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- informal name of the kingdom of mostly unicellular eukaryotes. Advances in eukaryotic systematics- caused the classification of protists to change. Protists-a paraphyletic group; some argue that Protista is no longer valid as a kingdom.

Fig Figure 28.1 Which of these organisms are prokaryotes and which are eukaryotes? Figure 28.1 Which of these organisms are prokaryotes and which are eukaryotes? 1 µm Only the cell right above the scale bar is a prokarytote

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

Structural and Functional Diversity in Protists
Protists -more structural/ functional diversity than any other group of euk. Single-celled protists-very complex; all biological functions are carried out by organelles in each cell.

Protists- most nutritionally diverse of all eukaryotes:
Photoautotrophs- contain chloroplasts Heterotrophs-absorb organic molecules/ ingest food particles Mixotrophs-photosynthesis and heterotrophic nutrition ex: species of euglenoids

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

Endosymbiosis in Eukaryotic Evolution
Evidence that much protist diversity- due to endosymbiosis. Mitochondria-endosymbiosis of an aerobic prokaryote. Plastids-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 Figure 28.2 Diversity of plastids produced by secondary endosymbiosis 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

plastid-bearing lineage of protists-red algae and green algae.
During eukaryotic evolution- red and green algae underwent secondary endosymbiosis, in which they were ingested by a heterotrophic eukaryote.

Five Supergroups of Eukaryotes
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 Figure 28.3 Protist diversity 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

5 µm Giardia intestinalis-diplomonad parasite- Camper’s fever
Fig g Figure 28.3 Protist diversity 5 µm Giardia intestinalis-diplomonad parasite- Camper’s fever

Diatoms-silica shells
Fig h Figure 28.3 Protist diversity Diatoms-silica shells 50 µm

extend out from cytoskeleton
Fig i 20 µm Figure 28.3 Protist diversity Foram –pseodopods extend out from cytoskeleton

Volvox- colonial organisms
Fig j Volvox- colonial organisms 50 µm 20 µm Figure 28.3 Protist diversity

Amoeboid – feeding by endocytosis
Fig l Amoeboid – feeding by endocytosis Figure 28.3 Protist diversity 100 µm

Concept 28.2: Excavates include protists with modified mitochondria and protists with unique flagella The clade Excavata-characterized by its cytoskeleton Some members-feeding groove Controversial group (taxonomically)-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
2 groups-anaerobic environments; lack plastids, have modified mitochondria Diplomonads modified mitochondria- mitosomes energy anaerobically ex: glycolysis two equal-sized nuclei; multiple flagella often parasites; ex: Giardia intestinalis

Parabasalids reduced mitochondria- hydrogenosomes-generate some energy anaerobically Ex: Trichomonas vaginalis, pathogen, causes yeast infections in human females

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

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

Euglenoid-most have crys. rod in flagella
Fig Flagella 0.2 µm Figure 28.5 Euglenozoan flagellum Crystalline rod Euglenoid-most have crys. rod in flagella Ring of microtubules

Kinetoplastids Kinetoplastids-single mitochondrion w/ organized mass of DNA -kinetoplast Include free-living consumers of prokaryotes in freshwater, marine, and moist terrestrial ecosystems. Group includes Trypanosoma-sleeping sickness in humans; other trypanosomes- Chagas’ disease (congestive heart failure)

Causes African Sleeping Sickness
Fig Figure 28.6 Trypanosoma, the kinetoplastid that causes sleeping sickness 9 µm Causes African Sleeping Sickness

Euglenids Euglenids-one or two flagella-from a pocket at one end
Some species-both auto- and heterotrophic Video: Euglena Video: Euglena Motion

Figure 28.7 Euglena, a euglenid commonly found in pond water
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 Figure 28.7 Euglena, a euglenid commonly found in pond water

Concept 28.3: Chromalveolates may have originated by secondary endosymbiosis
clade Chromalveolata- may be monophyletic; originated by a secondary endosymbiosis event. proposed endosymbiont- red alga Clade- controversial; includes 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 clade Alveolata-membrane-bounded sacs (alveoli) just under the plasma membrane The function of the alveoli-unknown; hypothesis- may help stabilize cell surface or regulate cell’s water and ion content Alveolata-dinoflagellates, apicomplexans, and ciliates

Flagellum Alveoli Alveolate 0.2 µm Fig. 28-08 Figure 28.8 Alveoli

Video: Dinoflagellate
Dinoflagellates Dinoflagellates-diverse group of aquatic mixotrophs and heterotrophs abundant components of both marine and freshwater phytoplankton has a characteristic shape-many species are reinforced by internal plates of cellulose Two flagella -spin as they move through water Dinoflagellate- blooms = toxic “red tides” Video: Dinoflagellate

