Chapter 28 Protists.

Chapter 28 Protists

Overview: Living Small
Even a low-power microscope can reveal a great variety of organisms in a drop of pond water Protist is the informal name of the kingdom of mostly unicellular eukaryotes Advances in eukaryotic systematics have caused the classification of protists to change significantly Protists constitute a paraphyletic group, and Protista is no longer valid as a kingdom

Fig Figure 28.1 Which of these organisms are prokaryotes and which are eukaryotes? 1 µm

Concept 28.1: Most eukaryotes are single-celled organisms
Protists are eukaryotes and thus have organelles and are more complex than prokaryotes Most protists are unicellular, but there are some colonial and multicellular species

Structural and Functional Diversity in Protists
Protists exhibit more structural and functional diversity than any other group of eukaryotes Single-celled protists can be very complex, as all biological functions are carried out by organelles in each individual cell

Protists, the most nutritionally diverse of all eukaryotes, include:
Photoautotrophs, which contain chloroplasts Heterotrophs, which absorb organic molecules or ingest larger food particles Mixotrophs, which combine photosynthesis and heterotrophic nutrition

Protists can reproduce asexually or sexually, or by the sexual processes of meiosis and syngamy

Endosymbiosis in Eukaryotic Evolution
There is now considerable evidence that much protist diversity has its origins in endosymbiosis Mitochondria evolved by endosymbiosis of an aerobic prokaryote Plastids evolved by endosymbiosis of a photosynthetic cyanobacterium

1 µm Cyanobacterium Red alga Heterotrophic eukaryote Over the course
Fig Cyanobacterium Red alga Primary endosymbiosis Heterotrophic eukaryote Figure 28.2 Diversity of plastids produced by secondary endosymbiosis Over the course of evolution, this membrane was lost. Green alga 1 µm

Plastid Dinoflagellates Apicomplexans Cyanobacterium Red alga
Fig Plastid Dinoflagellates Secondary endosymbiosis Apicomplexans Cyanobacterium Red alga Primary endosymbiosis Stramenopiles Heterotrophic eukaryote Plastid Secondary endosymbiosis Figure 28.2 Diversity of plastids produced by secondary endosymbiosis Over the course of evolution, this membrane was lost. Euglenids Secondary endosymbiosis Green alga Chlorarachniophytes

The plastid-bearing lineage of protists evolved into red algae and green algae
On several occasions during eukaryotic evolution, red and green algae underwent secondary endosymbiosis, in which they were ingested by a heterotrophic eukaryote

Five Supergroups of Eukaryotes
It is no longer thought that amitochondriates (lacking mitochondria) are the oldest lineage of eukaryotes Our understanding of the relationships among protist groups continues to change rapidly One hypothesis divides all eukaryotes (including protists) into five supergroups

Figure 28.3 Protist diversity
Fig a Diplomonads Parabasalids Excavata Euglenozoans Dinoflagellates Apicomplexans Alveolates Ciliates Diatoms Chromalveolata Golden algae Stramenopiles Brown algae Oomycetes Chlorarachniophytes Forams Rhizaria Radiolarians Red algae Chlorophytes Green algae Archaeplastida Figure 28.3 Protist diversity For the Cell Biology Video Demonstration of Chemotaxis, go to Animation and Video Files. Charophyceans Land plants Slime molds Amoebozoans Gymnamoebas Entamoebas Nucleariids Unikonta Fungi Opisthokonts Choanoflagellates Animals

Diplomonads Excavata Parabasalids Euglenozoans Fig. 28-03b
Figure 28.3 Protist diversity

Alveolates Chromalveolata Stramenopiles
Fig c Dinoflagellates Apicomplexans Alveolates Ciliates Diatoms Chromalveolata Golden algae Stramenopiles Brown algae Figure 28.3 Protist diversity Oomycetes

Chlorarachniophytes Rhizaria Forams Radiolarians Fig. 28-03d
Figure 28.3 Protist diversity

