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Chapter 15
The Evolution of Microbial Life
PowerPoint® Lectures for
Campbell Essential Biology, Fifth Edition, and
Campbell Essential Biology with Physiology,
Fourth Edition
– Eric J. Simon, Jean L. Dickey, and Jane B. Reece
Lectures by Edward J. Zalisko
© 2013 Pearson Education, Inc.
Biology and Society:
Has Life Been Created in the Lab?
• How did life first arise on Earth?
• To gain insight, scientists have
– synthesized from scratch the entire genome of a
small bacterium known as Mycoplasma mycoides
and
– transplanted the artificial genome into the cells of a
closely related species called Mycoplasma
capricolum.
© 2013 Pearson Education, Inc.
Figure 15.0
Biology and Society:
Has Life Been Created in the Lab?
• The newly installed genome
– took over the recipient cells,
– began cranking out M. mycoides proteins, and
– reproduced to make more cells containing the
synthetic M. mycoides genome.
© 2013 Pearson Education, Inc.
MAJOR EPISODES IN THE HISTORY OF
LIFE
• Earth was formed about 4.6 billion years ago.
• Prokaryotes
– evolved by about 3.5 billion years ago,
– began oxygen production about 2.7 billion years
ago,
– lived alone for more than a billion years, and
– continue in great abundance today.
© 2013 Pearson Education, Inc.
MAJOR EPISODES IN THE HISTORY OF
LIFE
• 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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Figure 15.1a
Precambrian
Ancestor to
all present-day life
Origin of
Earth
4,500
Earth’s crust
solidifies
4,000
Oldest
prokaryotic fossils
3,500
Millions of years ago
3,000
Atmospheric
oxygen begins
to appear
2,500
Figure 15.1b
Precambrian
Oldest eukaryotic
fossils
2,000
Origin of
multicellular
organisms
1,500
Millions of years ago
Oldest
animal
fossils
1,000
Figure 15.1c
Paleozoic Meso- Cenozoic
zoic
Bacteria
Archaea
Fungi
Animals
Cambrian explosion
Oldest animal
fossils
1,000
Extinction of
Plants
colonize land dinosaurs
First humans
500
Millions of years ago
0
Eukaryotes
Protists
Plants
Prokaryotes
Precambrian
MAJOR EPISODES IN THE HISTORY OF
LIFE
• 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 ago
and
– were followed by amphibians that evolved from
fish.
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MAJOR EPISODES IN THE HISTORY OF
LIFE
• 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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Figure 15.2
Humans
Origin of solar
system and Earth
0
1
4
2
3
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 1800s, it was commonly believed that life
regularly arises from nonliving matter, an idea
called spontaneous generation.
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Resolving the Biogenesis Paradox
• Today, most biologists think it is possible that life
on early Earth evolved from simple cells produced
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 was the first to
be extensively studied 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 early Earth.
• Question: Could biological molecules arise
spontaneously under conditions like those on
early Earth?
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The Process of Science:
Can Biological Monomers Form Spontaneously?
• Hypothesis: A closed system designed 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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The Process of Science:
Can Biological Monomers Form Spontaneously?
• 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 that were discharged into the chamber to
mimic the prevalent lightning of early Earth, and
– a condenser that cooled the atmosphere, causing
water and dissolved compounds to “rain” into the
miniature “sea.”
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Figure 15.4
“Atmosphere”
CH4
Water vapor
NH3
H2
Electrode
Condenser
Cold water
Cooled water
containing organic
molecules
H2O
“Sea”
Sample for
chemical analysis
Miller and Urey’s experiment
The Process of Science:
Can Biological Monomers Form Spontaneously?
• 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.
• These laboratory experiments
– have been repeated and extended by other
scientists and
– support the idea that organic molecules could have
arisen abiotically on early Earth.
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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, or
– 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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Stage 3: Formation of Pre-Cells
• 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, and
– 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.
© 2013 Pearson Education, Inc.
