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Chapter 16 Microbial Life: Prokaryotes and Protists
PROKARYOTES
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16.1 Prokaryotes are diverse and widespread
 Prokaryotic cells are smaller than eukaryotic cells.
– Prokaryotes range from 1–5 µm in diameter.
– Eukaryotes range from 10–100 µm in diameter.
 The collective biomass of prokaryotes is at least 10
times that of all eukaryotes.
© 2012 Pearson Education, Inc.
Figure 16.1 Bacteria on a
pin point
16.1 Prokaryotes are diverse and widespread
 Prokaryotes live in habitats
– too cold,
– too hot,
– too salty,
– too acidic, and
– too alkaline for eukaryotes to survive.
 Some bacteria are pathogens, causing disease.
But most bacteria on our bodies are benign or
beneficial.
© 2012 Pearson Education, Inc.
16.1 Prokaryotes are diverse and widespread
 Several hundred species of bacteria live in and on
our bodies,
– decomposing dead skin cells,
– supplying essential vitamins, and
– guarding against pathogenic organisms.
 Prokaryotes in soil decompose dead organisms,
sustaining chemical cycles.
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16.2 External features contribute to the success of
prokaryotes
 Prokaryotic cells have three common cell shapes.
– Cocci are spherical prokaryotic cells. They sometimes
occur in chains that are called streptococci.
– Bacilli are rod-shaped prokaryotes. Bacilli may also be
threadlike, or filamentous.
– Spiral prokaryotes are like a corkscrew.
– Short and rigid prokaryotes are called spirilla.
– Longer, more flexible cells are called spirochetes.
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Figure 16.2A
Cocci
Bacilli
Spirochete
16.2 External features contribute to the success of
prokaryotes
 Nearly all prokaryotes have a cell wall. Cell walls
– provide physical protection and
– prevent the cell from bursting in a hypotonic
environment.
 When stained with Gram stain, cell walls of
bacteria are either
– Gram-positive, with simpler cell walls containing
peptidoglycan, or
– Gram-negative, with less peptidoglycan, and more
complex and more likely to cause disease.
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Figure 16.2B Gram-positive
(purple) and gram-negative
(pink) bacteria
16.2 External features contribute to the success of
prokaryotes
 The cell wall of many prokaryotes is covered by a
capsule, a sticky layer of polysaccharides or
protein.
 The capsule
– enables prokaryotes to adhere to their substrate or to
other individuals in a colony and
– shields pathogenic prokaryotes from attacks by a host’s
immune system.
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Figure 16.2C
Tonsil cell
Capsule
Bacterium
16.2 External features contribute to the success of
prokaryotes
 Some prokaryotes have external structures that
extend beyond the cell wall.
– Flagella help prokaryotes move in their environment.
– Hairlike projections called fimbriae enable prokaryotes
to stick to their substrate or each other.
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Figure 16.2D
Flagella
Fimbriae
16.3 Populations of prokaryotes can adapt rapidly
to changes in the environment
 Prokaryote population growth
– occurs by binary fission,
– can rapidly produce a new generation within hours, and
– can generate a great deal of genetic variation
– by spontaneous mutations,
– increasing the likelihood that some members of the population
will survive changes in the environment.
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16.3 Populations of prokaryotes can adapt rapidly
to changes in the environment
 The genome of a prokaryote typically
– has about one-thousandth as much DNA as a
eukaryotic genome and
– is one long, circular chromosome packed into a distinct
region of the cell.
 Many prokaryotes also have additional small,
circular DNA molecules called plasmids, which
replicate independently of the chromosome.
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Figure 16.3A
Chromosome
Plasmids
16.3 Populations of prokaryotes can adapt rapidly
to changes in the environment
 Some prokaryotes form specialized cells called
endospores that remain dormant through harsh
conditions.
 Endospores can survive extreme heat or cold.
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Figure 16.3b
Bacterium
Endospores
16.4 Prokaryotes have unparalleled nutritional
diversity
 Prokaryotes exhibit much more nutritional diversity
than eukaryotes.
 Two sources of energy are used.
– Phototrophs capture energy from sunlight.
– Chemotrophs harness the energy stored in chemicals.
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16.4 Prokaryotes have unparalleled nutritional
diversity
 Two sources of carbon are used by prokaryotes.
– Autotrophs obtain carbon atoms from carbon dioxide.
– Heterotrophs obtain their carbon atoms from the
organic compounds present in other organisms.
