Chapter 15
The Evolution of Microbial Life
Laura Coronado
Bio 10
Chapter 15
Biology and Society:
Can Life Be Created in the Lab?
– A research group led by Craig Venter
• 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
– 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
Laura Coronado
Bio 10
Chapter 15
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
– Single-celled eukaryotes first evolved about 2.1 billion
years ago.
– Multicellular eukaryotes first evolved at least 1.2 billion
years ago.
Laura Coronado
Bio 10
Chapter 15
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
Laura Coronado
Bio 10
Atmospheric oxygen
begins to appear due
to photosynthetic
prokaryotes
3,000
Chapter 15
2,500
Figure 15.1a
Paleozoic
Mesozoic
Cenozoic
Archaea
Prokaryotes
Bacteria
Protists
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
Laura Coronado
Extinction of
dinosaurs
500
Bio 10
Chapter 15
First humans
0
Figure 15.1b
Eukaryotes
Plants
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
Laura Coronado
Bio 10
Chapter 15
Figure 15.UN03
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
• Were followed by amphibians that evolved from fish
– What if we use a clock analogy to tick down all of the
major events in the history of life on Earth?
Laura Coronado
Bio 10
Chapter 15
Humans
Origin of solar
system and Earth
0
4
1
2
Laura Coronado
3
Bio 10
Chapter 15
Figure 15.2
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.
– Today, most biologists think it is possible that life
on early Earth produced simple cells by chemical
and physical processes.
Laura Coronado
Bio 10
Chapter 15
Laura Coronado
Bio 10
Chapter 15
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.
– 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.
Laura Coronado
Bio 10
Chapter 15
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?
– 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.
Laura Coronado
Bio 10
Chapter 15
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 were 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”
Laura Coronado
Bio 10
Chapter 15
“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
Laura Coronado
Bio 10
Chapter 15
Figure 15.4
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.
– Since Miller and Urey’s experiments, laboratory
analogues of the primeval Earth have produced
• All 20 amino acids
• Several sugars
Laura Coronado
Bio 10
Chapter 15
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
Laura Coronado
Bio 10
Chapter 15
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.
– 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
Laura Coronado
Bio 10
Chapter 15
Inorganic compounds
Abiotic synthesis
of organic monomers
Organic monomers
Abiotic synthesis
of polymers
Polymer
Formation
of pre-cells
Membrane-enclosed compartment
Self-replicating
molecules
Complementary
chain
Laura Coronado
Bio 10
Chapter 15
Figure 15.UN04
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.
Laura Coronado
Bio 10
Chapter 15
Original “gene”
Complementary
RNA chain
Laura Coronado
Bio 10
Chapter 15
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
– Prokaryotes lived and evolved all alone on Earth for 2
billion years before eukaryotes evolved.
•
•
•
•
Are found wherever there is life
Far outnumber eukaryotes
Can cause disease
Can be beneficial
– 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.
Laura Coronado
Bio 10
Chapter 15
Laura Coronado
Bio 10
Chapter 15
Figure 15.6
Prokaryotes
– Compared to eukaryotes, prokaryotes are
• Much more abundant
• Typically much smaller
– 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
Laura Coronado
Bio 10
Chapter 15
Colorized SEM
Laura Coronado
Bio 10
Chapter 15
Figure 15.7
The Structure and Function of Prokaryotes
– Prokaryotic cells
• Lack true nuclei
• Lack other membrane-enclosed organelles
• Have cell walls exterior to their plasma
membranes
– Prokaryotes come in several shapes:
• Spherical (cocci)
• Rod-shaped (bacilli)
• Spiral
– Most prokaryotes are unicellular & very small
Laura Coronado
Bio 10
Chapter 15
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)
Laura Coronado
Bio 10
Chapter 15
Figure 4.4
Ribosomes
Centriole
Lysosome
Flagellum
Cytoskeleton
Not in most
plant cells
Plasma
membrane
Nucleus
Mitochondrion
Rough
endoplasmic
reticulum (ER)
Golgi
apparatus
Idealized animal cell
Cytoskeleton
Smooth
endoplasmic
reticulum (ER)
Central
vacuole
Mitochondrion
Nucleus
Not in animal cells
Cell wall
Rough endoplasmic
reticulum (ER)
Chloroplast
Ribosomes
Plasma
membrane
Smooth
endoplasmic
reticulum (ER)
Channels between
cells
Idealized plant cell
Laura Coronado
Golgi apparatus
Bio 10
Chapter 15
Figure 4.5
SHAPES OF PROKARYOTIC CELLS
Colorized TEM
Spiral
Colorized SEM
Rod-shaped (bacilli)
Colorized SEM
Spherical (cocci)
Laura Coronado
Bio 10
Chapter 15
Figure 15.8
(b) Cyanobacteria
Laura Coronado
Bio 10
Chapter 15
LM
LM
Colorized SEM
(a) Actinomycete
(c) Giant bacterium
Figure 15.9
The Structure and Function of
Prokaryotes
– Some prokaryotes
• Form true colonies
• Show specialization of cells
• Are very large
– 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.
Laura Coronado
Bio 10
Chapter 15
Colorized TEM
Flagellum
Plasma
membrane
Cell wall
Laura Coronado
Rotary movement of
each
flagellum
Bio 10
Chapter
15
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
Laura Coronado
Bio 10
Chapter 15
Colorized SEM
Endospore
Laura Coronado
Bio 10
Chapter 15
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.
