Download Figure 16.6C

Chapter 16
The Origin and Evolution of
Microbial Life: Prokaryotes
and Protists
http://genomed.dlearn.kmu.edu.tw
PowerPoint Lectures for
生物醫學暨環境生物學系
Biology: Concepts and Connections, Fifth Edition
– Campbell,
Reece, Taylor, and Simon
張學偉
助理教授
[email protected]
Lectures by Chris Romero
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How Ancient Bacteria Changed the World
• Mounds of rock found near the Bahamas
– Contain photosynthetic prokaryotes
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• Fossilized mats 2.5 billion years old mark a time
when photosynthetic prokaryotes
– Were producing enough O2 to make the
atmosphere aerobic
Stromatolites Rocklike structure composed
of many layers of bacteria
and sediments.
希臘文 Stroma- bed;
litos- rock
Layers of a bacterial mat
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EARLY EARTH AND THE ORIGIN OF LIFE
16.1 Life began on a young Earth
• 宇宙起源學說「大爆炸」- The "big bang"
- the universe is occurred sometime between 10
and 20 billion yrs ago. (wiki; 二○○六年諾貝爾物理學獎 )
• Planet Earth formed some 4.6 billion years ago
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• The first early atmosphere probably contained
- mostly hot H2 (but hard to hold)
• The secondly early atmosphere probably contained
- H2O, CO2, N2, H2S and some CH4 , NH3
•Volcanic activity, lightning, and UV radiation were
intense also in early Earth.
Figure 16.1A
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• Fossilized prokaryotes called stromatolites
– Date back 3.5 billion years (photosynthetic prok.)
Figure 16.1B
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• A clock analogy tracks the origin of the Earth to the
present day  major events and its life
補充
The geologic record is
divided into:
Three eons: Archaean,
Proterozoic, Phanerozoic
Cenozoic
Humans
Land plants
Origin of solar
system and
Earth
Animals
Many eras and periods
http://tw.knowledge.yahoo.co
m/question/?qid=12050
81201537
4
1
Proterozoic Archaean
eon
eon
Multicellular
eukaryotes
2
3
Prokaryotes
Single-celled
eukaryotes
Figure 16.1C
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Atmospheric
oxygen
Planet Earth
• formed some 4.6 billion years ago
Prokaryotes
• Appeared about 3.5 billion years ago
Oxygen production
• Began about 2.5 billion years ago
Single-celled eukaryotic organisms
• Evolved about 1.7 billion years ago
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16.2 How did life originate?
• Early - life arose spontaneously
• 1600s – large organism can’t do as early guess
• 1860s – Pasteur confirmed all life today arises
only from preexisting life. However, no deal with
the origin of life.
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•Most biologists hypothesis that the earliest life
forms evolved from nonliving matter.
•Life arose from nonorganic molecules present in
Earth’s early oceans and atmosphere.
•Organic molecules - May have been formed
abiotically in the conditions on early Earth
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TALKING ABOUT SCIENCE
16.3 Stanley Miller’s experiments showed organic
molecules could have arisen on a lifeless earth
•1920s, Oparin and Haldane - proposed that organic
chemistry could have evolved in early Earth’s
environment because it contained no oxygen (a
reducing environment).
• An oxidizing environment (e.g. Earth’s O2-rich
today) is corrosive.
• A reducing environment tends to add electrons to
molecules, building more complex forms from simple
ones.
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Figure 16.3A
(23yr-graduate student)
• In 1953, Miller tested this hypothesis using an
artificial mixture of inorganic molecules (H2O, H2,
CH4, and NH3) in a laboratory environment that
simulated conditions on early Earth.
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• Simulations of such conditions
– Have produced amino acids, sugars, lipids,
and the nitrogenous bases found in DNA and
RNA
“Atmosphere”
CH
Water vapor
4
Electrode
How about Today’s updated
Miller’s experiments? Better!
Condenser
Which
provided the
chemicals
required for
the origin of
life.