Red algae Chlorophytes Green algae Archaeplastida Charophyceans
Fig e Red algae Chlorophytes Green algae Archaeplastida Charophyceans Land plants Figure 28.3 Protist diversity

Slime molds Gymnamoebas Entamoebas Unikonta Nucleariids Fungi
Fig f Slime molds Amoebozoans Gymnamoebas Entamoebas Nucleariids Unikonta Fungi Opisthokonts Figure 28.3 Protist diversity Choanoflagellates Animals

Fig g Figure 28.3 Protist diversity 5 µm

Fig h Figure 28.3 Protist diversity 50 µm

Fig i 20 µm Figure 28.3 Protist diversity

Fig j 20 µm 50 µm Figure 28.3 Protist diversity

Fig l Figure 28.3 Protist diversity 100 µm

Concept 28.2: Excavates include protists with modified mitochondria and protists with unique flagella The clade Excavata is characterized by its cytoskeleton Some members have a feeding groove This controversial group includes the diplomonads, parabasalids, and euglenozoans

Diplomonads Excavata Parabasalids Kinetoplastids Euglenozoans
Fig. 28-UN1 Diplomonads Parabasalids Excavata Kinetoplastids Euglenozoans Euglenids Chromalveolata Rhizaria Archaeplastida Unikonta

Diplomonads and Parabasalids
These 2 groups live in anaerobic environments, lack plastids, and have modified mitochondria Diplomonads Have modified mitochondria called mitosomes Derive energy anaerobically, for example, by glycolysis Have two equal-sized nuclei and multiple flagella Are often parasites, for example, Giardia intestinalis

Parabasalids Have reduced mitochondria called hydrogenosomes that generate some energy anaerobically Include Trichomonas vaginalis, the pathogen that causes yeast infections in human females

Flagella Undulating membrane 5 µm Fig. 28-04
Figure 28.4 The parabasalid Trichomonas vaginalis (colorized SEM) Undulating membrane 5 µm

Euglenozoans Euglenozoa is a diverse clade that includes predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites The main feature distinguishing them as a clade is a spiral or crystalline rod of unknown function inside their flagella This clade includes the kinetoplastids and euglenids

Flagella 0.2 µm Crystalline rod Ring of microtubules Fig. 28-05
Figure 28.5 Euglenozoan flagellum Crystalline rod Ring of microtubules

Kinetoplastids Kinetoplastids have a single mitochondrion with an organized mass of DNA called a kinetoplast They include free-living consumers of prokaryotes in freshwater, marine, and moist terrestrial ecosystems This group includes Trypanosoma, which causes sleeping sickness in humans Another pathogenic trypanosome causes Chagas’ disease

Fig Figure 28.6 Trypanosoma, the kinetoplastid that causes sleeping sickness 9 µm

Some species can be both autotrophic and heterotrophic
Euglenids Euglenids have one or two flagella that emerge from a pocket at one end of the cell Some species can be both autotrophic and heterotrophic Video: Euglena Video: Euglena Motion

Long flagellum Eyespot Short flagellum Light detector
Fig Long flagellum Eyespot Short flagellum Light detector Contractile vacuole Nucleus Chloroplast Figure 28.7 Euglena, a euglenid commonly found in pond water Plasma membrane Pellicle Euglena (LM) 5 µm

Concept 28.3: Chromalveolates may have originated by secondary endosymbiosis
Some data suggest that the clade Chromalveolata is monophyletic and originated by a secondary endosymbiosis event The proposed endosymbiont is a red alga This clade is controversial and includes the alveolates and the stramenopiles

Excavata Dinoflagellates Apicomplexans Alveolates Ciliates
Fig. 28-UN2 Excavata Dinoflagellates Apicomplexans Alveolates Ciliates Chromalveolata Diatoms Golden algae Stramenopiles Brown algae Oomycetes Rhizaria Archaeplastida Unikonta

Alveolates Members of the clade Alveolata have membrane-bounded sacs (alveoli) just under the plasma membrane The function of the alveoli is unknown Alveolata includes the dinoflagellates, apicomplexans, and ciliates

