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Chapter 15
The Evolution of Microbial Life
PowerPoint® Lectures for
Campbell Essential Biology, Fourth Edition
– Eric Simon, Jane Reece, and Jean Dickey
Campbell Essential Biology with Physiology, Third Edition
– Eric Simon, Jane Reece, and Jean Dickey
Lectures by Chris C. Romero, updated by Edward J. Zalisko
© 2010 Pearson Education, Inc.
Biology and Society:
Can Life Be Created in the Lab?
• How did life first arise on Earth?
• To gain insight, scientists have
– Synthesized the entire genome of Mycoplasma genitalium, a species of
bacteria found naturally in the human urinary tract
– Transplanted the complete genome of one species of Mycoplasma
bacteria into another
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Figure 15.00
• A research group led by Craig Venter hopes to
– Create an artificial genome
– Transplant it into a genome-free host cell
• An artificial organism that could be completely controlled might
– Clean up toxic wastes
– Generate biofuels
– Be unable to survive outside rigidly controlled conditions
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MAJOR EPISODES IN THE HISTORY OF
LIFE
• Earth was formed about 4.6 billion years ago.
• Prokaryotes
– Evolved by 3.5 billion years ago
– Began oxygen production about 2.7 billion years ago
– Lived alone for almost 2 billion years
– Continue in great abundance today
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• Single-celled eukaryotes first evolved about 2.1 billion years
ago.
• Multicellular eukaryotes first evolved at least 1.2 billion years
ago.
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Precambrian
Common ancestor to
all present-day life
Origin of
Earth
4,500
Earth cool enough
for crust to solidify
4,000
Oldest prokaryotic fossils
3,500
Millions of years ago
3,000
Atmospheric oxygen
begins to appear due
to photosynthetic
prokaryotes
2,500
Figure 15.1a
Paleozoic
Mesozoic Cenozoic
Archaea
Prokaryotes
Bacteria
Protists
Eukaryotes
Plants
Fungi
Animals
Oldest eukaryotic
fossils
2,000
Cambrian
explosion
Oldest
Plants and
animal
symbiotic fungi
fossils
colonize land
Origin of
multicellular
organisms
1,500
1,000
Millions of years ago
500
Extinction of
dinosaurs
First humans
0
Figure 15.1b
• All the major phyla of animals evolved by the end of the
Cambrian explosion, which began about 540 million years ago
and lasted about 10 million years.
• Plants and fungi
– First colonized land about 500 million years
– Were followed by amphibians that evolved from fish
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• What if we use a clock analogy to tick down all of the major
events in the history of life on Earth?
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Humans
Origin of solar
system and Earth
0
4
1
2
3
Figure 15.2
THE ORIGIN OF LIFE
• We may never know for sure how life on Earth began.
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Resolving the Biogenesis Paradox
• All life today arises by the reproduction of preexisting life, or
biogenesis.
• If this is true, how could the first organisms arise?
• From the time of the ancient Greeks until well into the 19th
century, it was commonly believed that life regularly arises from
nonliving matter, an idea called spontaneous generation.
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• Today, most biologists think it is possible that life on early Earth
produced simple cells by chemical and physical processes.
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Figure 15.3
A Four-Stage Hypothesis for the Origin of Life
• According to one hypothesis, the first organisms were products of
chemical evolution in four stages.
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Stage 1: Abiotic Synthesis of Organic Monomers
• The first stage in the origin of life has been the most extensively
studied by scientists in the laboratory.
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The Process of Science: Can Biological
Monomers Form Spontaneously?
• Observation: Modern biological macromolecules are all
composed of elements that were present in abundance on the early
Earth.
• Question: Could biological molecules arise spontaneously under
conditions like those on the early Earth?
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• Hypothesis: A closed system designed in the laboratory to
simulate early Earth conditions could produce biologically
important organic molecules from inorganic ingredients.
• Prediction: Organic molecules would form and accumulate.
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• Experiment: An apparatus was built to mimic the early Earth
atmosphere and included
– Hydrogen gas (H2), methane (CH4), ammonia (NH3), and water vapor
(H2O)
– Sparks, discharged into the chamber to mimic the prevalent lightning of
the early Earth
– A condenser to cool the atmosphere, causing water and dissolved
compounds to “rain” into the miniature “sea”
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“Atmosphere”
CH4
Water vapor
NH3
H2
Electrode
Condenser
Cold water
Cooled water
containing organic
molecules
H2O
Stanley Miller re-creating
his 1953 experiment
“Sea”
Sample for
chemical analysis
Miller and Urey’s experiment
Figure 15.4
• Results: After the apparatus had run for a week, an abundance of
organic molecules essential for life had collected in the “sea,”
including amino acids, the monomers of proteins.
