MODERN BIOLOGY
Learning Targets 1, 2.
“HISTORY OF LIFE”
Biogenesis: All living things come from other living things.
vs.
Spontaneous generation: Living things could arise from nonliving things.
Examples:
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Maggots appeared on rotting meat.
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Fish appeared in ponds that were dry the previous season
(they came from the mud).
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Baby mice appeared from wheat grains left overnight in a
sweaty shirt.
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Eels arose from the mud at the bottom of the river.
Scientists performed controlled, repeatable, experiments to
learn more about spontaneous generation.
Redi (1668) Studied the life cycle of flies.
Adult fly  maggot  pupa  fly emerges.
He questioned spontaneous generation and tried to prove that
maggots came from adult flies, not meat. p.279.
Control group: jar with meat open to the air.
Experimental group: jar with meat covered with cheese cloth.
(Air could enter but not flies.)
Results: Maggots were found only in the control (open) jars.
No maggots were found in the experimental (covered) jars.
Conclusion: Flies come only from eggs laid by other flies
(biogenesis) not from the meat (spontaneous generation).
Microscopes and the discovery of microorganisms
led many investigators at the time to conclude that
microorganisms arise spontaneously from a “vital force” in
the air. All experiments to disprove spontaneous generation
must not exclude the vital force from the experiment.
Spallanzani (1700’s) Microorganisms grew from other
microorganisms. Kill the microorganisms and prevent more
from entering the experiment, and the experiment will remain
free of microorganisms. p.280.
Used meat broth. Boiled two flasks of meat broth. He sealed
one before it cooled (experimental) and left the other open to
the air (control).
Results: The sealed flask stayed clear while the open flask
grew cloudy from the growth of microorganisms.
Conclusion: Microorganisms come only from other
microorganisms (biogenesis) not from a “vital force” in the air
(spontaneous generation).
Opponents rejected his conclusion because they said he
omitted the vital force.
In the mid-1800’s the Paris Academy of Science offered a prize
to anyone who could clear up the issue once and for all.
Mrs. Loyd
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Pasteur’s Experiment Takes Prize!
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Pasteur’s experiment was very similar to Spallanzani’s
with the exception of the equipment he used.
Why did the swan-neck flask make such a difference?
p.281
It allowed the vital force into the experiment but the
U-shape of the neck trapped microorganisms preventing
them from reaching the broth.
Proponents of spontaneous generation gave up their fight.
The principle of biogenesis became a cornerstone of
biology.
?
If spontaneous generation does not occur and the principle of
biogenesis is true, how did the first living things on Earth form?
Ch.14.2 Earth’s History
The Formation of the Earth
Use your notes from “Origins”
Evolution of Life
Heterotrophic Prokaryotes
Graze on organic molecules
Glycolysis & Fermentation:

Requires no cell organelles.

Occurs in cytoplasm.
Photosynthetic Prokaryotes
Photosynthesis:

Cyanobacteria

Archeabacteria
First Eukaryotes (nucleus evolved first:
many hypotheses):
Endosymbiotic Theory
1. Mitochondria became animal cells
2. Chloroplasts (cyanobacteria
engulfed by Euk. With
mitochondria. Became plant cells.
Chemistry Review:
All atoms of the same element have the same # of protons
and therefore the same atomic #.
Atoms of the same element with differing numbers of neutrons
are called isotopes.
mass # = # of protons plus # of neutrons.
isotope names: symbol plus mass #
Example: H-1, H-2, H-3 (protium, deuterium, tritium)
C-12, C-14 (say: carbon twelve, carbon fourteen)
Rounding the atomic mass from the periodic table gives you
the mass of the most common isotope in nature. (Atomic
mass is the average of the mass of the isotopes in the ratio
that they occur in nature.)
Mrs. Loyd
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Radioactive Isotopes: Some isotopes have unstable nuclei
that undergo radioactive decay, that is, they release
particles or radiant energy (radiation) or both, until the
nuclei become stable.
Rate of Decay or Half-life: length of time it takes for one-half
of any size sample of an isotope to decay to a stable form.
Each isotope has a definite rate but the rates vary from
isotope to isotope. p.284
Isotope
Carbon-14
Uranium-235
Potassium-40
Uranium-238
Half-life (years)
5,730
704 million
1,250 million
4,500 million
Radiometric Dating (radioactive-dating,
radiocarbon-dating)
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Used to determine the age of materials.
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Radioactive isotopes occur naturally in all
matter. When an organism dies, its uptake
of carbon stops, and decay of the existing
carbon-14 continues. Thus, over time, the
amount of carbon-14 declines with respect to
the original amount of the stable carbon-12.

