Protists Chapter 25

Learning Objective 1 What features are common to the members of kingdom Protista?

Protists Mostly unicellular eukaryotic organisms that live in aquatic environments

Sizes of Protists Unicellular organisms Colonies Coenocytes microscopic Colonies loosely connected groups of cells Coenocytes multinucleate masses of cytoplasm Multicellular organisms composed of many cells

Chlamydomonas A unicellular protist

Flagella Cell wall Nucleus Chloroplast Starch granule Figure 25.1: Chlamydomonas, a unicellular protist. Chlamydomonas is a motile organism with two flagella and a cup-shaped chloroplast. Chloroplast Starch granule Fig. 25-1, p. 531

KEY CONCEPTS Protists are a diverse group of eukaryotic organisms, most of which are microscopic

Learning Objective 2 Discuss in general terms the diversity inherent in the protist kingdom means of locomotion modes of nutrition interactions with other organisms habitats modes of reproduction

Locomotion Pseudopodia Flagella Cilia Some are nonmotile

Nutrition Protists obtain their nutrients autotrophically or heterotrophically

Interactions Protists are free-living or symbiotic Symbiotic relationships range from mutualism to parasitism

Habitats Most protists live in ocean freshwater ponds lakes streams Parasitic protists live in body fluids of hosts

Reproduction Many protists reproduce both sexually and asexually Others reproduce only asexually

KEY CONCEPTS Protists vary in body plan (unicellular, colonial, coenocytic, multicellular), method of motility (pseudopodia, cilia, flagella), nutrition type (autotrophic, heterotrophic), and mode of reproduction (asexual, sexual)

Learning Objective 3 What is the hypothesis of serial endosymbiosis? Explain some evidence that supports it

Serial Endosymbiosis Hypothesis: Mitochondria and chloroplasts arose from symbiotic relationships between larger cells and smaller prokaryotes that were incorporated and lived within them

Mitochondria Probably originated from aerobic bacteria Ribosomal RNA data suggests ancient purple bacteria were ancestors of mitochondria

Chloroplasts Single primary endosymbiotic event in red algae, green algae, and plants cyanobacterium incorporated into a cell Multiple secondary endosymbioses in euglenoids, dinoflagellates, diatoms, golden algae, brown algae nonfunctional chloroplasts in apicomplexans

Chloroplast Evolution

Eukaryotic cell with mitochondria Mitochondrion Nucleus Eukaryotic cell with mitochondria Bacterial DNA (a) Primary endosymbiosis Cyanobacterium (ancestor of chloroplast) Figure 25.2: Chloroplast evolution by primary and secondary endosymbiosis. (a) In primary endosymbiosis, an ancient eukaryotic cell engulfed a cyanobacterium, which survived and evolved into a chloroplast. The ancient cell is depicted as a eukaryotic cell because mitochondria almost certainly evolved before chloroplasts. Fig. 25-2a, p. 532

Eukaryotic cell with mitochondria Chloroplast DNA (b) Secondary endosymbiosis Chloroplast with two membranes Eukaryotic cell with mitochondria and chloroplasts (red alga) Figure 25.2: Chloroplast evolution by primary and secondary endosymbiosis. (b) In a secondary endosymbiotic event, a heterotrophic eukaryotic cell (with mitochondria) engulfed a eukaryotic cell with chloroplasts (a red alga is depicted). The red alga survived and evolved into a chloroplast surrounded by three membranes (a dinoflagellate chloroplast is depicted). Other secondary endosymbiotic events resulted in more complex chloroplast membrane structures. Chloroplast with three membranes Eukaryotic cell with mitochondria and chloroplasts (dinoflagellate?) Fig. 25-2b, p. 532

