2024 Unit 3 - PROTISTS (1).pdf

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S3512ED/BLG 3512 DIVERSITY of LIFE UNIT 3: PROTISTS Semester 2, 2024 1 µm Overview: Living Small Even a low-power microscope can reveal a great variety of organisms in a drop of pond water Protist = mostly unicellular eukaryotes Advances in eukaryotic systematics have caused th...

S3512ED/BLG 3512 DIVERSITY of LIFE UNIT 3: PROTISTS Semester 2, 2024 1 µm Overview: Living Small Even a low-power microscope can reveal a great variety of organisms in a drop of pond water Protist = mostly unicellular eukaryotes Advances in eukaryotic systematics have caused the classification of protists to change significantly Protists constitute a polyphyletic group, and Protista is no longer valid as a kingdom Protists/ Protozoans Protists are eukaryotes and thus have organelles and are more complex than prokaryotes Most protists are unicellular, but there are some colonial and multicellular species Protists exhibit more structural and functional diversity than any other group of eukaryotes Single-celled protists can be very complex, as all biological functions are carried out by organelles in each individual cell Protists NUTRITION: Most 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 REPRODUCTION: Asexually or sexually (processes of meiosis and fertilization) Endosymbiosis in Eukaryotic Evolution There is now considerable evidence that much protist diversity has its origins in endosymbiosis  Primary endosymbiosis: eukaryotic cell engulfs another living prokaryotic cell. E.g eukaryotic cell engulfs a photosynthetic algal cell and becomes an autotrophic organism  Secondary endosymbiosis: an eukaryotic cell engulfs another eukaryote cell that has undergone primary endosymbiosis Endosymbiosis evolution of protists Five Supergroups of Eukaryotes It is no longer thought that amitochondriates (lacking mitochondria) are the oldest lineage of eukaryotes Our understanding of the relationships among protist groups continues to change rapidly One hypothesis divides all eukaryotes (including protists) into five supergroups Clade EXCAVATA  Include protists with modified mitochondria and protists with unique flagella Most are Asymetrical and single-celled (only slime molds, limited multicellularity) Some members have a feeding groove “excavated” from one side. Diplomonads and Parabasalids These 2 groups live in anaerobic environments, lack plastids, and have modified mitochondria Diplomonads Have modified mitochondria called mitosomes Derive energy anaerobically, for example, by glycolysis Have two equal-sized nuclei and multiple flagella Are often parasites, for example, Giardia intestinalis Parabasalids Have reduced mitochondria called hydrogenosomes that generate some energy anaerobically, releasing hydrogen gas a by-product Include Trichomonas vaginalis a parasite, causes common sexually transmitted infection Trichomoniasis. Euglenozoans Euglenozoa is a diverse group that includes predatory heterotrophs, photosynthetic autotrophs, and pathogenic parasites The main feature distinguishing them as a clade is a spiral or crystalline rod of unknown function inside their flagella This clade includes the ORDERS:  Kinetoplastids Euglenids Kinetoplastids Kinetoplastids have a single mitochondrion with an organized mass of DNA called a kinetoplast Widespread & flagellated, parasitzes all animal groups as well as plants and insects Free-living kinetoplastids feed on bacteria in aquatic, marine and terrestial environments. This group includes Trypanosoma, which causes sleeping sickness in humans Another pathogenic trypanosome causes Chagas’ disease Euglenids Euglenids have one or two flagella that emerge from a pocket at one end of the cell Many species can be both autotrophic and heterotrophic = Mixotrophs Chromalveolates Clade Chromalveolata is monophyletic and originated by a secondary endosymbiosis event The proposed endosymbiont is a red alga Contain some most important oceanic organisms Range from single cell to complex multicellular taxa This clade is controversial and includes the Alveolates and the Stramenopiles Alveolates Members of the clade Alveolata have membrane-bounded sacs (alveoli) just under the plasma membrane. The function of the alveoli is unknown. Alveolata includes:  DINOFLAGELLATES (group of flagellates), APICOMPLEXANS (group of parasites), and CILIATES (protists that move by cilia) Dinoflagellates Dinoflagellates are a diverse group of aquatic mixotrophs and heterotrophs They are abundant components of both marine and freshwater phytoplankton Each has a characteristic shape that in many species is reinforced by internal plates of cellulose Two flagella make them spin as they move through the water Dinoflagellate blooms are the cause of toxic “red