• Since Miller and Urey’s experiments, laboratory analogues of the
primeval Earth have produced
– All 20 amino acids
– Several sugars
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Stage 2: Abiotic Synthesis of Polymers
• Researchers have brought about the polymerization of monomers
to form polymers, such as proteins and nucleic acids, by dripping
solutions of organic monomers onto
– Hot sand
– Clay
– Rock
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Stage 3: Formation of Pre-Cells
• A key step in the origin of life was the isolation of a collection of
abiotically created molecules within a membrane.
• Laboratory experiments demonstrate that pre-cells could have
formed spontaneously from abiotically produced organic
compounds.
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• Such pre-cells produced in the laboratory display some lifelike
properties. They:
– Have a selectively permeable surface
– Can grow by absorbing molecules from their surroundings
– Swell or shrink when placed in solutions of different salt concentrations
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Stage 4: Origin of Self-Replicating Molecules
• Life is defined partly by the process of inheritance, which is based
on self-replicating molecules.
• One hypothesis is that the first genes were short strands of RNA
that replicated themselves without the assistance of proteins,
perhaps using RNAs that can act as enzymes, called ribozymes.
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Original “gene”
Complementary
RNA chain
Figure 15.5
From Chemical Evolution to Darwinian Evolution
• Over millions of years
– Natural selection favored the most efficient pre-cells
– The first prokaryotic cells evolved
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PROKARYOTES
• Prokaryotes lived and evolved all alone on Earth for 2 billion
years before eukaryotes evolved.
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They’re Everywhere!
• Prokaryotes
– Are found wherever there is life
– Far outnumber eukaryotes
– Can cause disease
– Can be beneficial
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• 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.
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• Compared to eukaryotes, prokaryotes are
– Much more abundant
– Typically much smaller
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Figure 15.7
Colorized SEM
• Prokaryotes
– Are ecologically significant, recycling carbon and other vital chemical
elements back and forth between organic matter, the soil, and atmosphere
– Cause about half of all human diseases
– Are more typically benign or beneficial
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The Structure and Function of Prokaryotes
• Prokaryotic cells
– Lack true nuclei
– Lack other membrane-enclosed organelles
– Have cell walls exterior to their plasma membranes
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Plasma membrane
(encloses cytoplasm)
Cell wall (provides
Rigidity)
Capsule (sticky
coating)
Colorized TEM
Prokaryotic
flagellum
(for propulsion)
Ribosomes
(synthesize
proteins)
Nucleoid
(contains DNA)
Pili (attachment structures)
Figure 4.4
Ribosomes
Cytoskeleton
Centriole
Lysosome
Flagellum
Not in most
plant cells
Plasma
membrane
Nucleus
Mitochondrion
Rough
endoplasmic
reticulum (ER)
Golgi
apparatus
Cytoskeleton
Mitochondrion
Nucleus
Rough endoplasmic
reticulum (ER)
Idealized animal cell
Smooth
endoplasmic
reticulum (ER)
Central
vacuole
Cell wall
Not in animal cells
Chloroplast
Ribosomes
Plasma
membrane
Smooth
endoplasmic
reticulum (ER)
Channels between
cells
Idealized plant cell
Golgi apparatus
Figure 4.5
Procaryotic Forms
• Prokaryotes come in several shapes:
– Spherical (cocci)
– Rod-shaped (bacilli)
– Spiral
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SHAPES OF PROKARYOTIC CELLS
Colorized TEM
Spiral
Colorized SEM
Rod-shaped (bacilli)
Colorized SEM
Spherical (cocci)
Figure 15.8
• Most prokaryotes are
– Unicellular
– Very small
• Some prokaryotes
– Form true colonies
– Show specialization of cells
– Are very large
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(b) Cyanobacteria
LM
LM
Colorized SEM
(a) Actinomycete
(c) Giant bacterium
Figure 15.9
• About half of all prokaryotes are mobile, using flagella.
• Many have one or more flagella that propel the cells away from
unfavorable places or toward more favorable places, such as
nutrient-rich locales.
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Colorized TEM
Flagellum
Plasma
membrane
Cell wall
Rotary movement of
each flagellum
Figure 15.10
Procaryotic Reproduction
• Most prokaryotes can reproduce by binary fission and at very
high rates if conditions are favorable.
• Some prokaryotes
– Form endospores, thick-coated, protective cells that are produced within
the cells when they are exposed to unfavorable conditions
– Can survive very harsh conditions for extended periods, even centuries
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Colorized SEM
Endospore
Figure 15.11
Procaryotic Nutrition
• Prokaryotes exhibit four major modes of nutrition.