After 5,730 years, half of the carbon-14 in a
sample will have decayed. After another
5,730 years half of the remaining C-14decays and leaves only 25% of the original
amount.
Example:
If a bone is found that contains 25% of the
original amount of C-14 remaining, how old is it?
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(½ of a ½ = 25%)
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(number of times you said “½” = 2) or 2
half-lives
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How long is the half-life for C-14? = 5,730
years (chart)
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2 half-lives x 5,730 years = 11,460 years
old.
Which isotope to use?
Carbon-14 dating is limited to dating organic remains less than
60,000 years old.
Which isotope from the chart above would you want to use to
date the oldest rocks on Earth?
Isotopes with short half-lives are most useful for dating
relatively young rocks, while those with long half-lives are
most useful for dating older rocks.
Activity: Half-Life Lab
First Organic Compounds
(Haldane and Oparin’s Hypothesis)
If the early earth had an atmosphere containing simple
molecules life: ammonia, hydrogen gas, water vapor and
compounds made of hydrogen and carbon like methane, how
did those become more complex molecules like amino acids
(the building blocks of proteins) and nucleotides (monomers of
DNA, RNA)?
Urey/Miller Experiment fig.14-6 p.285: starting with the
above hypothesis, they set up an experiment to test it. It was a
closed system and included a boiling chamber, electrodes to
simulate lightening bursts, a condenser, and a U-fitting with a
valve to extract samples without letting air in.
Results:
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It produced a variety of organic compounds
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including amino acids (monomers of protein)
Subsequent experiments produced
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ATP (energy shuttle)
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Nucleotides (monomers of nucleic acids)
Conclusions: Basic organic compounds could have formed
under the conditions of the early Earth.
Mrs. Loyd
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The atmospheric conditions using carbon dioxide and
oxygen showed that both interfere with the production of
organic compounds
Therefore, formation of the first organic compounds may
have occurred in areas protected from the atmosphere,
such as those that exist in undersea hot springs.
Meteorites may have introduced organic compounds from
space.
From Molecules to Cell-Like Structures
TedTalks: Mark Hanczyc : Protocells
http://www.ted.com/talks/martin_hanczyc_the_line_between_life_and_not_life?language=en - t-860819
Protocells (aka: Microspheres and coacervates)
form spontaneously in the laboratory from solutions of simple
organic chemical.
have cell-like properties:
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Take up certain substances from their surroundings.
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can grow.
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can bud to form smaller microspheres.
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Do not have hereditary characteristics and do not respond
to natural selection.
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This shows that some important aspects of cellular life can
arise without direction from genes. The gap between the
nonliving chemical compounds and cellular life may not be
clear as once believed, but a continuum.
The First Cells
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No direct evidence
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No oxygen gas
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Oldest cells are size and shape of prokaryotes
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developed in environment filled with organic molecules for
food, “primordial soup”
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anaerobic, heterotrophic prokaryotes
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competition for limited food
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autotrophs would have big advantage
Chemosynthesis (chemoautotroph)
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CO2 serves as a carbon source for organic molecules.
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Energy obtained from oxidation of inorganic substances
(S)
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Example: modern Archaea: unicellular, harsh environs.
Photosynthesis and Aerobic Respiration
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3 bya photosynthesis began
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chemical traces of photosynthetic activity
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fossil stromatolites (blue-green algal colonies)
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Example: modern blue-green algae
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Accumulation of O2 as ozone, O3, took 1 b.y.
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Absorbed U.V. radiation allowing life to move to land.
First Eukaryotes: created by evolution of a nucleus
Endosymbiosis: small prokaryotes taken in by larger
prokaryotes created membrane-bound organelles
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aerobic prokaryotes  mitochondria
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photosynthetic prokaryotes  chloroplasts
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mitochondria and chloroplasts contain own DNA.
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DNA is circular like prokaryotic DNA.
Mrs. Loyd
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