Protists are an extremely diverse assortment (品種)
of eukaryotes
ƒ 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.
A protist from a termite gut covered by thousands of flagella
© 2012 Pearson Education, Inc.
Protists are an extremely diverse assortment of
eukaryotes
ƒ Protists obtain their nutrition in many ways. Protists
include
Autotrophy
Heterotrophy
Mixotrophy
– 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
Caulerpa, a green alga
Giardia, a parasite
Euglena
– mixotrophs, using photosynthesis and heterotrophy.
© 2012 Pearson Education, Inc.
Protists are an extremely diverse assortment of
eukaryotes
Protists are an extremely diverse assortment of
eukaryotes
ƒ Protists are found in many habitats including
ƒ Recent molecular and cellular studies indicate that
nutritional modes used to categorize protists do not
reflect natural clades (支序).
– anywhere there is moisture and
– the bodies of host organisms.
ƒ Protist phylogeny remains unclear.
ƒ One hypothesis, used here, proposes five
monophyletic supergroups.
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
1
Secondary endosymbiosis is the key to much of
protist diversity
ƒ The endosymbiont theory explains the origin of
mitochondria and chloroplasts.
– Eukaryotic cells evolved when prokaryotes established
residence within other, larger prokaryotes.
Primary
endosymbiosis
Evolved into
Cyanobacterium chloroplast
2
– This theory is supported by present-day mitochondria and
chloroplasts that
Nucleus
Heterotrophic
eukaryote
1
– 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.
Primary
endosymbiosis
Primary
endosymbiosis
Green alga
Chloroplast
Evolved into
Cyanobacterium chloroplast
Green alga
Chloroplast
Evolved into
Cyanobacterium chloroplast
2
2
3
Nucleus
Heterotrophic
eukaryote
1
Autotrophic
eukaryotes
3
Nucleus
Heterotrophic
eukaryote
1
Chloroplast
Autotrophic
eukaryotes
4
Heterotrophic
eukaryotes
Chloroplast
Red alga
Red alga
Secondary endosymbiosis is the key to much of
protist diversity
Primary
endosymbiosis
ƒ Secondary endosymbiosis is
– the process in which an autotrophic eukaryotic protist
became endosymbiotic in a heterotrophic eukaryotic
protist and
Secondary
endosymbiosis
Green alga
Chloroplast
Evolved into
Cyanobacterium chloroplast
2
3
– key to protist diversity.
Nucleus
Heterotrophic
eukaryote
1
Autotrophic
eukaryotes
4
Heterotrophic
eukaryotes
5
Chloroplast
Red alga
© 2012 Pearson Education, Inc.
2
Chromalveolates (囊泡藻界) represent the range
of protist diversity
Primary
endosymbiosis
ƒ Chromalveolates include
Secondary
endosymbiosis
Green alga
Remnant of
green alga
Chloroplast
Evolved into
Cyanobacterium chloroplast
– diatoms, unicellular algae with a glass cell wall
containing silica,
Euglena
2
3
1
Nucleus
Heterotrophic
eukaryote
Autotrophic
eukaryotes
4
Heterotrophic
eukaryotes
5
Chloroplast
Red alga
© 2012 Pearson Education, Inc.
Chromalveolates (囊泡藻界) represent the range
of protist diversity
ƒ 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,
© 2012 Pearson Education, Inc.
Chromalveolates (囊泡藻界) represent the range
of protist diversity
ƒ 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,
A red tide caused by Gymnodinium, a dinoflagellate
© 2012 Pearson Education, Inc.
3
Chromalveolates (囊泡藻界) represent the range
of protist diversity
ƒ 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 (水黴), unicellular heterotrophs,
© 2012 Pearson Education, Inc.
Chromalveolates (囊泡藻界) represent the range
of protist diversity
ƒ 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,
© 2012 Pearson Education, Inc.
Chromalveolates (囊泡藻界) represent the range
of protist diversity
ƒ Chromalveolates include
Mouth
– 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 (瘧原
蟲), which causes malaria.
© 2012 Pearson Education, Inc.
4
Can algae provide a renewable source of energy?