Fig Flagellum Alveoli Alveolate Figure 28.8 Alveoli 0.2 µm

Video: Dinoflagellate
Dinoflagellates Dinoflagellates are a diverse group of aquatic mixotrophs and heterotrophs They are abundant components of both marine and freshwater phytoplankton Each has a characteristic shape that in many species is reinforced by internal plates of cellulose Video: Dinoflagellate

Two flagella make them spin as they move through the water
Dinoflagellate blooms are the cause of toxic “red tides”

Fig Flagella Figure 28.9 Pfiesteria shumwayae, a dinoflagellate 3 µm

Apicomplexans Apicomplexans are parasites of animals, and some cause serious human diseases One end, the apex, contains a complex of organelles specialized for penetrating a host They have a nonphotosynthetic plastid, the apicoplast Most have sexual and asexual stages that require two or more different host species for completion

The apicomplexan Plasmodium is the parasite that causes malaria
Plasmodium requires both mosquitoes and humans to complete its life cycle Approximately 2 million people die each year from malaria Efforts are ongoing to develop vaccines that target this pathogen

Merozoite Liver Liver cell Apex Red blood Merozoite cell 0.5 µm (n)
Fig Inside human Merozoite Liver Liver cell Apex Red blood cell Merozoite (n) 0.5 µm Red blood cells Figure The two-host cycle of Plasmodium, the apicomplexan that causes malaria Gametocytes (n) Key Haploid (n) Diploid (2n)

Merozoite Liver Liver cell Apex Red blood 0.5 µm Merozoite cell (n)
Fig Inside mosquito Inside human Merozoite Liver Liver cell Apex Red blood cell Merozoite (n) 0.5 µm Zygote (2n) Red blood cells Figure The two-host cycle of Plasmodium, the apicomplexan that causes malaria FERTILIZATION Gametes Gametocytes (n) Key Haploid (n) Diploid (2n)

Merozoite Sporozoites (n) Liver Liver cell Oocyst Apex MEIOSIS
Fig Inside mosquito Inside human Merozoite Sporozoites (n) Liver Liver cell Oocyst Apex MEIOSIS Red blood cell Merozoite (n) 0.5 µm Zygote (2n) Red blood cells Figure The two-host cycle of Plasmodium, the apicomplexan that causes malaria FERTILIZATION Gametes Gametocytes (n) Key Haploid (n) Diploid (2n)

Ciliates Ciliates, a large varied group of protists, are named for their use of cilia to move and feed They have large macronuclei and small micronuclei The micronuclei function during conjugation, a sexual process that produces genetic variation Conjugation is separate from reproduction, which generally occurs by binary fission

Figure 28.11 Structure and function in the ciliate Paramecium caudatum
Contractile vacuole Oral groove Cell mouth Cilia 50 µm Micronucleus Food vacuoles Macronucleus (a) Feeding, waste removal, and water balance MEIOSIS Haploid micronucleus Diploid micronucleus Compatible mates Figure Structure and function in the ciliate Paramecium caudatum The original macronucleus disintegrates. Diploid micronucleus MICRONUCLEAR FUSION Key ConjugationReproduction (b) Conjugation and reproduction

(a) Feeding, waste removal, and water balance
Fig a Contractile vacuole Oral groove Cell mouth Cilia 50 µm Micronucleus Food vacuoles Macronucleus Figure Structure and function in the ciliate Paramecium caudatum (a) Feeding, waste removal, and water balance

(b) Conjugation and reproduction
Fig b-1 MEIOSIS Haploid micronucleus Diploid micronucleus Compatible mates Figure Structure and function in the ciliate Paramecium caudatum Key Conjugation Reproduction (b) Conjugation and reproduction

(b) Conjugation and reproduction
Fig b-2 MEIOSIS Haploid micronucleus Diploid micronucleus Compatible mates The original macronucleus disintegrates. Diploid micronucleus MICRONUCLEAR FUSION Figure Structure and function in the ciliate Paramecium caudatum Key Conjugation Reproduction (b) Conjugation and reproduction

