2/19/2015 1 Chapter 28: Protists 1. General Features of Protists 2. Survey of the Protista A. The Excavata B. The SAR Clade C. The Archaeplastida D. The Unikonta 1. General Features of Protists All Protists are Eukaryotes Eukaryotic organisms consist of 1 or more eukaryotic cells: Prokaryotic cell Nucleus Eukaryotic cell Organelles • eukaryotic cells contain a “true nucleus” and other membrane- bound organelles Most eukaryotes are single-celled organisms, most of which are protists (i.e., not fungi, plants or animals).
Transcript
2/19/2015
1
Chapter 28: Protists
1. General Features of Protists
2. Survey of the ProtistaA. The Excavata
B. The SAR Clade
C. The Archaeplastida
D. The Unikonta
1. General Features of Protists
All Protists are Eukaryotes
Eukaryotic organisms consist of 1 or more eukaryotic cells:Prokaryotic cell
Nucleus
Eukaryotic cell Organelles
• eukaryotic cells contain a “true nucleus” and other membrane-bound organelles
Most eukaryotes are single-celled organisms, most of which are protists(i.e., not fungi, plants or animals).
2/19/2015
2
Protists have Diverse Characteristics
Protists are much more diverse that plants, animals & fungi:
• most are unicellular, though some are multicellular
• some are photoautotrophs (commonly called “algae”)
• protists can reproduce sexually, asexually, or both
• some are chemoheterotrophs (commonly called “protozoa”)
• some have characteristics of both (mixotrophs)
Endosymbiosis in Eukaryotic EvolutionPlasma membrane
DNA
Cytoplasm
Ancestralprokaryote
Nuclear envelope
Nucleus Endoplasmic
reticulum
Aerobic heterotrophicprokaryote
Mitochondrion
Ancestralheterotrophic eukaryote
Photosyntheticprokaryote
Mitochondrion
Plastid
Ancestral photosyntheticeukaryote
The endosymbiont theory proposes
that mitochondria & chloroplasts are
derived from internalized prokaryotes.
Cyanobacterium
Nucleus
Membranes
are represented
as dark lines
in the cell.
1 23
Heterotrophic
eukaryote One of thesemembraneswas lost inred andgreen algaldescendants.
Red alga
Green alga
Primary
endosymbiosis
Secondary
endosymbiosis
Dinoflagellates
Plastid
Stramenopiles
Plastid
Euglenids
Chlorarachniophytes
Secondary
endosymbiosis
Secondary
endosymbiosis
A Closer Look at Plastid Evolution
2/19/2015
3
Protists No Longer Constitute a Single Kingdom
The traditional grouping of eukaryotes involved 4 kingdoms:
PROTISTA
FUNGI
PLANTAE
ANIMALIA
However this is not consistent with phylogenies based on recent molecular analysis which supports the following 4 supergroups…
Diplomonads
Parabasalids
Euglenozoans
Ex
ca
va
ta
Diatoms
Golden algae
Brown algae
Dinoflagellates
Apicomplexans
Ciliates
Forams
Cercozoans
Radiolarians
“S
AR
” c
lad
e
Stra
me
no
pile
sA
lve
ola
tes
Rh
iza
rian
s
Gre
en
alg
ae
Red algae
Chlorophytes
Charophytes
Land plants
Arc
ha
ep
las
tida
Slime molds
Tubulinids
Entamoebas
Nucleariids
Fungi
Un
iko
nta
Choanoflagellates
Animals
Am
oe
bo
zo
an
sO
pis
tho
ko
nts
Figure 28.2
Giardia intestinalis,
5 μm■ Excavata
Diatom diversity
50 μm■ “SAR” Clade
Volvox, a colonial freshwater green alga
50 μm■ Archaeplastida
A unikont amoeba
100 μm
■ Unikonta
4 SupergroupsThe evolutionary
history of all eukaryotes
currently consists of 4 supergroups:
1. Excavata
2. SAR Clade
3. Archaeplastida• includes all land plants
4. Unikonta• includes fungi & animals
All eukaryotes that are not plants, animals or fungi are considered to be Protists.
2A. Survey of the Protista
The Excavata
Diplomonads
Parabasalids
Euglenozoans
SAR clade
Archaeplastida
Unikonta
Ex
ca
va
ta
2/19/2015
4
General Characteristics of Excavates
Below are some of the characteristics seen in Excavates:
• some members have an “excavated” feeding groovesthat are associated with unique cytoskeletal structures
• many have modified “unclassical” mitochondria
• most have 2 or more flagella
• includes the following major groups:
DIPOMONADS PARABASALIDS EUGLENOZOANS
Diplomonads
Diplomonads have reduced mitochondria called mitosomes and derive energy by anaerobic processes. They also have 2 nuclei and multiple flagella.
