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Protists

Introduction

  • Protists: eukaryotes that are not classified in the plant, animal, or fungal kingdoms, though some protists are closely related to plants or animals or fungi

  • Two common characteristics

    • Most abundant in moist habitats

    • Most of them are microscopic in size

Classification

  • Classified by ecological role

    • Three major groups:

      • Algae: generally photoautotrophic

      • Protozoa: heterotrophic

      • Fungus-like: resemble fungi in body form and absorptive nutrition

    • Terms lack taxonomic or evolutionary meaning

  • Classified by habitat

    • Particularly common and diverse in oceans, lakes, wetlands and rivers

    • Plankton: swimming or floating

      • Phytoplankton: photosynthetic

      • protozoan plankton: heterotrophic

      • Occur primarily as single cells, colonies or short filaments

  • Classified by motility

    • Swim using eukaryotic flagella

      • Flagellates

      • Some flagellated reproductive cells

    • Cilia: shorter and more abundant than flagella

      • Ciliates

    • Amoeboid movement: using pseudopodia

      • Amoebae

    • Gliding on protein or carbohydrate slime

Evolution and Relationships

  • At one time, protists were in a single kingdom

    • However, “protists” is not a monophyletic group

  • Evolutionary understanding is in flux

    • Some relationships are uncertain or disputed

    • New protists still being discovered

  • Classified into supergroups

Supergroup Excavata

  • Related to some of Earth’s earliest eukaryotes

  • Named for a feeding groove “excavated” into the cells of many representatives

  • Food particles are taken into cells by phagotrophy

    • Endocytosis

    • Evolutionary basis for endosymbiosis

  • Some are parasites

  • Trichomonas vaginalis and Giardia lamblia

  • Once thought to lack mitochondria

  • Possess highly modified mitochondria

  • Euglenozoa: protein strips under plasma membrane allow crawling

    • Some are heterotrophic, but Euglena is photosynthetic

  • Kinetoplastids: named for unusually large mass of DNA (kinetoplast) in a single large mitochondrion

    • Leishmania

    • Trypansosoma brucei

Supergroup and Plants and Relatives

  • Supergroup that includes land plants also encompasses several algal phyla

  • Kingdom plantae (land plants) evolved from green algal ancestors

  • Phylum chlorophyta: green algae

  • Phylum rhodophyta: red algae

  • Green algae

    • Phylum Chlorophyta

    • Diverse structural types

    • Occur in fresh waters, the ocean, and on land

    • Most are photosynthetic

    • Cells contain same type of plastids and photosynthetic pigments as in land plants

  • Red algae

    • Most are multicellular marine macroalgae

      • Red appearance due to distinctive photosynthetic pigments

      • Lack flagella

      • Unusually complex life cycles

    • Cryptomonads

      • Unicellular flagellates

      • Most contain red, blue-green, or brown plastids from secondary endosymbiosis

      • Photosynthetic

    • Haptophytes

      • Also unicellular photosynthesizers with secondary plastids

      • Some known as coccolithophorids

        • Have a covering of white calcium carbonate discs called coccoliths

Supergroup Alveolata

  • Ciliophora

    • Ciliates - conjugation

  • Apicomplexa: medically important parasites

    • Plasmodium

  • Dinozoa

    • Dinoflagelllates - some photosynthetic, others not

    • Red tide and mutualistic relationship with coral

    • About half of dinoflagellates are heterotrophic

    • Other half possess photosynthetic plastids of diverse types that originated by secondary or even tertiary endosymbiosis

    • Tertiary plastids are obtained by tertiary endosymbiosis

      • Acquisition by hosts of plastids from cells that already possessed secondary plastids

  • Named for saclike membranous vesicles (alveoli) present in cell periphery

Supergroup Stramenopila

  • Wide range of algae, protozoa, and fungus-like protists

  • Usually produce flagellate cells at some point

  • Named for distinctive strawlike hairs on the surface of flagella

  • Heterotrophic or photosynthetic

    • Plastids from secondary endosymbiosis
      with red algae

Supergroup Rhizaria

  • Have thin, hairlike extensions of the cytoplasm called filose pseudopodia

  • Phylum Chlorarachniophyta

  • Phylum Radiolaria

  • Phylum Foraminifera

Supergroup Amoebozoa

  • Many types of amoebae

  • Move using pseudopodia

  • ex: Dictyostelium discoideum*, ***slime mold

    • Model organism for understanding movement, cell communication, and development.