Video: Paramecium Cilia
Video: Paramecium Vacuole Video: Vorticella Cilia Video: Vorticella Detail Video: Vorticella Habitat

Stramenopiles The clade Stramenopila includes several groups of heterotrophs as well as certain groups of algae Most have a “hairy” flagellum paired with a “smooth” flagellum

Hairy flagellum Smooth flagellum 5 µm Fig. 28-12
Figure Stramenopile flagella 5 µm

Diatoms Diatoms are unicellular algae with a unique two-part, glass-like wall of hydrated silica Diatoms usually reproduce asexually, and occasionally sexually

Fig Figure A freshwater diatom (colorized SEM) 3 µm

Video: Various Diatoms
Diatoms are a major component of phytoplankton and are highly diverse Fossilized diatom walls compose much of the sediments known as diatomaceous earth Video: Diatoms Moving Video: Various Diatoms

Golden Algae Golden algae are named for their color, which results from their yellow and brown carotenoids The cells of golden algae are typically biflagellated, with both flagella near one end All golden algae are photosynthetic, and some are also heterotrophic Most are unicellular, but some are colonial

Flagellum Outer container Living cell 25 µm Fig. 28-14
Figure Dinobryon, a colonial golden alga found in fresh water (LM) 25 µm

Brown Algae Brown algae are the largest and most complex algae All are multicellular, and most are marine Brown algae include many species commonly called “seaweeds” Brown algae have the most complex multicellular anatomy of all algae

Giant seaweeds called kelps live in deep parts of the ocean
The algal body is plantlike but lacks true roots, stems, and leaves and is called a thallus The rootlike holdfast anchors the stemlike stipe, which in turn supports the leaflike blades

Blade Stipe Holdfast Fig. 28-15
Figure Seaweeds: adapted to life at the ocean’s margins Holdfast

Alternation of Generations
A variety of life cycles have evolved among the multicellular algae The most complex life cycles include an alternation of generations, the alternation of multicellular haploid and diploid forms Heteromorphic generations are structurally different, while isomorphic generations look similar

Key Haploid (n) Diploid (2n) Sporangia 10 cm Sporophyte (2n) Zoospore
Fig Sporangia 10 cm MEIOSIS Sporophyte (2n) Zoospore Female Figure The life cycle of the brown alga Laminaria: an example of alternation of generations Gametophytes (n) Male Egg Key Sperm Haploid (n) Diploid (2n)

Key Haploid (n) Diploid (2n) Sporangia 10 cm Sporophyte (2n) Zoospore
Fig Sporangia 10 cm MEIOSIS Sporophyte (2n) Zoospore Female Developing sporophyte Figure The life cycle of the brown alga Laminaria: an example of alternation of generations Gametophytes (n) Zygote (2n) Mature female gemetophyte (n) Male Egg FERTILIZATION Key Sperm Haploid (n) Diploid (2n)

Oomycetes (Water Molds and Their Relatives)
Oomycetes include water molds, white rusts, and downy mildews They were once considered fungi based on morphological studies Most oomycetes are decomposers or parasites They have filaments (hyphae) that facilitate nutrient uptake Their ecological impact can be great, as in Phytophthora infestans causing potato blight

Germ tube Cyst Hyphae ASEXUAL REPRODUCTION Zoospore (2n) Zoosporangium
Fig Germ tube Cyst Hyphae ASEXUAL REPRODUCTION Zoospore (2n) Zoosporangium (2n) Key Haploid (n) Diploid (2n) Figure The life cycle of a water mold

Antheridial hypha with sperm nuclei (n) Hyphae
Fig Oogonium Germ tube Egg nucleus (n) Cyst Antheridial hypha with sperm nuclei (n) MEIOSIS Hyphae ASEXUAL REPRODUCTION Zoospore (2n) Zoosporangium (2n) Key Haploid (n) Diploid (2n) Figure The life cycle of a water mold

