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Protists Chapter 29

3 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

The nucleus and endoplasmic reticulum arose from infoldings of prokaryotic cell membrane 4

5 Many organelles evolved via endosymbiosis between an ancestral eukaryote and a bacterial cell –Mitochondria Aerobic bacteria engulfed by larger bacteria

6 Chloroplasts –Larger bacteria engulfed smaller photosynthetic bacteria –Chloroplasts come from single line of cyanobacteria –Hosts are not monophyletic Brown algae engulfed red algae that already had chloroplasts –Secondary endosymbiosis

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 7

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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 9

Protista is not monophyletic –Paraphyletic –Does not represent any evolutionary relationships Grouping 15 major protist phyla into 7 monophyletic groups –60 lineages are still not placed 10

11 Working model for protists classification

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Cell surface –Plasma membrane –Extracellular material (ECM) in some Diatoms – Silica shells Cysts –Dormant cell with resistant outer covering –Used for disease transmission 13

Locomotion –Flagella One or more –Cilia Shorter and more numerous than flagella –Pseudopodia (“false feet”) Lobopods – large, blunt Filopods – thin, branching Axopods – thin, long 14

Nutrition –Phototrophs –Heterotrophs Phagotrophs – Ingest particulate food matter Osmotrophs – Soluble food matter –Mixotrophs are both phototrophic and heterotrophic 15

Asexual reproduction –Typical mode of reproduction –Some species have an unusual mitosis Mitosis – equal size daughter cells Budding – one daughter cell smaller Schizogony – cell division preceded by several nuclear divisions; produces several individuals Sexual reproduction –May be obligate, or only under stress –Meiosis is a major eukaryote innovation –Union of haploid gametes which are produced by meiosis –Advantage in allowing frequent genetic recombination 16

Multicellularity –From single cells to colonies to true multicellularity –Arisen multiple times –Fosters specialization –Few innovations have had as great an influence on the history of life 17

Diplomonads Unicellular Move with flagella 2 nuclei Giardia Degenerate mitochondria 18

Parabasalids Live in termite guts –Host cellulose degrading bacteria Trichomonas vaginalis – STD Undulating membrane for locomotion Use flagella Lack mitochondria – derived trait 19

Euglenozoa Among the earliest eukaryotes to possess mitochondria 1/3 rd 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 20

Euglena –Two anterior (and unequal) flagella Attached at reservoir –Contractile vacuoles – collect excess water –Stigma – movement towards light –Numerous small chloroplasts From ingestion of green algae –Concept of a single Euglena genus is now being debated 21 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. a. 6.5 µm © Andrew Syred/Photo Researchers, Inc.

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Kinetoplastids –2 nd major group in Euglenozoa –Unique, single mitochondrion DNA maxicircles and minicircles –Trypanosomes cause human diseases African sleeping sickness – tsetse fly Leishmaniasis – sand fly Chagas disease – skin contact with urine or blood of infected wild animal 23

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 24

Alveolata Flattened vesicles called alveoli Dinoflagellates Apicomplexans Ciliates Common lineage despite diverse modes of locomotion 25

26 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 DNA not complexed with histones

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 27

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Other apicomplexans Gregarines –Found in the intestines of arthropods, annelids, and mollusks Toxoplasma gondii –Causes infections in humans with immunosuppression –Can cross placental barrier to harm fetus 29

30 Ciliates 3 rd 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

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Conjugation –Only different mating types can conjugate 32

Stramenopila Brown algae, diatoms, and oomycetes Very fine hairs on their flagella –A few species have lost their hairs during evolution 33

Brown algae Conspicuous seaweeds of northern regions Life cycle involves alternation of generations –Sporophyte – multicellular and diploid –Gametophyte – multicellular and haploid Not plants 34

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Diatoms –Phylum Chrysophyta –Photosynthetic, unicellular organisms –Unique double shells made of silica –Some move using raphes Two long grooves lined with vibrating fibrils 36

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 37

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) 38

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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 40

Protists Without a Clade Amoebas are paraphyletic –Rhizopoda (True amoebas) Move by means of cytoplasmic projections called pseudopods 41

–Actinopoda (Radiolarians) Glassy exoskeletons made of silica Needlelike pseudopods 42

Foraminifera –Heterotrophic marine protists –Pore-studded shells called tests, through which thin podia emerge –Use podia for swimming and feeding –Complex life cycles with haploid and diploid generations –Limestones are rich in forams White Cliffs of Dover 43

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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 45

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 46

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 –Slug differentiates into a sorocarp 47

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