Chapter 28

1. Chapter 28 Protists

2. 50 m Figure 28.1 • Overview: A World in a Drop of Water • Even a low-power microscope • Can reveal an astonishing menagerie of organisms in a drop of pond water

3. These amazing organisms • Belong to the diverse kingdoms of mostly single-celled eukaryotes informally known as protists • Advances in eukaryotic systematics • Have caused the classification of protists to change significantly

4. Concept 28.1: Protists are an extremely diverse assortment of eukaryotes • Protists are more diverse than all other eukaryotes • And are no longer classified in a single kingdom • Most protists are unicellular • And some are colonial or multicellular

5. 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

6. (a) The freshwater ciliate Stentor,a unicellular protozoan (LM) 100 m 100 m (b) Ceratium tripos, a unicellular marine dinoflagellate (LM) 4 cm (c) Delesseria sanguinea, a multicellular marine red alga 500 m Figure 28.2a–d (d) Spirogyra, a filamentous freshwater green alga (inset LM) • Protist habitats are also diverse in habitat • And including freshwater and marine species

7. Reproduction and life cycles • Are also highly varied among protists, with both sexual and asexual species

8. Table 28.1 • A sample of protist diversity

9. Endosymbiosis in Eukaryotic Evolution • There is now considerable evidence • That much of protist diversity has its origins in endosymbiosis

10. The plastid-bearing lineage of protists • Evolved into red algae and green algae • On several occasions during eukaryotic evolution • Red algae and green algae underwent secondary endosymbiosis, in which they themselves were ingested

11. Plastid Dinoflagellates Alveolates Apicomplexans Secondary endosymbiosis Cyanobacterium Ciliates Red algae Primary endosymbiosis Stramenopiles Heterotrophic eukaryote Plastid Euglenids Secondary endosymbiosis Green algae Figure 28.3 Chlorarachniophytes • Diversity of plastids produced by secondary endosymbiosis

12. Concept 28.2: Diplomonads and parabasalids have modified mitochondria • A tentative phylogeny of eukaryotes • Divides eukaryotes into many clades Chlorophyta Rhodophyta Diplomonadida Animalia Plantae Euglenozoa Fungi Parabasala Radiolaria Cercozoa Alveolata Stramenopila (Viridiplantae) Amoebozoa (Opisthokonta) Fungi Plants Ciliates Diatoms Euglenids Red algae Metazoans Oomycetes Brown algae Dinoflagellates Chlorophytes Entamoebas Golden algae Parabasalids Radiolarians Diplomonads Apicomplexans Kinetoplastids Foraminiferans Gymnamoebas Charophyceans Choanoflagellates Chlorarachniophytes Cellular slime molds Plasmodial slime molds Ancestral eukaryote Figure 28.4

13. Diplomonads and parabasalids • Are adapted to anaerobic environments • Lack plastids • Have mitochondria that lack DNA, an electron transport chain, or citric-acid cycle enzymes

14. 5 µm (a) Giardia intestinalis, a diplomonad (colorized SEM) Figure 28.5a Diplomonads • Diplomonads • Have two nuclei and multiple flagella

15. Parabasalids • Parabasalids include trichomonads • Which move by means of flagella and an undulating part of the plasma membrane Flagella Undulating membrane 5 µm (b) Trichomonas vaginalis, a parabasalid (colorized SEM) Figure 28.5b

16. Concept 28.3: Euglenozoans have flagella with a unique internal structure • Euglenozoa is a diverse clade that includes • Predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites

17. Flagella 0.2 µm Crystalline rod Figure 28.6 Ring of microtubules • The main feature that distinguishes protists in this clade • Is the presence of a spiral or crystalline rod of unknown function inside their flagella

18. Kinetoplastids • Kinetoplastids • Have a single, large mitochondrion that contains an organized mass of DNA called a kinetoplast • Include free-living consumers of bacteria in freshwater, marine, and moist terrestrial ecosystems

19. 9 m Figure 28.7 • The parasitic kinetoplastid Trypanosoma • Causes sleeping sickness in humans