Eukaryotic cell with mitochondria Mitochondrion Nucleus Cyanobacterium (ancestor of chloroplast) Bacterial DNA Chloroplast DNA Chloroplast with two membranes Eukaryotic cell with mitochondria and chloroplasts (red alga) (a) Primary endosymbiosis Eukaryotic cell with mitochondria Chloroplast with three membranes Eukaryotic cell with mitochondria and chloroplasts (dinoflagellate?) (b) Secondary endosymbiosis Figure 25.2: Chloroplast evolution by primary and secondary endosymbiosis. (b) In a secondary endosymbiotic event, a heterotrophic eukaryotic cell (with mitochondria) engulfed a eukaryotic cell with chloroplasts (a red alga is depicted). The red alga survived and evolved into a chloroplast surrounded by three membranes (a dinoflagellate chloroplast is depicted). Other secondary endosymbiotic events resulted in more complex chloroplast membrane structures. Stepped Art Fig. 25-2b, p. 532

Learning Objective 4 What kinds of data do biologists use to classify eukaryotes?

Relationships Among Protists Protist kingdom paraphyletic group Determined by ultrastructure (electron microscopy) comparative molecular data

Eukaryote Phyla

Zooflagellates (diplomonads) Zooflagellates (euglenoids) Apicomplexans Water molds Brown algae Land plants Green algae slime molds Red algae Plasmodial slime molds Animals Fungi Amoebas Ciliates Cellular A Figure 25.3: Evolutionary relationships among eukaryotes. Relationships among eukaryotes are diverse and debated; this cladogram presents just one interpretation. It is based on comparisons of four protein sequences among many eukaryotic phyla. Foraminiferans, actinopods, dinoflagellates, diatoms, and golden algae are not included. Groups within ovals represent separate eukaryotic kingdoms in the six-kingdom system used in this text. All other eukaryotes (without the ovals) are in kingdom Protista, a paraphyletic group. Node A indicates the common ancestor of red algae, green algae, and plants. (Based on S. L. Baldauf, A. J. Roger, I. Wenk-Siefert, and W. F. Doolittle, “A Kingdom-Level Phylogeny of Eukaryotes Based on Combined Protein Data,” Science, Vol. 290, Nov. 3, 2000.) Ancestral eukaryote Fig. 25-3, p. 533

Eukaryote Clades

Foraminiferans and actinopods Zooflagellates (diplomonads) Excavates Alveolates Plants Discicristates Heterokonts Cercozoa Amoebozoa Opisthokonts Apicomplexans Foraminiferans and actinopods Zooflagellates (diplomonads) Zooflagellates, (euglenoids) Plasmodial slime molds Cellular slime molds Water molds Brown algae Green algae Land plants Red algae Animals Amoebas Fungi Ciliates ? Figure 25.4: The eight monophyletic clades of eukaryotes. The major groups of eukaryotes are superimposed over Figure 25-3. Because classification of the protists is in a state of flux, biologists will modify this diagram as more data are collected and evaluated. (Based on S. L. Baldauf, “The Deep Roots of Eukaryotes,” Science, Vol. 300, June 13, 2003.) Ancestral eukaryote Fig. 25-4, p. 535

KEY CONCEPTS Protists are descendants of early eukaryotes

Learning Objective 5 Why are zooflagellates no longer classified in a single phylum? Distinguish among diplomonads, euglenoids, and choanoflagellates

Zooflagellates Mostly unicellular heterotrophs Move by whiplike flagella Polyphyletic separated into several monophyletic groups

Diplomonads Diplomonads are excavates Diplomonads have with a deep (excavated) oral groove Diplomonads have one or two nuclei no mitochondria no Golgi complex up to eight flagella

Excavates

Nucleus Figure 25.5: The excavates. Flagella 50 µm Fig. 25-5b, p. 536

Euglenoids Euglenoids are discicristates Euglenoids Trypanosoma with disclike cristae in mitochondria Euglenoids are unicellular and flagellate some are photosynthetic Trypanosoma causes African sleeping sickness

Discicristates

Flagellum for locomotion Paramylon body (stored food) Eyespot Contractile vacuole Chloroplast Nucleus Paramylon body (stored food) Figure 25.6: The discicristates. Pellicle 25 µm Fig. 25-6a, p. 537

