Protista

Protista

Brief IntroductionDutch microscopist Anti van Leewenhoek was the 1st to lay eyes on protists 300 yrs agoViewed a droplet of pond water under a light microscopeVan Leewenhoek wrote, No more pleasant sight has met my eyes than this, of so many thousands of living creatures. Some protists propel themselves w/ whipping flagella others creep along by means of blob-like appendagesCont.All protists were once classified as 1 kingdom, Protista, but recently advances have brought the kingdom downSome are more closely related to plants, fungi, or animals than other plantsVarious protists are now recognizied as kingdoms in their own rightBiologists still use the term protist today

Structural & Functional DiversityUnicelluar or can be multicelluarUnicelluar protists use organelles such as nucleus, endoplasmic reticulium, golgi apparatus, and lysosomes, and some rely on organelles not found in eukaryotes such as a vacuoleSome are photoautotrophs and contain chlorplasts, others can be heterotrophs (absorbing organic molecules or ingesting larger food prticles) Endosymbiosis in Eukaryotic EvolutionWhat makes protists so diverse?Endosymbiosis, the process in which certain unicelluar organisms engulf other cells

ExcavataDiplomonads & ParabasalidsLack plastids and have modified mitochondria Found in anaerobic environments

DiplomonadsHave modified mitchondria called mitosomesLack functional electron transport chain so they cannot use oxygen to help extract energy from carbohydrates and other organic moleculesHave 2 equal sized nuclei and multiple flagella

Parabasalids

Have reduced mitochondria called hydrogenosomes, generate some energy Anaerobically release hydrogen gas as a by-productMost well known parabasalid is Trchomonas vaginalis

ChromalveolatesTheory proposed on 2 lines of evidence1st : Some (not all) DNA sequence data suggest tht the chromaveolates form a monophyletic group2nd: Some data support the hypothesis that the chromalveolates originated more than a billion yrs ago, when a common ancestor of the group engulfed a single-celled photosynthetic red alga (endosymbosis)

Cont.Red algae are thought to have originated by primary endosymbiosis the origin of the chromalveolates is referred to as secondary endosymbosisEvidence: in many species the plastid structure and DNA indicate that they are of red agal origin ApicompelxansParasites of animals and some cause serious human diseasesThe parasites spread through their host as sporozoites (tiny infectious cells)Have their name because the apex of the sporozite cell contains a complex of organells specialized for penetrating host cells and tissuesNot photosynthetic, recent data shows they can retain a modified plastid (apicoplast), most likely of red algal descent

Most have intricate life cycles sexual and asexual stages (require 2 or more host species for completion an example is the parasite Plasmadium which causes malaria

Brown AlgaeMulticelluar & marine organismsCommonly found along cool water temp. coastsIts brown or olive color is due to a carotenoid in plastid Most commonly known as seaweed

Cont. Brown algae: include species that have some of the most complex multi-celluar anatomy of all algae some have specialized organs that resemble those found in plantsMorphological and DNA evidence indicate that the similarites evolved independently in the algal and plant lineages and are thus analogous, not homologous

Cont.Some species of brown algae are eaten, Laminaria (Japanese kombu) used in soupsThe gel-forming substance in the cell walls (algin) is used to thicken many prcessed foods such as pudding, ice cream, and salad dressings

RhizariansProposal based on results from molecular systematicsMembers vary morphologicallyReferred to as amoebasAmoebas were once defined as protists that move and feed by means of pseudopdia, extension that may bulge from almost anywhere on the cell surfaceBased on molecular systematics it is now clear amoebas do not constitute a monophyletic group but are dispersed across many distantly related eukaryotic taxa

RadiolariansHave intricately symmetrical internal skeletons which are generally made of silicaThe pseudopdia radiate from the body and are reinforced by a bundles of microtubules, covered by a layer of cytoplasm which engulf smaller micro-organisms that become attached to the pseudopodia

Red & Green AlgaeMore than a billion years ago, heterotrophic protist aquired a cyanobacterial endosymbiont, and the photosynthetic descendents of this ancient protist evolved into red and green algae474 million years ago the linage that produced green algae gave rise to land plantsCont. Red algae, green algae, and land plants make up the 4th eukaryotic supergroup, ArchaeplastidaMonophyletic group that descended from ancient protists that engulfed a cyanbacterium

UnikontsDiverse subgroup of eukaryotes (animals, fungi, and some protists)Concern of the root of the eukaryotic treeIf the root of the tree were known, scientists could infer characteristics of the common ancestor of all eukaryotes

Cont.In 2002, Alexandria Stechman & Thomas Cavalier Smith of Oxford University proposed a new hypothesis about the root of the eukaryotic treeHypothesis: the unikants were the 1st eukaryotes to diverge from other eukaryotesProposes that animal and fungi belong to an early-diverging group of eukaryotes Protists that lack typical mitochondria diverged much later in the history of lifeControversial and requires more supporting evidence to be widely acceptedPlasmdial Slime MoldsBrightly colored (yellow, orange)Despite its size, the plasmodium is not multicellular it is a single mass of cytoplasm that is undivided by plasma membranes and that contains manay diploid nucleiPlasmodium extends pseudopodia through moist soil, leaf mulch, or rotting logs engulfing food particles by phagosytosisIf habitat begins to dry or there is no food left the plasmodium stops growing and differentiates into friuting bodies which function in sexual reproduction

Protists Play a Key Role These guys are everywhere!Many have symbiotic relationships with species Photosynthetic dinoflagellates provide nourishment to their symbiotic partners, the coral polyps that build coral reefs. Corals are highly diverse but also depend on the mutualistic protists symbionts that provide corals with an essential source of energyMany protists are important producers, organisms that use energy from light (or inorganic chem.) to convert carbon dioxide to organic compundsProducers are the base of ecological food webs

Key WordsProtist: an informal term applied to any eukaryote that not a plant, animal, or fungusMixotroph:combination of photosynthesis and heterotrophic nutrition Secondary endosymbiosisa process in eukaryotic evolution in which a heterotrophic eukaryotic cell engulfed a photosynthetic eukaryotic cell, which srvived in a symbiotic relationship inside the heterotrophic cellExacata: one of the 5 subgraoups Diplomonads: protists with modified mitochondria called mitsomesParabasalids: protists with reduces mitochondria called hydrogenosomesEuglenozoan: protists that belong to a diverse clade that incledes predatory heterotrophs, photosynthetic autotrophs, and parasitesKineoplastids: protists that have a single large mitochondrion that contains an organized mass of DNA called kinetoplastEuglenid:a protists that has a pocket at one end of the cell from which 1 or 2 flagella emergeChromalveolata: one of the 5 subgroupsAlveolates: groups of protist swhos monophyly is well supported by molecular systematicsDinoflagellates: portists that are characterized by cells that are reinforced by cellulose platesApicomplexans: parasites of animals, and some serious human diseasesCiliates: a large group of varied protists named for their use of cilia to move and feed Stramenopiles:a group of marine algae that include some of the most important photosynthetic organisms on the planet, as well as several heterotrophsDiatoms: unicellular algae that have a unique glass-like wall made ofhydrated silica embedded in an organic matrixGolden algae: a biflagellated, photosynthetic protist named for its color, which results from itsyellow and brown cartenoidsThe End!

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