Figure 16.3B
Cold water
Cooled water
containing
organic
molecules
H2O
“Sea”
early
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Sample for
chemical analysis
16.4 The first polymers may have formed on hot
rocks or clay
• Review: polymerization occurs by dehydration synthesis.
(ch3)
• Organic polymers (e.g. proteins, nucleic acids) can make
by:
- (now) enzyme
- (early Earth)
hot clays (e- charge concentrate monomer, metallic atoms
as catalysts)
hot mineral surfaces (heat forces dehydration synthesis)
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16.5 The first genetic material and enzymes may
both have been RNA - The hypothetical period is termed
the RNA world
Ribozymes - that catalyzed their own replication
(the essential difference between cells and nonliving)
– assemble spontaneously without cells or enzymes
A
G
U
C
G
G
G
G
C
A C
G
U
G
C
A
U
U
C
A
G
G
C
U
U
G
U
U
A
C
C
A
A
U
U
A
U
A
G
U
C
G
A
Monomers Figure 16.5
U
1 Formation of short RNA
polymers: simple “genes”
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2 Assembly of a
complementary RNA
chain, the first step in
replication of the
original “gene”
16.6 Membrane-enclosed molecular cooperatives
may have preceded the first cells
RNA
Self-replication of RNA
Self-replicating RNA acts as
template on which polypeptide forms.
Polypeptide
Figure 16.6A
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Polypeptide acts as primitive
enzyme that aids RNA
replication.
• Membranes may have separated various
aggregates of self-replicating molecules
LM 650
Polypeptides and lipids selfassemble into microscopic
spheres called protobionts,
fluid-filled droplets with
semipermeable, membrane-like
coatings.
Figure 16.6B, C
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If these cooperating molecules were incorporated into
a protobiont, the basic structures for self-replicating
cells would be present.
Membrane
RNA
Which could be acted on by
natural selection
 easy for growing and
replicating
Protobiont relies in the
environment and diversity is
favored.
Figure 16.6C
Polypeptide
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PROKARYOTES
16.7 Prokaryotes have inhabited Earth for billions
of years
• Prokaryotes are the oldest life-forms
Colorized SEM 650 
– And remain the most numerous and
widespread organisms
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Size (diameters)
Prokaryotes – 1-5 mm
Eurkaryotes – 10-100 mm
pathogen
Figure 16.7.
Bacteria on the point of a pin
16.8 Bacteria and archaea are the two main
branches of prokaryotic evolution
• Domains Bacteria and Archaea
– Are distinguished on the basis of
nucleotide sequences and other molecular
and cellular features
Greek archaios, ancient
Past view – diverged from each other
Current view – see next page
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• Differences between Bacteria and Archaea
In most
features,
archaea are
more similar
to eukaryotes
than to
bacteria.
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Review:
modern
archaea and
eukaryotes
16.9 Prokaryotes come in a variety of shapes
• Prokaryotes may be shaped as
coccus
bacillus
Colorized SEM 9,000 
Curves or spirals
spirochete
Colorized SEM 3,000 
Rods (bacilli)
Colorized SEM 12,000 
Spheres (cocci)
Figure 16.9A–C
• often occur in defined
groups of two or more
•in clusters - staphylococci.
•in chains - streptococci.
•usually occur
unaggregated
•in pairs - Diplobacilli
•in chains - streptobacilli
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• commas - Vibrios
• spiral - spirilla and spirochetes.
• Spirilla are shorter than
spirochetes
16.10 Various structural features contribute to the
success of prokaryotes
One of the most important features of nearly all
prokaryotic cells- cell wall.
• maintains cell shape,
• provides physical protection
• prevents the cell from bursting in a hypotonic
environment
Plasmolysis occurs in a hypertonic environment and
prevents binary fission (reproduction). Thus, salting is a
method of preserving food.
