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 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 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caused the classification of protists to change significantly Protists constitute a polyphyletic group, and Protista is no longer valid as a kingdom Lectures by Erin Barley Kathleen Fitzpatrick Figure 28.1 Concept 28.1: Most eukaryotes are single-celled organisms Protists are eukaryotes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 1 m 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 1
Endosymbiosis in Eukaryotic Evolution Some protists reproduce asexually, while others reproduce sexually, or by the sexual processes of meiosis and fertilization 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 Figure 28.2 Figure 28.2a Membranes are represented as dark lines in the cell. Cyanobacterium 1 2 3 Red alga Secondary endosymbiosis Plastid Dinoflagellates Apicomplexans Cyanobacterium Primary endosymbiosis Membranes are represented as dark lines in the cell. 1 2 3 Red alga Primary endosymbiosis Heterotrophic eukaryote One of these membranes was lost in red and green algal descendants. Green alga Secondary endosymbiosis Secondary endosymbiosis Stramenopiles Plastid Euglenids Heterotrophic eukaryote One of these membranes was lost in red and green algal descendants. Chlorarachniophytes Green alga Figure 28.2b Figure 28.2c Plastid Dinoflagellates Secondary endosymbiosis Apicomplexans Secondary endosymbiosis Plastid Euglenids Red alga Secondary endosymbiosis Green alga Stramenopiles Chlorarachniophytes 2
Five Supergroups of Eukaryotes 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 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 Figure 28.3a Alveolates Stramenopiles Amoebozoans Opisthokonts Green algae 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 Excavata Chromalveolata Rhizaria Archaeplastida Unikonta Figure 28.3aa Alveolates Stramenopiles Diplomonads Parabasalids Euglenozoans Dinoflagellates Apicomplexans Ciliates Diatoms Golden algae Brown algae Oomycetes Excavata Chromalveolata Figure 28.3ab Figure 28.3ac Green algae Cercozoans Forams Radiolarians Red algae Chlorophytes Charophytes Land plants Rhizaria Archaeplastida Amoebozoans Opisthokonts Slime molds Gymnamoebas Entamoebas Nucleariids Fungi Choanoflagellates Animals Unikonta 3
Figure 28.3b Figure 28.3c 5 m 50 m Giardia intestinalis, a diplomonad parasite Diatom diversity Figure 28.3d Figure 28.3da 100 m Globigerina, a foram in the supergroup Rhizaria Figure 28.3db Figure 28.3e 100 m 20 m 50 m Globigerina, a foram in the supergroup Rhizaria Volvox, a colonial freshwater green alga 4
Figure 28.3ea Figure 28.3eb 50 m 20 m Volvox, a colonial freshwater green alga Figure 28.3f Concept 28.2: Excavates include protists with modified mitochondria and protists with unique flagella 100 m A unikont amoeba The clade Excavata is characterized by its cytoskeleton Some members have a feeding groove This controversial group includes the diplomonads, parabasalids, and euglenozoans Figure 28.UN01 Diplomonads Parabasalids Kinetoplastids Euglenozoans Euglenids 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) 5
5 m 2/14/2012 Figure 28.4 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 Figure 28.5 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 8 m Flagella 0.2 m Crystalline rod (cross section) Ring of microtubules (cross section) Figure 28.5a Kinetoplastids 0.2 m Crystalline rod (cross section) Ring of microtubules (cross section) 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 6
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 Figure 28.7 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 Long flagellum Eyespot Short flagellum Contractile vacuole Light detector Nucleus Chloroplast Video: Euglena Euglena (LM) 5 m Plasma membrane Pellicle Video: Euglena Motion Figure 28.7a Long flagellum Concept 28.3: Chromalveolates may have originated by secondary endosymbiosis Eyespot Contractile vacuole Nucleus Chloroplast 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 Plasma membrane Euglena (LM) 5 m 7
3 m 0.2 m 0.2 m 2/14/2012 Figure 28.UN02 Alveolates Excavata Dinoflagellates Apicomplexans Ciliates Diatoms Golden algae Brown algae Oomycetes Alveolates Stramenopiles Chromalveolata Rhizaria Archaeplastida Unikonta 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 Figure 28.8 Figure 28.8a Flagellum Alveoli Flagellum Alveoli Alveolate Figure 28.9 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 Flagella Video: Dinoflagellate 8
