Origin of life

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Origin of LifeOrigin of Life
copyright cmassengale

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Aristotle (384 –322 BC)Aristotle (384 –322 BC)
Proposed the theory ofProposed the theory of
spontaneous generationspontaneous generation
Also calledAlso called abiogenesisabiogenesis
Idea thatIdea that living things canliving things can
arise from nonlivingarise from nonliving mattermatter
Idea lasted almostIdea lasted almost 20002000
yearsyears

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Spontaneous GenerationSpontaneous Generation
For centuriesFor centuries,, people basedpeople based theirtheir
beliefsbeliefs onon their interpretations oftheir interpretations of
what they sawwhat they saw going on in the worldgoing on in the world
around them without testing theiraround them without testing their
ideasideas
TheyThey didn’t use the scientificdidn’t use the scientific
methodmethod to arrive at answers to theirto arrive at answers to their
questionsquestions
Their conclusions were based onTheir conclusions were based on
untested observationsuntested observations

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Examples ofExamples of
SpontaneousSpontaneous
GenerationGeneration

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Example #1Example #1
Observation:Observation: Every year in theEvery year in the
spring, thespring, the Nile River floodedNile River flooded
areas of Egypt along the river,areas of Egypt along the river,
leaving behind nutrient-rich mudleaving behind nutrient-rich mud
that enabled the people to growthat enabled the people to grow
that year’s crop of food.that year’s crop of food.
However, along with the muddyHowever, along with the muddy
soil,soil, large numbers of frogslarge numbers of frogs
appeared that weren’t around inappeared that weren’t around in
drier timesdrier times

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Conclusion:Conclusion: It was perfectlyIt was perfectly
obvious to people back thenobvious to people back then
thatthat muddy soil gave rise tomuddy soil gave rise to
the frogsthe frogs

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Observation:Observation: In many parts ofIn many parts of
Europe, medieval farmers storedEurope, medieval farmers stored
grain in barnsgrain in barns with thatchedwith thatched
roofs (like Shakespeare’s house).roofs (like Shakespeare’s house).
As a roof aged, it was notAs a roof aged, it was not
uncommon for it to start leaking.uncommon for it to start leaking.
This could lead toThis could lead to spoiled orspoiled or
moldy grainmoldy grain, and of course there, and of course there
werewere lots of mice aroundlots of mice around..

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Conclusion: It was obvious toIt was obvious to
them that thethem that the mice camemice came
from the moldy grain.from the moldy grain.

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Observation:Observation: In the citiesIn the cities
centuries ago, there were nocenturies ago, there were no
sewers, no garbage trucks, nosewers, no garbage trucks, no
electricity, and no refrigeration.electricity, and no refrigeration.
Sewage flowed down the streets,Sewage flowed down the streets,
and chamber pots and left overand chamber pots and left over
foodfood were thrown out into thewere thrown out into the
streets each morning. Manystreets each morning. Many
cities also had majorcities also had major ratrat
problemsproblems and a disease calledand a disease called
Bubonic plagueBubonic plague..

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Conclusion:Conclusion: Obviously, allObviously, all
thethe sewage and garbagesewage and garbage
turned into the ratsturned into the rats.

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Observation:Observation: Since there were noSince there were no
refrigerators, the mandatory,refrigerators, the mandatory,
daily trip to the butcher shop,daily trip to the butcher shop,
especially in summer,especially in summer, meantmeant
battling the flies around thebattling the flies around the
carcassescarcasses. Typically, carcasses. Typically, carcasses
were “hung by their heels,” andwere “hung by their heels,” and
customers selected which chunkcustomers selected which chunk
the butcher would carve off forthe butcher would carve off for
them.them.

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Conclusion: Obviously, theObviously, the
rotting meatrotting meat that had beenthat had been
hanging in the sun all day washanging in the sun all day was
thethe source of the fliessource of the flies..

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Abiogenesis RecipesAbiogenesis Recipes
Recipe for bees:Recipe for bees:
Kill a young bullKill a young bull, and, and bury itbury it
in an upright position soin an upright position so
that itsthat its horns protrude fromhorns protrude from
the groundthe ground. After a month,. After a month,
a swarm of bees will fly outa swarm of bees will fly out
of the corpse.of the corpse.

