Chapter 28 Protists

Changes All protists were once classified in a single kingdom, Protista Protista is in fact polyphyletic ◦Developed from more than one ancestral type ◦Some are more closely related to plants, animals and fungi than they are to other protists. This unit looks at the various groups of protists instead of a single kingdom

The Basics Found almost everywhere Can be very small – 0.5um to very large, over 10meters in length.

Domain Eukarya Protists are Eukaryotes ◦Have a nucleus and membrane bound organelles ◦Most are unicellular

Structural and Functional Diversity The most structural and functional diversity of any other group of eukaryotes Cell Structure ◦Unicellular  Complex single celled organisms  Organelles perform specific functions ◦Colonial ◦Multicellular  Functions carried out by organs

Structural and Functional Diversity Nutritional Diversity ◦Photoautotrophs-contain chloroplasts ◦Heterotrophs-absorb organic molecules or ingest larger food particles ◦Mixotrophs-combine photosynthesis and heterotrophic nutrition Reproduction ◦Asexual types ◦Some sexual reproduction or employ the sexual processes of meiosis and fertilization

Endosymbiosis in Eukaryotic Evolution There is now considerable evidence that much of protist diversity has its origins in endosymbiosis Certain unicellular organisms engulf other cells, which become endosymbionts and ultimately organelles in the host cell

Endosymbiosis Mitochondria were acquired first by eukaryotes engulfing an aerobic prokaryote ◦Support: all eukaryotes have or either had mitochondria Later, a heterotrophic eukaryote acquired a photosynthetic cyanobacterium that then evolved into plastids ◦Plastid – plant organelles that are closely related (ex: chloroplast)

Supergroup – Excavata some members have an “excavated” feeding groove on one side of the cell body Clade – Diplomonads Lack plastids Have Modified mitochondria Lack functional electron transport chains (cannot use oxygen) Energy from glycolysis Two equal sized nuclei Multiple flagella

Diplomonads Example: Parasite inhabits the intestines of mammals Diplomonads Example: Parasite inhabits the intestines of mammals Giardia intestinalis, a diplomonad (colorized SEM) 5 µm

Supergroup – Excavata Supergroup – Excavata Clade Parabasalids ◦Lack plasmids ◦Have reduced mitochondria  Generate some energy anaerobically Trichomonas vaginalis, a parabasalid (colorized SEM) Parasite – sexually transmitted. Infects vagina Undulating membrane Flagella

Clade Parabasalids ◦Example symbiotic relationship ◦Lives in gut of termites and enables them to break down wood Supergroup – Excavata Supergroup – Excavata

Supergroup-Excavata Clade- Euglenozoans ◦Main morphological feature is the presence of a spiral or crystalline rod of unknown function inside their flagella Two Subgroups ◦Kinetoplastids ◦Euglenids

Supergroup-Excavata Clade Euglenozoans Subgroup – Kinetoplastids ◦Have a single large mitochondrion that contains an organized mass of DNA called a kinetoplast ◦Feed on prokaryotes in freshwater, marine and moist terrestrial ecosystems ◦Some are parasites of animals, plants and other protists

Subgroup - Kinetoplastid example ◦The parasitic Trypanosoma causes sleeping sickness in humans Carried by the African tsetse fly A neurological disease Some cause Chagas’ disease – transmitted by bloodsucking insects

Supergroup – Excavata Clade Euglenozoans Subgroup – Euglenids ◦Have a pocket at one end of the cell from which one or two flagella emerge ◦Many are mixotrophs  In sunlight-autotrophs  No sunlight become heterotrophic  Can engulf prey by phagocytosis

LE µm Euglena (LM) Plasma membrane Nucleus Short flagellum Eyespot Light detector Contractile vacuole Chloroplast Paramylon granule Pellicle Long flagellum Detects light Subgroup Euglenids – Example Euglena

Supergroup-Chromalveolata Clade - Alveolates Alveolates ◦Have membrane-bounded sacs (alveoli) just under the plasma membrane (function, unknown) ◦Three subgroups  Dinoflagellates  Apicomplexans  Ciliates alveoli

