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This document provides an overview of key concepts about protists from Chapter 28 of Campbell Biology. It discusses how protists exhibit structural and functional diversity as mostly unicellular eukaryotes. It describes important protist groups like excavates, which include organisms with modified mitochondria and unique flagella. It also discusses how chromalveolates and alveolates may have originated via secondary endosymbiosis and includes examples like dinoflagellates, apicomplexans, and ciliates. The document aims to classify protists and explain their diversity in organelles, nutrition, reproduction, and evolutionary origins from endosymbiosis.

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LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson © 2011 Pearson Education, Inc. Lectures by Erin Barley Kathleen Fitzpatrick Protists Chapter 28
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 group of mostly unicellular eukaryotes • Advances in eukaryotic systematics have caused the classification of protists to change significantly • Protists constitute a polyphyletic group, and Protista is no longer valid as a kingdom © 2011 Pearson Education, Inc.
1 m Figure 28.1
Concept 28.1: Most eukaryotes are single-celled organisms • Protists are eukaryotes • Eukaryotic cells have organelles and are more complex than prokaryotic cells • Most protists are unicellular, but there are some colonial and multicellular species © 2011 Pearson Education, Inc.
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 © 2011 Pearson Education, Inc.
• 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 © 2011 Pearson Education, Inc.
• Some protists reproduce asexually, while others reproduce sexually, or by the sexual processes of meiosis and fertilization © 2011 Pearson Education, Inc.
Endosymbiosis in Eukaryotic Evolution • There is now considerable evidence that much protist diversity has its origins in endosymbiosis • Endosymbiosis is the process in which a unicellular organism engulfs another cell, which becomes an endosymbiont and then organelle in the host cell • Mitochondria evolved by endosymbiosis of an aerobic prokaryote • Plastids evolved by endosymbiosis of a photosynthetic cyanobacterium © 2011 Pearson Education, Inc.
Cyanobacterium Heterotrophic eukaryote Primary endosymbiosis Membranes are represented as dark lines in the cell. 1 2 3 One of these membranes was lost in red and green algal descendants. Plastid Red alga Secondary endosymbiosis Secondary endosymbiosis Secondary endosymbiosis Green alga Dinoflagellates Apicomplexans Stramenopiles Plastid Euglenids Chlorarachniophytes Figure 28.2
Figure 28.2a Cyanobacterium Heterotrophic eukaryote Primary endosymbiosis Membranes are represented as dark lines in the cell. 1 2 3 One of these membranes was lost in red and green algal descendants. Red alga Green alga
Figure 28.2b Plastid Red alga Secondary endosymbiosis Dinoflagellates Apicomplexans Stramenopiles
Figure 28.2c Secondary endosymbiosis Green alga Plastid Euglenids Chlorarachniophytes Secondary endosymbiosis
• The plastid-bearing lineage of protists evolved into red and green algae • The DNA of plastid genes in red algae and green algae closely resemble the DNA of cyanobacteria • On several occasions during eukaryotic evolution, red and green algae underwent secondary endosymbiosis, in which they were ingested by a heterotrophic eukaryote © 2011 Pearson Education, Inc.
Five Supergroups of Eukaryotes • It is no longer thought that amitochondriates (lacking mitochondria) are the oldest lineage of eukaryotes • Many have been shown to have mitochondria and have been reclassified • Our understanding of the relationships among protist groups continues to change rapidly • One hypothesis divides all eukaryotes (including protists) into five supergroups © 2011 Pearson Education, Inc.
