Biological Science 11 >>> Origin of Life

7/30/2019 Biological Science 11 >>> Origin of Life

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Origin of Life

copyright cmassengale


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Aristotle (384 322 BC)

Proposed the theory ofspontaneous generationAlso called abiogenesis

Idea that living things canarise from nonliving matter

Idea lasted almost 2000years



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3copyright cmassengale


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Spontaneous Generation

For centuries, people based theirbeliefs on their interpretations ofwhat they saw going on in the worldaround them without testing their

ideasThey didnt use the scientificmethod to arrive at answers to theirquestionsTheir conclusions were based onuntested observations



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Examples of

SpontaneousGeneration



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Example #1

Observation: Every year in thespring, the Nile River floodedareas of Egypt along the river,leaving behind nutrient-rich mudthat enabled the people to growthat years crop of food.However, along with the muddy

soil, large numbers of frogsappeared that werent around indrier times



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Example #1Conclusion: It was perfectly

obvious to people back thenthat muddy soil gave rise tothe frogs



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Example #2

Observation: In many parts ofEurope, medieval farmers storedgrain in barns with thatchedroofs (like Shakespeares house).As a roof aged, it was notuncommon for it to start leaking.This could lead to spoiled or

moldy grain, and of course therewere lots of mice around.



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Example #2

Conclusion:It was obvious tothem that the mice camefrom the moldy grain.


E l #


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Example #3Observation: In the cities

centuries ago, there were nosewers, no garbage trucks, noelectricity, and no refrigeration.

Sewage flowed down the streets,and chamber pots and left overfood were thrown out into the

streets each morning. Manycities also had major ratproblems and a disease calledBubonic plague.


E l #


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Example #3

Conclusion: Obviously, allthe sewage and garbageturned into the rats.


E l #4


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Example #4

Observation:Since there were norefrigerators, the mandatory,daily trip to the butcher shop,especially in summer, meantbattling the flies around thecarcasses. Typically, carcasseswere hung by their heels, and

customers selected which chunkthe butcher would carve off forthem.


E l #4


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Example #4

Conclusion: Obviously, therotting meat that had beenhanging in the sun all day wasthe source of the flies.



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Abiogenesis Recipes

Recipe for bees:Kill a young bull, and bury itin an upright position so

that its horns protrudefrom the ground. After a

month, a swarm of bees willfly out of the corpse.



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Abiogenesis Recipes

Recipe for mice:

Place a dirty shirt or some rags inan open pot or barrel containing afew grains of wheat or some wheat

bran, and in 21 days, mice willappear. There will be adult malesand females present, and they will

be capable of mating andreproducing more mice.



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Disproving

SpontaneousGeneration


F i R di (1668)


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Francisco Redi (1668)

In 1668, Francisco Redi, anItalian physician, did anexperiment with flies and wide-

mouth jars containing meat


R di E i t


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Redis Experiment

Redi used open & closedflasks which contained meat.His hypothesis was that

rotten meat does not turninto flies.He observed these flasks to

see in which one(s) maggotswould develop.


R di Fi di


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Redis Findings

He found that if a flask was

closed with a lid so adult fliescould not get in, no maggotsdeveloped on the rotting meat

within.In a flask without a lid,maggots soon were seen in the

meat because adult flies had laideggs and more adult flies soonappeared.



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Redis (1626-1697) Experiments

Evidence against spontaneous generation:

1. Unsealed

maggots on meat2. Sealed no maggots on meat3. Gauze few maggots on gauze, none on meat


R l f R di E i


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Results of Redis Experiments

The results of thisexperiment disproved the ideaof spontaneous generation for

larger organisms, but peoplestill thought microscopicorganisms like algae orbacteria could arise that way.


F i R di


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Francisco Redi



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Did Redi Use the

Scientific Method?



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The Scientific MethodObservation

HypothesisExperiment

Accept, Reject, or Modify hypothesis


St 1 Ob ti


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Step 1 - Observation

There were flies around meatcarcasses at the Butchershop.

Where do the flies comefrom?

Does rotting meat turn intoor produce rotting flies?


St p 2 H p th i


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Step 2 - Hypothesis

Rotten meat does not turninto flies. Only flies canmake more flies.


St p 3 T stin


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Step 3 - Testing

Wide-mouth jars each containing a piece of

meat were subjected to several variationsof openness while all other variables werekept the same.

Control group These jars of meat wereset out without lids so the meat would beexposed to whatever it might be in thebutcher shop.

Experimental group(s) One group of jarswere sealed with lids, and another group of

jars had gauze placed over them.


