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Theories

Theories. Unit 5 – Lecture 2. Spontaneous Generation. Experience vs. the Scientific Method. Spontaneous Generation. Spontaneous Generation – the idea that life suddenly appears / that non-living materials produce life also called abiogenesis believed until the late 1800s

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Theories

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  1. Theories Unit 5 – Lecture 2

  2. Spontaneous Generation • Experience vs. the Scientific Method

  3. Spontaneous Generation • Spontaneous Generation – the idea that life suddenly appears / that non-living materials produce life • also called abiogenesis • believed until the late 1800s • Examples? See this week’sfun facts – but here’s one: flies come from rotting meat.

  4. Spontaneous Gen. – cont’d • Spontaneous generation was shown to be incorrect by: • Redi – mid/late 1600s • Pasteur – mid 1800s

  5. Spontaneous Gen. – cont’d • Now shown and accepted to be incorrect • Current evolutionary theory holds that this did indeed happen under just the right circumstances once – in order for life to have come about. • It is believed that since that time, all life has come from pre-existing life [cell theory] • aka biogenesis

  6. Development - Scientists • Oparin – primordial soup model [1930s] • life originated in a nutrient-rich oceanusing energy from the sun or from lightening.

  7. Development – cont’d • Miller & Urey [1953] • tested Oparin’s model – and successfully created certain organic compounds[but not life] • many scientists reject the experiment because it is no longer believed that the early atmospherewas similar to that oftheir experiment

  8. Development – cont’d • Miller & Urey • this idea is still being tested today, because it is one of the principle ideas of the evolutionary theory

  9. Development – cont’d • Protocells [1950s] • amino acids heated w/o oxygen present [like the hypothesized ancient earth conditions] can produce linked proteins that are capable of division undercycles of heat and cold [expansion, contraction  split]

  10. Development – cont’d • Protocells [1950s] • some problems may include: • possibility of oxygen in higher concentrations • intensity of UV light due to lack of oxygen could have hindered formation • mirror-image of amino acidshinder bonding which would have lead to bondedmolecules

  11. Development – cont’d • Science is actually now moving away from the idea that life evolved in water, due to other problems. • suggestions? • crystalline life • because crystals form in repeating patterns and can grow after being split; certain types of crystals are better “adapted” to certain environmental conditions

  12. Development – cont’d • Science is actually now moving away from the idea that life evolved in water, due to other problems. • suggestions? • life in ice • cooling substances can lead to formation and joining of nucleotides, and can change the behavior of certain enzymes as well

  13. First Cells • According to evolutionary theory, the first cells would have: • been anaerobic [because of assumed low oxygen conditions] • been prokaryotic

  14. First Cells • According to evolutionary theory, the first cells would have: • been photo-autotrophs [use light to make food] • over time, it is hypothesized that they then would have become chemo-autotrophs [use chemicals]

  15. First Cells • According to evolutionary theory, the first cells would have: • been similar to archaebacteria [live in harsh conditions] • current DNA evidence on this is confusing…we seem to be more genetically like archaebacteria than eubacteria… • over time, evolved into aerobic cells

  16. Development – cont’d • Margulis – Endosymbiont Theory [1960s] • “endo” = inner; “symbiont” refers to symbiosis • recall: chloroplasts and mitochondria have their own DNA and replicate on their own as well • this theory explains why this would be • prokaryotes may have ingested other bacteria which weren’t broken down • mitochondria made energy • chloroplast supplied food

  17. Development – cont’d • Margulis – Endosymbiont Theory [1960s] • over time, ingested bacteria perhaps could not live on their own outside of the cell • cells with ingested bacteria are hypothesized to have evolved into animal and plant cells

  18. Homework • use whatever time you have left in class today to read the HET packet [from Fri] and finish the questions. • DUE Tomorrow. • Didn’t finish in class? • Go online to the Course Materials page • Come by after school or tomorrow before school • BRING YOUR TRANSCRIPTS THIS WEEK, PLEASE

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