Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 28 Protists

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Protist habitats are also diverse in habitat And including freshwater and marine species Figure 28.2a–d 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)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Reproduction and life cycles – Are also highly varied among protists, with both sexual and asexual species

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A sample of protist diversity Table 28.1

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Endosymbiosis in Eukaryotic Evolution There is now considerable evidence – That much of protist diversity has its origins in endosymbiosis

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Diplomonads – Have two nuclei and multiple flagella Figure 28.5a 5 µm (a) Giardia intestinalis, a diplomonad (colorized SEM)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Parabasalids Parabasalids include trichomonads – Which move by means of flagella and an undulating part of the plasma membrane Figure 28.5b (b) Trichomonas vaginalis, a parabasalid (colorized SEM) Flagella Undulating membrane 5 µm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Euglenozoans have flagella with a unique internal structure – Is the presence of a spiral or crystalline rod of unknown function inside their flagella

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Kinetoplastids – Have a single, large mitochondrion that contains an organized mass of DNA called a kinetoplast

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The parasitic kinetoplastid Trypanosoma – Causes sleeping sickness in humans Figure  m

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Euglenids – Have one or two flagella that emerge from a pocket at one end of the cell 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Alveolates have sacs beneath the plasma membrane Figure 28.9 Flagellum Alveoli 0.2 µm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Dinoflagellates – Are a diverse group of aquatic photoautotrophs and heterotrophs – internal plates of cellulose Two flagella – Make them spin as they move through the water

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Rapid growth of some dinoflagellates – Is responsible for causing “red tides,” which can be toxic to humans

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure Inside mosquitoInside human Sporozoites (n) Oocyst MEIOSIS Liver Liver cell Merozoite (n) Red blood cells Gametocytes (n) FERTILIZATION Gametes Zygote (2n) Key Haploid (n) Diploid (2n) Merozoite Red blood cell Apex 0.5 µm Most apicomplexans have intricate life cycles – With both sexual and asexual stages that often require two or more different host species for completion 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The micronuclei – Function during conjugation, a sexual process that produces genetic variation Conjugation is separate from reproduction – Which generally occurs by binary fission

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 28.5: Stramenopiles have “hairy” and smooth flagella The clade Stramenopila – Includes several groups of heterotrophs as well as certain groups of algae

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oomycetes (Water Molds and Their Relatives) Oomycetes – Include water molds, white rusts, and downy mildews – Were once considered fungi based on morphological studies

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Most oomycetes – Are decomposers or parasites – Have filaments (hyphae) that facilitate nutrient uptake – Phytophthora infestans causes late blight of potatoes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Diatoms Diatoms are unicellular algae – With a unique two-part, glass-like wall of hydrated silica Figure µm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Accumulations of fossilized diatom walls – Compose much of the sediments known as diatomaceous earth

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Golden Algae Golden algae, or chrysophytes – Are named for their color, which results from their yellow and brown carotenoids – Are typically biflagellated, with both flagella attached near one end of the cell

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Most golden algae are unicellular – But some are colonial Figure µm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Brown Algae Brown algae, or phaeophytes – Are the largest and most complex algae – Are all multicellular, and most are marine Seaweeds – Have the most complex multicellular anatomy of all algae

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Kelps, or giant seaweeds – Live in deep parts of the ocean Figure 28.19

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Alternation of Generations The most complex life cycles include an alternation of generations – The alternation of multicellular haploid and diploid forms

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Foraminiferans (Forams) Foraminiferans, or forams – Are named for their porous, generally multichambered shells, called tests Figure µm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pseudopodia extend through the pores in the test

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Radiolarians Radiolarians are marine protists – made of silica – That phagocytose microorganisms with their pseudopodia

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Amoebozoans have lobe-shaped pseudopodia Amoebozoans – Are amoeba that have lobe-shaped, rather than threadlike, pseudopodia – Include gymnamoebas, entamoebas, and slime molds

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Gymnamoebas – Are common unicellular amoebozoans in soil as well as freshwater and marine environments

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Most gymnamoebas are heterotrophic – And actively seek and consume bacteria and other protists Figure Pseudopodia 40 µm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Entamoebas – Are parasites of vertebrates and some invertebrates Entamoeba histolytica – Causes amebic dysentery in humans

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Slime Molds Slime molds, or mycetozoans – Were once thought to be fungi Molecular systematics – Places slime molds in the clade Amoebozoa

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Plasmodial Slime Molds Many species of plasmodial slime molds – Are brightly pigmented, usually yellow or orange Figure cm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings At one point in the life cycle – They form a mass called a plasmodium Figure Feeding plasmodium Mature plasmodium (preparing to fruit) Young sporangium Mature sporangium Spores (n) Germinating spore Amoeboid cells (n) Zygote (2n) 1 mm Key Haploid (n) Diploid (2n) 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The plasmodium – Is undivided by membranes and contains many diploid nuclei

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cellular Slime Molds Cellular slime molds form multicellular aggregates – In which the cells remain separated by their membranes

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Red algae and green algae are the closest relatives of land plants Over a billion years ago, a heterotrophic protist acquired a cyanobacterial endosymbiont

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Red Algae Red algae are reddish in color – Due to an accessory pigment call phycoerythrin, which masks the green of chlorophyll

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Red algae – Are usually multicellular; the largest are seaweeds 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)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Green Algae Green algae – Are named for their grass-green chloroplasts – Are divided into two main groups: chlorophytes and charophyceans – Are closely related to land plants

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Most chlorophytes – Live in fresh water, although many are marine Figure 28.29

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chlorophytes include – Unicellular, colonial, and multicellular forms 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 fila- ments lack cross-walls and thus are multi- nucleate. 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure Flagella Cell wall Nucleus Regions of single chloroplast Zoospores ASEXUAL REPRODUCTION Mature cell (n) SYNGAMY SEXUAL REPRODUCTION Zygote (2n) MEIOSIS 1 µm Key Haploid (n) Diploid (2n)  + +   + + Most chlorophytes have complex life cycles – With both sexual and asexual reproductive stages 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