Figure 28.3a Diplomonads Parabasalids Euglenozoans Dinoflagellates Apicomplexans Ciliates Diatoms Golden algae Brown algae Oomycetes Cercozoans Forams Radiolarians Red algae Chlorophytes Charophytes Land plants Slime molds Gymnamoebas Entamoebas Nucleariids Fungi Choanoflagellates Animals Alveolates Stramenopiles Green algae Amoebozoans Opisthokonts Excavata Chromalveolata Rhizaria Archaeplastida Unikonta
Figure 28.3aa Diplomonads Parabasalids Euglenozoans Dinoflagellates Apicomplexans Ciliates Diatoms Golden algae Brown algae Oomycetes Alveolates Stramenopiles Excavata Chromalveolata
Figure 28.3ab Cercozoans Forams Radiolarians Red algae Chlorophytes Charophytes Land plants Green algae Rhizaria Archaeplastida
Figure 28.3ac Slime molds Gymnamoebas Entamoebas Nucleariids Fungi Choanoflagellates Animals Amoebozoans Opisthokonts Unikonta
Figure 28.3b Giardia intestinalis, a diplomonad parasite 5 m
Figure 28.3c Diatom diversity 50 m
Globigerina, a foram in the supergroup Rhizaria 100 m Figure 28.3d
Figure 28.3da
Figure 28.3db Globigerina, a foram in the supergroup Rhizaria 100 m
Figure 28.3e Volvox, a colonial freshwater green alga 20 m 50 m
Figure 28.3ea 20 m
Figure 28.3eb Volvox, a colonial freshwater green alga 50 m
Figure 28.3f A unikont amoeba 100 m
• The clade Excavata is characterized by its cytoskeleton • Some members have a feeding groove • This controversial group includes the diplomonads, parabasalids, and euglenozoans Concept 28.2: Excavates include protists with modified mitochondria and protists with unique flagella © 2011 Pearson Education, Inc.
Figure 28.UN01 Kinetoplastids Euglenids Euglenozoans Diplomonads Parabasalids Excavata Chromalveolata Rhizaria Archaeplastida Unikonta
Diplomonads and Parabasalids • These two groups lack plastids, have modified mitochondria, and most live in anaerobic environments • Diplomonads – Have modified mitochondria called mitosomes – Derive energy from anaerobic biochemical pathways – Have two equal-sized nuclei and multiple flagella – Are often parasites, for example, Giardia intestinalis (also known as Giardia lamblia) © 2011 Pearson Education, Inc.
• Parabasalids – Have reduced mitochondria called hydrogenosomes that generate some energy anaerobically – Include Trichomonas vaginalis, the pathogen that causes yeast infections in human females © 2011 Pearson Education, Inc.
Figure 28.4 Flagella 5 m Undulating membrane
Euglenozoans • Euglenozoa is a diverse clade that includes predatory heterotrophs, photosynthetic autotrophs, and 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 © 2011 Pearson Education, Inc.
Figure 28.5 Crystalline rod (cross section) Flagella Ring of microtubules (cross section) 8 m 0.2 m
Figure 28.5a Crystalline rod (cross section) Ring of microtubules (cross section) 0.2 m
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 © 2011 Pearson Education, Inc.
Figure 28.6 9 m
• Trypanosomes evade immune responses by switching surface proteins • A cell produces millions of copies of a single protein • The new generation produces millions of copies of a different protein • These frequent changes prevent the host from developing immunity © 2011 Pearson Education, Inc.
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 © 2011 Pearson Education, Inc. Video: Euglena Motion Video: Euglena
Figure 28.7 Long flagellum Eyespot Short flagellum Contractile vacuole Nucleus Chloroplast Plasma membrane Euglena (LM) 5 m Pellicle Light detector
Figure 28.7a Long flagellum Eyespot Contractile vacuole Nucleus Chloroplast Plasma membrane Euglena (LM) 5 m
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 © 2011 Pearson Education, Inc.
Figure 28.UN02 Apicomplexans Ciliates Diatoms Stramenopiles Alveolates Chromalveolata Rhizaria Archaeplastida Unikonta Dinoflagellates Golden algae Brown algae Oomycetes Excavata
Alveolates • Members of the clade Alveolata have membrane-bounded sacs (alveoli) just under the plasma membrane • The function of the alveoli is unknown • The alveolates include – Dinoflagellates – Apicomplexans – Ciliates © 2011 Pearson Education, Inc.
