28 protists

[object Object],[object Object],[object Object],Figure 28.1 50 m

[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],Figure 28.2a–d 100 m 100 m 4 cm 500 m The freshwater ciliate Stentor, a unicellular protozoan (LM) Ceratium tripos, a unicellular marine dinoflagellate (LM) Delesseria sanguinea, a multicellular marine red alga Spirogyra, a filamentous freshwater green alga (inset LM) (a) (b) (c) (d)

[object Object],[object Object]

Endosymbiosis in Eukaryotic Evolution ,[object Object],[object Object]

[object Object],Cyanobacterium Heterotrophic eukaryote Primary endosymbiosis Red algae Green algae Secondary endosymbiosis Secondary endosymbiosis Plastid Dinoflagellates Apicomplexans Ciliates Stramenopiles Euglenids Chlorarachniophytes Plastid Alveolates Figure 28.3

[object Object],[object Object],[object Object],Figure 28.4 Diplomonads Parabasalids Kinetoplastids Euglenids Dinoflagellates Apicomplexans Ciliates Oomycetes Diatoms Golden algae Brown algae Chlorarachniophytes Foraminiferans Radiolarians Gymnamoebas Entamoebas Plasmodial slime molds Cellular slime molds Fungi Choanoflagellates Metazoans Red algae Chlorophytes Charophyceans Plants Ancestral eukaryote Chlorophyta Plantae Rhodophyta Animalia Fungi (Opisthokonta) (Viridiplantae) Diplomonadida Parabasala Euglenozoa Alveolata Stramenopila Cercozoa Radiolaria Amoebozoa

Diplomonads ,[object Object],[object Object],Figure 28.5a 5 µm (a) Giardia intestinalis, a diplomonad (colorized SEM)

Parabasalids ,[object Object],[object Object],Figure 28.5b (b) Trichomonas vaginalis, a parabasalid (colorized SEM) Flagella Undulating membrane 5 µm

[object Object],[object Object],[object Object]

[object Object],[object Object],Flagella 0.2 µm Crystalline rod Ring of microtubules Figure 28.6

Kinetoplastids ,[object Object],[object Object],[object Object]

[object Object],[object Object],Figure 28.7 9 m

Euglenids ,[object Object],[object Object],[object Object],Figure 28.8 Long flagellum Short flagellum Nucleus Plasma membrane Paramylon granule Chloroplast Contractile vacuole Light detector: swelling near the base of the long flagellum; detects light that is not blocked by the eyespot; as a result, Euglena moves toward light of appropriate intensity, an important adaptation that enhances photosynthesis Eyespot: pigmented organelle that functions as a light shield, allowing light from only a certain direction to strike the light detector Pellicle: protein bands beneath the plasma membrane that provide strength and flexibility ( Euglena lacks a cell wall) Euglena (LM) 5 µm

[object Object],[object Object],[object Object],Figure 28.9 Flagellum Alveoli 0.2 µm

Dinoflagellates ,[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],[object Object],Figure 28.10 3 µm Flagella

Apicomplexans ,[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],Figure 28.11 Inside mosquito Inside human Sporozoites ( n ) Oocyst MEIOSIS Liver Liver cell Merozoite ( n ) Red blood cells Gametocytes ( n ) FERTILIZATION Gametes Zygote (2 n ) Key Haploid ( n ) Diploid (2 n ) Merozoite Red blood cell Apex 0.5 µm An infected Anopheles mosquito bites a person, injecting Plasmodium sporozoites in its saliva. 1 The sporozoites enter the person’s liver cells. After several days, the sporozoites undergo multiple divisions and become merozoites, which use their apical complex to penetrate red blood cells (see TEM below). 2 The merozoites divide asexually inside the red blood cells. At intervals of 48 or 72 hours (depending on the species), large numbers of merozoites break out of the blood cells, causing periodic chills and fever. Some of the merozoites infect new red blood cells. 3 Some merozoites form gametocytes. 4 Another Anopheles mosquito bites the infected person and picks up Plasmodium gametocytes along with blood. 5 Gametes form from gametocytes. Fertilization occurs in the mosquito’s digestive tract, and a zygote forms. The zygote is the only diploid stage in the life cycle. 6 An oocyst develops from the zygote in the wall of the mosquito’s gut. The oocyst releases thousands of sporozoites, which migrate to the mosquito’s salivary gland. 7

Ciliates ,[object Object],[object Object],[object Object]

[object Object],Figure 28.12 FEEDING, WASTE REMOVAL, AND WATER BALANCE Contractile Vacuole 50 µm Thousands of cilia cover the surface of Paramecium. The undigested contents of food vacuoles are released when the vacuoles fuse with a specialized region of the plasma membrane that functions as an anal pore. Paramecium, like other freshwater protists, constantly takes in water by osmosis from the hypotonic environment. Bladderlike contractile vacuoles accumulate excess water from radial canals and periodically expel it through the plasma membrane. Food vacuoles combine with lysosomes. As the food is digested, the vacuoles follow a looping path through the cell. Paramecium feeds mainly on bacteria. Rows of cilia along a funnel-shaped oral groove move food into the cell mouth, where the food is engulfed into food vacuoles by phagocytosis. Oral groove Cell mouth Micronucleus Macronucleus

