Unit 5 – Lecture 2

Spontaneous GenerationExperience vs. the Scientific Method

Spontaneous GenerationSpontaneous Generation – the idea that life

suddenly appears / that non-living materials produce lifealso called abiogenesisbelieved until the late 1800sExamples? See this week’s

fun facts – but here’s one: flies come from rotting meat.

Spontaneous Gen. – cont’dSpontaneous generation was shown to be

incorrect by:Redi – mid/late 1600s

Pasteur – mid 1800s

Spontaneous Gen. – cont’dNow 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 - ScientistsOparin – primordial soup model [1930s]

life originated in a nutrient-rich oceanusing energy from the sun or from lightening.

Development – cont’dMiller & 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

Development – cont’dMiller & Urey

this idea is still being tested today, because it is one of the principle ideas of the evolutionary theory

Development – cont’dProtocells [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]

Development – cont’dProtocells [1950s]

some problems may include:possibility of oxygen in

higher concentrationsintensity of UV light due to

lack of oxygen could have hindered formation

mirror-image of amino acidshinder bonding which would have lead to bondedmolecules

Development – cont’dScience is actually now moving away from

the idea that life evolved in water, due to other problems.suggestions?

crystalline lifebecause crystals form in repeating

patterns and can grow after being split; certain types of crystals are better “adapted” to certain environmental conditions

Development – cont’dScience is actually now moving away from

the idea that life evolved in water, due to other problems.suggestions?

life in icecooling substances can lead to

formation and joining of nucleotides, and can change the behavior of certain enzymes as well

First CellsAccording to evolutionary theory, the first

cells would have:been anaerobic

[because of assumed low oxygen conditions]

been prokaryotic

First CellsAccording 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 CellsAccording 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’dMargulis – Endosymbiont Theory [1960s]

“endo” = inner; “symbiont” refers to symbiosis

recall: chloroplasts and mitochondria have their own DNA and replicate on their own as wellthis theory explains why this would be

prokaryotes may have ingested other bacteria which weren’t broken downmitochondria made energychloroplast supplied food

Development – cont’dMargulis – 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

Homeworkuse 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 pageCome by after school or tomorrow before school

BRING YOUR TRANSCRIPTS THIS WEEK, PLEASE