Figure 28.8 Flagellum Alveoli Alveolate 0.2 m
Figure 28.8a Flagellum Alveoli 0.2 m
Dinoflagellates • Dinoflagellates have two flagella and each cell is reinforced by cellulose plates • They are abundant components of both marine and freshwater phytoplankton • They are a diverse group of aquatic phototrophs, mixotrophs, and heterotrophs • Toxic “red tides” are caused by dinoflagellate blooms © 2011 Pearson Education, Inc. Video: Dinoflagellate
Figure 28.9 Flagella 3 m
Apicomplexans • Apicomplexans are parasites of animals, and some cause serious human diseases • They spread through their host as infectious cells called sporozoites • One end, the apex, contains a complex of organelles specialized for penetrating host cells and tissues • Most have sexual and asexual stages that require two or more different host species for completion © 2011 Pearson Education, Inc.
• The apicomplexan Plasmodium is the parasite that causes malaria • Plasmodium requires both mosquitoes and humans to complete its life cycle • Approximately 900,000 people die each year from malaria • Efforts are ongoing to develop vaccines that target this pathogen © 2011 Pearson Education, Inc.
Merozoite (n) Liver Liver cell Red blood cells Gametocytes (n) Merozoite Apex 0.5 m Red blood cell Key Haploid (n) Diploid (2n) Inside human Figure 28.10-1
Zygote (2n) Merozoite (n) Gametes Liver Liver cell Red blood cells Gametocytes (n) Merozoite Apex 0.5 m Red blood cell Key Haploid (n) Diploid (2n) Inside mosquito Inside human FERTILIZATION Figure 28.10-2
Sporozoites (n) Oocyst Zygote (2n) Merozoite (n) Gametes Liver Liver cell Red blood cells Gametocytes (n) Merozoite Apex 0.5 m Red blood cell Key Haploid (n) Diploid (2n) Inside mosquito Inside human MEIOSIS FERTILIZATION Figure 28.10-3
Figure 28.10a Merozoite Apex Red blood cell 0.5 m
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 • Genetic variation results from conjugation, in which two individuals exchange haploid micronuclei • Conjugation is a sexual process, and is separate from reproduction, which generally occurs by binary fission © 2011 Pearson Education, Inc.
Contractile vacuole Oral groove Cell mouth Food vacuoles Cilia Micronucleus Macronucleus 50 m (a) Feeding, waste removal, and water balance Conjugation Asexual reproduction Key MEIOSIS MICRONUCLEAR FUSION Diploid micronucleus Diploid micronucleus Haploid micronucleus Compatible mates The original macronucleus disintegrates. (b) Conjugation and reproduction Figure 28.11
Figure 28.11a Contractile vacuole Oral groove Cell mouth Food vacuoles Cilia Micronucleus Macronucleus 50 m (a) Feeding, waste removal, and water balance
Figure 28.11b-1 Conjugation Asexual reproduction Key MEIOSIS Diploid micronucleus Haploid micronucleus Compatible mates (b) Conjugation and reproduction
Figure 28.11b-2 Conjugation Asexual reproduction Key MEIOSIS MICRONUCLEAR FUSION Diploid micronucleus Diploid micronucleus Haploid micronucleus Compatible mates The original macronucleus disintegrates. (b) Conjugation and reproduction
Figure 28.11c 50 m
© 2011 Pearson Education, Inc. Video: Vorticella Habitat Video: Vorticella Detail Video: Vorticella Cilia Video: Paramecium Vacuole Video: Paramecium Cilia
Stramenopiles • The clade Stramenopila includes important phototrophs as well as several clades of heterotrophs • Most have a “hairy” flagellum paired with a “smooth” flagellum • Stramenopiles include diatoms, golden algae, brown algae, and oomycetes © 2011 Pearson Education, Inc.
Figure 28.12 Smooth flagellum Hairy flagellum 5 m
Diatoms • Diatoms are unicellular algae with a unique two- part, glass-like wall of hydrated silica • Diatoms usually reproduce asexually, and occasionally sexually © 2011 Pearson Education, Inc.