    • In response to starvation, single amoebae aggregate into a multicellular “slug” that develops into a stalked structure containing spores

    • Spores pop out and produce new amoebae

Supergroup Opisthokonta

  • Includes animal and fungal kingdoms and related protists

  • Named for single posterior flagellum on swimming cells

  • Choanoflagellate protists

    • Feature distinctive collar surrounding flagella

    • These are the modern protists most related to the common ancestor of animals

Nutritional and Defensive Adaptations

  • Phagotrophy: heterotrophs that ingest particles

  • Osmotrophy: heterotrophs that rely on uptake of small organic molecules

  • Photoautotrophy: photosynthetic

  • Mixotrophy: able to use autotrophy and phagotrophy or osmotrophy depending on conditions

  • Algal protists

    • Variety of pigments

      • Adapt photosystems to capture more light

      • Water absorbs the longer red and yellow wavelengths more than the shorter blue and green wavelengths

      • Accessory pigments absorb light and transfer it
        to chlorophyll a

    • Variety of types of food storage molecules

      • Starch, polysacchrides, and oil

  • Defense

    • Slimy mucilage or cell walls defend against herbivores and pathogens

      • Calcium carbonate, silica, iron, manganese armor

    • Trichocysts: spear-shaped projectiles to discourage herbivores

    • Bioluminescence: startles herbivores

    • Toxins: inhibit animal physiology

      • Ex: toxic dinoflagellate Pfiesteria

        • Responsible for fish kills – “killer alga” or “the cell from hell”

Reproductive Adaptations

  • Asexual reproduction

    • All protists can reproduce asexually

    • Many produce cysts with thick, protective       walls that remain dormant in bad conditions

    • Many protozoan pathogens spread from one  host to another via cysts

  • Sexual reproduction

    • Eukaryotic sexual reproduction with gametes and zygotes arose among the protists

    • Generally adaptive because it produces diverse genotypes

    • Zygotic and sporic life cycles

    • Zygotic life cycles

      • Most unicellular sexually reproducing protists

      • Haploid cells develop into gametes

        • and - mating strains

      • Thick-walled diploid zygotes

        • Survive like cysts

    • Sporic life cycle

      • Many multicellular green and brown seaweeds

      • Also known as alternation of generations

      • 2 types of multicellular organisms

        • Haploid gametophyte produces gametes

        • Diploid sporophyte produces spores by meiosis

      • Red seaweed variation involves 3 distinct multicellular generations

    • Gametic life cycle

      • All cells except the gametes are diploid

      • Gametes produced by meiosis

      • Diatoms: one of few protists with this life cycle

        • Asexual reproduction reduces the size of the daughter cells

        • Sexual reproduction restores maximal size

    • Ciliate sexual reproduction

      • Most complex sexual process in protists

      • Have 2 types of nuclei (single macronucleus and one or more micronuclei)

      • Macronuclei are the source of the information for cell function

      • 2 cell pairs and fuse -  conjugation

      • Micronuclei undergo meiosis, exchange, fusion, and mitosis

  • Parasitic protist life cycle

    • Parasitic protists often use more than one host organism**,** in which different life stages occur

    • ex: Malarial parasite Plasmodium

      • Alternates between humans and Anopheles mosquitoes

    • Different stages in different hosts and host tissues

Protists

Introduction

  • Protists: eukaryotes that are not classified in the plant, animal, or fungal kingdoms, though some protists are closely related to plants or animals or fungi

  • Two common characteristics

    • Most abundant in moist habitats

    • Most of them are microscopic in size

Classification

  • Classified by ecological role

    • Three major groups:

      • Algae: generally photoautotrophic

      • Protozoa: heterotrophic

      • Fungus-like: resemble fungi in body form and absorptive nutrition

    • Terms lack taxonomic or evolutionary meaning

  • Classified by habitat

    • Particularly common and diverse in oceans, lakes, wetlands and rivers

    • Plankton: swimming or floating

      • Phytoplankton: photosynthetic

      • protozoan plankton: heterotrophic

      • Occur primarily as single cells, colonies or short filaments

  • Classified by motility

    • Swim using eukaryotic flagella

      • Flagellates

      • Some flagellated reproductive cells

    • Cilia: shorter and more abundant than flagella

      • Ciliates

    • Amoeboid movement: using pseudopodia

      • Amoebae

    • Gliding on protein or carbohydrate slime

Evolution and Relationships

  • At one time, protists were in a single kingdom

    • However, “protists” is not a monophyletic group

  • Evolutionary understanding is in flux

    • Some relationships are uncertain or disputed

    • New protists still being discovered

  • Classified into supergroups

Supergroup Excavata

  • Related to some of Earth’s earliest eukaryotes

  • Named for a feeding groove “excavated” into the cells of many representatives

  • Food particles are taken into cells by phagotrophy

    • Endocytosis

    • Evolutionary basis for endosymbiosis

  • Some are parasites

  • Trichomonas vaginalis and Giardia lamblia

  • Once thought to lack mitochondria

  • Possess highly modified mitochondria

  • Euglenozoa: protein strips under plasma membrane allow crawling

    • Some are heterotrophic, but Euglena is photosynthetic

  • Kinetoplastids: named for unusually large mass of DNA (kinetoplast) in a single large mitochondrion

    • Leishmania

    • Trypansosoma brucei

Supergroup and Plants and Relatives

  • Supergroup that includes land plants also encompasses several algal phyla

  • Kingdom plantae (land plants) evolved from green algal ancestors

  • Phylum chlorophyta: green algae

  • Phylum rhodophyta: red algae

  • Green algae

    • Phylum Chlorophyta

    • Diverse structural types

    • Occur in fresh waters, the ocean, and on land

    • Most are photosynthetic

    • Cells contain same type of plastids and photosynthetic pigments as in land plants

