BIOL 213 Protists New.ppt

Chapter 28: Protists  Protists I. General Characteristics II. Excavates III. SAR IV. Archaeplastida V. Unikonta  Learning Objectives 1. Define what type of organisms protists are and how they are similar and different from other eukaryotes. 2. Describe the complexity of pr...

Chapter 28: Protists  Protists I. General Characteristics II. Excavates III. SAR IV. Archaeplastida V. Unikonta  Learning Objectives 1. Define what type of organisms protists are and how they are similar and different from other eukaryotes. 2. Describe the complexity of protists at the cellular level. 3. Explain the nutritional strategies among protists 4. Explain the alternation of generations in the life cycle of some protists 5. Justify the molecular and phylogenetic approach to protist classification 6. Describe the unifying features and representative clades of the supergroup Excavata 7. Describe the representative clades of the supergroup SAR 8. Describe the representative clades of the supergroup Archaeplastida 9. Describe the representative clades of the supergroup Unikonta 10. Identify representative species from all the protist clades studied in this class  A. General Characteristics A. Definition 1. Protist is the informal name of the group of mostly unicellular eukaryotes that are not fungi, plants or animals 2. Protists constitute a polyphyletic group, and Protista is no longer valid as a kingdom B. Characteristics 1.Most protists are unicellular, but there are some colonial and multicellular species 2.Single-celled protists can be very complex, as all biological functions are carried out by organelles in each individual cell 3. Protists, the most nutritionally 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 3. Some protists reproduce asexually, while others reproduce sexually, or by the sexual processes of meiosis and fertilization Alternation of generations is evident in brown and green algae C. Endosymbiosis and protist evolution Endosymbiosis is the process in which a unicellular organism engulfs another cell, which becomes an endosymbiont and then organelle in the host cell Mitochondria are believed to have evolved by endosymbiosis of an aerobic prokaryote Plastids are believed to have evolved by endosymbiosis of a photosynthetic cyanobacterium D. Diversity It is no longer thought that Excavates are the oldest lineage of eukaryotes Many have been shown to have mitochondria and have been reclassified Our understanding of the relationships among protist groups continues to change rapidly One hypothesis divides all eukaryotes (including protists) into four supergroups  II. Excavates Some members have a feeding groove that appears like “excavated” from the surface. This controversial group includes the diplomonads, parabasalids, and euglenozoans A. Diplomonads – Have modified mitochondria called mitosomes – Derive energy from anaerobic biochemical pathways – Have two equal-sized nuclei and multiple flagella – Are often parasites, for example, Giardia intestinalis (also known as Giardia lamblia)  Parabasalids – Have reduced mitochondria called hydrogenosomes that generate some energy anaerobically – Include Trichomonas vaginalis, the pathogen that causes yeast infections in human females C. Euglenozoa is a diverse clade that includes euglenids and kinetoplastids Some are predatory heterotrophs, photosynthetic autotrophs, and parasites The main feature distinguishing them as a clade is a spiral or crystalline rod of unknown function inside their flagella Euglenids have one or two flagella that emerge from a pocket at one end of the cell Kinetoplastids have a single mitochondrion with an organized mass of DNA called a kinetoplast They include free-living consumers of prokaryotes in freshwater, marine, and moist terrestrial ecosystems This group includes Trypanosoma gambiense, which causes sleeping sickness in humans Another pathogenic trypanosome causes Chagas’ disease leading to congestive heart failure  III. SAR Some data suggest that the supergroup SAR is monophyletic and originated by a secondary endosymbiosis event The proposed endosymbiont is a red alga This clade is controversial and includes the alveolates and the stramenopiles A. Members of the sub- group Alveolata have membrane- bounded sacs (alveoli) just under the plasma membrane The function of the alveoli is unknown The alveolates include – Dinoflagellates – Apicomplexans – Ciliates 1. Dinoflagellates have two flagella and each cell is reinforced by cellulose plates They are abundant components of both marine and freshwater phytoplankton They are a diverse group of aquatic phototrophs, mixotrophs, and heterotrophs Toxic “red tides” are caused by dinoflagellate blooms 2. Apicomplexans are parasites of animals, and some cause serious human diseases They spread through their host as infectious cells called sporozoites One end, the apex, contains a complex of organelles specialized for penetrating host cells and tissues Most have sexual and asexual