Can algae provide a renewable source of energy?
ƒ Fossil fuels
ƒ Lipid droplets in diatoms and other algae may
serve as a renewable source of energy.
– are the organic remains of organisms that lived
hundreds of millions of years ago and
– primarily consist of
– diatoms and
– primitive plants.
© 2012 Pearson Education, Inc.
ƒ If unicellular algae could be grown on a large scale,
this oil could be harvested and processed into
biodiesel.
ƒ Numerous technical hurdles (跨欄) remain before
industrial-scale production of biofuel from algae
becomes a reality.
© 2012 Pearson Education, Inc.
Rhizarians (有孔蟲界) include a variety of
amoebas
ƒ The two largest groups of Rhizaria are among the
organisms referred to as amoebas.
ƒ Amoebas move and feed by means of
pseudopodia, temporary extensions of the cell.
Green algae in a bioreactor
© 2012 Pearson Education, Inc.
Rhizarians (有孔蟲界) include a variety of
amoebas
ƒ Foraminiferans (有孔蟲目)
– 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.
© 2012 Pearson Education, Inc.
5
Rhizarians (有孔蟲界) include a variety of
amoebas
ƒ Radiolarians
– are mostly marine and
– produce a mineralized internal skeleton made of silica.
A radiolarian skeleton
© 2012 Pearson Education, Inc.
Some excavates (古蟲; 掘蟲) have modified
mitochondria
Some excavates (古蟲; 掘蟲) have modified
mitochondria
ƒ Excavata has recently been proposed as a clade
on the basis of molecular and morphological
similarities.
ƒ Excavates include
– heterotrophic termite endosymbionts
ƒ The name refers to an “excavated” feeding groove
possessed (擁有) by some members of the group.
ƒ Excavates
– have modified mitochondria that lack functional electron
transport chains and
– use anaerobic pathways such as glycolysis (糖酵解) to
extract energy.
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
Some excavates have modified mitochondria
ƒ Excavates include
– heterotrophic termite endosymbionts,
– autotrophic species,
– mixotrophs such as Euglena (眼蟲)
A protist from a termite gut covered by thousands of flagella
© 2012 Pearson Education, Inc.
6
Some excavates have modified mitochondria
ƒ Excavates include
Autotrophy
Heterotrophy
Mixotrophy
– heterotrophic termite endosymbionts,
– autotrophic species,
– mixotrophs such as Euglena (眼蟲),
– the common waterborne parasite Giardia intestinalis (蘭
氏賈第鞭毛蟲),
Caulerpa, a green alga
Giardia, a parasite
Euglena
© 2012 Pearson Education, Inc.
Some excavates have modified mitochondria
ƒ Excavates include
Flagella
– heterotrophic termite endosymbionts,
– autotrophic species,
– mixotrophs such as Euglena (眼蟲),
– the common waterborne parasite Giardia intestinalis (蘭
氏賈第鞭毛蟲),
Undulating (波浪形) membrane
– the parasite Trichomonas vaginalis (陰道滴蟲), which
causes 5 million new infections each year of human
reproductive tracts,
A parasitic excavate: Trichomonas vaginalis
© 2012 Pearson Education, Inc.
16.18 Some excavates have modified mitochondria
Figure 16.18B
ƒ Excavates include
– heterotrophic termite endosymbionts,
– autotrophic species,
– mixotrophs such as Euglena (眼蟲),
– the common waterborne parasite Giardia intestinalis (蘭
氏賈第鞭毛蟲),
– the parasite Trichomonas vaginalis (陰道滴蟲), which
causes 5 million new infections each year of human
reproductive tracts,
– the parasite Trypanosoma (錐蟲), which causes
sleeping sickness in humans.
A parasitic excavate: Trypanosoma (with blood cells)
© 2012 Pearson Education, Inc.
7
Unikonts (單鞭毛生物) include protists that are
closely related to fungi and animals
Unikonts (單鞭毛生物) include protists that are
closely related to fungi and animals
ƒ Unikonta is a controversial (爭議) grouping joining
ƒ Amoebozoans have lobe-shaped pseudopodia and
include
– amoebozoans and
– a group that includes animals and fungi, addressed at
the end of this unit on protists.