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Abiogenesis RecipesAbiogenesis Recipes
Recipe for mice:Recipe for mice:
Place aPlace a dirty shirtdirty shirt or some rags inor some rags in
anan open pot or barrelopen pot or barrel containing acontaining a
few grains of wheatfew grains of wheat or some wheator some wheat
bran, and inbran, and in 21 days21 days, mice will, mice will
appear. There will be adult malesappear. There will be adult males
and females present, and they willand females present, and they will
be capable of mating andbe capable of mating and
reproducing more mice.reproducing more mice.

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DisprovingDisproving
GenerationGeneration

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Francesco Redi (1668)Francesco Redi (1668)
In 1668, FrancescoIn 1668, Francesco RediRedi, an, an
Italian physician, did anItalian physician, did an
experiment withexperiment with fliesflies andand wide-wide-
mouth jars containing meatmouth jars containing meat

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Redi’s ExperimentRedi’s Experiment
Redi usedRedi used open & closedopen & closed
flasksflasks whichwhich contained meatcontained meat..
HisHis hypothesishypothesis was thatwas that
rotten meat does not turnrotten meat does not turn
into flies.into flies.
HeHe observedobserved these flasksthese flasks toto
see in which one(s) maggotssee in which one(s) maggots
would develop.would develop.

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Redi’s FindingsRedi’s Findings
He found that if a flask wasHe found that if a flask was
closedclosed with a lid sowith a lid so adult fliesadult flies
could not get in, no maggotscould not get in, no maggots
developed on the rotting meatdeveloped on the rotting meat
within.within.
In a flaskIn a flask without a lidwithout a lid,,
maggots soon were seenmaggots soon were seen in thein the
meat because adult flies had laidmeat because adult flies had laid
eggs and moreeggs and more adult flies soonadult flies soon
appeared.appeared.

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Redi’s (1626-1697) Experiments
Evidence against spontaneous generation:Evidence against spontaneous generation:
1.1. UnsealedUnsealed – maggots on meat– maggots on meat
2.2. SealedSealed – no maggots on meat– no maggots on meat
3.3. GauzeGauze – few maggots on gauze, none on meat– few maggots on gauze, none on meat

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Results of Redi’s ExperimentsResults of Redi’s Experiments
The results of thisThe results of this
experimentexperiment disproved the ideadisproved the idea
of spontaneous generation forof spontaneous generation for
larger organisms,larger organisms, but peoplebut people
still thought microscopicstill thought microscopic
organisms like algae ororganisms like algae or
bacteria could arise that way.bacteria could arise that way.

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Francesco RediFrancesco Redi

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Did Redi Use theDid Redi Use the
Scientific Method?Scientific Method?

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The Scientific MethodThe Scientific Method
ObservationObservation
HypothesisHypothesis
ExperimentExperiment
Accept, Reject, or Modify hypothesisAccept, Reject, or Modify hypothesis

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Step 1 - ObservationStep 1 - Observation
There were flies around meatThere were flies around meat
carcasses at the Butchercarcasses at the Butcher
shop.shop.
Where do the flies comeWhere do the flies come
from?from?
Does rotting meat turn intoDoes rotting meat turn into
or produce rotting flies?or produce rotting flies?

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Step 2 - HypothesisStep 2 - Hypothesis
Rotten meat does not turnRotten meat does not turn
into flies.into flies. Only flies canOnly flies can
make more flies.make more flies.

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Step 3 - TestingStep 3 - Testing
Wide-mouth jarsWide-mouth jars each containing a piece ofeach containing a piece of
meat were subjected to several variations ofmeat were subjected to several variations of
“openness”“openness” while allwhile all other variables wereother variables were
kept the same.kept the same.
Control groupControl group — These jars of meat were— These jars of meat were
set outset out without lidswithout lids so the meat would beso the meat would be
exposed to whatever it might be in theexposed to whatever it might be in the
butcher shop.butcher shop.
Experimental group(s)Experimental group(s) — One group of jars— One group of jars
werewere sealedsealed with lids, and another group ofwith lids, and another group of
jars had gauze placed over them.jars had gauze placed over them.