Figure 15.5-4
Original
“gene”
RNA
monomers
Formation of
short RNA
polymers:
simple “genes”
Assembly of a
complementary
RNA chain
The
complementary
chain serves as
a template of the
original “gene.”
From Chemical Evolution to Darwinian Evolution
• Over millions of years
– natural selection favored the most efficient precells and
– the first prokaryotic cells evolved.
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PROKARYOTES
• Prokaryotes lived and evolved all alone
on Earth for about 2 billion years.
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They’re Everywhere!
• Prokaryotes
– are found wherever there is life,
– have a collective biomass that is at least ten times
that of all eukaryotes,
– thrive in habitats too cold, too hot, too salty, too
acidic, or too alkaline for any eukaryote,
– cause about half of all human diseases, and
– are more commonly benign or beneficial.
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Figure 15.6
They’re Everywhere!
• Compared to eukaryotes, prokaryotes are
– much more abundant and
– typically much smaller.
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Colorized SEM
Figure 15.7
They’re Everywhere!
• Prokaryotes living in soil and at the bottom of
lakes, rivers, and oceans help to decompose
dead organisms and other organic waste
material, returning vital chemical elements to
the environment.
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The Structure and Function of Prokaryotes
• Prokaryotic cells
– lack a membrane-enclosed nucleus,
– lack other membrane-enclosed organelles,
– typically have cell walls exterior to their plasma
membranes, but
– display an enormous range of diversity.
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Figure 4.4
Plasma membrane
Cell wall
Capsule
Prokaryotic
flagellum
Ribosomes
Nucleoid
Colorized TEM
Pili
Figure 4.5
Ribosomes
Cytoskeleton
Not in most
plant cells
Centriole
Lysosome
Plasma
membrane
Nucleus
Mitochondrion
Rough endoplasmic
reticulum (ER)
Smooth
endoplasmic
reticulum (ER)
Golgi apparatus
Idealized animal cell
Cytoskeleton
Mitochondrion
Central vacuole
Cell wall
Chloroplast
Nucleus
Not in animal cells
Rough endoplasmic
reticulum (ER)
Ribosomes
Plasma
membrane
Smooth
endoplasmic
reticulum (ER)
Idealized plant cell
Channels between cells
Golgi apparatus
Prokaryotic Forms
• The three most common shapes of prokaryotes
are
1. spherical (cocci),
2. rod-shaped (bacilli), and
3. spiral or curved.
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Figure 15.8
SHAPES OF PROKARYOTIC CELLS
Rod-shaped (bacilli)
Colorized TEM
Spiral
Colorized SEM
Colorized SEM
Spherical (cocci)
Prokaryotic Forms
• All prokaryotes are unicellular.
• Some species
– exist as groups of two or more cells,
– exhibit a simple division of labor among specialized
cell types, or
– are very large, dwarfing most eukaryotic cells.
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Colorized SEM
Figure 15.9
LM
LM
(a) Actinomycete
(b) Cyanobacteria
(c) Giant bacterium
LM
Figure 15.9c
(c) Giant bacterium
Prokaryotic Forms
• About half of all prokaryotes are mobile, and many
of these travel using one or more flagella.
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Prokaryotic Forms
• In many natural environments, prokaryotes attach
to surfaces in a highly organized colony called a
biofilm, which
– may consist of one or several species of
prokaryotes,
– may include protists and fungi,
– can show a division of labor and defense against
invaders, and
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Prokaryotic Forms
– can form on almost any type of surface, including
– rocks,
– metal,
– plastic, and
– organic material including teeth.
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Colorized SEM
Figure 15.10
Prokaryotic Reproduction
• Most prokaryotes can reproduce
– by dividing in half by binary fission and
– at very high rates if conditions are favorable.
• Some prokaryotes form endospores, which are
– thick-coated, protective cells
– produced when the prokaryote is exposed to
unfavorable conditions.
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Figure 15.11
Colorized TEM
Endospore
Prokaryotic Nutrition
• Biologists use the phrase “mode of nutrition” to
describe how organisms obtain energy and
carbon.
