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 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caused the classification of protists to change significantly Protists constitute a polyphyletic group, and Protista is no longer valid as a kingdom © 2011 Pearson Education, Inc.

Figure 28.1 Figure 28.1 Which of these organisms are prokaryotes and which are eukaryotes? 1 m

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.

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.

Figure 28.2 Diversity of plastids produced by endosymbiosis.
Dinoflagellates Secondary endosymbiosis Membranes are represented as dark lines in the cell. Apicomplexans Red alga Cyanobacterium 1 2 3 Primary endosymbiosis Stramenopiles Heterotrophic eukaryote Secondary endosymbiosis Plastid Figure 28.2 Diversity of plastids produced by endosymbiosis. One of these membranes was lost in red and green algal descendants. Euglenids Secondary endosymbiosis Green alga Chlorarachniophytes

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 28.3 Exploring: Protistan Diversity.
Figure 28.3a Diplomonads Parabasalids Euglenozoans Excavata Dinoflagellates Apicomplexans Ciliates Diatoms Golden algae Brown algae Oomycetes Alveolates Chromalveolata Stramenopiles Cercozoans Forams Radiolarians Rhizaria Red algae Chlorophytes Charophytes Land plants Green algae Archaeplastida Figure 28.3 Exploring: Protistan Diversity. Slime molds Gymnamoebas Entamoebas Nucleariids Fungi Choanoflagellates Animals Amoebozoans Unikonta Opisthokonts

Excavata Chromalveolata
Figure 28.3aa Diplomonads Parabasalids Euglenozoans Excavata Dinoflagellates Apicomplexans Ciliates Diatoms Golden algae Brown algae Oomycetes Alveolates Chromalveolata Figure 28.3 Exploring: Protistan Diversity. Stramenopiles

Rhizaria Green algae Archaeplastida
Figure 28.3ab Cercozoans Forams Radiolarians Rhizaria Red algae Chlorophytes Charophytes Land plants Green algae Archaeplastida Figure 28.3 Exploring: Protistan Diversity.

Slime molds Gymnamoebas Entamoebas Nucleariids Fungi Choanoflagellates
Figure 28.3ac Slime molds Gymnamoebas Entamoebas Nucleariids Fungi Choanoflagellates Animals Amoebozoans Unikonta Opisthokonts Figure 28.3 Exploring: Protistan Diversity.

Giardia intestinalis, a diplomonad parasite
Figure 28.3b 5 m Figure 28.3 Exploring: Protistan Diversity. Giardia intestinalis, a diplomonad parasite

50 m Diatom diversity Figure 28.3c
Figure 28.3 Exploring: Protistan Diversity. Diatom diversity

Globigerina, a foram in the supergroup Rhizaria
Figure 28.3d 100 m Figure 28.3 Exploring: Protistan Diversity. Globigerina, a foram in the supergroup Rhizaria

Volvox, a colonial freshwater green alga
Figure 28.3e 20 m 50 m Figure 28.3 Exploring: Protistan Diversity. Volvox, a colonial freshwater green alga

A unikont amoeba 100 m Figure 28.3f
Figure 28.3 Exploring: Protistan Diversity. 100 m A unikont amoeba

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 © 2011 Pearson Education, Inc.

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.

Flagella 5 m Undulating membrane Figure 28.4
Figure 28.4 The parabasalid Trichomonas vaginalis (colorized SEM). 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.

Flagella 0.2 m 8 m Crystalline rod (cross section)
Figure 28.5 Flagella 0.2 m 8 m Crystalline rod (cross section) Figure 28.5 Euglenozoan flagellum. Ring of microtubules (cross section)

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 Figure 28.6 Trypanosoma, the kinetoplastid that causes sleeping sickness. 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 Video: Euglena Video: Euglena Motion © 2011 Pearson Education, Inc.

Long flagellum Eyespot Short flagellum Light detector
Figure 28.7 Long flagellum Eyespot Short flagellum Light detector Contractile vacuole Nucleus Figure 28.7 Euglena, a euglenid commonly found in pond water. Chloroplast Plasma membrane Pellicle 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.

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 Figure 28.8 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 Video: Dinoflagellate © 2011 Pearson Education, Inc.

Figure 28.9 Flagella Figure 28.9 Pfiesteria shumwayae, a dinoflagellate. 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.

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

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

Video: Paramecium Cilia
Video: Paramecium Vacuole Video: Vorticella Cilia Video: Vorticella Detail Video: Vorticella Habitat © 2011 Pearson Education, Inc.

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.

Hairy flagellum Smooth flagellum 5 m Figure 28.12
Figure Stramenopile flagella. 5 m

Figure 28.13 Figure The diatom Triceratium morlandii (colorized SEM). 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
Video: Diatoms Moving Video: Various Diatoms © 2011 Pearson Education, Inc.

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
Figure Dinobryon, a colonial golden alga found in fresh water (LM). 25 m

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.

Blade Stipe Holdfast Figure 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 © 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.