Flagellum for locomotion Nonemergent flagellum (indistinguishable in micrograph) Eyespot Contractile vacuole Mitochondria (indistinguishable in micrograph) Chloroplast Nucleolus Nucleus Chromatin Figure 25.6: The discicristates. Paramylon body (stored food) Pellicle Fig. 25-6b, p. 537

Trypanosome with undulating membrane Red blood cells Trypanosome with undulating membrane Flagellum Figure 25.6: The discicristates. 25 µm Fig. 25-6c, p. 537

Choanoflagellates Choanoflagellates are opisthokonts Choanoflagellates single posterior flagellum in flagellate cells collar of microvilli surrounds base of flagellum Choanoflagellates are related to fungi and animals

Choanoflagellate

Lorica (protective cover) Flagellum Collar of microvilli Cell Lorica (protective cover) Figure 25.25: Choanoflagellate. Choanoflagellates are free-living zooflagellates that obtain food by waving their flagella, causing water currents to carry bacteria and other small particles of food into the collar of microvilli. A colonial form is shown. Each cell is 5 to 10 μm long, not including the flagellum. Stalk Fig. 25-25, p. 551

Learning Objective 6 Describe and compare these alveolates: ciliates dinoflagellates apicomplexans

Ciliates Alveolates move by hairlike cilia micronuclei (for sexual reproduction) macronuclei (for cell metabolism and growth) undergo complex sexual reproduction (conjugation)

Ciliates

Cilia Food vacuoles Micronucleus Macronucleus Contractile vacuole Figure 25.7: Ciliates. [(d) by H. Machemer in K. G. Grell, Protozoology, © 1973 Springer-Verlag.] 50 µm Fig. 25-7a, p. 538

Cilia Food vacuoles Food Micronucleus Macronucleus Oral groove Figure 25.7: Ciliates. [(d) by H. Machemer in K. G. Grell, Protozoology, © 1973 Springer-Verlag.] Contractile vacuole Anal pore Food vacuole Fig. 25-7b, p. 538

Cytopharynx Macronucleus 250 µm Fig. 25-7c, p. 538 Figure 25.7: Ciliates. [(d) by H. Machemer in K. G. Grell, Protozoology, © 1973 Springer-Verlag.] 250 µm Fig. 25-7c, p. 538

Cirri Fig. 25-7d, p. 538 Figure 25.7: Ciliates. [(d) by H. Machemer in K. G. Grell, Protozoology, © 1973 Springer-Verlag.] Fig. 25-7d, p. 538

Conjugation

First meiotic division in each cell 4 One haploid micronucleus 2 First meiotic division in each cell 4 One haploid micronucleus divides by mitosis; others disintegrate Haploid micronuclei fuse 6 Disintegrating macronuclei Diploid nuclei (2n) Macronuclei Micronuclei (2n) Disintegrating micronuclei Figure 25.8: Conjugation in Paramecium caudatum. 1 Two sexually compatible individuals join at oral surfaces Second meiotic division in each cell 3 Each conjugating cell exchanges micronucleus 5 7 Cells separate Fig. 25-8, p. 539

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Dinoflagellates Mostly unicellular, biflagellate, photosynthetic alveolates major producers in marine ecosystems Alveoli flattened vesicles under plasma membrane contain cellulose plates with silicates Some produce toxic blooms (red tides)

Dinoflagellates

Apicomplexans Parasites Apical complex of microtubules Plasmodium produce sporozoites are nonmotile Apical complex of microtubules attaches apicomplexan to host cell Plasmodium causes malaria

Plasmodium

Sporozoites (n) DIPLOID (2n) HAPLOID (n) Zygote (2n) Infected female Anopheles mosquito bites uninfected human and transmits Plasmodium sporozoites to human blood. 1 Anopheles mosquito Liver cell Liver Sporozoites (n) Meiosis Merozoites released 2 Sporozoites enter liver cells and divide to produce merozoites. Merozoites released from liver cells infect red blood cells. 6 Zygote embeds in mosquito’s stomach lining and produces sporozoites (spores), which are released and migrate to salivary glands. DIPLOID (2n) HAPLOID (n) Red blood cells Zygote (2n) 3 In blood cells, merozoites divide to form more merozoites, which infect more red blood cells. Some merozoites form gametocytes. Anopheles mosquito Figure 25.10: The life cycle of Plasmodium, the causative agent of malaria. Gametes Fertilization Gametocytes 5 In mosquito’s digestive tract, gametocytes develop into gametes, and fertilization occurs. 4 Uninfected female Anopheles mosquito bites infected person and obtains Plasmodium gametocytes. Fig. 25-10, p. 541