– Energy
– Phototrophs obtain energy from light.
– Chemotrophs obtain energy from environmental
chemicals.
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Prokaryotic Nutrition
– Carbon
– Autotrophs obtain carbon from carbon dioxide
(CO2).
– Heterotrophs obtain carbon from at least one
organic nutrient—the sugar glucose, for instance.
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Prokaryotic Nutrition
• 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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Prokaryotic Nutrition
• Dominant among multicellular organisms are
– photoautotrophs and
– chemoheterotrophs.
• The other two modes are used only by certain
prokaryotes.
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Figure 15.12
MODES OF NUTRITION
Energy source
Chemical
Photoautotrophs
Chemoautotrophs
Elodea, an aquatic plant
Photoheterotrophs
Bacteria from a hot spring
Chemoheterotrophs
Colorized TEM
Organic compounds
Carbon source
CO2
Colorized TEM
Light
Rhodopseudomonas
Kingfisher with prey
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:
1. bacteria and
2. archaea (more closely related to eukaryotes).
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The Two Main Branches of Prokaryotic Evolution:
Bacteria and Archaea
• Thus, life is organized into three domains:
1. Bacteria,
2. Archaea, and
3. Eukarya.
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The Two Main Branches of Prokaryotic Evolution:
Bacteria and Archaea
• 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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Figure 15.13
(a) Salt-loving archaea
(b) Heat-loving archaea
Bacteria and Disease
Bacteria That Cause Disease
• Bacteria and other organisms that cause disease
are called pathogens.
• Most pathogenic bacteria produce poisons.
– Exotoxins are proteins bacterial cells secrete into
their environment.
– Endotoxins are
– not cell secretions but instead
– chemical components of the outer membrane of
certain bacteria.
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Colorized SEM
Figure 15.14
Haemophilus
influenzae
Cells of nasal
lining
Bacteria That Cause Disease
• The best defenses against bacterial disease are
– sanitation,
– antibiotics, and
– education.
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Bacteria That Cause Disease
• Lyme disease is
– caused by bacteria carried by ticks and
– treated with antibiotics, if detected early.
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SEM
Figure 15.15
Tick that carries
the Lyme disease
bacterium
“Bull’s-eye” rash
Spirochete that causes
Lyme disease
Figure 15.15a
“Bull’s-eye” rash
Figure 15.15b
Tick that carries the
Lyme disease
bacterium
Figure 15.15c
Tick that carries the Lyme
disease bacterium
SEM
Figure 15.15d
Spirochete that causes
Lyme disease
Biological Weapons
• In October 2001, endospores of the bacterium that
causes anthrax were mailed to members of the
news media and the U.S. Senate.
• Five people died from this attack.
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Biological Weapons
• Another bacterium considered to have
dangerous potential as a weapon is Clostridium
botulinum, producer of the exotoxin botulinum,
which
– blocks transmission of nerve signals that cause
muscle contraction and
– is the deadliest poison on Earth.
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Biological Weapons
• The bacterium that causes plague
– is also a potential biological weapon,
– is carried by rodents, and transmitted by fleas,
– produces egg-size swellings called buboes
under the skin, and
– can be treated with antibiotics if diagnosed early.
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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 and
– 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, and
– soil.
• A familiar example is the use of prokaryotic
decomposers in sewage treatment.
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Figure 15.17
Rotating arm spraying
liquid wastes
Rock bed coated
with aerobic
prokaryotes and
fungi
Liquid wastes
Outflow
Prokaryotes and Bioremediation
• Certain bacteria
– can decompose petroleum and
– are useful in cleaning up oil spills.
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Figure 15.18
PROTISTS
• Protists are
– eukaryotes that are not fungi, animals, or plants,
– mostly unicellular, and
– ancestral to all other eukaryotes.
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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
– a process known as endosymbiosis.
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The Origin of Eukaryotic Cells
• Symbiosis is a more general association between
organisms of two or more species.
