BIOGENESIS
Pages 279-281, 284-285
BIOGENESIS
Biogenesis: life comes from other living organisms
Ex. Caterpillars are born from butterflies
SPONTANEOUS GENERATION
Spontaneous generation: early and disproved theory that
life comes from non-living organisms
Ex. Fish appeared in ponds that were dry the previous season
Ex. Mice would appear from grain stores
EVIDENCE AGAINST SPONTANEOUS GENERATION
Redi’s Experiment
• He placed meat in two containers and covered one of them.
• He then observed the containers for the appearance of
maggots.
EVIDENCE AGAINST SPONTANEOUS GENERATION
Redi’s Results
Indicated that maggots didn’t come from rotting meat
because flies couldn’t land on the meat in the covered jar
VITAL FORCE
Vital force: Something in the air that gave rise to life
EVIDENCE AGAINST VITAL FORCE
Spallanzani’s experiment:
•Disproved that organisms came from “vital
force” by preventing air contact in flasks
•Flask without air did not grow microorganisms
Experiment: Boiled two flasks of
broth. Left one open and sealed the
other. Open flask grew
microorganisms and sealed did not.
 life comes from microorganisms
in air not vital force.
EVIDENCE AGAINST VITAL FORCE
Pasteur’s experiment: Showed that micro-organisms in the air
contaminated flasks disproving “vital force”
 Curved flasks ensured that only air would come in, not solid particles
(microorganisms)
• Boiled broth, but then used a curve-necked flask
• Allowed the air inside the flask to mix with the air outside
• Curve prevented entrance of particles (microorganisms)
NOW WHAT…
All of these experiments gave evidence to support the
idea of Biogenesis- all life comes from pre-existing life
Now scientists wanted to figure out how the first life forms
came about
All of the elements found in organic compounds are
thought to have been around since the formation of Earth.
FIRST LIFE FORMS/FIRST ORGANIC COMPOUNDS
Spontaneous Origin: the
process of life developing from
non-living chemical interactions
EVIDENCE SUPPORTING SPONTANEOUS ORIGIN
•Oparin: (1920) Hypothesized that primitive
Earth’s atmosphere was made of NH3 (ammonia),
H2 (hydrogen gas) , H2O, and CH4 (methane)
•There was no oxygen!
•He hypothesized that at high temperatures,
these gases might have formed simple organic
compounds
•Then through many chemical reactions
macromolecules would have formed
QUESTION
Which process, photosynthesis or cellular respiration,
would come about over time and put oxygen in to the
atmoshpere?
EVIDENCE SUPPORTING SPONTANEOUS ORIGIN
•Miller and Urey: (1953) set
up a chamber based on the
Oparin’s hypothesized
composition of the Earth’s
early atmosphere
•Created a “primordial soup”
that contained a variety of
simple organic compounds,
including amino acids