tides” Apicomplexans Parasites of animals, and some cause serious human diseases e.g Malaria Spread as tiny infectious cells called sporozoites One end, the apex, contains a complex of organelles specialized for penetrating a host They have a nonphotosynthetic plastid, called apicoplast Most have sexual and asexual stages that require two or more different host species for completion Apicomplexans The apicomplexan Plasmodium is the parasite that causes malaria Plasmodium requires both mosquitoes and humans to complete its life cycle Approximately 2 million people die each year from malaria Efforts are ongoing to develop vaccines that target this pathogen Ciliates  Ciliates, a large varied group of protists, named for their use of cilia to move and feed  They have large macronuclei and small micronuclei  During conjugation (sexual reproduction) two individuals exchange haploid micronuclei  Ciliates generally reproduce asexually by binary fission Stramenopiles Marine algae that include some of the important photosynthetic organisms and several groups of heterotrophs Most have a “hairy” flagellum paired with a “smooth” flagellum (nonhairy) Include: diatoms, golden algae, brown algae and oomycetes Diatoms Diatoms are unicellular algae with a unique two-part, glass-like wall of hydrated silica Diatoms usually reproduce asexually, and occasionally sexually Diatoms are a major component of phytoplankton and are highly diverse Fossilized diatom walls compose much of the sediments known as diatomaceous earth 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 All golden algae are photosynthetic, and some are also heterotrphic= mixotrophs Form cysts if conditions become unfavorable Brown Algae Brown algae are the largest and have most complex multicellular anatomy of all algae Large amounts of brown pigment (eg. fuxoxanthin) makes it brown Resemble plants and form underwater “forests” All are multicellular, and most are marine Brown algae include many species commonly called “seaweeds” 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 Heteromorphic generations are structurally different, while isomorphic generations look similar Oomycetes Oomycetes include water molds, white rusts, and downy mildews They were once considered fungi based on morphological studies Most oomycetes are decomposers or parasites of algae and fish They have filaments (hyphae) that facilitate nutrient uptake Their ecological impact can be great, as in Phytophthora infestans causing potato late blight Rhizarians DNA evidence supports Rhizaria as a monophyletic clade Rhizaria organisms (referred to as amoebas) have threadlike pseudopodia Amoebas move and feed by pseudopodia Rhizarians include forams and radiolarians Forams Foraminiferans, or forams, are named for their porous shells, called tests Pseudopodia extend through the pores in the test Pseudopodia are used for swimming and feeding Foram tests form an extensive fossil record and are part of marine sediments Radiolarians Marine protists called radiolarians have symmetrical internal skeletons made of silica The pseudopodia of radiolarians radiate from the central body Use their pseudopodia to engulf microorganisms through phagocytosis Archeaplastida Over a billion years ago, a heterotrophic protist acquired a cyanobacterial endosymbiont The photosynthetic descendants of this ancient protist evolved into red algae and green algae Land plants are descended from the green algae Archaeplastida is a supergroup used by some scientists and includes red algae, green algae, and land plants Red Algae (Rhodophytes)  Red algae are reddish in color due to an accessory pigment call phycoerythrin, which masks the green of chlorophyll  The color varies from greenish-red in shallow water to dark red or almost black in deep water  Red algae are usually multicellular; the largest are seaweeds  Red algae are the most abundant large algae in coastal waters of the tropics Fig. 28-19 Bonnemaisonia hamifera 20 cm 8 mm Dulse (Palmaria palmata) Nori. The red alga Porphyra is the source of a traditional Japanese food. The seaweed is grown on nets in shallow coastal waters. The harvested seaweed is spread on bamboo screens to dry. Paper-thin, glossy sheets of nori make a mineral-rich wrap for rice, seafood, and vegetables in sushi. Green Algae Named for their grass-green chloroplasts Plants are descended from green algae The two main groups are chlorophytes and charophytes Most chlorophytes live in fresh water, but also many marine and some terrestrial species Example of chlorophytes: unicellular Chlamydomonas Other chlorophytes live in damp soil, as symbionts in lichens, or in snow Fig. 28-20 Carotenoid pigments in snow- dwelling chlorophytes such as Chlamydomonas nivalis, turn snow red Chlorophytes include unicellular, colonial, and