• Endosymbiosis
– refers to one species living inside another host
species and
– is the process by which eukaryotes gained
mitochondria and chloroplasts.
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Figure 15.19
Plasma membrane
DNA
Cytoplasm
Membrane
infolding
Endoplasmic
reticulum
Nucleus
Ancestral
prokaryote
Nuclear
envelope
Cell with nucleus and
endomembrane system
(a) Origin of the endomembrane system
Photosynthetic
prokaryote
Endosymbiosis
Aerobic
heterotrophic
prokaryote
Chloroplast
Mitochondrion
Photosynthetic
eukaryotic cell
(b) Origin of mitochondria and chloroplasts
The Diversity of Protists
• The group called protists
– consists of multiple clades but
– remains a convenient term to refer to eukaryotes
that are not plants, animals, or fungi.
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The Diversity of Protists
• Protists obtain their nutrition in a variety of ways.
– Algae are autotrophs, producing their food by
photosynthesis.
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The Diversity of Protists
– Other protists are heterotrophs.
– Some protists eat bacteria or other protists.
– Other protists are fungus-like and obtain organic
molecules by absorption.
– Parasites derive their nutrition from a living host,
which is harmed by the interaction. Parasitic
trypanosomes infect blood and cause sleeping
sickness.
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(a) An autotroph: Caulerpa,
a multicellular alga
(b) A heterotroph: parasitic
trypanosome
LM
Colorized SEM
Figure 15.20
(c) A mixotroph: Euglena
The Diversity of Protists
• Protist habitats are diverse and include
– oceans, lakes, and ponds,
– damp soil and leaf litter, and
– the bodies of host organisms with which they share
mutually beneficial relationships, such as
– unicellular algae and reef-building coral animals,
and
– cellulose-digesting protists and termites.
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Figure 15.21
LM
Protozoans
• Protists that live primarily by ingesting food are
called protozoans.
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Another flagellate: Trichomonas
A foram
Red
blood
cell
An apicomplexan
Colorized TEM
Cilia
Cell
“mouth”
TEM
LM
Apical complex
An amoeba
A ciliate
LM
A flagellate: Giardia
Colorized SEM
Colorized SEM
Figure 15.22
Protozoans
• Protozoans with flagella are called flagellates and
– are typically free-living, but
– some are nasty parasites.
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Colorized SEM
Figure 15.22a
A flagellate: Giardia
Colorized SEM
Figure 15.22b
A flagellate: Trichomonas
Protozoans
• Amoebas are characterized by
– great flexibility in their body shape and
– 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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Colorized TEM
Figure 15.22c
An amoeba
Protozoans
• Other protozoans with pseudopodia include the
forams, which have shells.
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LM
Figure 15.22d
A foram
Protozoans
• Apicomplexans are
– named for a structure at their apex (tip) that is
specialized for penetrating host cells and tissues,
– all parasitic, and
– able to cause serious human diseases, such as
malaria caused by Plasmodium.
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Figure 15.22e
Red
blood
cell
An apicomplexan
TEM
Apical complex
Protozoans
• Another apicomplexan is Toxoplasma,
– occurring in the digestive tracts of millions of
people in the United States but
– held in check by the immune system.
• A woman newly infected with Toxoplasma during
pregnancy can pass the parasite to her unborn
child, who may suffer nervous system damage.
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Protozoans
• Ciliates are protozoans that
– are named for their use of hair-like structures called
cilia to move and sweep food into their mouths,
– are mostly free-living (nonparasitic), such as the
freshwater ciliate Paramecium, and
– include heterotrophs and mixotrophs.
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Figure 15.22f
Cell
“mouth”
A ciliate
LM
Cilia
Slime Molds
• Slime molds
– resemble fungi in appearance and lifestyle due to
convergence, but
– are more closely related to amoebas.
• The two main groups of these protists are
– plasmodial slime molds and
– cellular slime molds.
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Slime Molds
• Plasmodial slime molds
– are named for the feeding stage in their life cycle,
an amoeboid mass called a plasmodium,
– are decomposers on forest floors, and
– can be large.