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External Structures
Colorized TEM 70,000 
• The cell wall
– Is one of the most important features of
nearly all prokaryotes
– Is covered by a sticky capsule
Capsule
Figure 16.10A
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課本只有文字說明, 此圖補充可以涵蓋課文
Using a technique called the Gram stain
• classify bacterial species into two groups based on
cell wall composition: Gram-(+) and Gram-(-)
Lipopolysaccharide (LPS)
Cell wall
Peptidoglycan
layer
Cell wall
Outer
membrane
Peptidoglycan
layer
Plasma membrane
Plasma membrane
Protein
Protein
Grampositive
bacteria
Gramnegative
bacteria
20 mm
(b)
(a)
Gram-positive. Gram-positive bacteria have
a cell wall with a large amount of peptidoglycan
that traps the violet dye in the cytoplasm.
Figure 補充
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Gram-negative. Gram-negative bacteria have less
peptidoglycan, and it is located in a layer between the
plasma membrane and an outer membrane.
• Some prokaryotes
– Stick to their substrate with pili (fimbriae)
Pili - are protein filaments thinner than bacterial flagella
Sex pili are specialized fimbriae that are used to transfer plasmids
from one bacterial cell to another (conjugation) (Review ch10).
Figure 16.10B
Colorized TEM 16,000 
Pili
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Motility
Many bacteria and
archaea
Flagellum
Colorized TEM 14,000
--> Are equipped with
flagella, which enable
them to move
Flagella
compose
d of
Plasma
Figure 16.10C
protein in membrane
two parts:
1.
External,
nonmembr
anebounded
注意:單複數
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filaments
Cell wall
Rotary movement of
each flagellum
Reproduction and Adaptation
• Prokaryotes
– Have the potential to reproduce quickly
(several hours or less) in favorable
environments.
– Bacteria multiply by binary fission and,
under ideal conditions, divide once ever
twenty minutes.
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• Some prokaryotes can withstand harsh
conditions
– By forming endospores
Endospores are thick walls around a replicated copy of DNA
and are extremely resistant to decomposition or disintegration.
Figure 16.10D
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TEM 34,000 
Endospore
They can resist high
temperatures;
But autoclaves can kill
endospores (steam at 121oC
and 15 pounds of pressure for
15 to 20 minutes).
Internal Organization
• Some prokaryotic cells
– Have specialized membranes that perform
metabolic functions
Figure 16.10E
Thylakoid
membrane
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Aerobic
prok.
photosynthetic prok.
TEM 6,000
TEM 45,000
Respiratory
membrane
Ribosomes size:
Prok. < Euk.
containing
slightly different
proteins and
RNA.
 antibiotics that
block protein
Prokaryotic DNA
synthesis in
is smaller than
bacteria and not
eukaryotic DNA
eukaryotes.
(1/1000) and is
usually circular.
 Plasmids
16.11 Prokaryotes obtain nourishment in a variety
of ways
• As a group
– Prokaryotes exhibit much more nutritional
diversity than eukaryotes
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Types of Nutrition
Autotrophs = self-feeders
• Autotrophs make their own organic compounds
from inorganic sources & only CO2 as a carbon
source.
– Photoautotrophs harness sunlight for
energy & use CO2 for carbon
– Chemoautotrophs obtain energy from
inorganic chemicals instead of sunlight &
use CO2 for carbon
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Heterotrophs = other-feeders
• Heterotrophs obtain their carbon atoms from
organic compounds
– Photoheterotrophs can obtain energy from
sunlight
– Chemoheterotrophs are so diverse that
almost any organic molecule can serve as
food for some species. e.g. E. coli.
Figure 16.11A
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• Nutritional classification of organisms
Table 16.11
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Metabolic Cooperation
Colorized SEM 13,000 
• In some prokaryotes
– Metabolic cooperation occurs in surfacecoating colonies called biofilms
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Pearson Education,
Inc. Publishingplaque
as Benjamin Cummings
Colored
for dental
Figure 16.11B
Cells in colonies
secrete signals &
recruit nearby cells.
Internal cells use
channels for nutrient
and waste exchange.