multicellular forms Chlamydomonas Volvox Most chlorophytes have complex life cycles with both sexual and asexual reproductive stages Unikonts The supergroup Unikonta includes animals, fungi, and some protists that are closely related to fungi and animals This group includes two clades: the amoebozoans and the opisthokonts (animals, fungi, and related protists) The root of the eukaryotic tree remains controversial It is unclear whether unikonts separated from other eukaryotes relatively early or late Amoebozoans Amoebozoans are amoeba that have lobe- or tube-shaped, rather than threadlike, pseudopodia They include slime molds, gymnamoebas, and entamoebas Slime Molds Slime molds, or mycetozoans, were once thought to be fungi Molecular systematics places slime molds in the clade Amoebozoa Diverged into: plasmodial slime molds and cellular slime molds (based unique life cycles) Plasmodial Slime Molds Many species of plasmodial slime molds are brightly pigmented, usually yellow or orange At one point in the life cycle, plasmodial slime molds form a mass called a plasmodium (not to be confused with malarial genus Plasmodium) The plasmodium is not multicellular but is a single mass of cytoplasm, undivided by membranes and contains many diploid nuclei It extends pseudopodia through decomposing material, engulfing food by phagocytosis Cellular Slime Molds Form multicellular aggregates in which cells are separated by their membranes Cells feed individually, but can aggregate to function as unit when food is depleted Dictyostelium discoideum is an experimental model for studying the evolution of multicellularity Gymnamoebas Gymnamoebas are common unicellular amoebozoans present in soil as well as freshwater and marine environments Most gymnamoebas are heterotrophic and actively seek and consume bacteria and other protists Some feed on dead organic matter Entamoebas Entamoebas are parasites of vertebrates and some invertebrates Entamoeba histolytica causes ameobic dysentery in humans Dysentery: infection of intestines resulting in severe diarrhoea Spread via contaminated drinking water, food or eating utensils Opisthokonts Opisthokonts include animals, fungi, and several groups of protists (closely related to animals and fungi than they are to other protists) Protists play key roles in ecological relationships Protists are found in diverse aquatic environments Two key roles: Symbiotic protists Photosynthetic protists Symbiotic Protists Many protists form symbiotic relationships with other species Some protist symbionts benefit their hosts Dinoflagellates nourish coral polyps that build reefs Hypermastigotes digest cellulose in the gut of termites Some protists are parasitic Plasmodium causes malaria Pfesteria shumwayae is a dinoflagellate that causes fish kills Entamoeba histolytica causes amebic dysentry Phytophthora ramorum causes sudden oak death Photosynthetic Protists Many protists are important producers that obtain energy from the sun In aquatic environments they are main producers along with prokaryotes One third of world’s photosynthesis is performed by diatoms, dinoflagellates, multicellular algae etc. The availability of nutrients can affect the concentration of protists Fig. 28-28 Other consumers Herbivorous plankton Carnivorous plankton Bacteria absorbed by Soluble organic matter Protistan producers secrete Domain Eukarya: Protists Mostly unicellular eukaryotes Protista is no longer a valid kingdom Polyphyletic clade Some protists are more closely related to plants, fungi or animals Unicellular (Chlamydomonas), colonial (Volvox) and multicellular species (green algae) Can reproduce asexually and sexually Plastids and mitochondria evolved by endosymbiosis Primary vs secondary endosymbiosis Red and green algae underwent secondary endosymbiosis Different life cycles Apicomplexan Plasmodium: malaria causing parasite Requires 2 hosts to complete life cycle Ciliate Paramecium Conjugation (sexual reproduction) Cytokinesis produces 4 daughter cells Alternation of generations Alternation of multicellular haploid and diploid forms Heteromorphic generations: structurally different (Brown algae) Isomorphic generations: look similar (Ulva) Importance of Protists Form mutualistic and parasitic relationships E.g malaria causing Apicomplexan Plasmodium Important producers in aquatic environments You should now be able to: 1. Explain why the kingdom Protista is no longer considered a legitimate taxon 2. Explain the process of endosymbiosis and state what living organisms are likely relatives of mitochondria and plastids 3. Distinguish between endosymbiosis and secondary endosymbiosis 4. Name the five supergroups, list their key characteristics, and describe some representative taxa

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