stages that require two or more different host species for completion  The apicomplexan Plasmodium is the parasite that causes malaria Plasmodium requires both mosquitoes and humans to complete its life cycle Approximately 900,000 people die each year from malaria Efforts are ongoing to develop vaccines that target this pathogen 3. Ciliates, a large varied group of protists, are named for their use of cilia to move and feed They have large macronuclei and small micronuclei Genetic variation results from conjugation, in which two individuals exchange haploid micronuclei Conjugation is a sexual process, and is separate from reproduction, which generally occurs by binary fission B. The sub-group Stramenopila includes important phototrophs as well as several clades of heterotrophs Most have a “hairy” flagellum paired with a “smooth” flagellum Stramenopiles include diatoms, golden algae, brown algae, and oomycetes 1. Diatoms are unicellular algae with a unique two-part, glass-like wall of hydrated silica Diatoms are a major component of phytoplankton and are highly diverse Fossilized diatom walls compose much of the sediments known as diatomaceous earth After a diatom population has bloomed, many dead individuals fall to the ocean floor undecomposed Reproduction is mainly asexual 2. 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 All golden algae are photosynthetic, and some are mixotrophs Most are unicellular, but some are colonial 3. Brown algae are the largest and most complex algae All are multicellular, and most are marine Brown algae include many species commonly called “seaweeds” Kelp forests are important to marine fish reproduction as food sources and shelter Brown algae have the most complex multicellular anatomy of all algae  Giant seaweeds called kelps live in deep parts of the ocean The algal body is plantlike but lacks true roots, stems, and leaves and is called a thallus The rootlike holdfast anchors the stemlike stipe, which in turn supports the leaflike blades Gas-filled bladders help kelp grow vertically in search of light  Some brown algae show complex life cycles that include an alternation of generations, the alternation of multicellular haploid and diploid forms Heteromorphic generations are structurally different, while isomorphic generations look similar  The diploid sporophyte produces haploid flagellated spores called zoospores The zoospores develop into haploid male and female gametophytes, which produce gametes Fertilization of gamates results in a diploid zygote, which grows into a new sporophyte C. DNA evidence suggests that the sub- group Rhizaria is a monophyletic clade Amoeboid protists move and feed by pseudopodia; some but not all belong to the clade Rhizaria Rhizarians include radiolarians, forams, and cercozoans 1. Marine protists called radiolarians have tests fused into one delicate piece, usually made of silica Radiolarians use their pseudopodia to engulf microorganisms through phagocytosis The pseudopodia of radiolarians radiate from the central body 2. Foraminiferans, or forams, are named for porous, generally multichambered shells, called tests Pseudopodia extend through the pores in the test Foram tests in marine sediments form an extensive fossil record Many forams have endosymbiotic algae  IV. Archaeplastida Archaeplastida is the supergroup that includes red algae, green algae, and land plants A. Rhodophyta Red algae are reddish in color due to an accessory pigment called 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 B. Green algae are named for their grass-green chloroplasts Plants are descended from the green algae Green algae are a paraphyletic group The two main groups are chlorophytes and charophytes, the most closely related to land plants Most chlorophytes live in fresh water, although many are marine Other chlorophytes live in damp soil, as symbionts in lichens, or in snow  V. Unikonta The supergroup Unikonta includes animals, fungi, and some protists This group includes the amoebozoans and the opisthokonts (animals, fungi, and related protists) The root of the eukaryotic tree remains controversial A. Slime molds, or mycetozoans, were once thought to be fungi 1. 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 Plasmodium) The plasmodium is not multicellular It is undivided by plasma membranes and contains many diploid nuclei  Cellular slime molds form multicellular aggregates in which cells are separated by their membranes Cells feed individually, but can aggregate to form a fruiting body Dictyostelium discoideum is an experimental model for studying the evolution of multicellularity B. Gymnamoebas are common unicellular amoebozoans in soil as well as freshwater and marine environments Most gymnamoebas are heterotrophic and actively seek and consume bacteria and other protists C. Entamoebas are parasites of vertebrates and some invertebrates Entamoeba histolytica causes amoebic dysentery, the third- leading cause of human death due to eukaryotic parasites