– Phototrophs obtain energy from light.
– Chemotrophs obtain energy from environmental chemicals.
– Species that obtain carbon from carbon dioxide (CO2) are autotrophs.
– Species that obtain carbon from at least one organic nutrient—the sugar
glucose, for instance—are called heterotrophs.
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• We can group all organisms according to the four major modes of
nutrition if we combine the
– Energy source (phototroph versus chemotroph) and
– Carbon source (autotroph versus heterotroph)
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MODES OF NUTRITION
Energy source
Chemical
Photoautotrophs
Colorized TEM
Light
Elodea, an aquatic plant
Bacteria from a hot spring
Colorized TEM
Photoheterotrophs
Organic compounds
Carbon source
CO2
Chemoautotrophs
Rhodopseudomonas
Chemoheterotrophs
Little Owl (Athene noctua)
Figure 15.12
The Two Main Branches of Prokaryotic
Evolution: Bacteria and Archaea
• By comparing diverse prokaryotes at the molecular level,
biologists have identified two major branches of prokaryotic
evolution:
– Bacteria
– Archaea (more closely related to eukaryotes)
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• Some archaea are “extremophiles.”
– Halophiles thrive in salty environments.
– Thermophiles inhabit very hot water.
– Methanogens inhabit the bottoms of lakes and swamps and aid digestion
in cattle and deer.
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(a) Salt-loving archaea
(b) Heat-loving archaea
Figure 15.13
Bacteria and Humans
• Bacteria interact with humans in many ways.
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Bacteria That Cause Disease
• Bacteria and other organisms that cause disease are called
pathogens.
• Most pathogenic bacteria produce poisons.
– Exotoxins are poisonous proteins secreted by bacterial cells.
– Endotoxins are not cell secretions but instead chemical components of
the outer membrane of certain bacteria.
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Colorized SEM
Haemophilus
influenzae
Cells of nasal
lining
Figure 15.14
• The best defenses against bacterial disease are
– Sanitation
– Antibiotics
– Education
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• Lyme disease is
– Caused by bacteria carried by ticks
– Treated with antibiotics, if detected early
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SEM
Tick that carries the
Lyme disease bacterium
“Bull’s-eye” rash
Spirochete that causes
Lyme disease
Figure 15.15
Bioterrorism
• Humans have a long and ugly history of using organisms as
weapons.
–
During the Middle Ages, armies hurled the bodies of plague victims
into enemy ranks.
–
Early conquerors, settlers, and warring armies in South and North
America gave native peoples items purposely contaminated with
infectious bacteria.
–
In 1984, members of a cult in Oregon contaminated restaurant salad
bars with Salmonella bacteria.
–
In the fall of 2001, five Americans died from the disease anthrax in a
presumed terrorist attack.
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Figure 15.16
The Ecological Impact of Prokaryotes
• Pathogenic bacteria are in the minority among prokaryotes.
• Far more common are species that are essential to our well-being,
either directly or indirectly.
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Prokaryotes and Chemical Recycling
• Prokaryotes play essential roles in
– Chemical cycles in the environment
– The breakdown of organic wastes and dead organisms
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Prokaryotes and Bioremediation
• Bioremediation is the use of organisms to remove pollutants
from
– Water
– Air
– Soil
• A familiar example is the use of prokaryotic decomposers in
sewage treatment.
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Rotating
spray arm
Rock bed coated
with aerobic
prokaryotes and
fungi
Liquid wastes
Outflow
Figure 15.17
• Certain bacteria
– Can decompose petroleum
– Are useful in cleaning up oil spills
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Figure 15.18
PROTISTS
• Protists
– Are eukaryotic
– Evolved from prokaryotic ancestors
– Are ancestral to all other eukaryotes, which are
–
Plants
–
Fungi
–
Animals
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Figure 15.19
The Origin of Eukaryotic Cells
• Eukaryotic cells evolved by
– The infolding of the plasma membrane of a prokaryotic cell to form the
endomembrane system and
– Endosymbiosis, one species living inside another host species, in which
free-living bacteria came to reside inside a host cell, producing
mitochondria and chloroplasts
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Plasma
membrane
Photosynthetic
prokaryote
DNA
Cytoplasm
Membrane
infolding
(Some cells)
Endosymbiosis
Endoplasmic
reticulum
Nucleus
Ancestral
prokaryote
Aerobic
heterotrophic
prokaryote
Chloroplast
Mitochondrion
Nuclear
envelope
Photosynthetic
eukaryotic cell
Cell with nucleus and
endomembrane system
(a) Origin of the endomembrane system
(b) Origin of mitochondria and chloroplasts
Figure 15.20
The Diversity of Protists
• Protists can be
– Unicellular
– Multicellular
• More than any other group, protists vary in
– Structure
– Function
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• Protists are not one distinct group but instead represent all the
eukaryotes that are not plants, animals, or fungi.
