Origin of Life

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Origin of Life

• Chapter 14

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Aristotle (384 322 BC)

• Proposed the theory of spontaneous generation or
  abiogenesis
• Idea that living things can arise from nonliving
  matter
• Idea lasted almost 2000 years

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Spontaneous Generation

• 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 didnt use the scientific method to arrive
  at answers to their questions
• Their conclusions were based on untested
  observations

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Examples of Spontaneous Generation
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Example 1

• Observation Every year in the spring, the Nile
  River flooded areas of Egypt along the river,
  leaving behind nutrient-rich mud that enabled the
  people to grow that years crop of food. However,
  along with the muddy soil, large numbers of frogs
  appeared that werent around in drier times

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Example 1

• Conclusion It was perfectly obvious to people
  back then that muddy soil gave rise to the frogs

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Example 2

• Observation In many parts of Europe, medieval
  farmers stored grain in barns with thatched roofs
  (like Shakespeares house). As a roof aged, it
  was not uncommon for it to start leaking. This
  could lead to spoiled or moldy grain, and of
  course there were lots of mice around.

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Example 2

• Conclusion It was obvious to them that the mice
  came from the moldy grain.

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Example 3

• Observation In the cities centuries ago, there
  were no sewers, no garbage trucks, no
  electricity, and no refrigeration. Sewage flowed
  down the streets, and chamber pots and left over
  food were thrown out into the streets each
  morning. Many cities also had major rat problems
  and a disease called Bubonic plague.

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Example 3

• Conclusion Obviously, all the sewage and garbage
  turned into the rats.

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Example 4

• Observation Since there were no refrigerators,
  the mandatory, daily trip to the butcher shop,
  especially in summer, meant battling the flies
  around the carcasses. Typically, carcasses were
  hung by their heels, and customers selected
  which chunk the butcher would carve off for them.
  

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Example 4

• Conclusion Obviously, the rotting meat that had
  been hanging in the sun all day was the source of
  the flies.

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Abiogenesis Recipes

• Recipe for bees
• Kill a young bull, and bury it in an upright
  position so that its horns protrude from the
  ground. After a month, a swarm of bees will fly
  out of the corpse.

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Abiogenesis Recipes

• Recipe for mice
• Place a dirty shirt or some rags in an open pot
  or barrel containing a few grains of wheat or
  some wheat bran, and in 21 days, mice will
  appear. There will be adult males and females
  present, and they will be capable of mating and
  reproducing more mice.

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Disproving Spontaneous Generation
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Francesco Redi (1668)

• In 1668, Francesco Redi, an Italian physician,
  did an experiment with flies and wide-mouth jars
  containing meat

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Redis Experiment

• Redi used open closed flasks which contained
  meat.
• His hypothesis was that rotten meat does not
  turn into flies.
• He observed these flasks to see in which one(s)
  maggots would develop.

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Redis 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.

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Redis (1626-1697) Experiments
Evidence against spontaneous generation 1.
Unsealed maggots on meat 2. Sealed no
maggots on meat 3. Gauze few maggots on gauze,
none on meat
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Results of Redis Experiments

• The results of this experiment disproved the idea
  of spontaneous generation for larger organisms,
  but people still thought microscopic organisms
  like algae or bacteria could arise that way.

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Francesco Redi
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Did Redi Use the Scientific Method?
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The Scientific Method

• Observation
• Hypothesis
• Experiment
• Data
• Conclusion
• Accept, Reject, or Modify hypothesis
• Retest

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Step 1 - Observation

• There were flies around meat carcasses at the
  Butcher shop.
• Where do the flies come from?
• Does rotting meat turn into or produce rotting
  flies?

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Step 2 - Hypothesis

• Rotten meat does not turn into flies. Only flies
  can make more flies.

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Step 3 - Testing

• Wide-mouth jars each containing a piece of meat
  were subjected to several variations of
  openness while all other variables were kept
  the same.
• Control group These jars of meat were set out
  without lids so the meat would be exposed to
  whatever it might be in the butcher shop.
• Experimental group(s) One group of jars were
  sealed with lids, and another group of jars had
  gauze placed over them.

