Protista: The Misfit Kingdom Chapter 19 What is a Protist? Kingdom Protista is the most diverse group of organisms of any kingdom (Greek protistos = the very first) May be single-celled, colonial, or multicellular Heterotrophic and/or autotrophic Resemble organisms in other kingdoms Do NOT form differentiated tissue types Why are they grouped together? All eukaryotic, reproduce asexually by mitosis Dont quite fit into the other kingdoms Do not form a single clade (not related to a single common ancestor), called paraphyletic
Many consider the term Protista to be obsolete, preferring instead to classify them into supergroups (Archaeplastida, SAR, Excavata, Amoebazoa, Opisthokontha) These supergroups have developed as use of the electron microscope has helped distinguish important differences of cellular structures Protista was revised in 2015 to two separate but broad kingdoms: What are Protozoa? Proto first; zoon animal (first animals) Organisms in Kingdom Protozoa resemble animals in the way they get food Heterotrophic
Some are free-living single cells that move around Some feed as a group of cells; aggregate & reproduce as a group Some feed individually, reproduce as a group Many are parasitic (those lacking mitochondria) Many are saprophytic (feeding on dead organic matter) Include single-celled animal-like organisms (Amoebas, Ciliates, Euglenids) Also include fungus-like slime molds (Usually found on dead/decaying plants or microorganisms) Animal-like Protozoa Categorized according to how they move Phylum Amoebozoa Lack a cell wall, generally shapeless Move around using pseudopodia extensions of cytoplasm-containing plasma membrane, using actin
microfilaments Surround food and enclose it in a vacuole; fuse with lysosomes and digest food with enzymes; nutrients diffuse into cytoplasm (phagocytosis) Includes amoebas (mostly marine species, some freshwater, some parasitic) and slime molds Some may also have silica shells, single flagella https://www.youtube.com/watch?v=PsYpngBG394 Animal-like Protists Phylum Ciliophora Unicellular organisms covered in hair-like organelles called cilia identical in structure to flagella but shorter and present in larger numbers Ciliates live in every kind of aquatic habitat (ponds, streams, oceans, sulfur springs) Many structures found in ciliates cells work together to perform life functions Paramecia have oral groove, gullet, and food vacuoles that are coordinated for the
process of digestion Usually reproduce asexually by cloning, can exchange genetic material if environmental pressures exist (conjugation) Many ciliates are predators or top predators in their microscopic food chain https://www.youtube.com/watch?v=FcCvhYmjaXE Contractile vacuoles regulate osmolarity within cells by constantly pumping out excess water https://www.youtube.com/watch?v=9Ynm5ZOW59Q https://www.youtube.com/watch?v=MPnXIvprb_w Animal-like Protozoa Phylum Euglenozoa Unicellular, most have 2 flagella Animal-like: move around, heterotrophic Can inch around by extending lengthwise microtubules, swim using flagella Absorb food via phagocytosis (sometimes through a special siphon) https://www.youtube.com/watch?v=fI7nEWUjk3A
Plant-like: many possess chloroplasts and can photosynthesize, possess organelle called an eye spot with light-sensitive pigments Formerly classified as a type of algae (revised based on lack of chloroplasts in all euglenozoa, which are all heterotrophs) Make up part of the phytoplankton (group of microorganisms that act as a major producer food source for aquatic ecosystems) Animal-like Protozoa Other flagellated protozoa Can be autotrophic, free-living heterotrophic, parasitic, or symbiotic Makes classification VERY DIFFICULT Flagella are considered ancient structures, representing basal lineages Choanoflagellates are considered the closest related ancestor to multicellular Animals
cells similar to feeding cell types found in sponges; statistical DNA analysis confirms this May have evolved into colonial groups, which then led to specialization among colonial cells https://www.youtube.com/watch?v=UhcRyeJoMUg Parasitic Protozoa Supergroup SAR, Phylum Apicomplexia Includes plasmodium, babesia, cyclospora, toxoplasma https://www.youtube.com/watch?v=s3DSB1xXuec Supergroup Excavata Includes giardia, trichomonas, trypanosoma https://www.youtube.com/watch?v=HlhYAyNy36g
These organisms have an infectious stage the sporozoite; can reproduce sexually (with a motile, flagellated gamete) and asexually (via spores) Usually named and classified according to which host cells they parasitize Mutualistic Protozoa Endosymbiotic relationships (living within another organism) Earliest example of a mutualism (100 mya; oldest examples trapped in amber discovered in 2009) Primitive termites probably fed on a range
of things they could digest themselves Modern termites have protozoa living in their guts that secrete cellulase, an enzyme responsible for their ability to digest wood cellulose into sugar Young termites eat feces from adults and ingest the protozoa This relationship has helped termites exploit endless resources of dead wood for food, ~2300 species
Slime Molds Phylum Mycetozoa (the fungus animals) Decompose organic materials Plasmodial slime molds Feeding stage multinucleate mass of cytoplasm called a plasmodium Resembles amoeba feeding behaviors (phagocytosis) Usually found on decaying plant matter (logs, leaves, etc.) Reproductive stage happens when plasmodium runs out of food, transforms itself into many separate, stalked, spore-producing structures (sporangia) which produce haploid spores https://https://www.youtube.com/watch?v=GY_uMH8Xpy0 Cellular slime molds Feeding stage Amoeba-like during, feed as separate cells