CONJUGATION AND REPRODUCTION 8 7 2 MICRONUCLEAR FUSION Diploid micronucleus Diploid micronucleus Haploid micronucleus MEIOSIS Compatible mates Key Conjugation Reproduction Macronucleus Two cells of compatible mating strains align side by side and partially fuse. 1 Meiosis of micronuclei produces four haploid micronuclei in each cell. 2 3 Three micronuclei in each cell disintegrate. The remaining micronucleus in each cell divides by mitosis. The cells swap one micronucleus. 4 The cells separate. 5 Micronuclei fuse, forming a diploid micronucleus. 6 Three rounds of mitosis without cytokinesis produce eight micronuclei. 7 The original macronucleus disintegrates. Four micronuclei become macronuclei, while the other four remain micronuclei. 8 Two rounds of cytokinesis partition one macronucleus and one micronucleus into each of four daughter cells. 9

[object Object],[object Object],Smooth flagellum Hairy flagellum 5 µm Figure 28.13

Oomycetes (Water Molds and Their Relatives) ,[object Object],[object Object],[object Object]

[object Object],Figure 28.14 Cyst Zoospore (2 n ) ASEXUAL REPRODUCTION Zoosporangium (2 n ) Germ tube Zygote germination FERTILIZATION SEXUAL REPRODUCTION Zygotes (oospores) (2 n ) MEIOSIS Oogonium Egg nucleus ( n ) Antheridial hypha with sperm nuclei ( n ) Key Haploid ( n ) Diploid (2 n ) Encysted zoospores land on a substrate and germinate, growing into a tufted body of hyphae. 1 Several days later, the hyphae begin to form sexual structures. 2 Meiosis produces eggs within oogonia (singular, oogonium ). 3 On separate branches of the same or different individuals, meiosis produces several haploid sperm nuclei contained within antheridial hyphae. 4 Antheridial hyphae grow like hooks around the oogonium and deposit their nuclei through fertilization tubes that lead to the eggs. Following fertilization, the zygotes (oospores) may develop resistant walls but are also protected within the wall of the oogonium. 5 A dormant period follows, during which the oogonium wall usually disintegrates. 6 The zygotes germinate and form hyphae, and the cycle is completed. 7 The ends of hyphae form tubular zoosporangia. 8 Each zoosporangium produces about 30 biflagellated zoospores asexually. 9

Diatoms ,[object Object],[object Object],Figure 28.15 3 µm

[object Object],[object Object],Figure 28.16 50 µm

Golden Algae ,[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],Figure 28.17 25 µm

Brown Algae ,[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],[object Object],Figure 28.18 Blade Stipe Holdfast

[object Object],[object Object],Figure 28.19

Human Uses of Seaweeds ,[object Object],[object Object],[object Object],Figure 28.20a–c (a) The seaweed is grown on nets in shallow coastal waters. (b) A worker spreads the harvested seaweed on bamboo screens to dry. (c) Paper-thin, glossy sheets of nori make a mineral-rich wrap for rice, seafood, and vegetables in sushi.

Alternation of Generations ,[object Object],[object Object],[object Object],[object Object]

[object Object],Figure 28.21 Sporophyte (2 n ) Zoospores Female Gametophytes ( n ) MEIOSIS FERTILIZATION Developing sporophyte Zygote (2 n ) Mature female gametophyte ( n ) Egg Sperm Male Sporangia Key Haploid ( n ) Diploid (2 n ) The sporophytes of this seaweed are usually found in water just below the line of the lowest tides, attached to rocks by branching holdfasts. 1 In early spring, at the end of the main growing season, cells on the surface of the blade develop into sporangia. 2 Sporangia produce zoospores by meiosis. 3 The zoospores are all structurally alike, but about half of them develop into male gametophytes and half into female gametophytes. The gametophytes look nothing like the sporophytes, being short, branched filaments that grow on the surface of subtidal rocks. 4 Male gametophytes release sperm, and female gametophytes produce eggs, which remain attached to the female gametophyte. Eggs secrete a chemical signal that attracts sperm of the same species, thereby increasing the probability of fertilization in the ocean. 5 Sperm fertilize the eggs. 6 The zygotes grow into new sporophytes, starting life attached to the remains of the female gametophyte. 7

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Foraminiferans (Forams) ,[object Object],[object Object],Figure 28.22 20 µm

Radiolarians ,[object Object],[object Object]

[object Object],[object Object],Figure 28.23 200 µm Axopodia

Gymnamoebas ,[object Object],[object Object]

[object Object],[object Object],Figure 28.24 Pseudopodia 40 µm

Entamoebas ,[object Object],[object Object],[object Object],[object Object]