Figure 28.13 40 m
• Diatoms are a major component of phytoplankton and are highly diverse • Fossilized diatom walls compose much of the sediments known as diatomaceous earth • After a diatom population has bloomed, many dead individuals fall to the ocean floor undecomposed © 2011 Pearson Education, Inc.
• This removes carbon dioxide from the atmosphere and “pumps” it to the ocean floor © 2011 Pearson Education, Inc. Video: Various Diatoms Video: Diatoms Moving
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 mixotrophs • Most are unicellular, but some are colonial © 2011 Pearson Education, Inc.
Flagellum Outer container Living cell 25 m Figure 28.14
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 © 2011 Pearson Education, Inc.
• 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 © 2011 Pearson Education, Inc.
Figure 28.15 Blade Stipe 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 © 2011 Pearson Education, Inc.
• The diploid sporophyte produces haploid flagellated spores called zoospores • The zoospores develop into haploid male and female gametophytes, which produce gametes • Fertilization of gamates results in a diploid zygote, which grows into a new sporophyte © 2011 Pearson Education, Inc.
10 cm Haploid (n) Diploid (2n) Key Sporangia Gametophytes (n) Zoospore Female Male Sperm MEIOSIS Sporophyte (2n) Egg Figure 28.16-1
10 cm Mature female gametophyte (n) Developing sporophyte Zygote (2n) Haploid (n) Diploid (2n) Key Sporangia Gametophytes (n) Zoospore Female Male Sperm MEIOSIS FERTILIZATION Sporophyte (2n) Egg Figure 28.16-2
Figure 28.16a 10 cm
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 potato blight caused by Phytophthora infestans © 2011 Pearson Education, Inc.
Germ tube Cyst Hyphae ASEXUAL REPRODUCTION Zoospore (2n) Zoosporangium (2n) Key Haploid (n) Diploid (2n) Figure 28.17-1
Figure 28.17-2 Germ tube Cyst Hyphae ASEXUAL REPRODUCTION Zoospore (2n) Zoosporangium (2n) Key Haploid (n) Diploid (2n) MEIOSIS Antheridial hypha with sperm nuclei (n) Egg nucleus (n) Oogonium
Figure 28.17-3 Germ tube Cyst Hyphae ASEXUAL REPRODUCTION Zoospore (2n) Zoosporangium (2n) Zygote germination SEXUAL REPRODUCTION Key Haploid (n) Diploid (2n) MEIOSIS FERTILIZATION Zygotes (oospores) (2n) Antheridial hypha with sperm nuclei (n) Egg nucleus (n) Oogonium
Figure 28.17a
© 2011 Pearson Education, Inc. 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 radiolarians, forams, and cercozoans © 2011 Pearson Education, Inc.
Figure 28.UN03 Radiolarians Foraminiferans Cercozoans Rhizaria Excavata Chromalveolata Archaeplastida Unikonta
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 © 2011 Pearson Education, Inc.
Figure 28.18 Pseudopodia 200 m
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 • Many forams have endosymbiotic algae © 2011 Pearson Education, Inc.
Cercozoans • Cercozoans include most amoeboid and flagellated protists with threadlike pseudopodia • They are common in marine, freshwater, and soil ecosystems • Most are heterotrophs, including parasites and predators © 2011 Pearson Education, Inc.
• Paulinella chromatophora is an autotroph with a unique photosynthetic structure • This structure evolved from a different cyanobacterium than the plastids of other photosynthetic eukaryotes © 2011 Pearson Education, Inc.
Figure 28.19 Chromatophore 5 m
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 the supergroup that includes red algae, green algae, and land plants © 2011 Pearson Education, Inc.
Figure 28.UN04 Chlorophytes Charophytes Archaeplastida Excavata Chromalveolata Rhizaria Unikonta Red algae Green algae Land plants
Red Algae • Red algae are reddish in color due to an accessory pigment called 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 © 2011 Pearson Education, Inc.
