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The Evolution of Life on Earth
Earth was formed about 4.6 billion years ago.
Major Episodes in the History of Life
(3) Single-celled eukaryotes first evolved about 2.1 billion years ago.
(3) (4)
(4) Multicellular eukaryotes first evolved at least 1.2 billion years ago.
(5)
(5) Modern humans appeared about 200,000 years ago!
(2) Began oxygen production about 2.7 billion years ago
Lived alone for almost 2 billion years
Continue in great abundance today
(2) (1)
Prokaryotes
(1) Evolved by 3.5 billion years ago
Collective biomass is at least 10 times that of Eukaryotes
Prokaryotes: Domain Bacteria & Archaea
Mostly unicellular (single-celled), some are colonial organisms
Are the simplest organisms living on earth today and the most abundant
Domain
Domain
Domain
Kingdoms
2
Prokaryotes live deep within the Earth and in habitats too cold, too hot, too salty,
too acidic, or too alkaline for any eukaryote to survive.
Deep Sea chimneys (12,000 feet deep)
Temperature above 170F!
Head of a pin
Extremophile Archaea
Hot springs
Extremophile Archaea Halophiles
(Extremely salty
Environments)
Salt-producing ponds, San
Francisco bay, 5-8 times
more salty than sea water!
Main differences with Eukarya 1) Prokaryotes lack nuclei
2) Have cell walls exterior to their plasma
membranes
3) Cell size: Much smaller than Eukaryotes:
Bacteria <1μm, Eukaryotes >10 μm
4) DNA: No chromosomes in Prokaryotes
5) Cell division: Asexual by binary fission in bacteria, variable in Eukaryotes
6) Internal compartmentalization: Lack other membrane-enclosed organelles, only
ribosomes
7) Metabolic diversity: Only one
type of photosynthesis in
Eukaryotes. Several different
ways for processing energy in
prokaryotes
3
Ch 5
Domain Bacteria Prokaryotes Domain Archaea
Both bacteria and archaea have:
NO nucleus
A single loop of DNA: NO chromosomes!
Asexual reproduction
“Reproduction” by binary fission.
These are ancient “bacteria” which are also prokaryotic
but differ from bacteria in that:
They have no peptidoglycan on cell walls
They are found in extreme environments (hot springs, etc)
The bacteria we normally know exist
Many free-living
Some autotrophs
Some parasites and cause diseases
Some symbionts with eukaryotes
Why prokaryotes dominate the earth in number and biomass
(1)The have an incredibly genetic diversity
Two strains of Escherichia Coli are genetically more different than a human
and a platypus!
Specific ways to recombine DNA without sexual reproduction
(2) Prokaryotes reproduce quickly by
binary fission
And can divide every 1–3 hours
20 min in optimal conditions
Asexual reproduction
Female
Sexual reproduction
Female
Male
Generation 1
Generation 2
Generation 3
Generation 4
4
(3)Many prokaryotes form endospores
Which can remain viable in harsh conditions for centuries
Most endospores can survive in boiling water
Ch 5
Nutrient supply
Accumulation of metabolic wastes
Predation by other organisms
What prevents a prokaryotic colony to grow indefinitely?
Prokaryotic Nutrition
We can group all organisms in four major modes of nutrition based on…
Energy source (phototroph versus chemotroph) and
Carbon source (autotroph versus heterotroph)
Plants
Algae
Cyanobacteria
All other
Eukaryotes
Prokaryotes
Prokaryotes
Prokaryotes
5
Cyanobacteria: Photoautotrophic bacteria
Have different kinds of pigments to trap the sunlight
Chlorophyll a
Phycocyanin: bluish
Phycoerythrin: reddish
Bacteria may appear with a
different color depending on the
amount of these pigments
Pigments help the chlorophyll
trapping light that chlorophyll
cannot catch and pass the energy
to the chlorophyll
Ch 5
Diversity of Archaea in extreme environments
Some Archaea are extremophiles, or “lovers” of extreme environments
Extreme thermophiles prosper in hot environments.
The optimum temperatures for most thermophiles are 60°C–80°C
113°C in water near deep-sea hydrothermal vents
Extreme halophiles live in such salty places
as the Great Salt Lake and the Dead Sea.
