Transcript Section 1 - BiogenesisZ

+
History of Life
Chapter 14
Aristotle (384 –322 BC)
•Proposed
the theory of
spontaneous generation
•Also
called abiogenesis
•Idea
that living things can
arise from nonliving matter
•Idea
years
+
lasted almost 2000
+
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
didn’t use the scientific method to
arrive at answers to their questions
 Their
conclusions were based on untested
observations
+
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 year’s crop
of food. However, along with the muddy
soil, large numbers of frogs appeared that
weren’t around in drier times
Conclusion: muddy soil
gave rise to the frogs
+
Example #2
 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.
Conclusion: the rotting meat
that had been hanging in the
sun all day was the source
of the flies.
+
Spontaneous Generation 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.
+
Disproving Spontaneous
Generation
+
Francesco Redi
(1668)
 In
1668, Francesco Redi,
an Italian physician, did an
experiment with flies and
wide-mouth jars containing
meat
 His
hypothesis was that
rotten meat does not
turn into flies
Redi’s Experiment


One Jar contained
meat exposed to
both air and flies

Results: Found
maggots that
hatched into flies

A second jar
contained meat in a
container wrapped
in a fine cloth so
that the meat was
exposed to air, but
not flies
Results: No flies
A third jar was
sealed and thus
not exposed to
either air or
flies
Results: No
flies
+
Results of Redi’s Experiments
 The
results of this experiment disproved
the idea of spontaneous generation for
larger organisms
 People
still thought microscopic
organisms like algae or bacteria could
arise that way.
 ****Wide-mouth
jars each containing a
piece of meat were subjected to several
variations of “openness” while all other
variables were kept the same.
+
Disproving Spontaneous
Generation of Microbes
+
Lazzaro Spallanzani
(1765)
 Conducted
an experiment
where he boiled soups for
almost an hour and
sealed containers by
melting the slender necks
closed.
 His
hypothesis was that
microorganisms formed
not from the air but
from other
microorganisms
+ Spallanzani’s experiment
 Experimental
group – Boiled broth for several hours
to kill all the microorganisms in the broth and inside of
the container
Then: melted the necks
of the containers shut
while broth still hot
•Broth would remain
microbe free. However,
when the flask was
opened growth would occur
Control group – Boiled broth for several hours to kill
all the microorganisms in the broth and inside of the
container
•Broth became
contaminated and
cloudy
+
Results of Spallanzani’s
experiment
 Conclusion:
Boiled broth became
contaminated only when microorganisms
from the air entered the flask
 Critics
said Spallanzani heated the flasks
too long, destroying the “vital force” found
in the air inside them.
 Air
lacking “vital force”, they claimed,
could not generate life. Therefore,
spontaneous generation was kept alive for
another century
+ Warm
Broth is
boiled
 1.
up question
1 yr passes, broth
remains clear
Flask is
opened
One day passes,
broth becomes
cloudy
What does the 1st sealed flask contain?
 2.How
does the broth change during the
experiment?
+
 Pasteur
Louis Pasteur
(1822-1895)
 Hypothesis:
put broth into
several special S-shaped
flasks
Microbes
come from cells of
organisms on dust
particles in the air; not
the air itself.
+
Pasteur’s Experiment
 Pasture
filled beakers with broth and curved
the neck to create S-shaped Flasks that
trapped any dust particles containing bacteria
After boiling the broth to
kill any microbes present the
broth remained
uncontaminated indefinitely
If the neck was broken the
broth became cloudy and
contaminated with a day
+
The Theory of Biogenesis
 Pasteur’s
S-shaped flask kept microbes out
but let air in.
 Proved
microbes only come from other
microbes (life from life) - biogenesis
Activity- Earth’s timeline
 Materials:
1 ruler, 1 sheet of
paper, colored pencils or markers
 Instructions:
Draw a horizontal line that will
represent the timeline of Earth’s
History
 The far left side starts at the current
estimated formation of the Earth, mark
4.6 Billion Years ago
 The far right side represents present
day
 Place these key events where your
group estimates they happened and
include a date, ex 2.6Bya, 100Mya,
14,000 yrs

1.
1st flowering plants
2.
1st Life
3.
Multicellular
organisms
4.
Invasion of Land
5.
1st Eukaryotes
6.
1st Photosynthetic
bacteria
7.
Extinction of
Dinosaurs
8.
Last of the Glaciers
recede from
temperate zones
9.
Homo Sapiens
appeared
10.
Continents appear
essentially as they do
today
3.8 Bya
1st Life
4By
a
800 Mya
Multicellular
Organisms
250 Mya
1st flowering
20 Mya
Plants
Continents appear
15,000
Yrs do today
as they
Last Glaciers Recede
3 Bya
1st Photosynthetic
bacteria
3By
a
2By
a
2.1 Bya
1st Aerobic
Bacteria
4.6 Bya
Formation of
Earth
1.6 Bya
1st Eukaryotes
1By
a
160,000 yrs
Homo
sapiens
65 Mya
Extinction of
Dinos
300 Mya
Invasion of
+