Practice with Cladograms...D5Practice with Cladograms...D5• ActivityActivity

• P.455 first, to review.P.455 first, to review.

• Street Clean-Up Today after schoolStreet Clean-Up Today after school• Sat, 10am - 1 or 2pm: Garden Sat, 10am - 1 or 2pm: Garden

WorkWork• Practice Exam tomorrowPractice Exam tomorrow• TEST FRIDAYTEST FRIDAY

• Finish Skull Lab MeasurementsFinish Skull Lab Measurements– Posters tomorrowPosters tomorrow

Option D: EvolutionOption D: Evolution22 hours22 hours

http://www.saburchill.com/IBbiology/http://www.saburchill.com/IBbiology/chapters01/001.html chapters01/001.html

Has good evolution ppts!Has good evolution ppts!

Evolution...• Where do we come from??• How did life start on Earth??• What were our ancestors like

MILLIONS of years ago????

•TOK: We could question whether any investigation of the history of evolution of life on Earth can be scientific. The concept of falsifiability could be raised here.

D1: Origin of life on EarthD1: Origin of life on Earth

4 hours4 hours

D.1.1 D.1.1 Describe four processes needed for the spontaneous Describe four processes needed for the spontaneous origin of life on Earth. Include:origin of life on Earth. Include:• non-living synthesis of simple organic non-living synthesis of simple organic

moleculesmolecules– Early Earth was solely inorganic (rocks, Early Earth was solely inorganic (rocks,

minerals, gases, water)minerals, gases, water)• assembly of these molecules into assembly of these molecules into

polymerspolymers– Organisms are organized! Complex cmpds Organisms are organized! Complex cmpds

like proteins are polymers (many monomers).like proteins are polymers (many monomers).• origin of self-replicating molecules that origin of self-replicating molecules that

made inheritance possiblemade inheritance possible– ““alive” must be able to reproducealive” must be able to reproduce– (DNA now, but DNA’s too complex to have (DNA now, but DNA’s too complex to have

started it all)started it all)• packaging of these molecules into packaging of these molecules into

membranes with an internal chemistry membranes with an internal chemistry different from their surroundingsdifferent from their surroundings– Water tends to depolymerize molecules!Water tends to depolymerize molecules!

D.1.2 Outline the experiments of Miller and Urey D.1.2 Outline the experiments of Miller and Urey into the origin of organic compounds.into the origin of organic compounds.

• TOK: Scientific progress often TOK: Scientific progress often depends upon model building, a depends upon model building, a working hypothesis and possible working hypothesis and possible falsification. falsification. – Can it be Can it be disproveddisproved??– In this case we may be able to show In this case we may be able to show

that organic compounds could arise that organic compounds could arise under certain conditions, but we under certain conditions, but we should consider whether we can show should consider whether we can show that they did at some time in the that they did at some time in the past, or whether they certainly did past, or whether they certainly did not.not.

D.1.2 Outline the experiments of Miller and Urey D.1.2 Outline the experiments of Miller and Urey into the origin of organic compounds.into the origin of organic compounds.

• 19531953• Glass sphere, envt Glass sphere, envt

conditions of early Earth conditions of early Earth (Hadean): primordial soup(Hadean): primordial soup

• Gases: CH4, H2, NH3Gases: CH4, H2, NH3• Liquid water added, heated, Liquid water added, heated,

evaporated and cooled evaporated and cooled (condense…water cycle)(condense…water cycle)

• Warm tempWarm temp• UV radiation (b/c no ozone UV radiation (b/c no ozone

layer to protect from sun)layer to protect from sun)• Electric sparks inside Electric sparks inside

sphere ~ lightningsphere ~ lightning

Stanley Miller

RESULTS:RESULTS:• 1 week: organic cmpds (amino

acids, sugars, nucleic acids) had formed

• DIDN’T CREATE LIFE, but synthesized organic molecules from inorganic molecs, so it’s a possible explanation

D.1.3D.1.3 State that comets may have delivered organic State that comets may have delivered organic compounds to Earth.compounds to Earth.

• ““Chunks of ice wandering through Chunks of ice wandering through space”space”

• Panspermia (cosmozoan)Panspermia (cosmozoan)• Comets contain a variety of organic Comets contain a variety of organic

compounds. compounds. • Geol. Evidence--Heavy bombardment Geol. Evidence--Heavy bombardment

~4,000mya (comets, asteroids)~4,000mya (comets, asteroids)– ““Late Heavy Bombardment”Late Heavy Bombardment”

• NASA expts in 2001: organic molecules NASA expts in 2001: organic molecules hitchhiking on comets could’ve survived hitchhiking on comets could’ve survived the impactthe impact– Impact could actually help polymerize certain Impact could actually help polymerize certain

aa’s into polypeptides!aa’s into polypeptides!• More research is needed! Confirm? More research is needed! Confirm?