16.12 Archaea thrive in extreme environments—
and in other habitats
• Archaea are common in: Salt lakes, acidic hot
springs, deep-sea hydrothermal vents
• Archaea are also a major life-form in the ocean
Figure 16.12A, B
Great Salt Lake
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Yellowstone National Park
•Extreme halophiles - thrive in salty places, e.g.
Great Salt Lake.
•Extreme thermophiles - thrive in hot springs,
deep-ocean vents), high-temperature, verylow-pH environments, e.g.,Yellowstone National Park.
•Methanogens - are a group of anaerobic,
methane-producing bacteria.
- production of marsh gas & flatulence in
humans.
- digest cellulose in the gut of animals.
Archaea are turning up in environments that
are not so extreme.
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16.13 Bacteria include a diverse assemblage of
prokaryotes
 Bacteria are currently organized into 9 groups:
•
•
•
•
•
Proteobacteria- 5 groups, Gram (-) bact.
Chlamydias
Spirochetes
Gram (+) bact.
Cyanobacteria
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Thiomargarita namibiensis,
showing globules of sulfur wastes
Colorized TEM 5,000 
Figure 16.13A, B
LM 13,000 
Proteobacteria
Bdellovibrio bacteriophorus
(flagellated cell) attacking a larger
bacterium
• a subgroup - can fix atmospheric nitrogen in the nodules of legumes.
Agrobacterium, is used in genetic engineering and produce plant tumors.
• g subgroup (largest in the proteobacteria clade) - can oxidize sulfur
(Fig.16.13A). This group has many pathogens, e.g. Salmonella typhi and
Vibrio cholera. E. coli.
• d subgroup include the slime-secreting myxobacteria that aggregate to
form fruiting bodies during times of stress, releasing resistant spores.
Bdellovibrios (Fig.16.13B).
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Chlamydias - are responsible for causing blindness and a
common sexually transmitted disease called
nongonococcal urethritis (非淋菌性尿道炎)
Spirochetes
- move like corkscrews. , e.g. spirochetes (Fig.16.9).
- some are pathogens,Treponema pallidum (syphilis)
and Borrelia burgdorferi (Lyme disease)
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Gram-positive bacteria
- actinomycetes was once mistaken for fungus, found in soil
and is a major source of antibiotics (Fig.16.13C).
-Staphylococcus and Streptococcus - common pathogens
-Mycoplasma - the smallest living organism in this group.
Streptomyces, the source of
many antibiotics (colorized SEM)
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Colorized SEM 2,800
Nitrogen-fixing
cells
Photosynthetic
cells
Figure 16.13C, D
LM 650 
Colorized SEM 2,8000 
Cyanobacteria, generating oxygen during photosynthesis.
•cyanobacterium Anabaena
CONNECTION
16.14 Some bacteria cause disease
• Pathogenic bacteria cause disease by
producing: Exotoxins or endotoxins
Exotoxins are proteins secreted by prokaryotes.
- Clostridium botulinum causes botulism (肉毒桿菌中毒).
SEM 12,000 
Figure 16.14A Staphylococcus aureus, an exotoxin producer
•Normal microbiota found in moist
skin folds, but when it grows inside a
person, its exotoxin cause toxic
shock syndrome.
•cause food poisoning
•cause scalded skin syndrome
Harmless bacteria can develop pathogenic strains
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Endotoxins are components of the outer
membranes of some gram (-)bacteria.
• The signs and symptoms from all endotoxins are
the same: chills, fever, aches, weakness and
decreased blood pressure that can lead to
shock.
• Salmonella species causes typhoid fever (傷寒)
and food poisoning
Copyright
© 2005©Pearson
Education,Education,
Inc. Publishing
as publishing
Benjamin Cummings
Copyright
2002 Pearson
Inc.,
as Benjamin
Cummings
• Three of our defenses against bacterial diseases:
1.Sanitation,
2.the use of antibiotics, 3.education
.
