Leeuwenhoek
• Leeuwenhoek began making
and looking through simple
microscopes
• He often made a new
microscope for each specimen
• He examined water and
visualized tiny animals, fungi,
algae, and single celled
protozoa called animalcules
• By end of 19th century, these
organisms were called
microbes
John Needham
• Showed that microorganisms flourished in
various soups that had been exposed to the air
– Claimed that there was a life force present in the
molecules of all inorganic matter, including air and
the oxygen in it, that could cause spontaneous
generation to occur
Did Needham Prove Spontaneous
Generation was True?
• Needham’s experiments seemed to support
the idea of spontaneous generation
• People didn’t realize bacteria were already
present in Needham’s soups
• Needham didn’t boil long enough to kill the
microbes
Lazzaro Spallanzani (1765)
• Boiled soups for almost an hour and sealed
containers by melting the slender necks closed.
– The soups remained clear.
– Later, he broke the seals & the soups became cloudy
with microbes.
After Spallanzani’s Experiment..
• Critics said sealed vials did not allow enough
air for organisms to survive and that
prolonged heating destroyed life force
• Therefore, spontaneous generation remained
the theory of the time
The Theory Finally Changes..
How do Microbes Arise?
• By 1860, the debate had become so heated
that the Paris Academy of Sciences offered a
prize for any experiments that would help
resolve this conflict
• The prize was claimed in 1864 by Louis
Pasteur, as he published the results of an
experiment he did to disproved spontaneous
generation in microscopic organisms
Pasteur’s Problem
• Hypothesis: Microbes
come from cells of
organisms on dust
particles in the air; not
the air itself.
• Pasteur put broth into
several special Sshaped flasks. Each
flask was boiled and
placed at various
locations
Pasteur’s Experiment – Step 1
• S-shaped Flask - Filled with broth
• The special shaped was intended to trap any
dust particles containing bacteria
Pasteur’s Experiment – Step 2
Boiled broth in the flasks
which killed the microbes
Pasteur’s Experiment – Step 3
•
•
•
•
Flask left at various locations
Did not turn cloudy
Microbes not found
Notice the dust that collected in the neck of
the flask
Pasteur’s Experimental Results
The Theory of Biogenesis
• Pasteur’s S-shaped flask kept microbes out but let
air in.
• Proved microbes only come from other microbes
(life from life) - biogenesis
Cell Theory Websites
• http://www.smithlifescience.com/celltheory.
htm
• http://www.timetoast.com/timelines/celltheory-timeline--3
What are the three parts of the cell
theory…
1.)
2.)
3.)
What are the three parts of the cell
theory…
1.) All living things are composed of cells
2.) Cells are the basic unit of structure and
function
3.) New cells are produced from existing cells
Schleiden, Schwann & Virchow:
• http://en.wikipedia.org/wiki/Theodor_Schwan
n
• http://migration.wordpress.com/2007/03/02/
basics-cell-theory/
• http://science.jrank.org/pages/6408/Spontan
eous-Generation.html
• http://en.wikipedia.org/wiki/Rudolf_Virchow