Supergroup-Chromalveolata Clade-Alveolates Subgroup- Dinoflagellates ◦Cells are reinforced by cellulose plates ◦Two flagella make them spin like a top ◦Components of marine and freshwater plankton  Plankton live near surface of water ◦Very important photosynthetic species  Some can be mixotrophs or heterotrophs ◦Blooms cause Red Tide  Toxins can cause massive kills of invertebrates and fishes. Humans who eat mollusks with toxins can become sick or die

Dinoflagellate and red tide Flagella

Subgroup – Apicomplexans ◦Nearly all are parasites of animals ◦Spread through host as tiny cells called sporozoites ◦Most have sexual and asexual life cycles  Cycles usually require two or more host species to complete lifecycle Supergroup-Chromalveolata Clade-Alveolates

Apicomplexan example: Plasmodium Sporozoites (n) Inside mosquito Oocyst Zygote (2n) MEIOSIS Merozoite (n) Liver cell Liver FERTILIZATION Gametes Gametocytes (n) Red blood cells Inside human Merozoite Apex Red blood cell 0.5 µm Haploid (n) Key Diploid (2n) malaria

Subgroup – Ciliates ◦Use cilia to move and feed  Cilia can comver the cell or may be clustered in a few rows or tufts ◦Two types of nuclei  Micronuclei – tiny ◦ Important in conjugation – cells exchange haploid micronuclei ◦ Forms new macronucleus during binary fission  Macronucleus – large ◦ Copies of genome ◦ Controls everyday functions of the cell Supergroup-Chromalveolata Clade-Alveolates

Ciliate example: Paramecium

Marine algae Important photosynthetic organisms Some heterotrophs Flagellum has numerous fine, hairlike projections ◦The “hairy” flagellum will often be paired with a “smooth” flagellum Subgroups ◦Diatoms ◦Golden algae ◦Brown algae ◦oomycetes Supergroup-Chromalveolata Clade-Stramenopiles hairy smooth

Subgroup – Diatoms ◦Unicellular algae ◦Glass-like wall made of hydrated silica  Shape like a box and lid – gives organism great strength ◦Reproduce asexually by mitosis ◦Major component of plankton and highly diverse  Marine and freshwater varieties ◦Fossilized diatom walls make diatomaceous earth  Used for filtering Supergroup-Chromalveolata Clade-Stramenopiles

Diatom Examples

Subgroup – 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 ◦Most are unicellular, but some are colonial ◦Freshwater and marine plankton ◦Photosynthetic (some mixotrophic) ◦Most unicellular, some colonial Supergroup-Chromalveolata Clade-Stramenopiles

Colonial and unicellular Golden Algae 25 µm

Subgroup – Brown Algae ◦Largest and most complex algae ◦All are multicellular, and most are marine  Usually cool waters ◦Commonly called seaweed ◦Some have specialized tissues and organs that resemble those in plants ◦Photosynthetic ◦Kelp are brown algae that can reach 60meters ◦Some are eaten by humans ◦Used to thicken many processed foods like pudding, ice cream and salad dressing Supergroup-Chromalveolata Clade-Stramenopiles

Brown Algae Example Three labeled parts make up the thallus Blade Stipe Holdfast

Subgroup – Oomycetes (water molds and their relatives) Water molds, white rusts and downy mildews Have filaments that resemble fugal hyphae Have cell walls made of cellulose Do not have plastids Most are decomposers or parasites Water molds grow as cottony masses on dead algae and animals mainly in freshwater White rusts and downy mildews live as plant parasites Asexual and sexual stages to lifecycle Supergroup-Chromalveolata Clade-Stramenopiles

Supergroup Chromalveolata Clade - Stramenopiles Oomycetes Examples Water mold White rust Downy mildew Sudden Oak Disease

Supergroup – Rhizaria Clade Chlorarachniophytes All Rhizaria are “amoeboid like” Have threadlike pseudopodia Chlorarachniophyes came about due to secondary symbiosis ◦non-photosynthetic eukaryote engulfed an eukaryotic alga and retained it as a photosynthetic organelle ◦Contain chloroplasts ◦photosynthetic

Contain porous shells called tests ◦Consist of a single piece of organic material hardened with calcium carbonate ◦Pseudopodia extend through the pores ◦Ocean and fresh water ◦Live in sand or attach to rocks or algae ◦Fossilized tests are part of marine sediment that are now land formations Supergroup – Rhizaria Clade Foraminiferans (Forams)