Slime Molds ,[object Object],[object Object],[object Object],[object Object]

Plasmodial Slime Molds ,[object Object],[object Object],Figure 28.25 4 cm

[object Object],[object Object],Figure 28.26 Feeding plasmodium Mature plasmodium (preparing to fruit) Young sporangium Mature sporangium Spores ( n ) Germinating spore Amoeboid cells ( n ) Zygote (2 n ) 1 mm Key Haploid ( n ) Diploid (2 n ) MEIOSIS SYNGAMY Stalk Flagellated cells ( n ) The feeding stage is a multinucleate plasmodium that lives on organic refuse. 1 The plasmodium takes a weblike form. 2 The plasmodium erects stalked fruiting bodies (sporangia) when conditions become harsh. 3 Within the bulbous tips of the sporangia, meiosis produces haploid spores. 4 These cells are either amoeboid or flagellated; the two forms readily convert from one to the other. 6 The cells unite in pairs (flagellated with flagellated and amoeboid with amoeboid), forming diploid zygotes. 7 The resistant spores disperse through the air to new locations and germinate, becoming active haploid cells when conditions are favorable. 5

Cellular Slime Molds ,[object Object],[object Object]

[object Object],Spores ( n ) Emerging amoeba Solitary amoebas (feeding stage) ASEXUAL REPRODUCTION Fruiting bodies Aggregated amoebas Migrating aggregate SYNGAMY MEIOSIS SEXUAL REPRODUCTION Zygote (2 n ) Amoebas 600 µm 200 µm Key Haploid ( n ) Diploid (2 n ) Figure 28.27 In the feeding stage of the life cycle, solitary haploid amoebas engulf bacteria. 1 During sexual reproduction, two haploid amoebas fuse and form a zygote. 2 The zygote becomes a giant cell (not shown) by consuming haploid amoebas. After developing a resistant wall, the giant cell undergoes meiosis followed by several mitotic divisions. 3 The resistant wall ruptures, releasing new haploid amoebas. 4 When food is depleted, hundreds of amoebas congregate in response to a chemical attractant and form a sluglike aggregate (photo below left). Aggregate formation is the beginning of asexual reproduction. 5 The aggregate migrates for a while and then stops. Some of the cells dry up after forming a stalk that supports an asexual fruiting body. 6 Other cells crawl up the stalk and develop into spores. 7 Spores are released. 8 In a favorable environment, amoebas emerge from the spore coats and begin feeding. 9

Red Algae ,[object Object],[object Object]

[object Object],[object Object],[object Object],Figure 28.28a–c (a) Bonnemaisonia hamifera. This red alga has a filamentous form. Dulse (Palmaria palmata). This edible species has a “leafy” form. (b) A coralline alga. The cell walls of coralline algae are hardened by calcium carbonate. Some coralline algae are members of the biological communities around coral reefs. (c)

Green Algae ,[object Object],[object Object],[object Object],[object Object]

[object Object],[object Object],[object Object],[object Object],Figure 28.29

[object Object],[object Object],Volvox, a colonial freshwater chlorophyte. The colony is a hollow ball whose wall is composed of hundreds or thousands of biflagellated cells (see inset LM) embedded in a gelatinous matrix. The cells are usually connected by strands of cytoplasm; if isolated, these cells cannot reproduce. The large colonies seen here will eventually release the small “daughter” colonies within them (LM). (a) Caulerpa, an inter- tidal chlorophyte. The branched filaments lack cross-walls and thus are multinucleate. In effect, the thallus is one huge “supercell.” (b) Ulva, or sea lettuce. This edible seaweed has a multicellular thallus differentiated into leaflike blades and a rootlike holdfast that anchors the alga against turbulent waves and tides. (c) 20 µm 50 µm Figure 28.30a–c

[object Object],[object Object],Figure 28.31 Flagella Cell wall Nucleus Regions of single chloroplast Zoospores ASEXUAL REPRODUCTION Mature cell ( n ) SYNGAMY SEXUAL REPRODUCTION Zygote (2 n ) MEIOSIS 1 µm Key Haploid ( n ) Diploid (2 n )  + +   + + In Chlamydomonas, mature cells are haploid and contain a single cup-shaped chloroplast (see TEM at left). 1 In response to a shortage of nutrients, drying of the pond, or some other stress, cells develop into gametes. 2 Gametes of opposite mating types (designated + and –) pair off and cling together. Fusion of the gametes (syngamy) forms a diploid zygote. 3 The zygote secretes a durable coat that protects the cell against harsh conditions. 4 After a dormant period, meiosis produces four haploid individuals (two of each mating type) that emerge from the coat and develop into mature cells. 5 When a mature cell repro- duces asexually, it resorbs its flagella and then undergoes two rounds of mitosis, forming four cells (more in some species). 6 These daughter cells develop flagella and cell walls and then emerge as swimming zoospores from the wall of the parent cell that had enclosed them. The zoospores grow into mature haploid cells, completing the asexual life cycle. 7

28 protists

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28 protists