Protists Chapter 29

Protists Protists are the most diverse of the four eukaryotic kingdoms -Unicellular, colonial and multicellular groups The kingdom Protista is paraphyletic and grouped for convenience The 15 major protist phyla are grouped into seven major monophyletic groups -However, 60 lineages cannot be placed with confidence

Protists

Protists

Eukaryotic Origins Eukaryotic cells differ from prokaryotes by the presence of a cytoskeleton and organelles Appearance of eukaryotes in microfossils occurred about 1.5 BYA

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

Eukaryotic Origins Many organelles evolved via endosymbiosis between an ancestral eukaryote and a bacterial cell -Mitochondria – Aerobic bacteria Organisms that host chloroplasts are not monophyletic -Red and green algae engulfed cyanobacteria -Brown algae engulfed red algae -Secondary endosymbiosis

Eukaryotic Origins Over time, most organellar genes moved into the nucleus -Therefore, these organelles cannot be grown in pure culture Mitosis and cytokinesis did not evolve in eukaryotes all at once -Intermediate mechanisms survive today -Fungal nuclear membranes do not dissolve

General Biology of the Protists Cell surface -Plasma membrane -Extracellular material (ECM), in some -Diatoms – Silica shells Cysts -Dormant cell with resistant outer covering -Used for disease transmission

General Biology of the Protists Locomotion -Flagella -Cilia -Pseudopodia (“false feet”) -Lobopods – Large, blunt -Filopods – Thin, branching -Axopods – Thin, long

General Biology of the Protists Nutrition -Phototrophs -Heterotrophs -Phagotrophs – Particulate food matter -Osmotrophs – Soluble food matter -Mixotrophs are both phototrophic and heterotrophic

General Biology of the Protists Asexual reproduction -Typical mode of reproduction -Some species have an unusual mitosis -Binary fission = Equal cells -Budding = Progeny cell smaller -Schizogony = Multiple fission Sexual reproduction -Union of haploid gametes which are produced by meiosis

Diplomonads and Parabasalids Are closely related to the early, now extinct eukaryotic cell -Flagellated -Lack mitochondria -May have lost their mitochondria, rather than never acquired them

Diplomonads and Parabasalids -Have two nuclei -Giardia intestinalis Parabasalids -Have undulating membranes -Trichomonas vaginalis

Euglenozoa Euglenoids were among the earliest eukaryotes to possess mitochondria -1/3rd have chloroplasts -All have a flexible pellicle -None have sexual reproduction

Euglenozoa Euglena -Two anterior (and unequal) flagella -Contractile vacuoles – Collect excess water -Stigma – Movement towards light -Numerous small chloroplasts -The concept of a single Euglena genus is now being debated

Euglenozoa

Euglenozoa Kinetoplastids -Unique, single mitochondrion with DNA maxicircles and minicircles (RNA editing) -Trypanosomes cause human diseases -African sleeping sickness – Tsetse fly -Leishmaniasis – Sand fly -Difficult to control because organisms repeatedly change their protective coat

Euglenozoa

Alveolata Alveolata have flattened vesicles called alveoli -These function like Golgi bodies below the cell membrane

Alveolata Dinoflagellates -Unicellular with two unequal flagella -Live in aquatic environments -Most are photosynthetic -Do not appear to be directly related to any other phylum

Alveolata Dinoflagellates -Reproduction is primarily asexual -DNA is not complexed with histones -About 20 species produce powerful toxins that harm vertebrates -“Blooms” are responsible for red tide

Alveolata 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

Alveolata Plasmodium -An apicomplexan that causes malaria -Eradication of malaria 1. Elimination of mosquito vectors 2. Development of drugs 3. Development of vaccines -Organism has a very complex life cycle

Alveolata Other apicomplexans -Gregarines -Found in the intestines of arthropods, annelids and mollusks -Toxoplasma gondii -Causes infections in humans with immunosuppression

Alveolata Ciliates -Feature large numbers of cilia arranged in longtitudinal rows or spirals around the cell -Have two types of vacuoles -Food vacuoles = Digestion of food -Contractile vacuoles = Regulation of water balance

Alveolata Ciliates -Have two types of nuclei -Macronucleus = Divides by mitosis -Responsible for physiological functions -Micronucleus = Divides by meiosis -Involved in conjugation -Fusion of two cells of different mating types

Stramenopila Stramenopiles have very fine hairs on their flagella -A few species have lost their hairs during evolution

Stramenopila Brown algae -Kelps -Grow in relatively shallow waters throughout the world -Life cycle involves alternation of generations -Sporophyte = Multicellular and diploid -Gametophyte = Multicellular and haploid

Stramenopila Diatoms (Phylum Chrysophyta) -Unicellular organisms -Have unique double shells made of silica -Some move using raphes -Two long grooves lined with vibrating fibrils

Stramenopila

Stramenopila Oomycetes (“water molds”) -Were once considered fungi -Motile zoospores with two unequal flagella -Undergo sexual reproduction -Either parasites or saprobes -Phytophthora infestans -Irish potato famine (1845-1847)

Rhodophyta Rhodophyta, or red algae, range from microscopic to very large sizes -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)

Rhodophyta

Choanoflagellida Choanoflagellates are most like the common ancestor of all animals -Single emergent flagellum, surrounded by funnel-shaped contractile collar -Use collar to feed on bacteria -Have a surface tyrosine kinase receptor found in sponges

Choanoflagellida

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

Protists Without a Clade

Protists Without a Clade Foraminifera are heterotrophic marine protists -Have pore-studded shells called tests, through which thin podia emerge -Use podia for swimming and feeding -Have complex life cycles with haploid and diploid generations -Limestones are rich in forams -White cliffs of Dover

Protists Without a Clade

Protists Without a Clade Slime molds -Were once considered fungi -Include two lineages 1. Plasmodial slime molds 2. Cellular slime molds

Protists Without a Clade 1. Plasmodial slime molds -Stream along as a plasmodium, a nonwalled, multinucleate mass of cytoplasm -Ingests bacteria and other organic material -When food or moisture is scarce, organism forms sporangia, where spores are produced

Protists Without a Clade

Protists Without a Clade 2. Cellular slime molds -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

Protists Without a Clade