20. Long flagellum Eyespot: pigmented organelle that functions as a light shield, allowing light from only a certain direction to strike the light detector 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 Short flagellum Contractile vacuole Nucleus Euglena (LM) 5 µm Plasma membrane Pellicle: protein bands beneath the plasma membrane that provide strength and flexibility (Euglena lacks a cell wall) Chloroplast Figure 28.8 Paramylon granule Euglenids • Euglenids • Have one or two flagella that emerge from a pocket at one end of the cell • Store the glucose polymer paramylon

21. Alveoli 0.2 µm Flagellum Figure 28.9 • Concept 28.4: Alveolates have sacs beneath the plasma membrane • Members of the clade Alveolata • Have membrane-bounded sacs (alveoli) just under the plasma membrane

22. Dinoflagellates • Dinoflagellates • Are a diverse group of aquatic photoautotrophs and heterotrophs • Are abundant components of both marine and freshwater phytoplankton

23. Flagella 3 µm Figure 28.10 • Each has a characteristic shape • That in many species is reinforced by internal plates of cellulose • Two flagella • Make them spin as they move through the water

24. Rapid growth of some dinoflagellates • Is responsible for causing “red tides,” which can be toxic to humans

25. Apicomplexans • Apicomplexans • Are parasites of animals and some cause serious human diseases • Are so named because one end, the apex, contains a complex of organelles specialized for penetrating host cells and tissues • Have a nonphotosynthetic plastid, the apicoplast

26. 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 An infected Anopheles mosquito bites a person, injecting Plasmodium sporozoites in its saliva. 1 Inside mosquito Inside human Merozoite Sporozoites (n) Liver 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 Liver cell Apex Oocyst MEIOSIS 0.5 µm Red blood cell Merozoite (n) Zygote (2n) Red blood cells 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 FERTILIZATION Gametocytes (n) Gametes Key Some merozoites form gametocytes. Haploid (n) 4 Diploid (2n) 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. Another Anopheles mosquito bites the infected person and picks up Plasmodium gametocytes along with blood. 6 5 Figure 28.11 • Most apicomplexans have intricate life cycles • With both sexual and asexual stages that often require two or more different host species for completion

27. Ciliates • Ciliates, a large varied group of protists • Are named for their use of cilia to move and feed • Have large macronuclei and small micronuclei

28. The micronuclei • Function during conjugation, a sexual process that produces genetic variation • Conjugation is separate from reproduction • Which generally occurs by binary fission

29. 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. 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 50 µm Thousands of cilia cover the surface of Paramecium. Food vacuoles combine with lysosomes. As the food is digested, the vacuoles follow a looping path through the cell. Macronucleus Micronucleus 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. • Exploring structure and function in a ciliate FEEDING, WASTE REMOVAL, AND WATER BALANCE Contractile Vacuole Figure 28.12

30. CONJUGATION AND REPRODUCTION 2 Two cells of compatible mating strains align side by side and partially fuse. Meiosis of micronuclei produces four haploidmicronuclei in each cell. Three micronuclei in each cell disintegrate. The remaining micro-nucleus in each cell divides by mitosis. MEIOSIS The cells swap one micronucleus. Macronucleus Haploidmicronucleus Compatiblemates Diploidmicronucleus Diploidmicronucleus 9 2 1 3 7 4 5 6 8 MICRONUCLEARFUSION The cellsseparate. 7 8 Key Conjugation The original macro-nucleus disintegrates. Four micronuclei become macronuclei, while the other four remain micronuclei. Two rounds of cytokinesis partition one macronucleus and one micronucleus into each of four daughter cells. Three rounds of mitosis without cytokinesis produce eight micronuclei. Reproduction Micronuclei fuse,forming a diploid micronucleus.