Many are parasites such as Giardia intestinalisshown here:
Flagella
Undulating
membrane 5 μm
Parabasalids
Parabasalids have reduced mitochondria called hydrogenosomes and thrive in anaerobic environments.
• Trichomonas vaginalis, a sexually transmitted human pathogenshown below is one example
2/19/2015
5
Flagella
8 μm
0.2 μm
Crystalline rod(cross section)
Ring of microtubules(cross section)
Euglenozoans
The Euglenozoa is a diverse clade that includes predatory heterotrophs,photosynthetic autotrophs, mixotrophs, and parasites.
• a characteristic feature of this clade is the crystalline rod structure within their flagella
• members of this clade include:
KINETOPLASTIDS
EUGLENIDS
9 μm
Kinetoplastids
Kinetoplastids have a single mitochondrion containing an unusual organized mass of DNA called a kinetoplast.
• includes the genus Trypanosomawhich contains parasites that cause “sleeping sickness” and Chaga’s disease
RBC
Long flagellum
5 μm
Eyespot
Short flagellum
Contractile vacuole
Nucleus
Chloroplast
Plasma
membrane
Light
detector
PellicleEuglena (LM)
EuglenidsEuglenids have 1 or 2 flagella, and some members of this clade, such as the genus Euglena, are both autotrophic and heterotrophic (i.e., mixotrophs).
2/19/2015
6
2B. Survey of the Protista
The SAR Clade
Diatoms
SA
R c
lad
e
ArchaeplastidaUnikonta
Excavata
Golden algae
Brown algae
Dinoflagellates
Apicomplexans
Ciliates
Forams
Cercozoans
Radiolarians
Stramenopiles
Alveolates
Rhizarians
General Characteristics of the SAR Clade
The SAR clade is a highly diverse monophyletic supergroupbased on DNA similarities that includes the following:
STRAMENOPILES
ALVEOLATES
RHIZARIANS
Smoothflagellum
5 μm
Hairyflagellum
Stramenopiles
Most members of the Stramenopile clade have both “hairy” and smooth flagella.
• this clade includes the following ecologically important groups of photosynthetic organisms:
DIATOMS
GOLDEN ALGAE
BROWN ALGAE
2/19/2015
7
40 μ
mDiatoms
Diatoms have unique glass-like walls made of silicon dioxide and are a significant portion of phytoplankton in the oceans.
• their remains are the main components of white sediments referred to as “diatomaceous earth” (e.g., the “white cliffs of Dover”)
Flagellum
25 μm
Outer container
Living cell
Golden Algae
• contain yellow and brown carotenoids which give them their characteristic color
• typically have two flagella
• most are single-celled though some are colonial
Blade
Stipe
Holdfast
Brown Algae
Brown algae are all multicellular and are the largest algae.
• includes many “seaweeds” such as kelp
• although brown algae are not plants, many have plant-like structures shown in this image
2/19/2015
8
Haploid (n)
Diploid (2n)
Sporangia
MEIOSIS
Sporophyte(2n) Zoospore
Gameto-phytes(n)
Female
Male
Sperm
Egg
Zygote(2n)
Mature femalegametophyte(n)
Developingsporophyte
FERTILIZATION
10 cm
Alternation ofGenerations
• many multicellular algae have a life cycle similar to that of plants called the “Alternation of Generations” – the alternation between multicellular haploidand diploid forms
Flagellum Alveoli
Alveolate
0.2
μm
Alveolates
Members of the Alveolate clade have membrane enclosed sacs called alveoli must beneath the plasma membrane.
• this clade includes the following:
DINOFLAGELLATES
APICOMPLEXANS
CILIATES
Flagella
3 μm
(a) Dinoflagellateflagella
(b) Red tide in the Gulfof Carpentaria innorthern Australia
Dinoflagellates
Dinoflagellates are also an important component of phytoplankton and have 2 flagella, one of which wraps around the cell and causes it to rotate.
• are responsible for the algal blooms known as “red tides”
2/19/2015
9
Apicomplexans
The Apicomplexans are parasites of animals that have complex life cycles with multiple hosts.
• the most significant genus in this clade is Plasmodium, the cause of malaria
• nearly 1 million people each year die from malaria
Merozoite
0.5 μm
Apex
Red bloodcell
Haploid (n)
Diploid (2n)
Sporozoites(n)
Inside mosquito Inside human
Liver
Livercell
Redbloodcells
Merozoite(n)
Game-tocytes(n)
Gametes
Zygote(2n)
Oocyst
MEIOSIS
FERTILIZATION
PlasmodiumLife Cycle
• mosquitoes are the definitive host (in which sexualreproduction occurs)
• humans are the intermediate host (in which reproduction is asexual)
Contractile
vacuole
50 μmCilia
Micronucleus
Macronucleus
Oral groove
Cell mouth
Food
vacuoles
(a) Feeding, waste removal, and water balance.