Supergroup – Rhizaria Clade - Radiolarians Have delicate internal skeletons made of silica Pseudopodia radiate from the central body Mostly marine Covered by layer of cytoplasm which engulfs smaller microorganisms Skeletons settle to seafloor creating an ooze that can be hundreds of meters thick

Supergroup – Archaeplastida Clade- Red Algae Evolved when a heterotrophic protist acquired a cyanobacterial endosymbiont Can be greenish red, to red, to black depending on ocean depth Most abundant large algae in warm coastal waters of tropical oceans Most are multicellular Alternation of generations is common

Red Algae Uses by humans The seaweed is grown on nets in shallow coastal waters. A worker spreads the seaweed on bamboo screens to dry. Paper-thin, glossy sheets of nori make a nutritious wrap for rice, seafood, and vegetables in sushi.

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. ◦The term applies only to life cycles in which both haploid and diploid stages are multicellular (not seen in human sexual life cycles – haploid stage is unicellular)

LE Developing sporophyte Zygote (2n) FERTILIZATION Mature female gametophyte (n) Egg Sperm MEIOSIS Haploid (n) Key Diploid (2n) Sporangia Sporophyte (2n) Zoospores Female Gametophytes (n) Male

Pigment much like chloroplasts of land plants Cell walls made of cellulose Two groups of Green Algae ◦Charophytes – closest relative to land plants  Inhabit shallow waters in ponds or lakes  Can survive periods of drying  Have distinctive traits shared with land plants Supergroup – Archaeplastida Clade- Green Algae

Chlorophytes ◦Most live in fresh water, also marine and terrestrial species (even snow!) ◦Some are unicellular  Exist as plankton or live in damp soil  some live symbiotically within other eukaryotes ◦Some form colonies, others are multicellular ◦Have complex life cycles (sexual and asexual reproduction)  Alternation of generations in some Supergroup – Archaeplastida Clade- Green Algae

Green Algae - examples Watermelon snow Volvox, Caulerpa and Ulva or sea lettuce

Supergroup – Unikonta Clade- Amoebozoans Includes many species of amoebas that have lobe or tube shaped, rather than threadlike, pseudopodia Includes three subgroups ◦Slime molds ◦Gymnamoebas ◦Entamoebas

Subgroup – Slime Molds ◦Produce fruiting bodies that aid in spore dispersal ◦Two main branches  plasmodial and cellular slime molds ◦ Distinguished by life cycles Supergroup – Unikonta Clade- Amoebozoans

Subgroup – Slime molds Plasmodial slime molds ◦Brightly colored – yellow or orange ◦Form a mass called a plasmodium  A single mass of cytoplasm that is undivided by plasma membranes and contains many diploid nuclei  Engulfs food particles by phagocytosis  When habitat is not favorable it differentiates into fruiting bodies which function in sexual reproduction Supergroup – Unikonta Clade- Amoebozoans

Subgroup – Slime molds Cellular slime molds ◦ feeding stage is an individual cell ◦Food loss results in an aggregate of cells that functions as a unit ◦Cells are separated by plasma membranes ◦Haploid organisms ◦Fruiting bodies function in asexual reproduction Supergroup – Unikonta Clade- Amoebozoans Fruiting body Migrating slug aggregate

Subgroup – Gymnamoebas ◦Unicellular ◦Found in soil, freshwater and marine environments ◦Most are heterotrophs – consume bacteria and other protists, or non-living matter Supergroup – Unikonta Clade- Amoebozoans

Subgroup – Entamoebas ◦Parasitic ◦Infect vertebrates (some invertebrates) ◦E.histolytica causes amebic dysentery. Spread through contaminated drinking water and food. Supergroup – Unikonta Clade- Amoebozoans

Supergroup – Unikonta Clade - Opisthokonts Subgroup – Nucleariids ◦Closely related to fungi ◦Unicellular ◦Amoebas that feed on algae and bacteria Subgroup – Choanoflagellates ◦Close relative of animals ◦In fresh and ocean waters ◦Flagella filters bacteria and other food from the water All have posterior flagella