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 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 Figure 28.10-1 Inside human Figure 28.10-2 Inside mosquito Inside human Merozoite Merozoite Liver Liver Liver cell Liver cell Apex Apex Merozoite Red blood cell 0.5 m Merozoite Red blood cell 0.5 m Red blood cells Zygote Red blood cells FERTILIZATION Gametocytes Haploid Gametes Gametocytes Haploid Figure 28.10-3 Figure 28.10a Inside mosquito Inside human Sporozoites Liver Liver cell Merozoite Merozoite Oocyst Apex Merozoite Red blood cell 0.5 m Zygote Red blood cells Apex FERTILIZATION Red blood cell 0.5 m Gametes Gametocytes Haploid 9
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 Figure 28.11 Contractile vacuole Oral groove Cell mouth Cilia 50 m Micronucleus Food vacuoles Macronucleus (a) Feeding, waste removal, and water balance Conjugation Asexual reproduction Haploid Diploid micronucleus Compatible micronucleus mates The original Diploid macronucleus micronucleus disintegrates. MICRONUCLEAR FUSION (b) Conjugation and reproduction Figure 28.11a Figure 28.11b-1 50 m Contractile vacuole Cilia Oral groove Cell mouth Compatible mates Diploid micronucleus Haploid micronucleus Micronucleus Macronucleus Food vacuoles (a) Feeding, waste removal, and water balance (b) Conjugation and reproduction Conjugation Asexual reproduction Figure 28.11b-2 Figure 28.11c Compatible mates Diploid micronucleus The original Diploid macronucleus micronucleus disintegrates. Haploid micronucleus 50 m (b) Conjugation and reproduction MICRONUCLEAR FUSION Conjugation Asexual reproduction 10
40 m 2/14/2012 Stramenopiles Video: Paramecium Cilia Video: Paramecium Vacuole Video: Vorticella Cilia 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 Video: Vorticella Detail Video: Vorticella Habitat Figure 28.12 Diatoms Smooth flagellum Hairy flagellum Diatoms are unicellular algae with a unique twopart, glass-like wall of hydrated silica Diatoms usually reproduce asexually, and occasionally sexually 5 m Figure 28.13 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 11
Golden Algae This removes carbon dioxide from the atmosphere and pumps it to the ocean floor 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 Video: Diatoms Moving Video: Various Diatoms Figure 28.14 Flagellum Outer container Living cell 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 25 m Figure 28.15 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 12
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 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 Figure 28.16-1 Haploid Figure 28.16-2 Haploid Sporangia Sporangia 10 cm Sporophyte Zoospore 10 cm Sporophyte Zoospore Egg Female Gametophytes Sperm Male Mature female gametophyte Developing sporophyte Zygote FERTILIZATION Egg Female Gametophytes Sperm Male Figure 28.16a Oomycetes (Water Molds and Their Relatives) 10 cm 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 13
Figure 28.17-1 Figure 28.17-2 Cyst Zoospore Germ tube Hyphae ASEXUAL REPRODUCTION Cyst Zoospore Germ tube Hyphae ASEXUAL REPRODUCTION Oogonium Egg nucleus Antheridial hypha with sperm nuclei Zoosporangium Zoosporangium Haploid Haploid Figure 28.17-3 Cyst Zoospore Germ tube Hyphae ASEXUAL REPRODUCTION Zoosporangium Zygote germination SEXUAL REPRODUCTION Zygotes (oospores) Oogonium Egg nucleus Antheridial hypha with sperm nuclei FERTILIZATION Figure 28.17a Haploid 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 Video: Water Mold Oogonium 14
Figure 28.UN03 Radiolarians Radiolarians Foraminiferans Cercozoans Excavata Chromalveolata Rhizaria Archaeplastida Unikonta 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 Figure 28.18 Forams Pseudopodia 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 200 m Cercozoans Cercozoans include most amoeboid and flagellated protists with threadlike pseudopodia They are common in marine, freshwater, and soil ecosystems Most are heteroptrophs, including parasites and predators Paulinella chromatophora is an autotroph with a unique photosynthetic structure This structure evolved from a different cyanobacterium than the plastids of other photosynthetic eukaryotes 15