Antheridial hypha with sperm nuclei (n) Hyphae
Fig Oogonium Germ tube Egg nucleus (n) Cyst Antheridial hypha with sperm nuclei (n) MEIOSIS Hyphae ASEXUAL REPRODUCTION Zoospore (2n) FERTILIZATION Zygote germination Zygotes (oospores) (2n) SEXUAL REPRODUCTION Zoosporangium (2n) Key Haploid (n) Diploid (2n) Figure The life cycle of a water mold

Video: Water Mold Oogonium Video: Water Mold Zoospores

Concept 28.4: Rhizarians are a diverse group of protists defined by DNA similarities
DNA evidence supports Rhizaria as a monophyletic clade Amoebas move and feed by pseudopodia; some but not all belong to the clade Rhizaria Rhizarians include forams and radiolarians

Excavata Chromalveolata Chlorarachniophytes Rhizaria Foraminiferans
Fig. 28-UN3 Excavata Chromalveolata Chlorarachniophytes Foraminiferans Rhizaria Radiolarians Archaeplastida Unikonta

Forams Foraminiferans, or forams, are named for porous, generally multichambered shells, called tests Pseudopodia extend through the pores in the test Foram tests in marine sediments form an extensive fossil record

Radiolarians Marine protists called radiolarians have tests fused into one delicate piece, usually made of silica Radiolarians use their pseudopodia to engulf microorganisms through phagocytosis The pseudopodia of radiolarians radiate from the central body

Fig Figure A radiolarian Pseudopodia 200 µm

Concept 28.5: Red algae and green algae are the closest relatives of land plants
Over a billion years ago, a heterotrophic protist acquired a cyanobacterial endosymbiont The photosynthetic descendants of this ancient protist evolved into red algae and green algae Land plants are descended from the green algae Archaeplastida is a supergroup used by some scientists and includes red algae, green algae, and land plants

Excavata Chromalveolata Rhizaria Red algae Archaeplastida Chlorophytes
Fig. 28-UN4 Excavata Chromalveolata Rhizaria Red algae Chlorophytes Green algae Archaeplastida Charophyceans Land plants Unikonta

Red Algae Red algae are reddish in color due to an accessory pigment call phycoerythrin, which masks the green of chlorophyll The color varies from greenish-red in shallow water to dark red or almost black in deep water Red algae are usually multicellular; the largest are seaweeds Red algae are the most abundant large algae in coastal waters of the tropics

Fig. 28-19 Figure 28.19 Red algae Bonnemaisonia hamifera 20 cm 8 mm
Dulse (Palmaria palmata) Nori. The red alga Porphyra is the source of a traditional Japanese food. The seaweed is grown on nets in shallow coastal waters. The harvested seaweed is spread on bamboo screens to dry. Figure Red algae Paper-thin, glossy sheets of nori make a mineral-rich wrap for rice, seafood, and vegetables in sushi.

Fig a Bonnemaisonia hamifera Figure Red algae 8 mm

Dulse (Palmaria palmata)
Fig b 20 cm Figure Red algae Dulse (Palmaria palmata)

Nori. The red alga Porphyra is the
Fig c Nori. The red alga Porphyra is the source of a traditional Japanese food. The seaweed is grown on nets in shallow coastal waters. The harvested seaweed is spread on bamboo screens to dry. Figure Red algae Paper-thin, glossy sheets of nori make a mineral-rich wrap for rice, seafood, and vegetables in sushi.

Green Algae Green algae are named for their grass-green chloroplasts Plants are descended from the green algae The two main groups are chlorophytes and charophyceans

Most chlorophytes live in fresh water, although many are marine
Other chlorophytes live in damp soil, as symbionts in lichens, or in snow

Fig Figure Watermelon snow

Chlorophytes include unicellular, colonial, and multicellular forms
Video: Volvox Colony Video: Volvox Daughter Video: Volvox Female Spheroid Video: Volvox Flagella Video: Volvox Inversion 1 Video: Volvox Inversion 2 Video: Volvox Sperm and Female