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Step 4 - Data

• Presence or absence of flies and maggots observed
  in each jar was recorded.
• Control group flies entered, laid eggs,
  maggots emerged
• Gauze covered flies on gauze, but not in jar
• Sealed jars No maggots or flies on the meat

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Step 5 - Conclusion

• Only flies can make more flies. In the uncovered
  jars, flies entered and laid eggs on the meat.
  Maggots hatched from these eggs and grew into
  more adult flies. Adult flies laid eggs on the
  gauze on the gauze-covered jars. These eggs or
  the maggots from them dropped through the gauze
  onto the meat. In the sealed jars, no flies,
  maggots, nor eggs could enter, thus none were
  seen in those jars. Maggots arose only where
  flies were able to lay eggs. This experiment
  disproved the idea of spontaneous generation for
  larger organisms.

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Disproving Spontaneous Generation of Microbes
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Anton van Leeuwenhoek (1674)

• 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
  animalcules
• By end of 19th century, these organisms were
  called microbes

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Anton van Leeuwenhoek 1632-1723
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Leeuwenhoeks Microscope
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John Needham (1745)

• 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

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Needhams Results

• Needhams experiments seemed to support the idea
  of spontaneous generation
• People didnt realize bacteria were already
  present in Needhams soups
• Needham didnt boil long enough to kill the
  microbes

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Needhams Experiment
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Lazzaro Spallanzanis (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.

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Spallanzanis Results
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Conclusion

• Critics said sealed vials did not allow enough
  air for organisms to survive and that prolonged
  heating destroyed life force or vital force
• Therefore, spontaneous generation remained the
  theory of the time

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The Theory Finally Changes
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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

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Louis Pasteur (1822-1895)
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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 S-shaped
  flasks
• Each flask was boiled and placed at various
  locations

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Pasteur's Experiment - Step 1

• S-shaped Flask
• Filled with broth
• The special shape was intended to trap any dust
  particles containing bacteria

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Pasteur's Experiment - Step 2

• Flasks boiled
• Microbes Killed

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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

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Pasteur's Experimental Results
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The Theory of Biogenesis

• Pasteurs S-shaped flask kept microbes out but
  let air in.
• Proved microbes only come from other microbes
  (life from life) - biogenesis

Figure 1.3
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Review
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Evidence Pro and Con

• 1668 Francisco Redi filled six jars with
  decaying meat.

Conditions Results
3 jars covered with fine net 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? From where did the maggots come? What was the purpose of the sealed jars? Spontaneous generation or biogenesis?
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Evidence Pro and Con

• 1745 John Needham put boiled nutrient broth into
  covered flasks.

Conditions Results
Nutrient broth heated, then placed in sealed flask Microbial growth
From where did the microbes come? Spontaneous generation or biogenesis? From where did the microbes come? Spontaneous generation or biogenesis?
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Evidence Pro and Con

• 1765 Lazzaro Spallanzani boiled nutrient
  solutions in flasks.

Conditions Results
Nutrient broth placed in flask, heated, then sealed No microbial growth
Spontaneous generation or biogenesis? Spontaneous generation or biogenesis?
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Evidence Pro and Con

• 1861 Louis Pasteur demonstrated that
  microorganisms are present in the air.

Conditions Results
Nutrient broth placed in flask, heated, not sealed Microbial growth
Nutrient broth placed in flask, heated, then sealed No microbial growth
Spontaneous generation or biogenesis? Spontaneous generation or biogenesis?
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Development of Theories

• Primordial Soup natural processes formed early
  organic compounds
• Oparin 1923 (http//leiwenwu.tripod.com/primordi
  als.htm)
• Miller-Urey experiment 1953 to test Oparins
  atmosphere theory
• Bubble Theory formed protocells
• Stanley Fox 1912

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Video of Miller explaining the experiement
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Origin of Cells

• Prokaryotes Archaebacteria
• 1st cells were anerobic because no oxygen
• Obtain energy by chemosynthesis which is a
  process that uses chemicals i.e. sulfur to form
  energy
• Eukaryotes endosymbiosis hypothesis
• Large prokaryotic unicellular organisms were
  invaded by smaller prokaryotic unicellular
  organisms but they eventually gave rise to modern
  mitochondria and chloroplasts
• Separate DNA in chloroplasts and mitochondria
• Both organelles the same size and shape of
  bacteria

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