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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

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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

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(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

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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

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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

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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

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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

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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

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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!

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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)