1. Practice 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 WorkSat, 10am - 1 or 2pm: Garden Work Practice Exam tomorrowPractice Exam tomorrow TEST FRIDAYTEST FRIDAY Finish Skull Lab MeasurementsFinish Skull Lab Measurements –Posters tomorrow

3. Option D: Evolution 22 hours http://www.saburchill.com/IBbiology/chapters0 1/001.html http://www.saburchill.com/IBbiology/chapters0 1/001.html Has good evolution ppts!

4. 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.

5. D1: Origin of life on Earth 4 hours

6. D.1.1 Describe four processes needed for the spontaneous origin of life on Earth. Include: non-living synthesis of simple organic moleculesnon-living synthesis of simple organic molecules –Early Earth was solely inorganic (rocks, minerals, gases, water) assembly of these molecules into polymersassembly of these molecules into polymers –Organisms are organized! Complex cmpds like proteins are polymers (many monomers). origin of self-replicating molecules that made inheritance possibleorigin of self-replicating molecules that made inheritance possible –“alive” must be able to reproduce –(DNA now, but DNA’s too complex to have started it all) packaging of these molecules into membranes with an internal chemistry different from their surroundingspackaging of these molecules into membranes with an internal chemistry different from their surroundings –Water tends to depolymerize molecules!

7. D.1.2 Outline the experiments of Miller and Urey into the origin of organic compounds. TOK: Scientific progress often depends upon model building, a working hypothesis and possible falsification.TOK: Scientific progress often depends upon model building, a working hypothesis and possible falsification. –Can it be disproved? –In this case we may be able to show that organic compounds could arise under certain conditions, but we should consider whether we can show that they did at some time in the past, or whether they certainly did not.

8. D.1.2 Outline the experiments of Miller and Urey into the origin of organic compounds. 19531953 Glass sphere, envt conditions of early Earth (Hadean): primordial soupGlass sphere, envt conditions of early Earth (Hadean): primordial soup Gases: CH4, H2, NH3Gases: CH4, H2, NH3 Liquid water added, heated, evaporated and cooled (condense…water cycle)Liquid water added, heated, evaporated and cooled (condense…water cycle) Warm tempWarm temp UV radiation (b/c no ozone layer to protect from sun)UV radiation (b/c no ozone layer to protect from sun) Electric sparks inside sphere ~ lightningElectric sparks inside sphere ~ lightning Stanley Miller

9. 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

10. D.1.3State that comets may have delivered organic compounds to Earth. “Chunks of ice wandering through space”“Chunks of ice wandering through space” Panspermia (cosmozoan)Panspermia (cosmozoan) Comets contain a variety of organic compounds.Comets contain a variety of organic compounds. Geol. Evidence--Heavy bombardment ~4,000mya (comets, asteroids)Geol. Evidence--Heavy bombardment ~4,000mya (comets, asteroids) –“Late Heavy Bombardment” NASA expts in 2001: organic molecules hitchhiking on comets could’ve survived the impactNASA expts in 2001: organic molecules hitchhiking on comets could’ve survived the impact –Impact could actually help polymerize certain aa’s into polypeptides! More research is needed! Confirm? Disprove?More research is needed! Confirm? Disprove?

11. Antarctica D.1.4Discuss possible locations where conditions would have allowed the synthesis of organic compounds. Examples should include communities around deep-sea hydrothermal ventscommunities around deep-sea hydrothermal vents –Cracks in the seabed crust  HOT water, minerals –Rich diversity of species today, symbioses, chemoautotrophs VolcanoesVolcanoes –Water vapor, gases, minerals, heat extraterrestrial locationsextraterrestrial locations –Glycine (amino acid) may be present @ distant cosmic dust particles –Comets could carry these molecules to earth earth science australia

12. D.1.5Outline two properties of RNA that would have allowed it to play a role in the origin of life. Include the self-replicatingself-replicating –Single stranded; replicates w/o enzymes catalytic activitiescatalytic activities –Helps replication! –“ribozyme” –ALSO...reverse transcriptase Passing info from RNA to DNAPassing info from RNA to DNA

13. Crazy!! Dry clay...heat it... 200 amino acids can spontaneously join & form polypeptides!...can possibly form microspheres--

14. D.1.6State that living cells may have been preceded by protobionts, with an internal chemical environment different from their surroundings. MicrospheresMicrospheres –Tiny protenoid “bubbles” –Could enclose other molecules CoacervatesCoacervates –Form from lipids in water –Hydrophobic forces –Selectively permeable! Allowed for true cell membranes to evolve! Stromatolites, Shark Bay Australia

15. D.1.8Discuss the endosymbiotic theory for the origin of eukaryotes. Bacteria only ~~ 3.8 bya – 2 byaBacteria only ~~ 3.8 bya – 2 bya Then...eukaryotes!Then...eukaryotes! Organelles were once independent prokaryotes, engulfed by bigger cell, symbiosisOrganelles were once independent prokaryotes, engulfed by bigger cell, symbiosis Photosynthetic symbionts more advantageous...survival, adaptationPhotosynthetic symbionts more advantageous...survival, adaptation Mitochondria, chloroplasts:Mitochondria, chloroplasts: –double membranes –Own DNA (circular, naked—like prokaryote) –Protein synthesis w/ribosomes –Self-replicating Mitochondrion Cyanobacterium heterocyst

16. D.1.8Discuss the endosymbiotic theory for the origin of eukaryotes. Xref- relative sizes- 2.1.4; prokaryotes vs eukaryotes- 2.3.4Xref- relative sizes- 2.1.4; prokaryotes vs eukaryotes- 2.3.4 TOK:TOK: –As with other theories that aim to explain the evolution of life on Earth, we can obtain evidence for a theory and we can assess the strength of the evidence. –However, can we ever be sure that the theory explains what actually happened in the past? For something to be a scientific theory, we must also be able to test whether it is false. –Can we do this if the theory relates to a past event? –Is a special standard required for claims about events in the past to be scientific? –If they cannot be falsified, is it enough if they allow us to make predictions?