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16.4 Prokaryotes have unparalleled nutritional
diversity
 The terms that describe how prokaryotes obtain
energy and carbon are combined to describe their
modes of nutrition.
– Photoautotrophs obtain energy from sunlight and use
carbon dioxide for carbon.
– Photoheterotrophs obtain energy from sunlight but get
their carbon atoms from organic molecules.
– Chemoautotrophs harvest energy from inorganic
chemicals and use carbon dioxide for carbon.
– Chemoheterotrophs acquire energy and carbon from
organic molecules.
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Figure 16.4-0
ENERGY SOURCE
Sunlight
Chemicals
Chemoautotrophs
Oscillatoria
Unidentified “rock-eating” bacteria
Photoheterotrophs
Chemoheterotrophs
Organic compounds
CARBON
SOURCE
CO2
Photoautotrophs
Salmonella typhimurium
Rhodopseudomonas
16.6 CONNECTION: Prokaryotes help clean up
the environment
 Prokaryotes are useful for cleaning up contaminants
in the environment because prokaryotes
– have great nutritional diversity,
– are quickly adaptable, and
– can form biofilms.
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16.6 CONNECTION: Prokaryotes help clean up
the environment
 Bioremediation is the use of organisms to remove
pollutants from
– soil,
– air, or
– water.
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16.6 CONNECTION: Prokaryotes help clean up
the environment
 Prokaryotic decomposers are the mainstays of
sewage treatment facilities.
– Raw sewage is first passed through a series of screens
and shredders.
– Solid matter then settles out from the liquid waste,
forming sludge.
– Sludge is gradually added to a culture of anaerobic
prokaryotes, including bacteria and archaea.
– The microbes decompose the organic matter into material
that can be placed in a landfill or used as fertilizer.
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16.6 CONNECTION: Prokaryotes help clean up
the environment
 Liquid wastes are treated separately from the
sludge.
– Liquid wastes are sprayed onto a thick bed of rocks.
– Biofilms of aerobic bacteria and fungi growing on the
rocks remove much of the dissolved organic material.
– Fluid draining from the rocks is sterilized and then
released, usually into a river or ocean.
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Figure 16.6A
Rotating
spray arm
Rock bed coated
with aerobic
prokaryotes
and fungi
Liquid wastes
Outflow
16.6 CONNECTION: Prokaryotes help clean up
the environment
 Bioremediation is becoming an important tool for
cleaning up toxic chemicals released into the soil
and water by industrial processes.
 Environmental engineers change the natural
environment to accelerate the activity of naturally
occurring prokaryotes capable of metabolizing
pollutants.
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Figure 16.6b
16.7 Bacteria and archaea are the two main
branches of prokaryotic evolution
 New studies of representative genomes of
prokaryotes and eukaryotes strongly support the
three-domain view of life.
– Prokaryotes are now classified into two domains:
– Bacteria and
– Archaea.
– Archaea have at least as much in common with
eukaryotes as they do with bacteria.
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Table 16.7
16.8 Archaea thrive in extreme environments—
and in other habitats
 Archaeal inhabitants of extreme environments
have unusual proteins and other molecular
adaptations that enable them to metabolize and
reproduce effectively.
– Extreme halophiles thrive in very salty places.
– Extreme thermophiles thrive in
– very hot water, such as geysers, and
– acid pools.
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Figure 16.8A Orange and
yellow colonies of heat-loving
archaea growing in a Nevada
geyser
16.8 Archaea thrive in extreme environments—
and in other habitats
 Methanogens
– live in anaerobic environments,
– give off methane as a waste product from
– the digestive tracts of cattle and deer and
– decomposing materials in landfills.
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16.9 Bacteria include a diverse assemblage of
prokaryotes
 The domain Bacteria is currently divided into five
groups, based on comparisons of genetic
sequences.
 1. Proteobacteria
– are all gram negative,
– share a particular rRNA sequence, and
– represent all four modes of nutrition.
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16.9 Bacteria include a diverse assemblage of
prokaryotes
– Proteobacteria also include Rhizobium species that
– live symbiotically in root nodules of legumes and
– convert atmospheric nitrogen gas into a form usable
by their legume host.
– Symbiosis is a close association between
organisms of two or more species.
– Rhizobium is an endosymbiont, living within another
species.
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Figure 32.13B Root nodules
on a soybean plant
Shoot
Bacteria within
vesicle in an
infected cell
Nodules
Roots
16.9 Bacteria include a diverse assemblage of
prokaryotes
 2. Gram-positive bacteria
– rival proteobacteria in diversity and
– include the actinomycetes common in soil.