Spirochete
that causes
Lyme disease
Prevention of Lyme disease
is best accomplished
through public education.
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“Bull’s-eye”rash
SEM 2,800
The cause of Lyme disease, Borrelia burgdorferi, is carried by
a tick and elicits a distinctive set of symptoms and potential
disorders.
Tick that
carries
the Lyme
disease
bacterium
Figure 16.14B
萊姆症(又稱萊姆關節炎,由扁蝨傳染,症
狀有紅斑、頭疼、發燒等等)
CONNECTION
16.15 Bacteria can be used as biological weapons
Bacillus anthracis (炭疽桿菌), a spore-forming bacterium,
causes anthrax
• Animals, plants, fungi, and viruses have all served as
weapons, but bacteria is the most frequent.
•The route of infection determines
the mortality rate.
•Cutaneous (skin) anthrax is easy
to treat, while pulmonary anthrax
is treatable if detected early;
•However, it is usually ignored as
a common cold.
Figure 16.15
Cleaning up a site where anthrax spores were released in October 2001
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CONNECTION
16.16 Prokaryotes help recycle chemicals and
clean up the environment
• Bioremediation
– Is the use of organisms to clean up
pollution from water, soil, air
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• Prokaryotes are decomposers in
– Sewage treatment to remove toxic wastes
– help mine
– clean up oil spills
Rotating
spray arm
Rock bed
coated with
aerobic
bacteria
and fungi
Liquid wastes
Outflow
The trickling filter system at a sewage treatment plant
Figure 16.16A, B
aerobic and anaerobic
communities of organisms
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Treatment of an oil spill in Alaska
Natural bacteria or
recombinant strains are used
PROTISTS
16.17 The eukaryotic cell probably originated as
a community of prokaryotes
• Eukaryotic cells
– Evolved from prokaryotic cells more than 2
billion years ago
Two theories of how the membrane-enclosed
organelles arose:
• endomembrane
• Symbiosis (endosymbiosis)
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• The nucleus and endomembrane system
– Probably evolved from infoldings of the plasma
membrane
– membrane-bounded organelles except
mitochondria and chloroplasts
• Mitochondria and chloroplasts
– Probably evolved from aerobic (alpha
proteobacteria) and photosynthetic
(cyanobacteria) endosymbionts, respectively
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Figure 16.17 A model of the origin of eukaryotes (layer 1)
Cytoplasm
Plasma
membrane
Endoplasmic
reticulum
Ancestral prokaryote
Nucleus
Nuclear
envelope
Membrane infolding
Aerobic heterotrophic
prokaryote
Cell with nucleus and
endomembrane system
Some
cells
Ancestral host cell
Photosynthetic
prokaryote
Endosymbiosis
Mitochondrion
Chloroplast
Mitochondrion
Photosynthetic
eukaryotic cell
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Figure 16.17 A model of the origin of eukaryotes (layer 2)
Cytoplasm
Plasma
membrane
Endoplasmic
reticulum
Ancestral prokaryote
Nucleus
Nuclear
envelope
Membrane infolding
Aerobic heterotrophic
prokaryote
Cell with nucleus and
endomembrane system
Some
cells
Ancestral host cell
Photosynthetic
prokaryote
Endosymbiosis
Mitochondrion
Chloroplast
Mitochondrion
Photosynthetic
eukaryotic cell
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16.18 Protists (單細胞生物) are an extremely
diverse assortment of eukaryotes
• Protists are diverse and represent several
kingdoms within Domain Eukarya. (Old:
protists kindom)
LM 275 
• Protists are found in all habitats but most
common in aquatic.
Figure 16.18
Protists in pond water
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Protists are nutritionally
diverse.
Algae - Photosynthetic protists.
Protozoa are heterotrophs that
eat bacteria and other protists.
Other protists are fungus-like.
• Protists are more complex than
prokaryotes: a nucleus, organelles, and
cilia & flagella (9+2).
• The simplest eukaryotes, as most are
single-celled organisms.