Step 4 Data


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Step 4 - Data

Presence or absence of fliesand maggots observed in each

jar was recorded.Control group flies entered,laid eggs, & maggots emergedGauze covered flies on gauze,but not in jarSealed jars No maggots orflies on the meat


Step 5 Conclusion


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Step 5 - Conclusion

Only flies can make more flies. In the

uncovered jars, flies entered and laid eggson the meat. Maggots hatched from theseeggs and grew into more adult flies. Adultflies laid eggs on the gauze on the gauze-

covered jars. These eggs or the maggotsfrom them dropped through the gauze ontothe meat. In the sealed jars, no flies,maggots, nor eggs could enter, thus none

were seen in those jars. Maggots arose onlywhere flies were able to lay eggs. Thisexperiment disproved the idea ofspontaneous generation for larger organisms.



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DisprovingSpontaneous

Generation ofMicrobes


A t L h k (1674)


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Anton van Leeuwenhoek (1674)Leeuwenhoek began making and

looking through simple microscopesHe often made a new microscopefor each specimen

He examined water and visualizedtiny animals, fungi, algae, andsingle celled protozoa;

animalculesBy end of 19th century, theseorganisms were called microbes


Ant n v n L u nh k 1632 1723


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Anton van Leeuwenhoek 1632-1723


Leeuwenhoeks Microscope


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Leeuwenhoek s Microscope


John Needham (1745)


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John Needham (1745)

Showed that microorganismsflourished in various soups thathad been exposed to the airClaimed that there was a lifeforce present in the moleculesof all inorganic matter, includingair and the oxygen in it, that

could cause spontaneousgeneration to occur


N dh m R lt


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Needhams Results

Needhams experimentsseemed to supportthe ideaof spontaneous generation

People didnt realizebacteriawere already present inNeedhams soups

Needham didnt boil longenough to kill the microbes


Needhams Experiment


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Needham s Experiment


L S ll i (1765)


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Lazzaro Spallanzanis (1765)

Boiled soups for almost an hour

and sealed containers by meltingthe slender necks closed.

The soups remained clear.

Later, he broke the seals & thesoups became cloudy with

microbes.


Spallanzanis Results


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Spallanzani s Results


Conclusion


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Conclusion

Critics said sealed vials didnot allow enough air fororganisms to survive and that

prolonged heating destroyedlife force

Therefore, spontaneousgeneration remained thetheory of the time



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The TheoryFinally Changes


How Do Microbes Arise?


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How Do Microbes Arise?

By 1860, the debate had become soheated that the Paris Academy ofSciences offered a prize for anyexperiments that would help resolve

this conflictThe prize was claimed in 1864 byLouis Pasteur, as he published the

results of an experiment he did todisproved spontaneous generation inmicroscopic organisms


Louis Pasteur (1822-1895)


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Louis Pasteur (1822-1895)


Pasteur's Problem


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Pasteur s Problem

Hypothesis:Microbes comefrom cells of organisms on dustparticles in the air; not the air

itself.Pasteur put broth into severalspecial S-shaped flasks

Each flask was boiled and placedat various locations


Pasteur's Experiment - Step 1


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Pasteur s Experiment - Step 1

S-shaped FlaskFilled withbroth

The special shaped wasintended to trap anydust particles

containing bacteria




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FlasksboiledMicrobes Killed




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Flask left at variouslocationsDid not turn cloudy

Microbes not foundNotice the dust thatcollected in the neck of

the flask


Pasteur's Experimental Results


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Pasteur s Experimental Results


The Theory of Biogenesis


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Pasteurs S-shaped flask kept microbes

out but let air in.Proved microbes only come from othermicrobes (life from life) - biogenesis

The Theory of Biogenesis

Figure 1.3copyright cmassengale


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Review


Evidence Pro and Con


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1668: Francisco Redi filled six

jars with decaying meat.


Conditions: Results:

3 jars covered with finenet

No maggots

3 open jars Maggots appeared

From where did the maggots come?What was the purpose of the sealed jars?

Spontaneous generation or biogenesis?




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1745: John Needham put boiled

nutrient broth into covered flasks.



Nutrient brothheated, then placedin sealed flask

Microbial growth

From where did the microbes come?





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1765: Lazzaro Spallanzani boiled

nutrient solutions in flasks.



Nutrient brothplaced in flask,heated, then

sealed

No microbialgrowth

Spontaneous generation orbiogenesis?




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1861: Louis Pasteur demonstrated

that microorganisms are present inthe air.



Nutrient broth placed inflask, heated, notsealed

Microbial growth

Nutrient broth placed inflask, heated, thensealed

No microbial growth




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Biological Science 11 >>> Origin of Life

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