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Step 4 - DataStep 4 - Data
Presence or absence of fliesPresence or absence of flies
and maggots observed in eachand maggots observed in each
jar wasjar was recordedrecorded..
Control groupControl group – flies entered,– flies entered,
laid eggs, & maggots emergedlaid eggs, & maggots emerged
Gauze coveredGauze covered – flies on gauze,– flies on gauze,
but not in jarbut not in jar
Sealed jarsSealed jars – No maggots or– No maggots or
flies on the meatflies on the meat

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Step 5 - ConclusionStep 5 - Conclusion
Only flies can make more fliesOnly flies can make more flies. In the. In the
uncovered jarsuncovered jars, flies entered and laid eggs, flies entered and laid eggs
on the meat. Maggots hatched from theseon the meat. Maggots hatched from these
eggs and grew into more adult flies. Adulteggs and grew into more adult flies. Adult
flies laid eggs on the gauze on the gauze-flies laid eggs on the gauze on the gauze-
covered jars. These eggs or the maggotscovered jars. These eggs or the maggots
from them dropped through the gauze ontofrom them dropped through the gauze onto
the meat. In thethe meat. In the sealed jarssealed jars, no flies,, no flies,
maggots, nor eggs could enter, thus nonemaggots, nor eggs could enter, thus none
were seen in those jars. Maggots arose onlywere seen in those jars. Maggots arose only
where flies were able to lay eggs.where flies were able to lay eggs. ThisThis
experiment disproved the idea ofexperiment disproved the idea of
spontaneous generation for larger organisms.spontaneous generation for larger organisms.

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DisprovingDisproving
Generation ofGeneration of
MicrobesMicrobes

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Anton van Leeuwenhoek (1674)Anton van Leeuwenhoek (1674)
Leeuwenhoek beganLeeuwenhoek began makingmaking andand
looking throughlooking through simple microscopessimple microscopes
He often made a new microscopeHe often made a new microscope
for each specimenfor each specimen
HeHe examined waterexamined water and visualizedand visualized
tiny animals, fungi, algae, andtiny animals, fungi, algae, and
single celled protozoa;single celled protozoa;
“animalcules”“animalcules”
By end of 19By end of 19thth
century, thesecentury, these
organisms were calledorganisms were called microbesmicrobes

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Anton van Leeuwenhoek 1632-1723Anton van Leeuwenhoek 1632-1723

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Leeuwenhoek’s MicroscopeLeeuwenhoek’s Microscope

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John Needham (1745)John Needham (1745)
Showed that microorganismsShowed that microorganisms
flourished in various soups thatflourished in various soups that
had been exposed to the airhad been exposed to the air
Claimed that there was aClaimed that there was a “life“life
force” present in the moleculesforce” present in the molecules
of all inorganic matterof all inorganic matter, including, including
air and the oxygen in it, thatair and the oxygen in it, that
could cause spontaneouscould cause spontaneous
generation to occurgeneration to occur

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Needham’s ResultsNeedham’s Results
Needham’s experimentsNeedham’s experiments
seemed to supportseemed to support the ideathe idea
ofof spontaneous generationspontaneous generation
PeoplePeople didn’t realizedidn’t realize bacteriabacteria
were already present inwere already present in
Needham’s soupsNeedham’s soups
NeedhamNeedham didn’t boil longdidn’t boil long
enoughenough to kill the microbesto kill the microbes

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Needham’s ExperimentNeedham’s Experiment

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Lazzaro Spallanzani’s (1765)Lazzaro Spallanzani’s (1765)
Boiled soups for almost an hourBoiled soups for almost an hour
and sealed containers byand sealed containers by meltingmelting
the slender necks closedthe slender necks closed.
TheThe soups remained clearsoups remained clear..
Later, heLater, he broke the sealsbroke the seals & the& the
soups became cloudysoups became cloudy withwith
microbes.microbes.