  • Red algae

    • Most are multicellular marine macroalgae

      • Red appearance due to distinctive photosynthetic pigments

      • Lack flagella

      • Unusually complex life cycles

    • Cryptomonads

      • Unicellular flagellates

      • Most contain red, blue-green, or brown plastids from secondary endosymbiosis

      • Photosynthetic

    • Haptophytes

      • Also unicellular photosynthesizers with secondary plastids

      • Some known as coccolithophorids

        • Have a covering of white calcium carbonate discs called coccoliths

Supergroup Alveolata

  • Ciliophora

    • Ciliates - conjugation

  • Apicomplexa: medically important parasites

    • Plasmodium

  • Dinozoa

    • Dinoflagelllates - some photosynthetic, others not

    • Red tide and mutualistic relationship with coral

    • About half of dinoflagellates are heterotrophic

    • Other half possess photosynthetic plastids of diverse types that originated by secondary or even tertiary endosymbiosis

    • Tertiary plastids are obtained by tertiary endosymbiosis

      • Acquisition by hosts of plastids from cells that already possessed secondary plastids

  • Named for saclike membranous vesicles (alveoli) present in cell periphery

Supergroup Stramenopila

  • Wide range of algae, protozoa, and fungus-like protists

  • Usually produce flagellate cells at some point

  • Named for distinctive strawlike hairs on the surface of flagella

  • Heterotrophic or photosynthetic

    • Plastids from secondary endosymbiosis
      with red algae

Supergroup Rhizaria

  • Have thin, hairlike extensions of the cytoplasm called filose pseudopodia

  • Phylum Chlorarachniophyta

  • Phylum Radiolaria

  • Phylum Foraminifera

Supergroup Amoebozoa

  • Many types of amoebae

  • Move using pseudopodia

  • ex: Dictyostelium discoideum*, ***slime mold

    • Model organism for understanding movement, cell communication, and development.

    • In response to starvation, single amoebae aggregate into a multicellular “slug” that develops into a stalked structure containing spores

    • Spores pop out and produce new amoebae

Supergroup Opisthokonta

  • Includes animal and fungal kingdoms and related protists

  • Named for single posterior flagellum on swimming cells

  • Choanoflagellate protists

    • Feature distinctive collar surrounding flagella

    • These are the modern protists most related to the common ancestor of animals

Nutritional and Defensive Adaptations

  • Phagotrophy: heterotrophs that ingest particles

  • Osmotrophy: heterotrophs that rely on uptake of small organic molecules

  • Photoautotrophy: photosynthetic

  • Mixotrophy: able to use autotrophy and phagotrophy or osmotrophy depending on conditions

  • Algal protists

    • Variety of pigments

      • Adapt photosystems to capture more light

      • Water absorbs the longer red and yellow wavelengths more than the shorter blue and green wavelengths

      • Accessory pigments absorb light and transfer it
        to chlorophyll a

    • Variety of types of food storage molecules

      • Starch, polysacchrides, and oil

  • Defense

    • Slimy mucilage or cell walls defend against herbivores and pathogens

      • Calcium carbonate, silica, iron, manganese armor

    • Trichocysts: spear-shaped projectiles to discourage herbivores

    • Bioluminescence: startles herbivores

    • Toxins: inhibit animal physiology

      • Ex: toxic dinoflagellate Pfiesteria

        • Responsible for fish kills – “killer alga” or “the cell from hell”

Reproductive Adaptations

  • Asexual reproduction

    • All protists can reproduce asexually

    • Many produce cysts with thick, protective       walls that remain dormant in bad conditions

    • Many protozoan pathogens spread from one  host to another via cysts

  • Sexual reproduction

    • Eukaryotic sexual reproduction with gametes and zygotes arose among the protists

    • Generally adaptive because it produces diverse genotypes

    • Zygotic and sporic life cycles

    • Zygotic life cycles

      • Most unicellular sexually reproducing protists

      • Haploid cells develop into gametes

        • and - mating strains

      • Thick-walled diploid zygotes

        • Survive like cysts

    • Sporic life cycle

      • Many multicellular green and brown seaweeds

      • Also known as alternation of generations

      • 2 types of multicellular organisms

        • Haploid gametophyte produces gametes

        • Diploid sporophyte produces spores by meiosis

      • Red seaweed variation involves 3 distinct multicellular generations

    • Gametic life cycle

      • All cells except the gametes are diploid

      • Gametes produced by meiosis

      • Diatoms: one of few protists with this life cycle

        • Asexual reproduction reduces the size of the daughter cells

        • Sexual reproduction restores maximal size

    • Ciliate sexual reproduction

      • Most complex sexual process in protists

      • Have 2 types of nuclei (single macronucleus and one or more micronuclei)

      • Macronuclei are the source of the information for cell function

      • 2 cell pairs and fuse -  conjugation

      • Micronuclei undergo meiosis, exchange, fusion, and mitosis

  • Parasitic protist life cycle

    • Parasitic protists often use more than one host organism**,** in which different life stages occur

    • ex: Malarial parasite Plasmodium

      • Alternates between humans and Anopheles mosquitoes

    • Different stages in different hosts and host tissues

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