Figure 28.19 Chromatophore 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 5 m Figure 28.UN04 Red Algae Chlorophytes Charophytes Red algae Green algae Land plants Excavata Chromalveolata Rhizaria Archaeplastida Unikonta 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 Figure 28.20 Bonnemaisonia hamifera Figure 28.20a 20 cm 8 mm Dulse (Palmaria palmata) Nori Bonnemaisonia hamifera 8 mm 16
Figure 28.20b Figure 28.20c Nori Dulse (Palmaria palmata) 20 cm Figure 28.20d Figure 28.20e Nori 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 Most chlorophytes live in fresh water, although many are marine Other chlorophytes live in damp soil, as symbionts in lichens, or in snow 17
Figure 28.21 2 cm (a) Ulva, or sea lettuce 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) (b) Caulerpa, an intertidal chlorophyte Figure 28.21a Figure 28.21b 2 cm (a) Ulva, or sea lettuce (b) Caulerpa, an intertidal chlorophyte Video: Volvox Colony Video: Volvox Daughter Most chlorophytes have complex life cycles with both sexual and asexual reproductive stages Video: Volvox Female Spheroid Video: Volvox Flagella Video: Volvox Inversion 1 Video: Volvox Inversion 2 Video: Volvox Sperm and Female Video: Chlamydomonas 18
Figure 28.22 Figure 28.22a-1 Flagella 1 m Cell wall Gamete Nucleus Cross section of cup-shaped chloroplast (TEM) Zoospore ASEXUAL REPRODUCTION Mature cell FERTILIZATION SEXUAL REPRODUCTION Zygote Zoospore ASEXUAL REPRODUCTION Mature cell Haploid Haploid Figure 28.22a-2 Figure 28.22b Gamete Flagella 1 m Cell wall Zoospore ASEXUAL REPRODUCTION Mature cell FERTILIZATION SEXUAL REPRODUCTION Zygote Nucleus Cross section of cup-shaped chloroplast (TEM) Haploid Figure 28.UN05 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 Amoebozoans Nucleariids Fungi Choanoflagellates Animals Excavata Chromalveolata Rhizaria Archaeplastida Unikonta 19
Figure 28.23 RESULTS Common ancestor of all eukaryotes Choanoflagellates Animals Unikonta Fungl Amoebozoans Diplomonads Excavata Euglenozoans Amoebozoans Amoebozoans are amoeba that have lobe- or tube-shaped, rather than threadlike, pseudopodia They include slime molds, gymnamoebas, and entamoebas DHFR-TS gene fusion Alveolates Stramenopiles Rhizarians Red algae Green algae Chromalveolata Rhizaria Archaeplastida Plants 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 Figure 28.24 4 cm Figure 28.24a-1 FERTILIZATION Zygote Feeding plasmodium Mature plasmodium (preparing to fruit) Feeding plasmodium Mature plasmodium (preparing to fruit) Young sporangium Flagellated cells Amoeboid cells Germinating spore Spores Young sporangium Mature sporangium Mature sporangium 1 mm Stalk Haploid Haploid Stalk 20
Figure 28.24a-2 Figure 28.24a-3 Feeding plasmodium Mature plasmodium (preparing to fruit) FERTILIZATION Zygote Feeding plasmodium Mature plasmodium (preparing to fruit) Flagellated cells Amoeboid cells Germinating spore Spores Mature sporangium Young sporangium Flagellated cells Amoeboid cells Germinating spore Spores Mature sporangium Young sporangium Stalk Stalk Haploid Haploid Figure 28.24b Figure 28.24c 4 cm 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 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 21
Figure 28.25-1 600 m Spores Emerging amoeba Solitary amoebas Figure 28.25-2 600 m Spores Emerging amoeba Solitary amoebas FERTILIZATION Zygote SEXUAL REPRODUCTION Fruiting bodies ASEXUAL REPRODUCTION Fruiting bodies ASEXUAL REPRODUCTION Amoebas Aggregated amoebas Aggregated amoebas Migrating aggregate 200 m Migrating aggregate 200 m Haploid Haploid Figure 28.25a Figure 28.25b 200 m 600 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 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 Video: Amoeba Video: Amoeba Pseudopodia 22
10 m 2/14/2012 Opisthokonts Opisthokonts include animals, fungi, and several groups of protists 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 Symbiotic Protists Figure 28.26 Some protist symbionts benefit their hosts Dinoflagellates nourish coral polyps that build reefs Wood-digesting protists digest cellulose in the gut of termites Photosynthetic Protists Some protists are parasitic Plasmodium causes malaria Pfiesteria shumwayae is a dinoflagellate that causes fish kills Phytophthora ramorum causes sudden oak death 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 23
Figure 28.27 Herbivorous plankton Prokaryotic producers Other consumers Protistan producers Carnivorous plankton 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 Figure 28.28 Figure 28.UN06 Higher SST Lower 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.UN06a Figure 28.UN06b 24
Figure 28.UN07 Figure 28.UN08 25