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 Examples? See this week’s fun facts – but here’s one: flies come from rotting meat.

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

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

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

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 atmosphere was similar to that of their experiment

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

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 under cycles of heat and cold [expansion, contraction  split]

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 acids hinder bonding which would have lead to bonded molecules

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

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

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

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]

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

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

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

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