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

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

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

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

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

Working model for protists classification

Locomotion Nutrition Flagella Cilia Pseudopodia (“false feet”) One or more Cilia Shorter and more numerous than flagella Pseudopodia (“false feet”) Nutrition Phototrophs Heterotrophs

Asexual reproduction Sexual 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

Diplomonads Unicellular Move with flagella 2 nuclei Giardia

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

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

© Andrew Syred/Photo Researchers, Inc. 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.

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

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

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

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

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

Other apicomplexans Toxoplasma gondii Causes infections in humans with immunosuppression Can cross placental barrier to harm fetus

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

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

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

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

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

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)

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

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

Actinopoda (Radiolarians) Glassy exoskeletons made of silica Needlelike pseudopods

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

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

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

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