– Streptomyces is often cultured by pharmaceutical
companies as a source of many antibiotics.
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Figure 16.9B Streptomyces,
the source of many antibiotics
16.9 Bacteria include a diverse assemblage of
prokaryotes
 3. Cyanobacteria
– Cyanobacteria are the only group of prokaryotes with
plantlike, oxygen-generating photosynthesis.
– Some species, such as Anabaena, have specialized
cells that fix nitrogen.
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Figure 16.9c
Photosynthetic
cells
Capsule
Nitrogen-fixing cells
16.9 Bacteria include a diverse assemblage of
prokaryotes
 4. Chlamydias
– Chlamydias live inside eukaryotic host cells.
– Chlamydia trachomatis
– is a common cause of blindness in developing
countries and
– is the most common sexually transmitted disease in
the United States infecting urethral cells.
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Figure 16.9D Chlamydia cells
(arrows) inside an animal cell
16.9 Bacteria include a diverse assemblage of
prokaryotes
 5. Spirochetes are
– helical bacteria and
– notorious pathogens, causing
– syphilis and
– Lyme disease.
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Figure 16.9E Treponema
pallidum, the spirochete that
causes syphilis
16.10 CONNECTION: Some bacteria cause
disease
 All organisms are almost constantly exposed to
pathogenic bacteria.
 Most bacteria that cause illness do so by producing
a poison or toxins.
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16.11 Koch’s postulates are used to prove that a
bacterium causes a disease
 Koch’s postulates are four essential conditions used
to establish that a certain bacterium is the cause of a
disease. They are
1. find the bacterium in every case of the disease,
2. isolate the bacterium from a person who has the disease
and grow it in pure culture,
3. show that the cultured bacterium causes the disease
when transferred to a healthy subject, and
4. isolate the bacterium from the experimentally infected
subject.
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16.11 SCIENTIFIC DISCOVERY: Koch’s
postulates are used to prove that a
bacterium causes a disease
 Koch’s postulates were used to demonstrate that
the bacterium Helicobacter pylori is the cause of
most peptic ulcers.
 The 2005 Nobel Prize in Medicine was awarded to
Barry Marshall and Robin Warren for this
discovery.
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PROTISTS
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16.12 Protists are an extremely diverse assortment
of eukaryotes
 Protists
– are a diverse collection of mostly unicellular eukaryotes,
– may constitute multiple kingdoms within the Eukarya,
and
– refer to eukaryotes that are not
– plants,
– animals, or
– fungi.
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16.12 Protists are an extremely diverse assortment
of eukaryotes
 Protists obtain their nutrition in many ways. Protists
include
– autotrophs, called algae, producing their food by
photosynthesis,
– heterotrophs, called protozoans, eating bacteria and
other protists,
– heterotrophs, called parasites, deriving their nutrition
from a living host, and
– mixotrophs, using photosynthesis and heterotrophy.
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Figure 16.12A
Autotrophy
Caulerpa, a green alga
Heterotrophy
Giardia, a parasite
Mixotrophy
Euglena
16.12 Protists are an extremely diverse assortment
of eukaryotes
 Protists are found in many habitats including
– anywhere there is moisture and
– the bodies of host organisms.
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Figure 16.12B A protist
(excavate) from a termite gut
covered by thousands of
flagella
16.13 Endosymbiosis of unicellular algae is the key
to much protist diversity
 Recent molecular and cellular studies indicate that
nutritional modes used to categorize protists do not
reflect natural groups and that endosymbiosis has
occurred.
 Protist phylogeny remains unclear.
 One hypothesis, used here, proposes four
monophyletic supergroups.
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16.14 The SAR supergroup represents the range
of protist diversity
 Stramenopiles include
– diatoms, unicellular algae with a glass cell wall
containing silica,
– brown algae, large complex algae with characteristic
brown pigments in their chloroplasts like seaweed and
kelp
– water molds, unicellular heterotrophs that are usually
freshwater decomposers
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Figure 16.14A Diatom, a
unicellular alga that is a
stramenopile
16.17 Rhizarians include a variety of amoebas
 Foraminiferans
– are found in the oceans and in fresh water,
– have porous shells, called tests, composed of calcium
carbonate, and
– have pseudopodia that function in feeding and
locomotion.