Figure 28.20 20 cm 8 mm Bonnemaisonia hamifera Dulse (Palmaria palmata) Nori
Figure 28.20a 8 mm Bonnemaisonia hamifera
Figure 28.20b 20 cm Dulse (Palmaria palmata)
Figure 28.20c Nori
Figure 28.20d Nori
Figure 28.20e Nori
Green Algae • Green algae are named for their grass-green chloroplasts • Plants are descended from the green algae • Green algae are a paraphyletic group • The two main groups are chlorophytes and charophyceans • Charophytes are most closely related to land plants © 2011 Pearson Education, Inc.
• Most chlorophytes live in fresh water, although many are marine • Other chlorophytes live in damp soil, as symbionts in lichens, or in snow © 2011 Pearson Education, Inc.
• Larger size and greater complexity evolved in chlorophytes by 1. The formation of colonies from individual cells 2. The formation of true multicellular bodies by cell division and differentiation (e.g., Ulva) 3. The repeated division of nuclei with no cytoplasmic division (e.g., Caulerpa) © 2011 Pearson Education, Inc.
Figure 28.21 (a) Ulva, or sea lettuce (b) Caulerpa, an intertidal chlorophyte 2 cm
Figure 28.21a (a) Ulva, or sea lettuce 2 cm
Figure 28.21b (b) Caulerpa, an intertidal chlorophyte
© 2011 Pearson Education, Inc. Video: Volvox Sperm and Female Video: Volvox Inversion 2 Video: Volvox Inversion 1 Video: Volvox Flagella Video: Volvox Female Spheroid Video: Volvox Daughter Video: Volvox Colony
• Most chlorophytes have complex life cycles with both sexual and asexual reproductive stages © 2011 Pearson Education, Inc. Video: Chlamydomonas
Figure 28.22 Flagella Cell wall Nucleus Cross section of cup-shaped chloroplast 1 m (TEM) Zoospore ASEXUAL REPRODUCTION SEXUAL REPRODUCTION Gamete (n) Mature cell (n) Zygote (2n) FERTILIZATION MEIOSIS Key Haploid (n) Diploid (2n)        
Zoospore ASEXUAL REPRODUCTION Mature cell (n) Key Haploid (n) Diploid (2n) Figure 28.22a-1
Zoospore ASEXUAL REPRODUCTION SEXUAL REPRODUCTION Gamete (n) Mature cell (n) Zygote (2n) FERTILIZATION MEIOSIS Key Haploid (n) Diploid (2n)         Figure 28.22a-2
Figure 28.22b Flagella Cell wall Nucleus Cross section of cup-shaped chloroplast 1 m (TEM)
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 © 2011 Pearson Education, Inc.
Figure 28.UN05 Choanoflagellates Animals Unikonta Excavata Chromalveolata Rhizaria Archaeplastida Amoebozoans Nucleariids Fungi
Unikonta Excavata Chromalveolata Rhizaria Archaeplastida RESULTS Common ancestor of all eukaryotes DHFR-TS gene fusion Choanoflagellates Animals Fungl Amoebozoans Euglenozoans Alveolates Stramenopiles Rhizarians Diplomonads Red algae Green algae Plants Figure 28.23
Amoebozoans • Amoebozoans are amoeba that have lobe- or tube-shaped, rather than threadlike, pseudopodia • They include slime molds, gymnamoebas, and entamoebas © 2011 Pearson Education, Inc.
Slime Molds • Slime molds, or mycetozoans, were once thought to be fungi • Molecular systematics places slime molds in the clade Amoebozoa © 2011 Pearson Education, Inc.