Protists’ taxonomic groups are presented based on
the most current information obtained from
molecular and cellular studies.
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16.19 A tentative phylogeny of eukaryotes includes
multiple clades of protists
Plants
Closest algal relatives of plants
Green algae
Red algae
Animals
Choanoflagellates
Fungi
Cellular slime molds
Plasmodial slime molds
Amoebas
Brown algae
Diatoms
Water molds
Ciliates
Apicomplexans
Dinoflagellates
Euglenozoans
Diplomonads
• The taxonomy of protists is a work in progress
Kingdoms for plants, animals, fungi, and the groups that were once part of the Protista kingdom
Alveolates Stramenopila
Amoebozoa
Figure 16.19
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Ancestral eukaryote
16.20 Diplomonads (雙滴蟲類) and euglenozoans
include some flagellated parasites
• The parasitic Giardia
– Is a diplomonad with highly reduced
mitochondria (What makes Giardia particularly interesting is its lack of mitochondria)
Colorized SEM 4,000 
•Diplomonads contain two nuclei and
multiple flagella and are considered the
most ancient living eukaryotic lineage.
•Nutrition mode - Anaerobic heterotrophs
•Drinking water contaminated with Giardia
without boiling it first will lead to severe
diarrhea.
Figure 16.20A A diplomonad: Giardia intestinalis
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• Euglenozoans- containing photosynthetic
autotrophs (Euglena), heterotrophs (Euglena in dark),
and pathogenic parasites (trypanosomes).
Host: African tsetse fly
A euglenozoan: Trypanosoma
(with blood cells) (睡病蟲)
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One or two flagella from
one end of the cells
Colorized SEM 1,300 
RBC
Colorized SEM 1,300 
Alter molecular structure of
coats frequently (antigenic
variation)
 escape host immune
system
A euglenozoan: Euglena (眼蟲)
Figure 16.20B, C
16.21 Alveolates have sacs beneath the plasma
membrane & include 1. dinoflagellates, 2.
apicomplexans, and 3. ciliates
• Dinoflagellates (二鞭毛藻)- are unicellular algae
• Some dinoflagellates are responsible for toxin-releasing
blooms in warm coastal waters that are known as red tides.
 cause extensive fish kills and harmful to humans.
Figure 16.21A
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A dinoflagellate: Gymnodium
SEM 2,300
two flagella in perpendicular
grooves
are uniquely shaped
phytoplankton (浮游生物),
found in both fresh and
marine water.
Apicomplexans (頂覆蟲) are parasites
• have an apical structure designed to penetrate
the host. e.g. Plasmodium, which causes malaria
An apicomplexan: Plasmodium
Figure 16.21B
瘧原蟲
Apex
TEM 26,000
 are spread by mosquitoes;
 reproduce inside red blood cells;
 cause the cells to lyse,
 resulting in fever and severe
anemia
Red blood cell
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• Cilliates (纖毛蟲)
– Use cilia to move and feed
Cilia
looks like a string of beads
Macronucleus
Figure 16.21C
LM 60
performs the daily functions of the cell and
micronuclei involved in reproduction
A ciliate: Stentor
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16.22 Stramenopiles (髮鞭藻門) are named for their
“hairy” flagella and include the water molds,
diatoms, and brown algae
Greek stramen, straw
pilos, hair
• Water molds are not fungus, although they were
originally classified as fungus.
• They decompose dead plants and animals (like
fungus) and can be parasitic to fish.
Figure 16.22A
Downy mildew is a plant
parasite related to water molds
and caused the potato blight
famine in Ireland 1800s.
A water mold breaking down a dead insect
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Diatoms (矽藻) - Photosynthetic, unicellular with
uniquely shaped and sculptured silica walls
- food source for marine animal
LM
400
Fossilized diatoms make up
thick sediments of
diatomaceous earth, which can
be used either for filtering or as
an abrasive.