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• The classification of protists remains a work in progress.
• The four major categories of protists, grouped by lifestyle, are
– Protozoans
– Slime molds
– Unicellular algae
– Seaweeds
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Protozoans
• Protists that live primarily by ingesting food are called
protozoans.
• Protozoans with flagella are called flagellates and are typically
free-living, but sometimes are nasty parasites.
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Colorized SEM
A flagellate: Giardia
Figure 15.21a
Colorized SEM
Another flagellate: trypanosomes
Figure 15.21b
• Amoebas are characterized by
– Great flexibility in their body shape
– The absence of permanent organelles for locomotion
• Most species move and feed by means of pseudopodia (singular,
pseudopodium), temporary extensions of the cell.
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• Amoebas may have a shell, as seen in forams, or no shell at all.
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LM
An amoeba
Figure 15.21c
LM
A foram
Figure 15.21d
• Apicomplexans are
– Named for a structure at their apex (tip) that is specialized for penetrating
host cells and tissues
– All parasitic, such as Plasmodium, which causes malaria
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TEM
An apicomplexan
Figure 15.21e
• Ciliates
– Are mostly free-living (nonparasitic), such as the freshwater ciliate
Paramecium
– Use structures called cilia to move and feed
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LM
A ciliate
Figure 15.21f
LM
Colorized SEM
A flagellate: Giardia
An amoeba
Another flagellate: trypanosomes
Cilia
An apicomplexan
LM
Red
blood
cell
Oral
groove
TEM
LM
Apical complex
A foram
Pseudopodium
of amoeba
Colorized SEM
Food being
ingested
A ciliate
Figure 15.21
Slime Molds
• Slime molds resemble fungi in appearance and lifestyle, but the
similarities are due to convergence, and slime molds are not at all
closely related to fungi.
• The two main groups of these protists are
– Plasmodial slime molds
– Cellular slime molds
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• Plasmodial slime molds
– Can be large
– Are decomposers on forest floors
– Are named for the feeding stage in their life cycle, an amoeboid mass
called a plasmodium
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Figure 15.22
• Cellular slime molds have an interesting and complex life cycle
that changes between a
– Feeding stage of solitary amoeboid cells
– Sluglike colony that moves and functions as a single unit
– Stalklike reproductive structure
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LM
Slug-like colony
Amoeboid
cells
Reproductive
structure
Figure 15.23
Unicellular and Colonial Algae
• Algae are
– Photosynthetic protists
– Found in plankton, the communities of mostly microscopic organisms
that drift or swim weakly in aquatic environments
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• Unicellular algae include
– Diatoms, which have glassy cell walls containing silica
– Dinoflagellates, with two beating flagella and external plates made of
cellulose
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SEM
(a) A dinoflagellate, with its wall of protective plates
Figure 15.24a
LM
(b) A sample of diverse diatoms, which have glossy walls
Figure 15.24b
• Green algae are
– Unicellular
– Sometimes flagellated, such as Chlamydomonas
– Colonial, sometimes forming a hollow ball of flagellated cells, as seen in
Volvox
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Colorized SEM
(c) Chlamydomonas, a unicellular green alga with a pair of flagella
Figure 15.24c
LM
(d) Volvox, a colonial green alga
Figure 15.24d
Seaweeds
• Seaweeds
– Are only similar to plants because of convergent evolution
– Are large, multicellular marine algae
– Grow on or near rocky shores
– Are often edible
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• Seaweeds are classified into three different groups, based partly
on the types of pigments present in their chloroplasts:
– Green algae
– Red algae
– Brown algae (including kelp)
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Green algae
Red algae
Brown algae
Figure 15.25
Evolution Connection:
The Origin of Multicellular Life
• Multicellular organisms have interdependent, specialized cells
that perform different functions, such as feeding, waste disposal,
gas exchange, and protection—and are dependent on each other.
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• Colonial protists likely formed the evolutionary links between
unicellular and multicellular organisms.
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Unicellular
protist
Gamete
Locomotor
cells
Food-synthesizing
cells
Somatic
cells
Colony
Early multicellular organism
with specialized, interdependent cells
Later organism with
gametes and somatic cells
Figure 15.26-3