Methanogens obtain energy by using CO2 to
oxidize H2, producing methane as a waste
product
Some species live in swamps and
marshes where other microbes have
consumed all the oxygen
Ch 5
6
Main Prokaryotic Roles in Marine Ecosystems Ch 5
Nitrogen fixation & Nitrification
Prokaryotes
Prokaryotes Decomposition
Is a chemical recycling
Prokaryotes and fungi
are the main
decomposers in marine
ecosystems
Prokaryotes
Nitrogen is needed for
proteins and nucleic
acids (DNA, RNA)
Prokaryotes are the
only living things that
can convert
atmospheric N2 to a
form that can be used
by other organisms,
such as NH3
(Ammonia)
Ch 5
Trichodesmium, also called sea sawdust, is a genus
of filamentous cyanobacteria (photosynthetic) that
also fix nitrogen. They are found in nutrient poor
tropical and subtropical ocean waters
7
Ch 5 Photosynthesis
Together with eukaryotic microscopic
algae…
Cyanobacteria (colonial blue-green
bacteria) release more than 60% of the
O2 present in out atmosphere
Mutualistic symbionts
Are very important in the deep sea by producing bioluminescence in specific organs of many deep
sea organisms. This in turn is used for…
Avoiding predators
Attracting prey
Signaling potential mates
Symbiotic Bacteria Serve as Hydrogen "Fuel Cells" for Deep-
Sea Mussels by doing chemosynthesis
Symbiotic marine bacteria chemically defend crustacean
embryos from a pathogenic fungus
Symbiotic marine bacteria and marine worm in the deep sea
What is a protist?
Whatever thing that is alive, is a eukaryote, and does not fit inside the other
groups!
They can be microscopic (protozoa, phytoplankton) or multicellular (more
than 180 feet in some seaweeds)
Domain
Domain
Domain
Kingdoms
Kingdom Protista
Eukaryotic cells are larger than those
of prokaryotes (they typically have 1000 times more volume).
Complex organelles are almost
always present
Sexual reproduction is common and
becomes dominant in most groups of
plants and animals
4 Kingdoms of eukaryotes
8
A tentative phylogeny of protists
“fungus-like” protists
“plant-like” protists
Ch 5
All the others are considered “animal-like” protists
Most protists are aquatic and free-living
Seawater
Freshwater
Moist terrestrial environments (damp soil or leaf litter)
Symbionts: mutualistic or parasites
Not even algae and protozoa can be used as main monophyletic groups (having a
common evolutionary ancestor)
Ch 5
Ingestive: Animal-like PROTOZOA
Always unicellular
An “Ecological” classification: Photosynthetic: Plant-like
Microscopic Algae PHYTOPLANKTON
Microscopic Protista
9
24 17
Most algae have a cellulose cell wall.
They have chlorophyll inside chloroplasts
and carry on photosynthesis.
Plankton are small floating organisms
Phytoplankton are photosynthetic
plankton that forms the basis for most
aquatic food chains.
Multicellular
(Seaweeds)
Green algae
Brown algae
Red algae
Algae
Unicellular
(Phytoplankton)
Diatoms
Dinoflagellates
Others
Diatoms Diatoms the most common eukaryotic
producers in marine and
freshwater ecosystems
With a unique two-part, glass-like wall of
hydrated silica
Provides protection from predators
Can withstand pressure up to 1.4
million kg/m2
Photosynthetic: Plant-like Microscopic Algae PHYTOPLANKTON
Dinoflagellates
(2nd) components of both marine and
freshwater “net” phytoplankton
More common in tropical waters
Shape is reinforced by internal plates of cellulose
Flagella
Two flagella make them spin as they move through the water
Ch 5
Mutualism with coral polyps and others Dinoflagellates photosynthetic output
Is food for reef communities
A particular type of dinoflagellate called
“Zooxanthellae” provides about 98% of the food
a coral polyp needs to survive
Coral body
Polyp’s tentacles
with symbionts
Dinoflagellates
Corals provide
raw materials
algae need in
order to make
photosynthesis
10
Red tide
Red Tides
Rapid growth of some dinoflagellates and other
unicellular algae (diatoms, cyanobacteria, etc.)
Is responsible for causing “red tides,” which
can be toxic to humans
Tides appear red because of carotenoids
Gonyaulax polyedra:
Bioluminscent and
also risponsable for
red tides
Ch 5
Bioluminescence
ATP driven chemical reaction
Creates a glow when
water is agitated
Where dinoflagellates are
in great number
Noctiluca
Foraminiferans Have porous & generally multichambered shells called tests
Included before in the general group of amoebas
Have pseudopodia, extensions that project from the cell surface
Pseudopodia extend through the pores in the test
The biggest foram…several cm… in a single-celled
organism
Forams remains in marine sediments form an
extensive fossil record
Ch 5 Ingestive: Animal-like
PROTOZOA Are always unicellular!
11
Radiolarians
Tests are fused into one delicate piece, which is
generally made of silica
The pseudopodia of radiolarians, known as axopodia
Radiate from the central body axopodia
Also useful for fossil records
Ooze hundred of meters thick in
some places
Ch 5
Ciliates
Are the most complex of all protozoa
Use of cilia to move and feed, which are
powered by ATP and the contraction of
protein fibers like in muscles
Ch 5
Control the everyday
functions of the cell
Feeding
Waste disposal
Water balance
Function during conjugation, as
in bacteria is a sexual process
that produces genetic variation
Have large macronuclei and small micronuclei
marine tintinnids build
vase-like cases (loricas)
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