– 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)
Laura Coronado
Bio 10
Chapter 15
Nutritional Mode
Energy Source
Photoautotroph
Sunlight
Chemoautotroph
Inorganic chemicals
Photoheterotroph
Sunlight
Carbon Source
CO2
Organic compounds
Chemoheterotroph
Organic compounds
Laura Coronado
Bio 10
Chapter 15
Figure 15.UN06
MODES OF NUTRITION
Energy source
Light
Chemical
Photoautotrophs
Elodea, an aquatic plant
Bacteria from a hot spring
Colorized TEM
Photoheterotrophs
Organic compounds
Carbon source
CO2
Colorized TEM
Chemoautotrophs
Chemoheterotrophs
Rhodopseudomonas
Laura Coronado
Little Owl (Athene noctua)
Bio 10
Chapter 15
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)
– 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.
Laura Coronado
Bio 10
Chapter 15
(a) Salt-loving archaea
(b) Heat-loving archaea
Laura Coronado
Bio 10
Chapter 15
Figure 15.13
Bacteria and Humans
– Bacteria interact with humans in many ways.
– 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.
Laura Coronado
Bio 10
Chapter 15
Colorized SEM
Haemophilus
influenzae
Laura Coronado Bio 10 Chapter 15
Cells of nasal
lining
Figure 15.14
– The best defenses against bacterial disease are
• Education
• Sanitation
• Antibiotics
Laura Coronado
Bio 10
Chapter 15
SEM
Tick that carries the
Lyme disease bacterium
“Bull’s-eye” rash
Laura Coronado
Bio 10
Chapter 15
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.
Laura Coronado
Bio 10
Chapter 15
Laura Coronado
Bio 10
Chapter 15
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.
– Prokaryotes play essential roles in
• Chemical cycles in the environment
• The breakdown of organic wastes and dead organisms
– Prokaryotes are used Bioremediation is the use of
organisms to remove pollutants from
•
•
•
•
Water
Air
Soil
Decomposers in sewage treatment & petroleum spills.
Laura Coronado
Bio 10
Chapter 15
Rotating
spray arm
Rock bed coated
with aerobic
prokaryotes and
fungi
Outflow
Liquid wastes
Laura Coronado
Bio 10
Chapter 15
Figure 15.17
Laura Coronado
Bio 10
Chapter 15
Figure 15.18
PROTISTS
• Protists
– Are eukaryotic
– Evolved from
prokaryotic ancestors
– Are ancestral to all
other eukaryotes
• Plants
• Fungi
• Animals
Laura Coronado
Bio 10
Chapter 15
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
Laura Coronado
Bio 10
Chapter 15
Plasma
membrane
Photosynthetic
prokaryote
DNA
Cytoplasm
Membrane
infolding
(Some cells)
Endosymbiosis
Aerobic
heterotrophic
prokaryote
Endoplasmic
reticulum
Nucleus
Ancestral
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
Laura Coronado
Bio 10
Chapter 15
Figure 15.20
The Diversity of Protists
– Protists are not one distinct group but instead
represent all the eukaryotes that are not plants,
animals, or fungi.
– Protists can be
• Unicellular
• Multicellular
– More than any other group, protists vary in
• Structure
• Function
Laura Coronado
Bio 10
Chapter 15
Protists Classification
– 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
Laura Coronado
Bio 10
Chapter 15
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.
• 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.
• Amoebas may have a shell, as seen in forams, or no shell at
all.
Laura Coronado
Bio 10
Chapter 15
Protozoans
– 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
– Ciliates
• Are mostly free-living (nonparasitic), such as the freshwater
ciliate Paramecium
• Use structures called cilia to move and feed
Laura Coronado
Bio 10
Chapter 15
LM
Colorized SEM
A flagellate: Giardia
An amoeba
Another flagellate: trypanosomes
Cilia
Oral
groove
Red
blood
cell
A ciliate
An apicomplexan
Laura Coronado
Bio 10
LM
TEM
LM
Apical complex
A foram
Pseudopodium
of amoeba
Colorized SEM
Food being
ingested
Chapter 15
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
Laura Coronado
Bio 10
Chapter 15
Slime Molds
– 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
– 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
Laura Coronado
Bio 10
Chapter 15
Laura Coronado
Bio 10
Chapter 15
Figure 15.22
LM
Slug-like colony
Amoeboid
cells
Reproductive
structure
Laura Coronado
Bio 10
Chapter 15
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
– Unicellular algae include
• Diatoms, which have glassy cell walls containing
silica
• Dinoflagellates, with two beating flagella and
external plates made of cellulose
Laura Coronado
Bio 10
Chapter 15
Green Algae
– Green algae are
• Unicellular
• Sometimes flagellated, such as Chlamydomonas
• Colonial, sometimes forming a hollow ball of flagellated
cells, as seen in Volvox
Laura Coronado
Bio 10
Chapter 15
LM
SEM
(b) A sample of diverse diatoms,
which have glossy walls
(c) Chlamydomonas, a unicellular
green alga with a pair of flagellaLaura Coronado
LM
Colorized SEM
(a) A dinoflagellate, with its wall
of protective plates
(d) Volvox, a colonial green alga
Bio 10
Chapter 15
Figure 15.24
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
– 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)
Laura Coronado
Bio 10
Chapter 15
Green algae
Red algae
Laura Coronado
Brown algae
Bio 10
Chapter 15
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.
– Colonial protists likely formed the evolutionary links
between unicellular and multicellular organisms.
Laura Coronado
Bio 10
Chapter 15
Unicellular
protist
Gamete
Somatic
cells
Food-synthesizing
cells
Locomotor
cells
Colony
Early multicellular organism
with specialized, interdependent cells
Laura Coronado
Bio 10
Chapter 15
Later organism with
gametes and somatic cells
Figure 15.26-3