Transcript Bio 101 Aug 1 - UMDBIO101SUMMER2012

Outline
Origin of life
Major events in the history of life
Classification of organisms
Life on Earth Evolved Once
Same Macromolecules
-Same amino acids, universal code
-Same genetic code
-Other macromolecules are the same
Cell structure is similar - plasma membrane contains genetic material
Fig 18_9
Major events in the history of Life
200 kya
1.5 bya
2.5 bya
Fig 19_3
Hypothetical Origins of Life:
1 - Special creation - supernatural power created life
Not testable
2 - Extraterrestrial origin - life originated elsewhere, traveled to earth
Difficult to test
3 - Evolution - life evolved on earth from materials on earth
Testable
Each are valid hypotheses, will never know which is correct
without direct observation of the actual event
Testing the hypothesis that life evolved on earth
Miller-Urey experiment recreated conditions of early earth
Fig 19_2
Results of Miller-Urey and similar experiments
-Readily form all amino acids, nucleic acids
found in life, plus some
-Altering gases increases diversity of
molecules produced
-Long chains of amino acids degrade in
water
-Easy to form RNA chains which can act as
enzymes - can duplicate selves
(inheritance) and catalyze other reactions
Wikipedia
-Lipids form small spheres (cells) in
turbulent water - act like cell membranes
Plausible scenario: correct combination of organic molecules
trapped in lipid sphere, persisted and replicated
We will never know for certain how life
arose, plausible scenarios are best
guesses
Stromatolites - representatives of the earliest organisms
Modern stromatolites in Austrailia
Fossilized stromatolites
-Mats of bacteria, trap sediment
-Date back 2.75-3.45 billion years
-Sharp fall off in the fossil record 1 billion years ago
When life arose, organisms changed the environment
“morphological”
evolution
“metabolic”
evolution
Banded Iron Formations - 2.5-1 billion years ago
-Formed from Iron
oxydized by O2
-Becomes insoluble
in water and
precipitates out
The problem with oxygen…..
-Life arose in, and was like adapted to, anoxic conditions
-Oxygen can combine with atmospheric gases and
eliminate green house gases
Mass extinctions in the fossil record
The “cambrian explosion”
-“sudden” appearance of all the major
groups of animals 560-530 MYA
-Presents problem for “gradualism” mode of
evolution
-Lead Wolcott to hypothesize a time period
preceeding the cambrian that was under
represented in the fossil record
Modern life on earth arose from a single common ancestor, at least 2.5 bya
There are multiple hypothetical origins of life
Origin of life via organic evolution is plausible
Once life arose, it changed earths environment into what it is today
Massive extinctions happen repeatedly
Animals make a near sudden appearance in the fossil record
Millions of kinds of organisms exist, interact with humans
Naming/classifying avoids confusion
Aristotle, Romans used long descriptive names - changed frequently
Linnaeus used simple, unique, fixed names - Genus species
Scientific names are hierarchical
-Levels of classification
(genus, family, order, etc.)
are inclusive
-Organisms with similar
characteristics are
grouped together at each
level
QuickT ime™ and a
TI FF (Uncompressed) decompressor
are needed to see this picture.
Fig 18_3
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this pi cture.
Fig 18_9
Shared characteristics are due to shared evolutionary history
Phylogenies
are
evolutionary
family trees
QuickT ime™ and a
TIF F (Uncompressed) decompressor
are needed t o see this pict ure.
Fig 18_5
Phylogenies
are built using
shared
characters
A phylogeny is
a hypothesis
of
relationships
2 out of 3 Domains are prokaryotes
Bacteria:
Archea:
-Most well known prokaryotes
-Poorly understood
-Many cause disease
-Well known are “extremophiles”
-Cyanobacteria, various heterotrophs
-Methanogens, extremophiles
Prokaryotes are the dominant life form
-A spoonful of soil contains ~ 2.5 billion
prokaryotic cells
-There are more prokaryotic cells living
on your body than cells within your
body
Nodules in soybean roots house
nitrogen fixing bacteria
-Multicellular life depends on
prokaryotic life for many processes
such as decay and nitrogen fixation
Bacteria can obtain energy and materials by metabolizing
many types of materials
Oil metabolizing bacteria
Fig 19_6
Cyanobacteria are responsible for atmospheric oxygen
-Evolved photosynthesis
-Altered environment from
“reducing” to “oxidizing”
Fig 19_8
Stromatolites
in Shark Bay,
Australia
(some of the
oldest fossils
are
stromatolites)
-Atmosphere changed from
trace amounts of oxygen to
21% oxygen, which radically
altered the course of evolution
-Still responsible for 20-30% of
oxygen
Heterotrophic bacteria contribute to decay
Obtain materials and
energy from organic
sources
Help recycle materials
Animals and Fungi are also
heterotrophs and contribute
to decay
Archea diversity
Extremophiles in Yellowstone
Fig 19_7
Methane (natural
gas) is produced
from methanogens
in hypoxic
environments
Methanogens produce
methane gas from H rich
sources (chemoautotrophs)
Eukaryotes compared to Prokaryotes