BIO 104 4/3/96

The Origin of Life (con't)
Archaebacteria-like organisms were probably the first life forms present on the earth because they
were  able to live in the hot primitive Earth atmosphere, and the archaebacteria used anaerobic
respiration for energy. 

Major Episodes in the History of Precambrian Earth
     Billions of Years 
          Ago
          4.5       formation of the Earth
          3.8       oldest fossils (archaebacteria)
          3.0       autotrophic (self-feeding) bacteria (cyanobacteria) existed
          2.5       O2 from photosynthetic cyanobacteria                   accumulates in the Earth's atmosphere
          1.25      origin of eukaryotic cells
          .59       oldest known eukaryotic fossils

     Prior to the appearance of cyanobacteria the Earth's atmosphere had no oxygen, but
through the process of photosynthesis  the cyanobacteria produced oxygen which accumulated in
the atmosphere.
     Half a billion years ago we see the first multicellular structures.

Eukaryotes= eu="true", karyote="nucleus"
     -nucleus bound in a membrane
     -these cells posses mitochondria
          -plant cells have chloroplasts
     Origin of Eukaryotic Cells
          Endosymbiotic hypothesis:
               -This hypothesis was stated by Lynn Margulis in her              book "The Endosymbiotic Theory of the Origin of the Eukaryotic             Cell"
The theory basically says:  Eukaryotic cells acquired the precursors of mitochondria and
chloroplasts by engulfing cyanobacteria and bacteria which became endosymbionts.                    -Cells that engulfed only bacteria (mitochondria)became animal             cells.
               -Cells that engulfed both bacteria (mitochondria) and cyanobacteria             (chloroplasts) became plants and protists.

Prokaryotes:  without nucleus pro = "before", karyote = "nucleus"
     -Ribosomes are smaller (70s) and different in composition from those in eukaryotic    cells.
     -Prokaryotes have circular DNA.
     -They also have a sensitivity to streptomycin


           Mitochondria       Chloroplast         Eukaryotes
Ribosomes      
size:          70s                 70s            80s
DNA type: circular            circular       linear
Sensitivity
to strep-  posses             posses         no
tomycin    sensitivity                  sensitivity              sensitivity

The data in the table above is consistent with the idea that mitochondria and chloroplasts have
homology with prokaryotes and the ancestors of modern mitochondria and chloroplasts were
derived through endosymbiosis.

Begin material in Chapter 25 .... The six kingdoms of life
Classification of Organisms
     Cladistics is classification showing evolutionary relationships.   
     Phenetics is the classification showing similarities through morphological similarities.

Carolus Linnaeus (1707-1778)
     He is the father of the classification system we use today.
He came up with the binomial nomenclature system:  this is the system used world wide in
description of animals.  It is a two name system where the Genus is stated first then the species
name follows;  both of which are underlined.  The genus name shows morphological differences
and is capitalized, while the species name is used for description.  Often the person who discovers
or names the species may also add their name after the species name.For example:
Acer rubrum     Acer  = Maple (genus), rubrum = red

                     Classification Hierarchy
Kingdom  (country)
     Phylum  (state)
          Class     (county)
               Order     (city)
                    Family  (street)
                         Genus  (number)
Classification should show evolutionary relationships if possible:  This can be inferred by
structural similarities and DNA similarities which is known as homology.
     Using cladistics birds and crocodiles are grouped together.
     Using phenetics birds and crocodiles are grouped separately.
There are six kingdoms:
     1) Fungi
     2) Monera (eubacteria)
     3) Protista
     4) Archaebacteria
     5) Plantae
     6) Animal