Biodiversity – Sept. 19/12
- Historical perspective on classification of life: Linnaeus to mid 1900s – 2 kingdoms (plants and
animals). 1969, Whittaker – 5 kingdoms (protista, bacteria, plants, animals, fungi). This is still used,
but it is not a phylogenetic system. 1990, Woese – 3 domains. 2004, Cavalier-Smth – 6 kingdoms. This
is still being debated.
- The three domain system proposed by Woese is based on molecular (rRNA) analysis. It is only based
on sequence data (there were no other data sets used to support this system), but it is still preferable
to the 5 kingdom system because he used cladistics. The three domains are bacteria, archaea, and
eucaryota. Bacteria (also called eubacteria) and archaea are prokaryotic. Eucaryota contains
- Prokaryotes do not represent a phylogenetic group – it is just a name to describe bacteria. Examples
are cyanobacteria, spirochaetes, and archaea. Eukaryotes are everything else (ex. alveolates,
radiolarian, euglenozoa, amoebae, algae, plants, slime molds, fungi, animals).
- Prokaryotic cells vs. eukaryotic cells: Prokaryotic cells don’t have membrane bound organelles and
they don’t have a nucleus (circular DNA is located in a nucleoid). The genetic info is not organized
into chromosomes like in eukaryotic cells. Prokaryotic cells also do not have mitochondria.
Eukaryotic cells can be animal cells or plant cells and they have membrane bound organelles.
Prokaryotic cells are also really small compared to eukaryotic cells. Eukaryotic cells have developed
many different morphological forms.
- Prokaryotes are mostly unicellular and the size of the cells is much smaller (1-10 um). They have an
extreme diversity of metabolism and can exist in extreme environments. They were the first life
forms to evolve on earth. Eukaryotes are unicellular and multicellular. The cell size is much larger
(10x the size of prokaryotic cells). They have an extreme diversity of macro and morphological
- Evolution of life on earth: The earth is 4.6 billion years old, which is 1/3 the age of the universe. In
the 1 eon (Hadean), there were meteorites and volcanism, and then cooling and oceans. In the 2
eon (Early Archaean), oceans formed and the atmosphere was composed of: H2O, CH4, NH3, H2S, H2,
CO2, and CO. O2 and O3 were rare or absent. Energy sources were lightning and sunlight.
- Abiogenesis is the study of how life on earth arose from inanimate matter. The Miller-Urey
experiment in 1953 was able to simulate the conditions on early earth. All of the gases found in the
primitive atmosphere were put in a tube and exposed to lightning, and there was also another
connected tube with water in it to simulate the oceans. After a period of time, chemical reactions
between all of these components synthesized organic compounds (amino acids and sugars), which
are the building blocks of life.
- Early life: The early atmosphere plus energy produced simple organic compounds. There was like a
primordial soup, found along shorelines or deeper in oceans. More complex organic compounds were
being formed. Prokaryotes came about 3.9 BYA.
- The first life forms were probably anaerobic prokaryotes, but it is unknown if they were eubacteria
or archaea. They were obligate anaerobes (O2 kills them). They obtained energy by consuming
surrounding organic and inorganic compounds. 3.6 BYA, anaerobic prokaryotic organisms evolved
photosynthesis (purple and green bacteria), but it was anoxygenic photosynthesis (didn’t produce
- Cyanobacteria created and oxygen-rich atmosphere. 3.2 BYA, cyanobacteria (eubacteria) evolved
oxygenic photosynthesis. And there is fossil evidence of this (stromatolites). O2 is released as a waste
product of oxygenic photosynthesis. 2.5 BYA, O2 began to accumulate in the atmosphere. Stromatolites can be living or fossilized. They are layered structures found in shallow water that
were created by cyanobacteria.
- Because of the O2-rich atmosphere 2.5 BYA, pre-existing life (obligate anaerobes) died.
Cyanobacteria may have been responsible for the largest extinction event in history.
- Further developments: O2 plus UV produces O3. Cellular respiration using O2 evolved. 2 BYA, the
first eukaryotic cells were formed. Bacteria had dominated the earth for 2 billion years before
eukaryotes came to be.
- Bacteria today: There are 9000 described species in both domains. There is a lot of metabolic
diversity in both domains. There is anaerobic or aerobic respiration, as well as fermentation
(produces ATP by a different process). Sources of carbon can be organic or inorganic. Source of
energy can be sunlight, organic, or inorganic compounds. Examples: Anaerobic methanogens
produce methane. N2 fixers (bacteria) convert atmospheric N2 into ammonia (NH3). Plants get
nitrogen through absorption in the soil, but they can’t use atmo