31. Concept 28.5: Stramenopiles have “hairy” and smooth flagella • The clade Stramenopila • Includes several groups of heterotrophs as well as certain groups of algae

32. Hairy flagellum Smooth flagellum 5 µm Figure 28.13 • Most stramenopiles • Have a “hairy” flagellum paired with a “smooth” flagellum

33. Oomycetes (Water Molds and Their Relatives) • Oomycetes • Include water molds, white rusts, and downy mildews • Were once considered fungi based on morphological studies

34. Most oomycetes • Are decomposers or parasites • Have filaments (hyphae) that facilitate nutrient uptake

35. Oogonium Egg nucleus (n) On separate branches of the same or different individuals, meiosis produces several haploid sperm nuclei contained within antheridial hyphae. Several days later, the hyphae begin to form sexual structures. Encysted zoospores land on a substrate and germinate, growing into a tufted body of hyphae. Antheridial hypha with sperm nuclei (n) Meiosis produces eggs within oogonia (singular, oogonium). 4 1 2 3 MEIOSIS Germ tube Cyst Each zoospor- angium produces about 30 biflagellated zoospores asexually. 9 ASEXUAL REPRODUCTION Zoospore (2n) SEXUAL REPRODUCTION FERTILIZATION Zygote germination The ends of hyphae form tubular zoosporangia. 8 Zygotes (oospores) (2n) Zoosporangium (2n) Key Haploid (n) Diploid (2n) The zygotes germinate and form hyphae, and the cycle is completed. 7 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 Figure 28.14 • The life cycle of a water mold

36. The ecological impact of oomycetes can be significant • Phytophthora infestans causes late blight of potatoes

37. 3 µm Figure 28.15 Diatoms • Diatoms are unicellular algae • With a unique two-part, glass-like wall of hydrated silica

38. Figure 28.16 50 µm • Diatoms are a major component of phytoplankton • And are highly diverse

39. Accumulations of fossilized diatom walls • Compose much of the sediments known as diatomaceous earth

40. Golden Algae • Golden algae, or chrysophytes • Are named for their color, which results from their yellow and brown carotenoids • The cells of golden algae • Are typically biflagellated, with both flagella attached near one end of the cell

41. 25 µm Figure 28.17 • Most golden algae are unicellular • But some are colonial

42. Brown Algae • Brown algae, or phaeophytes • Are the largest and most complex algae • Are all multicellular, and most are marine

43. Blade Stipe Holdfast Figure 28.18 • Brown algae • Include many of the species commonly called seaweeds • Seaweeds • Have the most complex multicellular anatomy of all algae

44. Figure 28.19 • Kelps, or giant seaweeds • Live in deep parts of the ocean

45. (a) The seaweed is grown on nets in shallow coastal waters. (b) A worker spreads the harvested sea- weed on bamboo screens to dry. (c) Paper-thin, glossy sheets of nori make a mineral-rich wrap for rice, seafood, and vegetables in sushi. Figure 28.20a–c Human Uses of Seaweeds • Many seaweeds • Are important commodities for humans • Are harvested for food

46. 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

47. 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. Sporangia 2 Sporangia produce zoospores by meiosis. 3 MEIOSIS 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 sporo- phytes, being short, branched filaments that grow on the surface of subtidal rocks. Sporophyte (2n) 4 Zoospores The zygotes grow into new sporophytes, starting life attached to the remains of the female gametophyte. 7 Female Developing sporophyte Gametophytes (n) Zygote (2n) Egg Male gametophytes release sperm, and female gametophytes produce eggs, which remain attached to the female gameto- phyte. Eggs secrete a chemical signal that attracts sperm of the same species, thereby increasing the probability of fertilization in the ocean. 5 Male FERTILIZATION Mature female gametophyte (n) Sperm Key Sperm fertilize the eggs. 6 Haploid (n) Figure 28.21 Diploid (2n) • The life cycle of the brown alga Laminaria

48. Concept 28.6: Cercozoans and radiolarians have threadlike pseudopodia • A newly recognized clade, Cercozoa • Contains a diversity of species that are among the organisms referred to as amoebas • Amoebas were formerly defined as protists • That move and feed by means of pseudopodia • Cercozoans are distinguished from most other amoebas • By their threadlike pseudopodia

49. 20 µm Figure 28.22 Foraminiferans (Forams) • Foraminiferans, or forams • Are named for their porous, generally multichambered shells, called tests

50. Pseudopodia extend through the pores in the test • Foram tests in marine sediments • Form an extensive fossil record