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Learning Objective 7 Describe and compare these heterokonts: water molds diatoms golden algae brown algae

Water Molds Heterokonts Water molds Phytophthora have two different kinds of flagella Water molds have coenocytic mycelium reproduce asexually (biflagellate zoospores) reproduce sexually (oospores) Phytophthora causes late blight of potato, sudden oak death

A Water Mold

Figure 25.11: The life cycle of Saprolegnia, a water mold. Fig. 25-11a, p. 542

Oospheres within oogonium 2 Meiosis results in haploid sperm nuclei within antheridia and haploid oospheres (eggs) within oogonia. 3 Sperm nuclei move into oospheres. Antheridium (male reproductive structure) Meiosis Fertilization HAPLOID (n) GENERATION Haploid sperm nuclei 1 Saprolegnia reproduces sexually by antheridia and oogonia. Oospores DIPLOID (2n) GENERATION 4 After fertilization, oospores develop from fertilized oospheres. Each oospore may develop into new mycelium. SEXUAL REPRODUCTION Oogonium (female reproductive structure) Germination of oospore Figure 25.11: The life cycle of Saprolegnia, a water mold. Germination of the zoospore Mycelium Zoosporangium Encysted secondary zoospore ASEXUAL REPRODUCTION (by mitosis) Zoospores Secondary zoospore (bean-shaped) 5 Saprolegnia reproduces asexually by forming zoospores within zoosporangium. Encysted primary zoospore Primary zoospore (pear-shaped) Fig. 25-11b, p. 542

Diatoms Mostly unicellular heterokonts with shells containing silica major producers in aquatic ecosystems Some are part of floating plankton Some live on rocks and sediments move by gliding

Diatoms

Golden Algae Mostly unicellular, biflagellate freshwater and marine heterokonts major component of tiny nanoplankton Coccolithophorids golden algae covered by tiny, overlapping scales of calcium carbonate

Golden Algae

Brown Algae Multicellular heterokonts Kelps (largest brown algae) important in cooler ocean waters Kelps (largest brown algae) leaflike blades stemlike stipes anchoring holdfasts gas-filled bladders for buoyancy

Brown Algae

Blade Figure 25.14: Brown algae. Stipe Holdfast Laminaria is widely distributed on rocky coastlines of temperate and polar seas. It grows to 2 m (6.5 ft.) Fig. 25-14a, p. 544

Learning Objective 8 Describe foraminiferans and actinopods Why do many biologists classify them in the monophyletic group cercozoa?

Cercozoa Amoeboid cells Often have hard outer shells (tests) through which cytoplasmic projections extend

Foraminiferans Secrete many-chambered tests Pores through which cytoplasmic projections extend to move and obtain food

Foraminiferans

Actinopods Mostly marine plankton Obtain food with axopods slender cytoplasmic projections that extend through pores in shells Radiolarians actinopods with glassy shells

Actinopods

Learning Objective 9 Support the hypothesis that red algae and green algae should be included in a monophyletic group with land plants

Plants Monophyletic group including Based on red algae green algae land plants Based on molecular data presence of chloroplasts bounded by outer and inner membranes

Red Algae Mostly multicellular seaweeds important in warm tropical ocean waters Some red algae incorporate calcium carbonate in cell walls important in reef building

Red Algae

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Green Algae Wide diversity in size, structural complexity, and reproduction Botanists hypothesize that ancestral green algae gave rise to land plants