Reproductive stage aggregate together, migrate as a sluglike shape, and form sporangia https://www.youtube.com/watch?v=bkVhLJLG7ug Slime Mold Life Cycles Water Molds & Downy Mildews Oomycetes (egg fungus) fungus-like eukaryotes Filamentous, absorptive, with cell walls made of cellulose Many are saprophytes, others are obligate pathogens to plants or animals Water mold is actually incorrect, most are terrestrial pathogens Invade their host with filaments called hyphae that lack septa Cause many fish & invertebrate diseases Powdery mildew responsible for the potato blight that played major role in 1840s Irish famine Thrives in wetter, cooler climates Can destroy crops in a matter of days Other types of crops also affected
Reproduce asexually with spores, which germinate into new organisms Reproduce sexually by fusing two hyphae called gametangia (gamete vessels) which form a diploid oogonium (fertilized egg) Chromista the Protophyta Proto first; phyta plant (first plants) Mostly aquatic, photosynthetic, plantlike protists (algae), polyphyletic & do not all share common ancestry Most have chloroplasts that resemble cyanobacteria (cyanoplasts; endosymbiont evidence) Categorized based on type of pigments, physical structures and genetic similarities Colors: purple, rusty-red, olive-brown, yellow, golden-brown, green Unicellular and multicellular organisms Unicellular photosynthetic organisms: phytoplankton
Major food source and oxygen producer on Earth Multicellular algae look like plants but have no roots, stems or leaves (seaweed) Unicellular Algae Various single-celled algae have evolved through diverse lineages, no single common ancestry Diatoms single and colonial algae with silica shells Dinoflagellates thick shells of cellulose plates, many are photosynthetic Many form symbiotic relationships with protozoa and fungi Euglenids heterotrophs ingested algae that remained as endosymbionts, had the advantage of motility Lichens algae or cyanobacteria existing mutualistically with fungus, advantage of protection and nutrients
Diatoms: The Golden Algae Phylum Bacillariophyta - Unicellular, photosynthetic, cell wall made of silica Golden-yellow (chlorophyll a & carotenoids) Marine and freshwater Food is stored as oils (rather than starch) Helps diatoms float near surface where light is available Fish that eat diatoms have an oily taste Asexual division makes offspring smaller; continues until generations are size of original size
Reproduce sexually & asexually Dinoflagellates The Spinning Algae Phylum Dinoflagellata (dino = spinning, flagella = whip) https ://www.youtube.com/watch?v=Tl0I-LKTm-s Cell walls composed of cellulose plates 2 flagella in grooves at right angles, spin slowly A few freshwater species, mostly marine Major component of phytoplankton Many are photosynthetic, some live symbiotically within other organisms Toxin-producing species can lead to fish kills and red tides if populations explode (algal bloom), many are bioluminescent and can be seen at night
Algal Blooms Algae have very similar nutrient requirements to plants Some algal blooms are the result of excess nutrients (phosphorus, nitrogen) in waters, often from farmland runoff, warm temperatures, and climate changes Can be harmful to aquatic ecosystems Sometimes toxic, killing animals in food chain Eventually die and decompose, causing massive drop in available dissolved oxygen; fish and invertebrates suffer Dinoflagellates can be particularly harmful neurotoxin that concentrates in tissues of higher trophic levels, can be deadly to humans & other vertebrates https://www.youtube.com/watch?v=Fvob6L8q3I8 https://www.youtube.com/watch?v=PrVShZZDKk8 Green Algae
Chlorophyta: the most diverse algae (7000+ species) Can be unicellular, colonial, or multicellular Major pigments are chlorophyll a & b, chloroplasts probably descended from endosymbiotic cyanobacteria, food stored as starch https://www.youtube.com/watch?v=He9FSeGRi3A https://www.youtube.com/watch?v=GNb_MvFtTc8 Can reproduce sexually (forming gametes) and asexually (cloning & fragmentation) Some green algae exhibit alternation of generations https://www.youtube.com/watch?v=cmSs157KvTg These similarities + genetic evidence show that land plants developed from multicellular green algae
Alternation of Generations Some green algae (like Ulva) and ALL plants have a pattern called Alternation of Generations Gametophyte: Haploid form of the organism (gamete-producing) Sporophyte: Diploid form of the organism (spore-producing) Multicellular gametophytes produce flagellated gametes (n) in gametangia fuse to form a zygote (2n) Zygote undergoes mitosis, becomes multicellular sporophyte (2n) Sporophytes produce flagellated zoospores (n) via meiosis spores germinate and undergo mitosis to form mullticellular gametophyte
Red Algae Phylum Rhodophyta (rhodon = red; phyta = plant): 5000-6000 species, mostly multicellular & marine Unique group no flagellated species, chloroplasts contain unstacked thylakoids Have chlorophyll a & c and a special red pigment called phycobilins (able to absorb green, blue, violet wavelengths of light) Store food as a highly-branched starch Alternation of generations can have 3 generations rather than 2 Body of seaweed is called a thallus (lack roots, stems, & leaves) Anchors to rocks and other structures using holdfasts
Found in deep, cold waters along rocky coasts where most other seaweeds cannot thrive Brown Algae Phylum Heterokontophyta, division Phaeophyta (1500+ species, mainly marine, all multicellular) Found in cool waters along rocky coasts worldwide Play important role as habitat and food source (such as kelp forests) Largest and fastest-growing seaweeds (up to 50 cm/day) https://www.youtube.com/watch?v=ZQb9ZFWfNZE Contain chlorophyll and fucoxanthin (which gives them olive-green to brown colors) Body forms a thallus and anchors with holdfasts (rootlike structures), leaf-like structures called blades (also lamina, fronds) attached to a stem-like stipe Often have pneumatocysts (bladder-like
structures) to increase buoyancy, on or near the blades
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