PROTISTS
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16.13 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.
© 2012 Pearson Education, Inc.
16.13 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 16.13A
Autotrophy
Caulerpa, a green alga
Heterotrophy
Giardia, a parasite
Mixotrophy
Euglena
16.13 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.
© 2012 Pearson Education, Inc.
16.13 Protists are an extremely diverse assortment
of eukaryotes
 Recent molecular and cellular studies indicate that
nutritional modes used to categorize protists do not
reflect natural clades.
 Protist phylogeny remains unclear.
 One hypothesis, used here, proposes five
monophyletic supergroups.
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16.14 EVOLUTION CONNECTION: Secondary
endosymbiosis is the key to much of protist
diversity
 The endosymbiont theory explains the origin of
mitochondria and chloroplasts.
– Eukaryotic cells evolved when prokaryotes established
residence within other, larger prokaryotes.
– This theory is supported by present-day mitochondria and
chloroplasts that
– have structural and molecular similarities to
prokaryotic cells and
– replicate and use their own DNA, separate from the
nuclear DNA of the cell.
© 2012 Pearson Education, Inc.
Figure 16.14_s1
Primary
endosymbiosis
Evolved into
Cyanobacterium chloroplast
2
Nucleus
Heterotrophic
eukaryote
1
Figure 16.14_s2
Primary
endosymbiosis
Green alga
Chloroplast
Evolved into
Cyanobacterium chloroplast
2
3
1
Nucleus
Heterotrophic
eukaryote
Autotrophic
eukaryotes
Chloroplast
Red alga
3
Figure 16.14_s3
Primary
endosymbiosis
Green alga
Chloroplast
Evolved into
Cyanobacterium chloroplast
2
3
Nucleus
Heterotrophic
eukaryote
1
Autotrophic
eukaryotes
4
Heterotrophic
eukaryotes
Chloroplast
Red alga
16.14 EVOLUTION CONNECTION: Secondary
endosymbiosis is the key to much of protist
diversity
 Secondary endosymbiosis is
– the process in which an autotrophic eukaryotic protist
became endosymbiotic in a heterotrophic eukaryotic
protist and
– key to protist diversity.
© 2012 Pearson Education, Inc.
Figure 16.14_s4
Primary
endosymbiosis
Secondary
endosymbiosis
Green alga
Chloroplast
Evolved into
Cyanobacterium chloroplast
2
3
1
Nucleus
Heterotrophic
eukaryote
Autotrophic
eukaryotes
4
Heterotrophic
eukaryotes
5
Chloroplast
Red alga
4
Figure 16.14_s5
Primary
endosymbiosis
Secondary
endosymbiosis
Green alga
Remnant of
green alga
Chloroplast
Evolved into
Cyanobacterium chloroplast
Euglena
2
3
1
Nucleus
Heterotrophic
eukaryote
Autotrophic
eukaryotes
4
Heterotrophic
eukaryotes
5
Chloroplast
Red alga
16.15 Chromalveolates represent the range of
protist diversity
 Chromalveolates include
– diatoms, unicellular algae with a glass cell wall
containing silica,
– dinoflagellates, unicellular autotrophs, heterotrophs,
and mixotrophs that are common components of marine
plankton,
– brown algae, large, multicellular autotrophs,
– water molds, unicellular heterotrophs,
– ciliates, unicellular heterotrophs and mixotrophs that use
cilia to move and feed, and
– a group including parasites, such as Plasmodium, which
causes malaria.
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Figure 16.15B
5
16.16 CONNECTION: 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.
– Lipid droplets in diatoms and other algae may serve
as a renewable source of energy.
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16.17 Rhizarians include a variety of amoebas
 The two largest groups of Rhizaria are among the
organisms referred to as amoebas.
 Amoebas move and feed by means of
pseudopodia, temporary extensions of the cell.
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16.18 Some excavates have modified mitochondria
 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.
 Excavates include
– heterotrophic termite endosymbionts,
– autotrophic species,
– mixotrophs such as Euglena
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Figure 16.13A_3
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 16.18A
Flagella
Undulating
membrane
7
Figure 16.18B
16.19 Unikonts include protists that are closely
related to fungi and animals
 Unikonta 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,
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16.20 Archaeplastids include red algae, green
algae, and land plants
 Archaeplastids include:
– red algae (multicellular)
– green algae (unicellular)
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16.21 EVOLUTION CONNECTION: Multicellularity
evolved several times in eukaryotes
 The origin of the eukaryotic cell led to an
evolutionary radiation of new forms of life.
 . Multicellular organisms (seaweeds, plants,
animals, and most fungi) are fundamentally
different from unicellular organisms.
– A multicellular organism has various specialized cells
that perform different functions and are interdependent.
– All of life’s activities occur within a single cell in
unicellular organisms.
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16.21 EVOLUTION CONNECTION: Multicellularity
evolved several times in eukaryotes
 Multicellular organisms have evolved from three
different lineages:
– brown algae evolved from chromalveolates,
– fungi and animals evolved from unikonts, and
– red algae and green algae evolved from achaeplastids.
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16.21 EVOLUTION CONNECTION: Multicellularity
evolved several times in eukaryotes
 One hypothesis states that two separate unikont
lineages led to fungi and animals, diverging more
than 1 billion years ago.
 A combination of morphological and molecular
evidence suggests that choanoflagellates are the
closest living protist relative of animals.
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