Green Algae

Chlamydomonas

ASEXUAL REPRODUCTION (by mitosis) – 5 Both mating types reproduce asexually by mitosis; only (-) strain is shown. – – Zoospores – ASEXUAL REPRODUCTION (by mitosis) – – 4 Four haploid cells emerge, two (+) and two (-). 1 Gametes are produced by mitosis. + – SEXUAL REPRODUCTION – – + HAPLOID (n) GENERATION – – + Figure 25.17: The life cycle of Chlamydomonas. Chlamydomonas, a unicellular haploid green alga with two mating types, (+) and (−), is an example of isogamous sexual reproduction. from a different strain DIPLOID (2n) GENERATION 2 (+) and (-) gametes fuse, forming a diploid zygote. + Meiosis Fertilization 3 Meiosis occurs. Zygote (2n) Fig. 25-17, p. 547

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Ulva

DIPLOID (2n) GENERATION 4 Mature haploid alga Each zoospore develops into multicellular male or female individual. Zoospores Gamete 1 Male and female algae produce biflagellate gametes by mitosis. HAPLOID (n) GENERATION Zoospores Anisogamous gametes DIPLOID (2n) GENERATION Figure 25.18: The life cycle of Ulva. The green alga Ulva alternates between haploid and diploid multicellular generations, which are identical in overall appearance. Gametes are isogamous or anisogamous (shown), depending on the species. 3 Special cells in diploid alga undergo meiosis to form haploid zoospores. Meiosis Fertilization 2 Gametes fuse, forming zygote, which attaches to substrate and develops into multicellular individual. Motile zygote Mature diploid alga Fig. 25-18, p. 548

Spirogyra

Fig. 25-19a, p. 548 Figure 25.19: Conjugation in Spirogyra. (a, b) Filaments of two different mating types of the green alga Spirogyra align, and conjugation tubes grow between cells of the two haploid filaments. Fig. 25-19a, p. 548

Fig. 25-19b, p. 548 Figure 25.19: Conjugation in Spirogyra. (a, b) Filaments of two different mating types of the green alga Spirogyra align, and conjugation tubes grow between cells of the two haploid filaments. Fig. 25-19b, p. 548

Fig. 25-19c, p. 548 Figure 25.19: Conjugation in Spirogyra. (c) The contents of one cell passes into the other through the conjugation tube. Fig. 25-19c, p. 548

Fig. 25-19d, p. 548 Figure 25.19: Conjugation in Spirogyra. (d) The two cells fuse, forming a diploid zygote. Following a period of dormancy, the rounded zygote undergoes meiosis, restoring the haploid condition. Fig. 25-19d, p. 548

KEY CONCEPTS Animals, fungi, and plants evolved from protist ancestors

Learning Objective 10 Describe and compare these amoebozoa: amoebas plasmodial slime molds cellular slime molds

Amoebas Use cytoplasmic extensions (pseudopodia) Entamoeba histolytica to move and obtain food by phagocytosis Entamoeba histolytica parasitic amoeba causes amoebic dysentery

Amoeba

Green alga Pseudopodia 100 µm Fig. 25-22, p. 549 Figure 25.22: Amoeba. LM of a giant amoeba (Chaos carolinense). This unicellular protist, which moves and feeds by pseudopodia, is surrounding and ingesting a colonial green alga. Chaos amoebas are generally scavengers that feed on debris in freshwater habitats, but they ingest living organisms when the opportunity arises. Pseudopodia 100 µm Fig. 25-22, p. 549

Plasmodial Slime Molds Feeding stage is multinucleate plasmodium Reproduction is by haploid spores produced within sporangia

Physarum

Figure 25.23: The plasmodial slime mold Physarum polycephalum. Fig. 25-23a, p. 550

Figure 25.23: The plasmodial slime mold Physarum polycephalum. Fig. 25-23b, p. 550

Cellular Slime Molds Feed as individual amoeboid cells Reproduce by aggregating into a pseudoplasmodium (slug) then form asexual spores

Dictyostelium

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KEY CONCEPTS Biologists are making progress in understanding the evolutionary relationships among various protist taxa