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Spallanzani’s ResultsSpallanzani’s Results

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ConclusionConclusion
CriticsCritics said sealed vials didsaid sealed vials did
not allow enough air fornot allow enough air for
organisms to survive and thatorganisms to survive and that
prolonged heating destroyedprolonged heating destroyed
“life force”“life force”
Therefore,Therefore, spontaneousspontaneous
generation remainedgeneration remained thethe
theory of the timetheory of the time

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The TheoryThe Theory
Finally ChangesFinally Changes

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How Do Microbes Arise?How Do Microbes Arise?
ByBy 18601860, the debate had become so, the debate had become so
heated that theheated that the Paris Academy ofParis Academy of
SciencesSciences offered a prizeoffered a prize for anyfor any
experiments that would help resolveexperiments that would help resolve
this conflictthis conflict
TheThe prize was claimed in 1864 byprize was claimed in 1864 by
Louis PasteurLouis Pasteur, as he published the, as he published the
results of an experiment he did toresults of an experiment he did to
disproved spontaneous generation indisproved spontaneous generation in
microscopic organismsmicroscopic organisms

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Louis Pasteur (1822-1895)Louis Pasteur (1822-1895)

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Pasteur's ProblemPasteur's Problem
Hypothesis:Hypothesis: Microbes comeMicrobes come
from cells of organisms on dustfrom cells of organisms on dust
particles in the air; not the airparticles in the air; not the air
itself.itself.
Pasteur put broth into severalPasteur put broth into several
specialspecial S-shaped flasksS-shaped flasks
Each flask wasEach flask was boiled and placedboiled and placed
at various locationsat various locations

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Pasteur's Experiment -Pasteur's Experiment - Step 1Step 1
S-shaped FlaskS-shaped Flask
Filled withFilled with brothbroth
The special shaped wasThe special shaped was
intended tointended to trap anytrap any
dust particlesdust particles
containing bacteriacontaining bacteria

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FlasksFlasks boiledboiled
Microbes KilledMicrobes Killed

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Flask left at variousFlask left at various
locationslocations
DidDid not turn cloudynot turn cloudy
Microbes not foundMicrobes not found
Notice theNotice the dustdust thatthat
collected in the neckcollected in the neck ofof
the flaskthe flask

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Pasteur's Experimental ResultsPasteur's Experimental Results

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Pasteur’sPasteur’s S-shaped flask kept microbesS-shaped flask kept microbes
out but let air inout but let air in..
Proved microbes only come from otherProved microbes only come from other
microbes (life from life) -microbes (life from life) - biogenesisbiogenesis
The Theory of BiogenesisThe Theory of Biogenesis
Figure 1.3copyright cmassengale

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ReviewReview

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1668:1668: Francisco RediFrancisco Redi filled sixfilled six
jars with decaying meat.jars with decaying meat.
Evidence Pro and ConEvidence Pro and Con
Conditions:Conditions: Results:Results:
3 jars covered with fine3 jars covered with fine
netnet
No maggotsNo maggots
3 open jars3 open jars Maggots appearedMaggots appeared
From where did the maggots come?From where did the maggots come?
What was the purpose of the sealed jars?What was the purpose of the sealed jars?
SSpontaneous generation or biogenesis?pontaneous generation or biogenesis?

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1745:1745: John NeedhamJohn Needham put boiledput boiled
nutrient broth into covered flasks.nutrient broth into covered flasks.
Nutrient brothNutrient broth
heated, then placedheated, then placed
in sealed flaskin sealed flask
Microbial growthMicrobial growth
From where did the microbes come?From where did the microbes come?

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1765:1765: Lazzaro SpallanzaniLazzaro Spallanzani boiledboiled
nutrient solutions in flasks.nutrient solutions in flasks.
Evidence Pro and Con
Nutrient brothNutrient broth
placed in flask,placed in flask,
heated, thenheated, then
sealedsealed
No microbialNo microbial
growthgrowth
SSpontaneous generation orpontaneous generation or
biogenesis?biogenesis?

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1861:1861: Louis PasteurLouis Pasteur demonstrateddemonstrated
that microorganisms are present inthat microorganisms are present in
the air.the air.
Nutrient broth placed inNutrient broth placed in
flask, heated, notflask, heated, not
sealedsealed
Microbial growthMicrobial growth
Nutrient broth placed inNutrient broth placed in
flask, heated, thenflask, heated, then
sealedsealed
No microbial growthNo microbial growth

Origin of life

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