Flagella 3 µm Figure 28.9 Pfiesteria shumwayae, a dinoflagellate

Apicomplexans Apicomplexans-parasites of animals; some cause serious human diseases; Plasmodium Apex-contains organelles specialized for penetrating a host Have a nonphotosynthetic plastid-the apicoplast (remnant of red algal ancestor?) Most – sexual/ asexual stages that require two or more different host species

The apicomplexan Plasmodium is the parasite that causes malaria.
Plasmodium requires both mosquitoes and humans to complete its life cycle. Approx. 2 million people die/ year from malaria Ongoing efforts to develop vaccines to target this pathogen

Fig Inside human Figure The two-host cycle of Plasmodium, the apicomplexan that causes malaria 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- large varied group of protists- named for use of cilia- move and feed large macronuclei; small micronuclei Micronuclei-conjugation, a sexual process that produces genetic variation Conjugation-separate from repro. which 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 Clade Stramenopila-several groups of heterotrophs as well as groups of algae Most- “hairy” flagellum paired with a “smooth” flagellum

Hairy flagellum Smooth flagellum 5 µm
Fig Hairy flagellum Smooth flagellum Figure Stramenopile flagella Figure Stramenopile flagella 5 µm

Diatoms Diatoms-unicellular algae; unique two-part, glass-like wall of hydrated silica Diatoms- usually reproduce asexually, and occasionally sexually when ¼ of original size

3 µm Figure 28.13 A freshwater diatom (colorized SEM) Fig. 28-13

Video: Various Diatoms
Diatoms -major part of phytoplankton;highly diverse Fossilized diatom walls- compose sediments known as diatomaceous earth Video: Diatoms Moving Video: Various Diatoms

Golden Algae Golden algae-named for color; results from their yellow and brown carotenoids. cells are typically biflagellated, with both flagella near one end All –photosynthetic; some also heterotrophic Most are unicellular; some colonial

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

Brown Algae Brown algae- largest, most complex algae
All-multicellular; most marine Many species commonly called “seaweeds” Most complex multicellular anatomy of all algae

Giant seaweeds- kelps live in deep parts of the ocean
Algal body- “plantlike;” lacks true roots, stems, leaves so called a thallus “Rootlike” holdfast-anchors stemlike stipe, in turn supports leaflike blades

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

Alternation of Generations
Variety of life cycles-evolved among the multicellular algae Most complex life cycles include an alternation of generations, the alternation of multicellular haploid and diploid forms Heteromorphic generations- structurally different; 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-water molds, white rusts, and downy mildews Once considered fungi- based on morphological studies Most oomycetes-decomposers or parasites Have filaments (hyphae)-facilitate nutrient uptake Ecological impact can be great – Ex: Phytophthora infestans causing potato blight

Figure 28.17 The life cycle of a water mold Germ tube
Cyst Hyphae ASEXUAL REPRODUCTION Zoospore (2n) Zoosporangium (2n) Key Haploid (n) Diploid (2n) Figure The life cycle of a water mold

Figure 28.17 The life cycle of a water mold Germ tube Egg nucleus (n)
Oogonium Figure The life cycle of a water mold 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

Video: Water Mold Oogonium Video: Water Mold Zoospores
Fig Oogonium Figure The life cycle of a water mold 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

DNA evidence -Rhizaria as a monophyletic clade
Concept 28.4: Rhizarians are a diverse group of protists defined by DNA similarities DNA evidence -Rhizaria as a monophyletic clade Amoebas –move/feed -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 (forams)- porous, generally multichambered shells (tests) Pseudopodia-extend through the pores of test Foram tests-marine sediments-form an extensive fossil record

Radiolarians Radiolarians-marine- tests fused-one delicate piece- usually silica Use pseudopodia to engulf microorganisms through phagocytosis pseudopodia radiate from the central body

Pseudopodia 200 µm Figure 28.18 A radiolarian Fig. 28-18

Land plants descended from the green algae
Concept 28.5: Red algae and green algae are the closest relatives of land plants Over a billion years ago-heterotrophic protist acquired a cyanobacterial endosymbiont photosynthetic descendants of this ancient protist evolved into red algae and green algae Land plants descended from the green algae Archaeplastida-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-reddish -accessory pigment call phycoerythrin-masks the green chlorophyll color varies from greenish-red in shallow water to dark red/ almost black in deep water usually multicellular; largest-seaweeds most abundant large algae in tropical coastal waters

Figure 28.19 Red algae Fig. 28-19 Figure 28.19 Red algae Bonnemaisonia
hamifera Figure Red algae 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.

Figure 28.19 Red algae Bonnemaisonia hamifera 8 mm Fig. 28-19a

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

The supergroup Unikonta includes animals, fungi, and some protists.
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.

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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