Developing sporophyte
Figure Key Haploid (n) Diploid (2n) Sporangia MEIOSIS 10 cm 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) Male Egg Mature female gametophyte (n) FERTILIZATION Sperm

Figure 28.16a Figure The life cycle of the brown alga Laminaria: an example of alternation of generations. 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.

Antheridial hypha with sperm nuclei
Figure Germ tube Oogonium 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 Figure The life cycle of a water mold. Haploid (n) Diploid (2n)

Video: Water Mold Oogonium
© 2011 Pearson Education, Inc.

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.

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 Figure A radiolarian. 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 heteroptrophs, 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.

Chromatophore 5 m Figure 28.19
Figure A second case of primary endosymbiosis? 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.

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 Figure 28.20 Red algae. Bonnemaisonia hamifera 20 cm 8 mm
Dulse (Palmaria palmata) Nori Figure Red algae.

Bonnemaisonia hamifera 8 mm
Figure 28.20a Figure Red algae. Bonnemaisonia hamifera 8 mm

Dulse (Palmaria palmata) 20 cm
Figure 28.20b Figure Red algae. Dulse (Palmaria palmata) 20 cm

Figure 28.20c Figure Red algae. Nori

Figure 28.20d Figure Red algae. Nori

Figure 28.20e Figure Red algae. 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
The formation of colonies from individual cells The formation of true multicellular bodies by cell division and differentiation (e.g., Ulva) The repeated division of nuclei with no cytoplasmic division (e.g., Caulerpa) © 2011 Pearson Education, Inc.

(b) Caulerpa, an intertidal chlorophyte
Figure 28.21 2 cm (a) Ulva, or sea lettuce Figure Multicellular chlorophytes. (b) Caulerpa, an intertidal chlorophyte

Video: Volvox Daughter
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 © 2011 Pearson Education, Inc.

Most chlorophytes have complex life cycles with both sexual and asexual reproductive stages
Video: Chlamydomonas © 2011 Pearson Education, Inc.

Figure 28.22  1 m Flagella Cell wall  Gamete (n)   Nucleus Zoospore Mature cell (n) FERTILIZATION Cross section of cup-shaped chloroplast ASEXUAL REPRODUCTION SEXUAL REPRODUCTION Zygote (2n) (TEM)   Figure The life cycle of Chlamydomonas, a unicellular chlorophyte.   MEIOSIS Key Haploid (n) Diploid (2n)

  Gamete (n)   Zoospore FERTILIZATION Mature cell (n) ASEXUAL
Figure 28.22a-2   Gamete (n)   Zoospore FERTILIZATION Mature cell (n) ASEXUAL REPRODUCTION SEXUAL REPRODUCTION Zygote (2n) Figure The life cycle of Chlamydomonas, a unicellular chlorophyte.     MEIOSIS Key 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 © 2011 Pearson Education, Inc.

Common ancestor of all eukaryotes
Figure 28.23 RESULTS Choanoflagellates Animals Fungl Amoebozoans Unikonta Common ancestor of all eukaryotes Diplomonads Excavata Euglenozoans Alveolates Stramenopiles Rhizarians Chromalveolata Figure Inquiry: What is the root of the eukaryotic tree? DHFR-TS gene fusion Rhizaria Red algae Green algae Archaeplastida Plants

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 Video: Plasmodial Slime Mold Video: Plasmodial Slime Mold Streaming © 2011 Pearson Education, Inc.

Figure 28.24 The life cycle of a plasmodial slime mold.
4 cm FERTILIZATION Zygote (2n) Feeding plasmodium Mature plasmodium (preparing to fruit) Young sporangium Amoeboid cells (n) Flagellated cells (n) Mature sporangium Germinating spore Figure The life cycle of a plasmodial slime mold. Spores (n) MEIOSIS 1 mm Stalk Key Haploid (n) Diploid (2n)

The plasmodium is not multicellular
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) Emerging amoeba (n) Zygote (2n) SEXUAL REPRODUCTION
Figure Spores (n) FERTILIZATION Emerging amoeba (n) Zygote (2n) SEXUAL REPRODUCTION Solitary amoebas (n) 600 m MEIOSIS Amoebas (n) Fruiting bodies (n) ASEXUAL REPRODUCTION Aggregated amoebas Migrating aggregate Figure The life cycle of Dictyostelium, a cellular slime mold. 200 m Key Haploid (n) Diploid (2n)

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 © 2011 Pearson Education, Inc.

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.

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.

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.

Prokaryotic producers
Figure 28.27 Other consumers Herbivorous plankton Carnivorous plankton Figure Protists: key producers in aquatic communities. 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 In regions between the black lines, a layer of warm water rests on top of colder waters. Growth Growth Higher Lower SST Figure Impact: Marine Protists in a Warmer World. In the yellow regions, high SSTs increase the temperature differences between warm and cold waters, which reduces upwelling.

Figure 28.UN06 Figure 28.UN06 Summary table, Concepts 28.2–28.6

Figure 28.UN06a Figure IMPACT: Marine Protists in a Warmer World.

Figure 28.UN06b Figure IMPACT: Marine Protists in a Warmer World.

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