Transcript Chapter 29
CHAPTER 29 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Protists Chapter 29 Eukaryotic Origins • Eukaryotic cells differ from prokaryotes – Presence of a cytoskeleton – Compartmentalization (nucleus and organelles) • Appearance of eukaryotes in microfossils occurred about 1.5 BYA 3 • The nucleus and endoplasmic reticulum arose from infoldings of prokaryotic cell membrane 4 • Many organelles evolved via endosymbiosis between an ancestral eukaryote and a bacterial cell – Mitochondria • Aerobic bacteria engulfed by larger bacteria 5 • Endosymbiosis supported by – DNA inside mitochondria and chloroplasts • DNA similar to bacteria DNA in size and character – Ribosomes inside mitochondria similar to bacterial ribosomes – Chloroplasts and mitochondria replicate by binary fission – not mitosis 6 Defining Protists • Most diverse of the four eukaryotic kingdoms • United on the basis that they are not fungi, plants, or animals • Vary considerably in every other aspect – Unicellular, colonial, and multicellular groups – Most are microscopic but some are huge – All symmetries – All types of nutrition 7 Working model for protists classification 8 9 • Locomotion – Flagella • One or more – Cilia • Shorter and more numerous than flagella – Pseudopodia (“false feet”) • Nutrition – Phototrophs – Heterotrophs 10 • Asexual reproduction – Typical mode of reproduction – Some species have an unusual mitosis • Mitosis – equal size daughter cells • Budding – one daughter cell smaller • Sexual reproduction – Meiosis is a major eukaryote innovation – Union of haploid gametes which are produced by meiosis – Advantage in allowing frequent genetic recombination 11 Diplomonads • • • • Unicellular Move with flagella 2 nuclei Giardia 12 Parabasalids • Live in termite guts – Host cellulose degrading bacteria • • • • Trichomonas vaginalis – STD Undulating membrane for locomotion Use flagella Lack mitochondria – derived trait 13 Euglenozoa • Among the earliest eukaryotes to possess mitochondria • 1/3rd have chloroplasts and are autotrophic – May become heterotrophic in the dark • Others lack chloroplasts and are heterotrophic • All have a flexible pellicle • No sexual reproduction 14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Euglena – Two anterior (and unequal) flagella – Contractile vacuoles – collect excess water – Stigma – movement towards light – Numerous small chloroplasts – Concept of a single Euglena genus is now being debated a. 6.5 µm © Andrew Syred/Photo Researchers, Inc. 15 16 • Kinetoplastids – 2nd major group in Euglenozoa – Unique, single mitochondrion – Trypanosomes cause human diseases • African sleeping sickness – tsetse fly • Chagas disease – skin contact with urine or blood of infected wild animal 17 • Difficult to control because organisms repeatedly change their protective coat – Release of sterilized flies – Traps scented like cows but treated with insecticides – Sequencing of genomes revealed core of common genes in all 3 – hope for single drug target 18 Alveolata • Flattened vesicles called alveoli • Dinoflagellates • Apicomplexans • Ciliates • Common lineage despite diverse modes of locomotion 19 Dinoflagellates • • • • Photosynthetic, unicellular with flagella Live in aquatic environments Some are luminescent Do not appear to be directly related to any other phylum • “Red tide” are “blooms” – fish, birds, and marine mammals may die from toxins 20 Apicomplexans • Spore-forming animal parasites • Apical complex is a unique arrangement of organelles at one end of the cell – Enables the cell to invade its host • Plasmodium causes malaria – Complex life cycle – sexual, asexual, different hosts – Eradication focused on eliminating mosquito vector, drug development, vaccines • DDT-resistant mosquitoes 21 22 Other apicomplexans • Toxoplasma gondii – Causes infections in humans with immunosuppression – Can cross placental barrier to harm fetus 23 Ciliates • 3rd group of apicomplexans • Feature large numbers of cilia arranged in longitudinal rows or spirals around the cell • Pellicle – tough but flexible outer covering • 2 types of nuclei – Micronucleus – without will reproduce asexually – Macronucleus – essential for function • Have two types of vacuoles – Food vacuoles – digestion of food – Contractile vacuoles – regulation of water balance 24 25 Stramenopila • Brown algae, diatoms, and oomycetes • Very fine hairs on their flagella – A few species have lost their hairs during evolution 26 Brown algae • Conspicuous seaweeds of northern regions • Life cycle involves alternation of generations – Sporophyte – multicellular and diploid – Gametophyte – multicellular and haploid • Not plants 27 28 • Diatoms – Phylum Chrysophyta – Photosynthetic, unicellular organisms – Unique double shells made of silica – Some move using raphes • Two long grooves lined with vibrating fibrils 29 Oomycetes • • • • “Water molds” Either parasites or saprobes Were once considered fungi Motile zoospores with two unequal flagella – Produced asexually • Undergo sexual reproduction • Found in water or on land • Phytophthora infestans – Irish potato famine (1845–1847) – 400,000 people died 30 Rhodophyta • Red algae range from microscopic to very large • Lack flagella and centrioles • Have accessory photosynthetic pigments within phycobilisomes • Origin has been a source of controversy – Tentatively, treated as a sister clade of Chlorophyta (green algae) 31 32 Choanoflagellida • Most like common ancestor of all animals • Single emergent flagellum, surrounded by funnel-shaped contractile collar – Structure matched in sponges • Use collar to feed on bacteria • Have a surface tyrosine kinase receptor found in sponges 33 Protists Without a Clade • Amoebas are paraphyletic – Rhizopoda (True amoebas) • Move by means of cytoplasmic projections called pseudopods 34 – Actinopoda (Radiolarians) • Glassy exoskeletons made of silica • Needlelike pseudopods 35 • Foraminifera – Heterotrophic marine protists – Pore-studded shells called tests, through which thin podia emerge – Use podia for swimming and feeding – Limestones are rich in forams • White Cliffs of Dover 36 37 • Slime molds – Were once considered fungi – Include two lineages – Plasmodial slime molds • Huge, single-celled, multinucleate, oozing masses – Cellular slime molds • Single cells combine and differentiate, creating an early model of multicellularity 38 • Plasmodial slime molds – Stream along as a plasmodium • Nonwalled, multinucleate mass of cytoplasm • Form called feeding phase – Ingests bacteria and other organic material – When food or moisture is scarce, organism forms sporangia, where spores are produced 39 • Cellular slime molds – Important group for the study of cell differentiation because of their relatively simple developmental systems – Individual organisms behave as separate amoebas – Move through soil ingesting bacteria – When food is scarce, organisms aggregate to form a slug 40 41