Ciliates
The Ciliates clade is a large group characterized by cilia used for locomotion and/or feeding and 2 nuclei, one macronucleus and one micronucleus.
• the genus Paramecium is a good example
• Ciliates also engage in a form of sexual reproduction called conjugation…
2/19/2015
10
Compatible
mates
(b) Conjugation and reproduction.
MEIOSIS
The original macro-nucleus disintegrates.
Haploidmicronucleus
MICRO-NUCLEARFUSION
Conjugation
Asexual
reproduction
Diploidmicronucleus
Diploidmicronucleus
Conjugation in Ciliates
Rhizarians
The Rhizarians are mostly amoebas containing pseudopodia that are threadlike (unlike the Amoebozoa in the Unikonta clade.
• this clade includes the following:
RADIOLARIANS
FORAMS
CERCOZOANS
Pseudopodia
200 μm
Radiolarians
Radiolarians have delicate, symmetrical endoskeletons made typically of silica.
• the pseudopodia extend from the cell to catch prey
2/19/2015
11
Forams
Foraminiferans (“hole bearers”), or forams for short, are single-celled heterotrophs that characteristically have multi-chambered shells called tests.
• foram tests are found throughout the fossil record and their tests can be analyzed to estimate ocean temperatures in ancient times
Chromatophore
5 μm
Cercozoans
• most are heterotrophs, though a few such as Paulinellachromatophora are autotrophs that contain unique photosynthetic structures called chromatophores
Chlorophytes
SAR clade
Arc
ha
ep
lastid
a
Unikonta
Excavata
Charophytes
Red algae
Green algae
Land plants
2C. Survey of the Protista
The Archaeplastida
2/19/2015
12
The Archaeplastida
The supergroup Archaeplastida contains the following:
• molecular and other data indicate the land plants are descendants of the green algae, though only the red and green algae are considered to be protists
RED ALGAE
GREEN ALGAE
LAND PLANTS
▼ Nori
8 mm
20 cm
◀ Dulse (Palmaria palmata)
► Bonnemaisonia
hamiferaRed Algae
The red algae contain, in addition to chlorophyll, a red accessory pigment called phycoerythrin.
• phycoerythrin absorbs non-red light
• many red algae live in deep water where red light does not penetrate
This group includes many seaweeds some of which are edible.
(a) Ulva, or sea lettuce
(b) Caulerpa, anintertidalchlorophyte
2 cm
Green Algae
Green algae contain green chloroplasts (due to chlorophyll) and includes 2 main groups:
CHAROPHYTES
CHLOROPHYTES
• closest relatives to plants
• most live in fresh water
2/19/2015
13
Haploid (n)
1 μm
Diploid (2n)
Flagella
Cell wall
Nucleus
Cross
section
of cup-
shaped
chloroplast(TEM)
Zoospore
ASEXUAL
REPRODUCTION
Gamete
(n)
Mature cell
(n)
Zygote
(2n)
FERTILIZATION
MEIOSIS
+
+
+
+
−
−
−
−
SEXUAL
REPRODUCTION
Most chlorophytes have complex life cycles with both sexual and asexual reproductive stages:
Chlorophyte Life Cycle
SAR clade
Archaeplastida
Un
iko
nta
Excavata
Slime molds
Tubulinids
Entamoebas
Nucleariids
Fungi
Choanoflagellates
Animals
2D. Survey of the Protista
The Unikonta
Am
oeb
ozo
aO
pis
tho
kon
ts
The Unikonta
This group contains 2 major clades:
• all of which are protists:
• includes animals and fungi in addition to some protists:
AMOEBOZOA
OPISTHOKONTS
SLIME MOLDS TUBULINIDS ENTAMOEBAS
NUCLEARIIDS CHOANOFLAGELLATES
2/19/2015
14
Amoebozoans
Amoebozoans have tube or lobe-shaped pseudopodia (unlike the Rhizaria).
Amoeba proteus, a tubulinid Entamoeba histolytica
Slime Molds
Cellular slime molds form multicellular aggregates in which cells are separated by their membranes.
• cells feed individually and can aggregate to migrate and form a fruiting body
Plasmodial slime molds form multicellular aggregates in which there is no separation of nuclei by membranes (i.e., a plasmodium), thus they are not considered to be multicellular.
• species such as Dyctiostelium discoideum are studied to better understand the origins of multicellularity