– many species of free-living amoebas,
– some parasitic amoebas, and
– slime molds.
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
Unikonts (單鞭毛生物) include protists that are
closely related to fungi and animals
ƒ Plasmodial (原質) 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 (原質體).
An amoeba beginning to ingest an algal cell
© 2012 Pearson Education, Inc.
Unikonts (單鞭毛生物) include protists that are
closely related to fungi and animals
ƒ 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
A plasmodial slime mold: Physarum
(多頭絨泡菌)
– forms a stock supporting an asexual reproductive
structure that produces spores.
© 2012 Pearson Education, Inc.
8
Archaeplastids (古質體生物) include red algae,
green algae, and land plants
ƒ Archaeplastids include:
– red algae,
– green algae, and
– land plants.
© 2012 Pearson Education, Inc.
Archaeplastids (古質體生物) include red algae,
green algae, and land plants
ƒ Red algae
– are mostly multicellular,
– contribute to the structure of coral reefs, and
– are commercially valuable.
© 2012 Pearson Education, Inc.
Archaeplastids (古質體生物) include red algae,
green algae, and land plants
ƒ Green algae may be unicellular, colonial, or
multicellular.
– Volvox (團藻) is a colonial green algae, and
– Chlamydomonas (衣藻) is a unicellular alga propelled
by two flagella.
Volvox
Chlamydomonas
© 2012 Pearson Education, Inc.
9
Archaeplastids (古質體生物) include red algae,
green algae, and land plants
ƒ 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.
© 2012 Pearson Education, Inc.
Mitosis
Mitosis
Male
gametophyte
Male
gametophyte
Spores
Spores
Mitosis
Mitosis
Gametes
Female
gametophyte
Gametes
Female
gametophyte
Fusion of
gametes
Zygote
Key
Haploid (n)
Diploid (2n)
Multicellularity evolved several times in
eukaryotes
Mitosis
Male
gametophyte
ƒ The origin of the eukaryotic cell led to an
evolutionary radiation of new forms of life.
Spores
Mitosis
Meiosis
Key
Haploid (n)
Diploid (2n)
Gametes
ƒ Unicellular protists are much more diverse in form
than simpler prokaryotes.
Female
gametophyte
Fusion of
gametes
Sporophyte
Zygote
Mitosis
Key
Haploid (n)
Diploid (2n)
© 2012 Pearson Education, Inc.
10
Multicellularity evolved several times in
eukaryotes
Multicellularity evolved several times in
eukaryotes
ƒ Multicellular organisms (seaweeds, plants, animals,
and most fungi) are fundamentally different from
unicellular organisms.
ƒ Multicellular organisms have evolved from three
different lineages:
– A multicellular organism has various specialized cells
that perform different functions and are interdependent.
– brown algae evolved from chromalveolates,
– fungi and animals evolved from unikonts, and
– red algae and green algae evolved from achaeplastids.
– All of life’s activities occur within a single cell in
unicellular organisms.
© 2012 Pearson Education, Inc.
© 2012 Pearson Education, Inc.
Green algae
Other green algae
Charophytes
(plants and green algae)
Land plants
Amoebozoans
Unikonts
Ancestral eukaryote
Archaeplastids
Multicellularity evolved several times in
eukaryotes
Red algae
Nucleariids (絲偽足蟲)
Fungi
ƒ One hypothesis states that two separate unikont
lineages led to fungi and animals, diverging more
than 1 billion years ago.
ƒ A combination of morphological and molecular
evidence suggests that choanoflagellates (領鞭毛
生物) are the closest living protist relative of
animals.
Choanoflagellates (領鞭蟲)
Key
All unicellular
Both unicellular
and multicellular
All multicellular
Animals
© 2012 Pearson Education, Inc.
Nucleariids
Fungi
A nucleariid, closest living
protistan relative of fungi
1 billion
years ago
Individual
choanoflagellate
Choanoflagellates
Colonial
choanoflagellate
Sponge
collar cell
Animals
Sponge
11