Disprove?Disprove?

Antarctica

D.1.4D.1.4 Discuss possible locations where conditions Discuss possible locations where conditions would have allowed the synthesis of organic would have allowed the synthesis of organic compounds. Examples should include compounds. Examples should include

• communities around deep-communities around deep-sea hydrothermal ventssea hydrothermal vents– Cracks in the seabed crust Cracks in the seabed crust

HOT water, minerals HOT water, minerals– Rich diversity of species Rich diversity of species

today, symbioses, today, symbioses, chemoautotrophschemoautotrophs

• VolcanoesVolcanoes– Water vapor, gases, Water vapor, gases,

minerals, heatminerals, heat

• extraterrestrial locationsextraterrestrial locations– Glycine (amino acid) may be Glycine (amino acid) may be

present @ distant cosmic present @ distant cosmic dust particlesdust particles

– Comets could carry these Comets could carry these molecules to earth molecules to earth

earth science australia

D.1.5D.1.5 Outline two properties of RNA that would have Outline two properties of RNA that would have allowed it to play a role in the origin of life. Include allowed it to play a role in the origin of life. Include thethe

• self-replicating self-replicating – Single stranded; replicates w/o enzymesSingle stranded; replicates w/o enzymes

• catalytic activitiescatalytic activities– Helps replication!Helps replication!– ““ribozyme”ribozyme”

– ALSO...reverse transcriptaseALSO...reverse transcriptase• Passing info from RNA to DNAPassing info from RNA to DNA

Crazy!!• Dry clay...heat it...• 200 amino acids can

spontaneously join & form polypeptides!

• ...can possibly form microspheres--

D.1.6D.1.6 State that living cells may have been State that living cells may have been preceded by protobionts, with an internal chemical preceded by protobionts, with an internal chemical environment different from their surroundings.environment different from their surroundings.

• Microspheres Microspheres – Tiny protenoid “bubbles” Tiny protenoid “bubbles” – Could enclose other Could enclose other

moleculesmolecules

• CoacervatesCoacervates– Form from lipids in waterForm from lipids in water– Hydrophobic forcesHydrophobic forces– Selectively permeable!Selectively permeable!

Allowed for true cell Allowed for true cell membranes to evolve!membranes to evolve!

Stromatolites, Shark Bay Australia

D.1.8D.1.8 Discuss the endosymbiotic theory for the Discuss the endosymbiotic theory for the origin of eukaryotes.origin of eukaryotes.

• Bacteria only ~~ 3.8 bya – 2 byaBacteria only ~~ 3.8 bya – 2 bya• Then...eukaryotes!Then...eukaryotes!• Organelles were once independent Organelles were once independent

prokaryotes, engulfed by bigger cell, prokaryotes, engulfed by bigger cell, symbiosissymbiosis

• Photosynthetic symbionts more Photosynthetic symbionts more advantageous...survival, adaptationadvantageous...survival, adaptation

• Mitochondria, chloroplasts: Mitochondria, chloroplasts: – double membranesdouble membranes– Own DNA (circular, naked—like Own DNA (circular, naked—like

prokaryote)prokaryote)– Protein synthesis w/ribosomesProtein synthesis w/ribosomes– Self-replicating Self-replicating

Mitochondrion

Cyanobacterium heterocyst

D.1.8D.1.8 Discuss the endosymbiotic theory for the Discuss the endosymbiotic theory for the origin of eukaryotes.origin of eukaryotes.

• Xref- relative sizes- 2.1.4; prokaryotes vs eukaryotes- Xref- relative sizes- 2.1.4; prokaryotes vs eukaryotes- 2.3.42.3.4

• TOK: TOK: – As with other theories that aim to explain the As with other theories that aim to explain the

evolution of life on Earth, we can obtain evolution of life on Earth, we can obtain evidence for a theory and we can assess the evidence for a theory and we can assess the strength of the evidence. strength of the evidence.

– However, can we ever be sure that the theory However, can we ever be sure that the theory explains what actually happened in the past? explains what actually happened in the past? For something to be a scientific theory, we For something to be a scientific theory, we must also be able to test whether it is false. must also be able to test whether it is false.

– Can we do this if the theory relates to a past Can we do this if the theory relates to a past event? event?

– Is a special standard required for claims about Is a special standard required for claims about events in the past to be scientific? events in the past to be scientific?

– If they cannot be falsified, is it enough if they If they cannot be falsified, is it enough if they allow us to make predictions?allow us to make predictions?