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Figure 15.23
A plasmodial slime mold
Slime Molds
• Cellular slime molds have an interesting and
complex life cycle of successive stages:
– a feeding stage of solitary amoeboid cells,
– a swarming stage as a slug-like colony that can
move and function as a single unit, and
– a stage during which they generate a stalk-like
multicellular reproductive structure.
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Figure 15.24
LM
Life stages of a
cellular slime mold
2 Slug-like colony
1 Amoeboid
cells
3 Reproductive
structure
Unicellular and Colonial Algae
• Algae are
– photosynthetic protists whose chloroplasts support
food chains in
– freshwater and
– marine ecosystems.
• Many unicellular algae are components of
plankton, the communities of mostly microscopic
organisms that drift or swim weakly in aquatic
environments.
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Unicellular and Colonial Algae
• Unicellular algae include
– dinoflagellates, with
– two beating flagella and
– external plates made of cellulose,
– diatoms, with glassy cell walls containing silica,
and
– green algae.
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Unicellular and Colonial Algae
• Green algae are
– unicellular in most freshwater lakes and ponds,
– sometimes flagellated, such as Chlamydomonas,
and
– sometimes colonial, forming a hollow ball of
flagellated cells as seen in Volvox.
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(b) A sample of diverse diatoms,
which have glassy walls
(c) Chlamydomonas, a unicellular
green alga with a pair of flagella
LM
Colorized SEM
(a) A dinoflagellate, with its wall of
protective plates
LM
SEM
Figure 15.25
(d) Volvox, a colonial green alga
Seaweeds
• Seaweeds
– are large, multicellular marine algae,
– grow on or near rocky shores,
– are only similar to plants because of convergent
evolution,
– are most closely related to unicellular algae, and
– are often edible.
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Seaweeds
• Seaweeds are classified into three different
groups, based partly on the types of pigments
present in their chloroplasts:
1. green algae,
2. red algae, and
3. brown algae (including kelp).
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Figure 15.26
Green algae
Red algae
Brown algae
Evolution Connection:
The Origin of Multicellular Life
• Multicellular organisms have
– specialized cells that are dependent on each other
and perform different functions, such as
– feeding,
– waste disposal,
– gas exchange, and
– protection.
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Evolution Connection:
The Origin of Multicellular Life
• Colonial protists likely formed the evolutionary
links between
– unicellular and
– multicellular organisms.
• The colonial green alga Volvox demonstrates one
level of specialization and cooperation.
© 2013 Pearson Education, Inc.
Figure 15.27-3
Unicellular
protist
An ancestral
colony may have
formed when a
cell divided and
remained
attached to
its offspring.
Cells in the
colony may
have become
specialized and
interdependent.
Additional
specialization may
have led to sex cells
(gametes) and
nonreproductive
cells (somatic cells).
Foodsynthesizing
cells
Locomotor
cells
Gamete
Somatic
cells
Figure 15.UN01
Bacteria
Prokaryotes
Archaea
Protists
Eukarya
Plants
Fungi
Animals
Figure 15.UN03
Major episode
Millions of years ago
Plants and fungi colonize land
All major animal phyla established
First multicellular organisms
Oldest eukaryotic fossils
Accumulation of O2 in atmosphere
Oldest prokaryotic fossils
Origin of Earth
500
530
1,200
1,800
2,400
3,500
4,600
Figure 15.UN04
Inorganic compounds
1 Abiotic synthesis
of organic monomers
Organic monomers
2
Abiotic synthesis
of polymers
3
Formation of
pre-cells
Polymer
Membrane-enclosed compartment
4
Complementary
chain
Self-replicating
molecules
Figure 15.UN05
Spherical
Rod-shaped
Spiral
Figure 15.UN06
Nutritional Mode
Energy Source
Photoautotroph
Sunlight
Carbon Source
CO2
Chemoautotroph
Inorganic chemicals
Photoheterotroph
Sunlight
Organic compounds
Chemoheterotroph
Organic compounds