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Figure 16.14B Brown algae: a
kelp “forest”, a stamenopile
Figure 16.14C Water mold, a
stramenopile
16.14 The SAR supergroup represents the range
of protist diversity
 Alveolata includes
– dinoflagellates, unicellular autotrophs, heterotrophs,
and mixotrophs that are common components of marine
plankton,
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Figure 16.14D A red tide
caused by Gymnodinium, a
dinoflagellate
16.14 The SAR supergroup represents the range
of protist diversity
 Alveolata include
– dinoflagellates, unicellular autotrophs, heterotrophs,
and mixotrophs that are common components of marine
plankton,
– ciliates, unicellular heterotrophs and mixotrophs that
use cilia to move and feed,
– a group including parasites, such as Plasmodium,
which causes malaria.
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Figure 16.14E A freshwater
ciliate showing cilia
distributed over the cell
surface and around the mouth
Mouth
Cell mouth
16.14 The SAR supergroup represents the range
of protist diversity
 The two largest groups of Rhizaria, foramniferans
and radiolarians, are among the organisms
referred to as amoebas.
 Amoebas move and feed by means of
pseudopodia, temporary extensions of the cell.
 Foramniferans have porous shells called tests
and are both freshwater and marine
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Figure 16.14F A
foraminiferan (inset SEM
shows a foram test of calcium
carbonate)
16.14 The SAR supergroup represents the range
of protist diversity
 Radiolarians
– are mostly marine and
– produce a mineralized internal skeleton made of silica.
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Figure 16.14G A radiolarian
skeleton of silica
16.15 Can algae provide a renewable source of
energy?
 Fossil fuels
– are the organic remains of organisms that lived
hundreds of millions of years ago and
– primarily consist of
– diatoms and
– primitive plants.
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16.15 Can algae provide a renewable source of
energy?
 Lipid droplets in diatoms and other algae may
serve as a renewable source of energy.
 If unicellular algae could be grown on a large scale,
this oil could be harvested and processed into
biodiesel.
 Numerous technical hurdles remain before
industrial-scale production of biofuel from algae
becomes a reality.
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Figure 16.15 Green algae in a
bioreactor
16.16 Some excavates have modified mitochondria
 Excavata has recently been proposed as a group
on the basis of molecular and morphological
similarities.
 The name refers to an “excavated” feeding groove
possessed by some members of the group.
 Excavates
– have modified mitochondria that lack functional electron
transport chains and
– use anaerobic pathways such as glycolysis to extract
energy.
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16.16 Some excavates have modified mitochondria
 Excavates include
– heterotrophic termite endosymbionts
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Figure 16.12B A protist from
a termite gut covered by
thousands of flagella
16.16 Some excavates have modified mitochondria
 Excavates include
– heterotrophic termite endosymbionts,
– autotrophic species,
– mixotrophs such as Euglena
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Figure 16.12A
Mixotrophy
Euglena
16.18 Some excavates have modified mitochondria
 Excavates include
– heterotrophic termite endosymbionts,
– autotrophic species,
– mixotrophs such as Euglena,
– the common waterborne parasite Giardia intestinalis,
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Figure 16.12A
Autotrophy
Caulerpa, a green alga
Heterotrophy
Giardia, a parasite
Mixotrophy
Euglena
16.18 Some excavates have modified mitochondria
 Excavates include
– heterotrophic termite endosymbionts,
– autotrophic species,
– mixotrophs such as Euglena,
– the common waterborne parasite Giardia intestinalis,
– the parasite Trichomonas vaginalis, which causes 5
million new infections each year of human reproductive
tracts,
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Figure 16.16A A parasitic
excavate: Trichomonas
vaginalis
Flagella
Undulating
membrane
16.18 Some excavates have modified mitochondria
 Excavates include
– heterotrophic termite endosymbionts,
– autotrophic species,
– mixotrophs such as Euglena,
– the common waterborne parasite Giardia intestinalis,
– the parasite Trichomonas vaginalis, which causes 5
million new infections each year of human reproductive
tracts, and
– the parasite Trypanosoma, which causes sleeping
sickness in humans.
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Figure 16.16B A parasitic
excavate: Trypanosoma (with
blood cells)
16.17 Unikonts include protists that are closely
related to fungi and animals
 Unikonta is a controversial grouping joining
– Amoebozoans, which are protists and
– a group that includes animals and fungi.
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16.17 Unikonts include protists that are closely
related to fungi and animals
 Amoebozoans have lobe-shaped pseudopodia and
include
– many species of free-living amoebas,
– some parasitic amoebas cause diseases like
dysentary, and
– slime molds.
