Transcript Evidence of Spontaneous Generation

Evidence of Spontaneous
Generation
•Maggots developing from rotting meat
•After spring rain people would observe
frogs and insects come to life from the
mud of dried up ponds
•Trees and other plants would
automatically grow when nothing was
planted
Origins of Life
Spontaneous Generation
• The idea that organisms originate directly
from nonliving matter.
• "life from nonlife"
• abiogenisis - (a-not bio-life genesis-origin)
Biogenesis
• The idea that organisms can only be
derived from other living organisms
Redi’s Experiment
• Redi left some meat out in the open
• Within several days maggots appeared on
the meat
• He then left the maggots and observed
that they transformed into hard shelled
structures after 20 days.
• Further observations showed that these
hard shelled structures transformed into
flies
Redi (continued)
• He remembered seeing flies around the
meat prior to the maggots being present
• He concluded that the maggots did not
spontaneously generate but were an
earlier part of the flies’ life.
Redi
• To test his new theory Redi placed
identical pieces of meat in identical glass
flasks and covered one but left the other
open. He observed that the open flask
produced maggots but the closed flask did
not produce maggots.
Redi Experiment # 3
• People did not believe his second
experiment because it did on allow air into
the flask.
• To prove his results he set up three jars
this time. One sealed. One open and one
with a piece of cloth over the meat.
• Maggots developed in the open jar but not
on the other two.
John Needham
• Designed an experiment to prove that
spontaneous generation did exist.
• He boiled two containers of broth, sealed
one with a cork and left one open.
• The boiling was to kill any bacteria or any
micro organisms that might be living in the
broth
• Days later they both turned cloudy with
microscopic organisms living in the broth
Lazzaro Spallanzani
• Noted some flaws in Needham’s experiment so
he did the experiment again but fixed the
problems.
• First he boiled the broth for an hour rather than 5
– 10 minutes like Needham did.
• Second he used different method to seal the
flask, instead of a cork he melted the neck shut.
• Conclusion – organisms don’t grow in sealed
containers
Louis Pasteur
• Performed an experiment similar to Spallazani
but instead of sealing the container he put an s
shaped tube at the top. This allowed air in, but
kept air born organisms out of the container.
This finally disproved the theory of spontaneous
generation and gave rise to the theory of
biogenesis.
• Biogenesis – all living things must come from
living things of the same type
Discovery and Importance of Cells
and the Cell Theory
• Robert Hooke in 1665 observed a piece of cork under a
microscope and called the small empty compartments
cells
• Felix Dujardin in 1835 concluded that many
microorganisms consisted of a single cell
• Theodor Schwann in 1838 reported that cells are present
in animals
• Mathais Schleiden in 1838 found that cells are also
present in plants
• Combined observations of Schwann ansd Schleiden
suggested that all organisms are made of cells
(continued)
• Rudolph Circhow in 1858 concluded from
his observations of dividing cells that cell
can only arise from other cells.
• Louis Pasteur in 1861 weakened the
theory of spontaneous generation by the
experiments he had done
Cell Theory
• The cell is the basic unit of organization for
all organisms
• All organisms are composed of cell or cell
products
• All cell come from other cells
Organisms composed of one cell are called
unicellular while those composed of many
cells are called multicellular.