(a) Ulva, or sea lettuce 2 cm (b) Caulerpa, an intertidal chloro-
Fig (a) Ulva, or sea lettuce 2 cm Figure Multicellular chlorophytes (b) Caulerpa, an intertidal chlorophyte

(a) Ulva, or sea lettuce 2 cm Fig. 28-21a
Figure Multicellular chlorophytes 2 cm

(b) Caulerpa, an intertidal chlorophyte Fig. 28-21b
Figure Multicellular chlorophytes

Most chlorophytes have complex life cycles with both sexual and asexual reproductive stages
Video: Chlamydomonas

Flagella Cell wall Nucleus Zoospore Mature cell (n) Cross section of
Fig Flagella 1 µm Cell wall Nucleus Zoospore Mature cell (n) ASEXUAL REPRODUCTION Cross section of cup-shaped chloroplast Figure The life cycle of Chlamydomonas, a unicellular chlorophyte Key Haploid (n) Diploid (2n)

– Flagella Cell wall + Gamete – (n) + Nucleus Zoospore Mature cell (n)
Fig Flagella – 1 µm Cell wall + Gamete (n) – + Nucleus Zoospore Mature cell (n) FERTILIZATION ASEXUAL REPRODUCTION SEXUAL REPRODUCTION Zygote (2n) Cross section of cup-shaped chloroplast Figure The life cycle of Chlamydomonas, a unicellular chlorophyte Key MEIOSIS Haploid (n) Diploid (2n)

Concept 28.6: Unikonts include protists that are closely related to fungi and animals
The supergroup Unikonta includes animals, fungi, and some protists This group includes two clades: the amoebozoans and the opisthokonts (animals, fungi, and related protists) The root of the eukaryotic tree remains controversial It is unclear whether unikonts separated from other eukaryotes relatively early or late

Excavata Chromalveolata Rhizaria Archaeplastida Amoebozoans
Fig. 28-UN5 Excavata Chromalveolata Rhizaria Archaeplastida Amoebozoans Nucleariids Fungi Unikonta Choanoflagellates Animals

RESULTS Choanoflagellates Animals Unikonta Fungi Common ancestor
Fig RESULTS Choanoflagellates Animals Unikonta Fungi Common ancestor of all eukaryotes Amoebozoans Diplomonads Excavata Euglenozoans Alveolates Chromalveolata Stramenopiles Figure What is the root of the eukaryotic tree? DHFR-TS gene fusion Rhizarians Rhizaria Red algae Green algae Archaeplastida Plants

Amoebozoans Amoebozoans are amoeba that have lobe- or tube-shaped, rather than threadlike, pseudopodia They include gymnamoebas, entamoebas, and slime molds

Slime Molds Slime molds, or mycetozoans, were once thought to be fungi Molecular systematics places slime molds in the clade Amoebozoa

Plasmodial Slime Molds
Many species of plasmodial slime molds are brightly pigmented, usually yellow or orange Video: Plasmodial Slime Mold Video: Plasmodial Slime Mold Streaming

Key Haploid (n) Diploid (2n) 4 cm Feeding plasmodium Mature plasmodium
Fig 4 cm Feeding plasmodium Mature plasmodium (preparing to fruit) Young sporangium Mature sporangium Figure The life cycle of a plasmodial slime mold 1 mm Stalk Key Haploid (n) Diploid (2n)

Key Haploid (n) Diploid (2n) 4 cm Feeding plasmodium Mature plasmodium
Fig 4 cm Feeding plasmodium Mature plasmodium (preparing to fruit) Flagellated cells (n) Young sporangium Amoeboid cells (n) Mature sporangium Germinating spore Spores (n) Figure The life cycle of a plasmodial slime mold MEIOSIS 1 mm Stalk Key Haploid (n) Diploid (2n)

Key Haploid (n) Diploid (2n) 4 cm Feeding Zygote (2n) plasmodium
Fig 4 cm FERTILIZATION Zygote (2n) Feeding plasmodium Mature plasmodium (preparing to fruit) Flagellated cells (n) Young sporangium Amoeboid cells (n) Mature sporangium Germinating spore Spores (n) Figure The life cycle of a plasmodial slime mold MEIOSIS 1 mm Stalk Key Haploid (n) Diploid (2n)