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Figure 16.17A An amoeba
beginning to ingest an algal
cell
16.17 Unikonts include protists that are closely
related to fungi and animals
 Plasmodial slime molds
– are common where there is moist, decaying organic
matter and
– consist of a single, multinucleate mass of cytoplasm
undivided by plasma membranes, called a
plasmodium.
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Figure 16.17B A plasmodial
slime mold: Physarum
16.17 Unikonts include protists that are closely
related to fungi and animals
 Cellular slime molds
– are common on rotting logs and decaying organic
matter and
– usually exist as solitary amoeboid cells, but when food
is scarce, amoeboid cells
– swarm together, forming a slug-like aggregate that
wanders around for a short time and then
– forms a stock supporting an asexual reproductive
structure that produces spores.
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Figure 16.17C An aggregate
of amoeboid cells (left) and
the reproductive structure of
a cellular slime mold,
Dictyostelium
16.18 Archaeplastids include red algae, green
algae, and land plants
 Archaeplastids include:
– red algae,
– green algae, and
– land plants.
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16.18 Archaeplastids include red algae, green
algae, and land plants
 Red algae
– are mostly multicellular,
– contribute to the structure of coral reefs, and
– are commercially valuable.
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Figure 16.18A An encrusted
red alga
16.18 Archaeplastids include red algae, green
algae, and land plants
 Green algae may be unicellular, colonial, or
multicellular.
– Volvox is a colonial green algae, and
– Chlamydomonas is a unicellular alga propelled by two
flagella.
© 2012 Pearson Education, Inc.
Figure 16.18B Green algae,
colonial (left) and unicellular
(right)
Volvox
Chlamydomonas
16.18 Archaeplastids include red algae, green
algae, and land plants
 Ulva, or sea lettuce, is
– a multicellular green alga with
– a complex life cycle that includes an alternation of
generations that consists of
– a multicellular diploid (2n) form, the sporophyte,
that alternates with
– a multicellular haploid (1n) form, the gametophyte.
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Figure 16.18C
Mitosis
Male
gametophyte
Spores
Mitosis
Gametes
Female
gametophyte
Key
Haploid (n)
Diploid (2n)
Figure 16.18C
Mitosis
Male
gametophyte
Spores
Mitosis
Gametes
Female
gametophyte
Fusion of
gametes
Zygote
Key
Haploid (n)
Diploid (2n)
Figure 16.18C
Mitosis
Male
gametophyte
Spores
Mitosis
Meiosis
Gametes
Female
gametophyte
Fusion of
gametes
Sporophyte
Zygote
Mitosis
Key
Haploid (n)
Diploid (2n)
16.19 EVOLUTION CONNECTION:
Multicellularity evolved several times in
eukaryotes
 The origin of the eukaryotic cell led to an
evolutionary radiation of new forms of life.
 Unicellular protists are much more diverse in form
than simpler prokaryotes.
16.19 EVOLUTION CONNECTION:
Multicellularity evolved several times in
eukaryotes
 Multicellular organisms (seaweeds, plants,
animals, and most fungi) are fundamentally
different from unicellular organisms.
– All of life’s activities occur within a single cell in
unicellular organisms.
– A multicellular organism has various specialized cells
that perform different functions and are interdependent.
16.19 EVOLUTION CONNECTION:
Multicellularity evolved several times in
eukaryotes
 Multicellular organisms have evolved from three
different lineages:
– SAR-stramenopiles, alveolata, rhizaria (brown algae),
– unikonts (fungi and animals), and
– archaeplastids (red algae, green algae, and plants).
Red algae
Green algae
Other green algae
Charophytes
Land plants
Amoebozoans
Unikonts
Ancestral eukaryote
Archaeplastids
Figure 16.19a A hypothesis for
the phylogeny of plants, fungi,
and animals
Nucleariid amoebas
Fungi
Choanoflagellates
Key
All unicellular
Both unicellular
and multicellular
All multicellular
Animals
16.19 EVOLUTION CONNECTION: Multicellularity evolved
several times in eukaryotes
 One hypothesis states that two separate unikont
lineages led to fungi and animals, which diverged
more than 1 billion years ago.
 A combination of morphological and molecular
evidence suggests that choanoflagellates are the
closest living protist relative of animals.
Figure 16.19b The closest living protist relatives of
fungi (top) and animals (bottom)
16.19b-0
Nucleariids
Fungi
A nucleariid (type of amoeba)
closest living protistan
relative of fungi
1 billion
years ago
Individual
choanoflagellate
Choanoflagellates
Colonial
choanoflagellate
Sponge
collar cell
Animals
Sponge