Plasmodial Slime Molds • Many species of plasmodial slime molds are brightly pigmented, usually yellow or orange © 2011 Pearson Education, Inc. Video: Plasmodial Slime Mold Streaming Video: Plasmodial Slime Mold
Stalk Zygote (2n) FERTILIZATION MEIOSIS Amoeboid cells (n) Germinating spore Spores (n) Flagellated cells (n) Mature sporangium Young sporangium Feeding plasmodium Mature plasmodium (preparing to fruit) 4 cm 1 mm Key Haploid (n) Diploid (2n) Figure 28.24
Stalk Mature sporangium Young sporangium Feeding plasmodium Mature plasmodium (preparing to fruit) Key Haploid (n) Diploid (2n) Figure 28.24a-1
Stalk MEIOSIS Amoeboid cells (n) Germinating spore Spores (n) Flagellated cells (n) Mature sporangium Young sporangium Feeding plasmodium Mature plasmodium (preparing to fruit) Key Haploid (n) Diploid (2n) Figure 28.24a-2
Stalk Zygote (2n) FERTILIZATION MEIOSIS Amoeboid cells (n) Germinating spore Spores (n) Flagellated cells (n) Mature sporangium Young sporangium Feeding plasmodium Mature plasmodium (preparing to fruit) Key Haploid (n) Diploid (2n) Figure 28.24a-3
Figure 28.24b 4 cm
Figure 28.24c 1 mm
• 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 not multicellular • It is undivided by plasma membranes and contains many diploid nuclei • It extends pseudopodia through decomposing material, engulfing food by phagocytosis © 2011 Pearson Education, Inc.
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 © 2011 Pearson Education, Inc.
Spores (n) 600 m 200 m Solitary amoebas (n) Emerging amoeba (n) Fruiting bodies (n) Aggregated amoebas ASEXUAL REPRODUCTION Migrating aggregate Key Haploid (n) Diploid (2n) Figure 28.25-1
Spores (n) 600 m 200 m Solitary amoebas (n) Emerging amoeba (n) Fruiting bodies (n) Aggregated amoebas Amoebas (n) ASEXUAL REPRODUCTION SEXUAL REPRODUCTION Zygote (2n) Migrating aggregate Key Haploid (n) Diploid (2n) FERTILIZATION MEIOSIS Figure 28.25-2
Figure 28.25a 600 m
Figure 28.25b 200 m
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 © 2011 Pearson Education, Inc. Video: Amoeba Pseudopodia Video: Amoeba
Entamoebas • Entamoebas are parasites of vertebrates and some invertebrates • Entamoeba histolytica causes amebic dysentery, the third-leading cause of human death due to eukaryotic parasites © 2011 Pearson Education, Inc.
Opisthokonts • Opisthokonts include animals, fungi, and several groups of protists © 2011 Pearson Education, Inc.
Concept 28.7: Protists play key roles in ecological communities • Protists are found in diverse aquatic environments • Protists often play the role of symbiont or producer © 2011 Pearson Education, Inc.
Symbiotic Protists • Some protist symbionts benefit their hosts – Dinoflagellates nourish coral polyps that build reefs – Wood-digesting protists digest cellulose in the gut of termites © 2011 Pearson Education, Inc.
Figure 28.26 10 m
• Some protists are parasitic – Plasmodium causes malaria – Pfiesteria shumwayae is a dinoflagellate that causes fish kills – Phytophthora ramorum causes sudden oak death © 2011 Pearson Education, Inc.
Photosynthetic Protists • Many protists are important producers that obtain energy from the sun • In aquatic environments, photosynthetic protists and prokaryotes are the main producers • In aquatic environments, photosynthetic protists are limited by nutrients • These populations can explode when limiting nutrients are added © 2011 Pearson Education, Inc.
Figure 28.27 Herbivorous plankton Other consumers Carnivorous plankton Protistan producers Prokaryotic producers
• Biomass of photosynthetic protists has declined as sea surface temperature has increased • If sea surface temperature continues to warm due to global warming, this could have large effects on – Marine ecosystems – Fishery yields – The global carbon cycle © 2011 Pearson Education, Inc.
Figure 28.28 Higher Lower SST SST Growth Growth In regions between the black lines, a layer of warm water rests on top of colder waters. In the yellow regions, high SSTs increase the temperature differences between warm and cold waters, which reduces upwelling.
Figure 28.UN06
Figure 28.UN06a
Figure 28.UN06b
Figure 28.UN07
Figure 28.UN08

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28_Lecture_Presentation.ppt