history of life.ppt [read-only]
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History of LifeHistory of Life
Ch t 14Chapter 14
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Biogenesis: Living things come from other living thingsliving things.
Li i thi iSpontaneous generation: Living things arise from nonliving things.
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Redi’s ExperimentRedi s Experiment
• Francesco Redi (1626-1697) noticed and d ib d th diff t d l t l fdescribed the different developmental forms of flies.Ti lik t t d i t t d• Tiny wormlike maggots turned into sturdy oval cases, from which flies eventually emergedemerged.
D fli t t l f ttiDo flies generate spontaneously from rotting meat?
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• Redi’s experimental group consisted of netting-covered jars that contained meat.
• The control group consisted of uncovered jars that also contained meat.j
• What was the purpose of the netting-covered jars?Aft f d t li i i th• After a few days, maggots were living in the meat in the open jars. The net-covered jars remained maggot free.
• The experiment showed that flies come only from eggs laid by other flies.
• What did this do to the theory of• What did this do to the theory of spontaneous generation?
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Spallanzani’s ExperimentSpallanzani s Experiment• Many investigators concluded thatMany investigators concluded that
microorganisms arise spontaneously from a “vital force” in the air.
• Spallanzani (1729-1799) designed an experiment to test the hypothesis of spontaneous generation of microorganisms.
• He hypothesized that microorganisms f d f i b f hformed not from air but from other microorganisms.
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• For his experimental group, he boiled clear, fresh broth until the flasks filled with steamfresh broth until the flasks filled with steam.
• While the broth was hot, he sealed the flasks by melting their glass necks.by melting their glass necks.
• The control-group flasks of broth were left open.p
• The broth in the sealed flasks remained clear and free of microorganisms.g
• The broth in the open flasks became cloudy because it became contaminated with microorganisms.
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• His opponents disagreed with his conclusionconclusion.
• They claimed that he had heated the experimental flasks too long destroying theexperimental flasks too long, destroying the “vital force” in the air inside them.
• Air lacking “vital force” could not generateAir lacking vital force could not generate life.
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Pasteur’s ExperimentPasteur s Experiment• Louis Pasteur (1822-1895) won a prize ( ) p
clearing up the issue over spontaneous generation.T k S ll i’ l l• Took Spallanzani’s up one level.
• He made a curve-necked flask that allowed the air inside the flask to mix with the airthe air inside the flask to mix with the air outside the flask.
• The curve of the neck prevented solid e cu e o t e ec p e e ted so dparticles, such as microorganisms, from entering the body of the flask.
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• Broth boiled inside the experimental flasks remained clear for up to one year.p y
• He then broke off the curved neck. The broth now became cloudy and contaminated with ymicroorganisms within a day.
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Earth’s History: FormationEarth s History: Formation
• 5 billion years ago, our solar system was a5 billion years ago, our solar system was a swirling mass of gas and dust.
• Most of the material was pulled together by p g ygravity and formed the sun.
• The remaining gas, dust, and debris circled g g , ,the sun forming the planets.
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Earth’s History: AgeEarth s History: Age
E th i b t 4 5 billi ld• Earth is about 4.5 billion years old.• Early estimates of its age were made by
studying layers of sedimentary rock instudying layers of sedimentary rock in earth’s crust.
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Radiometric DatingRadiometric Dating
Method of determining the absolute age of anMethod of determining the absolute age of an object by comparing the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope.
Isotope: atoms of the same element that differ in the number of neutrons.
The mass number of an isotope is the ptotal number of protons and neutrons in the nucleus.
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Radioactive decay: isotopes having unstableRadioactive decay: isotopes having unstable nuclei release particles or radiant energy, or both, until the nuclei become stable. Known as radioactive isotopes.
Half-life: time it takes for one-half of any size sample of an isotope to decay to a stable form. Range from a fraction of a second to billions of yearsbillions of years.
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Carbon DatingOrganic materials can be dated by comparingOrganic materials can be dated by comparing
the amount of Carbon-14 (radioactive isotope) with the amount of Carbon-12isotope) with the amount of Carbon 12 (stable isotope). Its half-life is 5,730 years.
Living things take carbon in their bodies constantly. Most is C-12 but a small yproportion of C-14 is also taken in. When an organism dies, its uptake of carbon stops,
d d f C 14 ti Aft 5 730and decay of C-14 continues. After 5,730 yrs., half the C-14 in a sample will have decayed After another 5 730yrs anotherdecayed. After another 5,730yrs., another half will have decayed.
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Other isotopes used in radiometric dating:I t H lf lifIsotope Half-lifeUranium-235 704,000,000Potassium-40 1,250,000,000Uranium-238 4,500,000,000
Earth’s age has been estimated based on the decay of uranium and thorium isotopes in rock crystalscrystals.
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First Organic Compoundsg p• How were the elements found on Earth and the
rest of the solar system assembled into organicrest of the solar system assembled into organic compounds?
• Hypothesis formed by Alexander Oparin (1894-• Hypothesis formed by Alexander Oparin (1894-1980) and John Haldane (1902-1964).
• Thought that the early atmosphere containedThought that the early atmosphere contained.NH3 – ammoniaH hydrogen gasH2 – hydrogen gasH2O – water vapor
and compounds made of H and C; CH methaneand compounds made of H and C; CH4 - methane
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• High temperatures caused the gases to formHigh temperatures caused the gases to form simple organic compounds.
• The cooling of the Earth caused there Amino acids
gcompounds to collect in the waters.
• Lightning and UV radiation may have caused g g ythese compounds to become more complex, resulting in macromolecules.
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Cell-like StructuresCell like Structures
• Formed spontaneously in the laboratory fromFormed spontaneously in the laboratory from solutions of simple organic chemicals.
2 types:yp1. microspheres: spherical in shape
and composed of many protein molecules p y pthat are organized as a membrane.
2. coacervates: collections of droplets that are composed of molecules of different types, including lipids, amino acids, and sugars.
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Microsphere vs. CoacervatesMicrosphere vs. Coacervates
Microspheres CoacervatesMicrospheres CoacervatesAble to take up certain substances from their
environment.Bud to form smaller microspheres can grow
Both do not have hereditary characteristics.C t d t t l l tiCannot respond to natural selection
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The First Life-FormsThe First Life Forms
Thomas Cech (1947- ) found that a type of RNAThomas Cech (1947 ) found that a type of RNA found in certain unicellular eukaryotes is able to act as a chemical catalyst.
Ribozyme: RNA molecule that can act as a catalyst and promote specific chemical reaction.
Supports the hypothesis that life started withSupports the hypothesis that life started with self-replicating molecules of RNA.
The first cells were probably anaerobicThe first cells were probably anaerobic, heterotrophic prokaryotes.
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The first autotrophs did not depend on photosynthesis the way most autotrophs
Chemosynthesis: CO2 serves as a carbon
photosynthesis the way most autotrophs do today.
Chemosynthesis: CO2 serves as a carbon source for the assembly of organic molecules. Energy is obtained from the oxidation of various inorganic substances, such as sulfur. Ex: Archae
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The First EukaryotesThe First Eukaryotes
Endosymbiosis: a mutually beneficialEndosymbiosis: a mutually beneficial relationship in which one organism lives within another.
Aerobic prokaryotes evolved into modernMitochondria.
Photosynthetic cyanobacteria may have evolved into Chloroplasts.