Figure 16.22B
Diatoms, unicellular algae
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Brown algae, large complex seaweeds
- the largest algae
- all are multicellular, and the brown color is due to pigments
in the chloroplast
Brown algae (along with
red and green algae) are
commonly referred to as
seaweed.
Figure 16.22C
Brown algae: a kelp “forest”
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Kelp forests are used as
feeding grounds by many
marine species.
16.23 Amoebozoans have pseudopodia and
include amoebas and slime molds
• Amoebas cross many taxonomic groups. Here, only focus on
amoebozoans.
•includes free-living and parasitic amoebas, and slime molds.
• All members of this group have lobe-shaped pseudopodia (單
數pseudopodium).
Figure 16.23A
LM 185 
Amoebas capture their prey by encasing them
in their pseudopodia and engulfing them into
food vacuoles
Copyright
© 2005 Pearson
Education, Inc.
Publishing as Benjamin
Cummings
An
amoeba
ingesting
a smaller
protist
• A plasmodial slime mold is a yellow cytoplasmic
mass with multinucleate, branched, single-celled
plasmodium (變形體)
– That forms reproductive structures under
adverse conditions
Figure 16.23B
A plasmodial slime mold: Physarum
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Cellular slime molds
– are amoeboid cells that feed on bacteria in
rotting vegetation.
– Have unicellular and multicellular stages
No food
with food
LM 1,000
Slug-like aggregate,
multicellular
45
Figure 16.23C
Reproductive
structure
15
Amoeboid cells
Stages in the life cycle of a cellular slime mold: Dictyostelium
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
16.24 Red algae and green algae are the closest
relatives of land plants
See. Fig.16.19
Red algae
– Contribute to coral reefs, most common in
tropical marine waters
– endosymbiosis of red algae led to the
alveolates (16.21) and stramenopiles (16.22)
Red color in red algae
comes from accessory
pigments that mask the
green color of chlorophyll
Figure 16.24A
A red alga: an encrusted type, on a coral reef
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• Green algae
– May be unicellular, colonial, or multicellular
– are common inhabitants of fresh water
– gave rise to the land plants (see. Fig.16.19)
Chlamydomonas (衣滴蟲屬)
Figure 16.24B
Green algae, colonial and unicellular (inset)
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
LM 80 
LM 1,200 
Volvox (團藻屬) colonies
• The life cycles of many algae
– Involve the alternation of haploid gametophyte
and diploid sporophyte generations
Mitosis
Male
gametophyte
Spores
Gametes
Mitosis
Meiosis
Female
gametophyt
e
Fusion of
gametes
Sporophyte
Zygote
Mitosis
Figure 16.24C
Key
Haploid (n)
Diploid (2n)
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A multicellular green alga: Ulva (sea lettuce) and its life cycle
16.25 Multicellularity evolved several times in
eukaryotes
1.Formation of ancestral colonies, with all cells
the same.
2.Specialization and cooperation among
different cells within the colony.
3.Differentiation of sexual cells from the
somatic cells
Gamete
Sex cells
Locomotor
cells
1
Unicellular protist
2
3
Somatic
cells
Foodsynthesizing
cells
Early multicellular organism
Later organism that
Colony
with specialized, interdepenproduces gametes
Figure 16.25
dent cells
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Pearson
Education,
Publishing
as Benjamin Cummings
model
forInc.the
evolution
of a multicellular organism from a unicellular protist
• Multicellular life arose over a billion years ago
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Ancestral eukaryote
Plants
Green algae
Red algae
Animals
Choanoflagellates
Fungi
Cellular slime molds
Amoebozoa
2
Closest algal relatives of plants
Alveolates Stramenopila
Amoeba
s
Brown algae
Diatoms
Water molds
Ciliates
Apicomplexans
Dinoflagellates
1
Plasmodial slime molds
The next chapter
traces the
evolution of
plants.
Euglenozoans
Diplomonads
Three distinct eukaryotic lineages that led to
multicellular organisms:
1.One that led to brown algae.
2.One that led to fungi and animals.
3.One that led to red and green algae and
plants.
3