At one point in the life cycle, plasmodial slime molds form a mass called a plasmodium (not to be confused with malarial Plasmodium) The plasmodium is undivided by membranes and contains many diploid nuclei It extends pseudopodia through decomposing material, engulfing food by phagocytosis

Cellular Slime Molds Cellular slime molds form multicellular aggregates in which cells are separated by their membranes Cells feed individually, but can aggregate to form a fruiting body Dictyostelium discoideum is an experimental model for studying the evolution of multicellularity

Spores (n) Emerging amoeba (n) Solitary amoebas 600 µm (feeding stage)
Fig Spores (n) Emerging amoeba (n) Solitary amoebas (feeding stage) (n) 600 µm Fruiting bodies (n) ASEXUAL REPRODUCTION Aggregated amoebas Migrating aggregate Figure The life cycle of Dictyostelium, a cellular slime mold Key Haploid (n) Diploid (2n) 200 µm

Spores (n) Emerging amoeba (n) Zygote (2n) SEXUAL REPRODUCTION
Fig Spores (n) FERTILIZATION Emerging amoeba (n) Zygote (2n) SEXUAL REPRODUCTION Solitary amoebas (feeding stage) (n) 600 µm MEIOSIS Fruiting bodies (n) ASEXUAL REPRODUCTION Amoebas (n) Aggregated amoebas Migrating aggregate Figure The life cycle of Dictyostelium, a cellular slime mold Key Haploid (n) Diploid (2n) 200 µm

Video: Amoeba Pseudopodia
Gymnamoebas Gymnamoebas are common unicellular amoebozoans in soil as well as freshwater and marine environments Most gymnamoebas are heterotrophic and actively seek and consume bacteria and other protists Video: Amoeba Video: Amoeba Pseudopodia

Entamoebas Entamoebas are parasites of vertebrates and some invertebrates Entamoeba histolytica causes amebic dysentery in humans

Opisthokonts Opisthokonts include animals, fungi, and several groups of protists

Concept 28.7: Protists play key roles in ecological relationships
Protists are found in diverse aquatic environments Protists often play the role of symbiont or producer

Some protist symbionts benefit their hosts
Symbiotic Protists Some protist symbionts benefit their hosts Dinoflagellates nourish coral polyps that build reefs Hypermastigotes digest cellulose in the gut of termites

Fig Figure A protist symbiont 10 µm

Some protists are parasitic
Plasmodium causes malaria Pfesteria shumwayae is a dinoflagellate that causes fish kills Phytophthora ramorum causes sudden oak death

Nurseries with P. ramorum infections (2004) on
Fig Key Figure Risk map for sudden oak death in the contiguous United States High risk Moderate risk Low risk Nurseries with P. ramorum infections (2004) on other host plants (such as rhododendron).

Photosynthetic Protists
Many protists are important producers that obtain energy from the sun In aquatic environments, photosynthetic protists and prokaryotes are the main producers The availability of nutrients can affect the concentration of protists

Other consumers Herbivorous plankton Carnivorous plankton Bacteria
Fig Other consumers Herbivorous plankton Carnivorous plankton Bacteria absorbed by Figure Protists are key producers in aquatic communities Soluble organic matter Protistan producers secrete

Fig. 28-UN6

Fig. 28-UN6a

Fig. 28-UN6b

Fig. 28-UN6c

Fig. 28-UN6d

Fig. 28-UN6e

Fig. 28-UN7

Fig. 28-UN8

You should now be able to:
Explain why the kingdom Protista is no longer considered a legitimate taxon Explain the process of endosymbiosis and state what living organisms are likely relatives of mitochondria and plastids Distinguish between endosymbiosis and secondary endosymbiosis Name the five supergroups, list their key characteristics, and describe some representative taxa

Chapter 28 Protists.

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